feat: implement approximate k-mer indexing and optimize query

Enable approximate k-mer indexing via the `--approx` flag, computing an effective k-mer size of `k - z + 1` and configuring the appropriate indexing mode with validated probabilistic parameters. Refactor the Findere z-window filter in the query command to improve performance and correctness by replacing the precomputed vector with a lazy closure, optimizing cache locality, and fixing a variable naming bug.

docmd/implementation/chunkreader.md

@@ -1,6 +1,24 @@
 # Chunk reader — implementation
 
-The `obiread` crate provides a streaming iterator that reads FASTA or FASTQ files in fixed-size blocks and yields self-contained chunks, each ending on a complete sequence record boundary. Chunks are consumed in parallel by downstream workers.
+`obiread` exposes two distinct sequence reading paths, each optimised for a different use case.
+
+## Two reading paths
+
+| Path | API | Output unit | Per-record identity | Use case |
+|------|-----|-------------|---------------------|----------|
+| **Record path** | `read_sequence_chunks` → `parse_chunk` | `SeqRecord` (id + raw sequence + normalised rope) | yes | `query` — must read complete records |
+| **Stream path** | `open_nuc_stream` | `NucPage` (flat normalised byte buffer) | no | `index`, `superkmer` — bulk throughput |
+
+The record path uses `Rope`-backed chunks and is described in detail below.
+The stream path (`NucStream` / `NucPage`) is described in the scatter section of [pipeline](pipeline.md).
+
+---
+
+## Record path: chunk reader
+
+The chunk reader reads FASTA or FASTQ files in fixed-size blocks and yields self-contained chunks, each ending on a complete sequence record boundary. `parse_chunk` then converts each chunk into a `Vec<SeqRecord>`, where each record carries its identifier, raw sequence bytes, and a normalised rope ready for superkmer building.
+
+This path is mandatory for `query`, where superkmers must be tracked back to their originating sequence (id, kmer offset) for output annotation.
 
 ## Output type: Rope
 

docmd/implementation/pipeline.md

@@ -19,7 +19,11 @@ The histogram gives:
 
 ## Phase 1 — Scatter
 
-Single streaming pass over raw input files (FASTA/FASTQ, gzip). FASTQ quality scores are ignored. For each read:
+Single streaming pass over raw input files (FASTA/FASTQ, gzip). FASTQ quality scores are ignored.
+
+Input files are read via `open_nuc_stream`, which opens and decompresses the file, auto-detects the format (FASTA / FASTQ / GenBank), and yields a sequence of `NucPage` buffers. Each `NucPage` is a flat 64 KB buffer of normalised bytes (`ACGT` + `\x00` separators), carrying a k−1 byte overlap from the preceding page so that no k-mer is lost at page boundaries. Per-record identity (sequence id, raw bytes) is not preserved; this is intentional — the scatter phase only needs normalised bases to produce superkmers.
+
+For each read fragment within a page:
 
 1. **Ambiguous base filter**: cut at any non-ACGT base; discard fragments shorter than k.
 2. **Entropy filter**: scan each fragment with a sliding window of size k. When the kmer $K_i = S[i \mathinner{..} i+k-1]$ ended by nucleotide $S[j]$ (with $j = i+k-1$) has entropy below threshold $\theta$, emit the current segment and start a new one (see algorithm below). $K_i$ belongs to neither segment, and no valid kmer is lost.

docmd/index.md

@@ -27,6 +27,18 @@
 - Canonical form: `min(kmer, revcomp(kmer))` reduces strand-symmetric space by half
 - Input formats: FASTA, FASTQ, gzip, streaming stdin; `index` reads from stdin automatically when no input files are provided (`-` can also be passed explicitly among other paths)
 
+## Parameter constraints (enforced at CLI)
+
+All constraints below are checked by `CommonArgs::validate()` at the start of `superkmer` and `index`. Invalid values exit immediately with an error.
+
+| Parameter | Constraint | Reason |
+|-----------|-----------|--------|
+| k (`--kmer-size`) | odd | even k allows palindromic k-mers: kmer == revcomp(kmer), breaking the canonical form invariant |
+| k (`--kmer-size`) | k ∈ [11, 31] | k > 31 overflows u64 at 2 bits/base; k < 11 gives insufficient specificity |
+| m (`--minimizer-size`) | odd | same palindrome argument as k |
+| m (`--minimizer-size`) | 3 ≤ m ≤ k−1 | minimizer must be strictly shorter than the kmer |
+| z (`-z`, Findere, `index --approx` only) | z ≤ k−1 | effective indexed kmer size is k−z+1; z ≥ k would make it ≤ 0 |
+
 ## Genome label constraints
 
 Genome labels are arbitrary Unicode strings with the following restrictions:

docmd/kmers.md

@@ -4,9 +4,11 @@
 
 A **kmer** is a DNA subsequence of fixed length k. Two constraints govern the choice of k:
 
-- **k ∈ [11, 31]**: the range ensures the kmer is long enough to be specific and short enough to fit in a single machine word.
+- **k ∈ [11, 31]**: the range ensures the kmer is long enough to be specific and short enough to fit in a single machine word (u64 at 2 bits/base requires k ≤ 32; k < 11 yields insufficient specificity).
 - **k is odd**: an odd-length sequence cannot equal its own reverse complement (no palindromes). This guarantees that the canonical form `min(kmer, revcomp(kmer))` is always strictly defined — the two orientations are always distinct — which is required for strand-independent counting.
 
+Both constraints are **enforced at CLI entry** by `CommonArgs::validate()` in `superkmer` and `index`. Passing an invalid k exits immediately with an error message.
+
 ## Super-kmers
 
 A **super-kmer** is a maximal run of consecutive kmers from a DNA read, each overlapping the next by k−1 nucleotides, sharing the same **canonical minimizer**. The **canonical minimizer** of a kmer is the m-mer (m < k) whose canonical hash `hash_kmer(min(m-mer, revcomp(m-mer)))` is smallest over all m-mers in the kmer window. The hash function is a `mix64`-based bijection; selection is purely hash-ordered with no degeneracy filter. A super-kmer is capped at 256 nucleotides; a longer run is split at that boundary.

src/Cargo.lock

@@ -1637,6 +1637,7 @@ dependencies = [
  "lazy_static",
  "obikrope",
  "obikseq",
+ "obiread",
 ]
 
 [[package]]

src/obikmer/src/cli.rs

@@ -1,9 +1,8 @@
-use std::io;
 use std::path::PathBuf;
 use std::sync::{Arc, Condvar, Mutex};
 
 use clap::Args;
-use obikrope::Rope;
+use obiread::NucPage;
 use obikseq::RoutableSuperKmer;
 
 // ── Shared arguments ──────────────────────────────────────────────────────────
@@ -45,9 +44,11 @@ pub struct CommonArgs {
     )]
     pub threads: usize,
 
-    /// Maximum number of input files open simultaneously
+    /// Maximum number of input files open simultaneously.
-    #[arg(long, default_value_t = 20)]
+    /// Defaults to threads/4 (minimum 1). Keep below the number of workers
-    pub max_open_files: usize,
+    /// to ensure CPU workers are always available for the transform stage.
+    #[arg(long)]
+    pub max_open_files: Option<usize>,
 }
 
 /// Smallest `b` such that `2^b >= n` (i.e. `n.next_power_of_two().ilog2()`).
@@ -63,6 +64,35 @@ pub fn block_size_to_bits(n: usize) -> u8 {
 }
 
 impl CommonArgs {
+    /// Validate k and m constraints. Exits on error.
+    pub fn validate(&self) {
+        let k = self.kmer_size;
+        let m = self.minimizer_size;
+
+        if k < 11 || k > 31 {
+            eprintln!("error: --kmer-size must be in [11, 31] (got {k})");
+            std::process::exit(1);
+        }
+        if k % 2 == 0 {
+            eprintln!("error: --kmer-size must be odd (got {k}); even k allows palindromic k-mers");
+            std::process::exit(1);
+        }
+        if m < 3 || m >= k {
+            eprintln!("error: --minimizer-size must be in [3, k−1] = [3, {}] (got {m})", k - 1);
+            std::process::exit(1);
+        }
+        if m % 2 == 0 {
+            eprintln!("error: --minimizer-size must be odd (got {m})");
+            std::process::exit(1);
+        }
+    }
+
+    pub fn effective_max_open(&self) -> usize {
+        self.max_open_files
+            .unwrap_or_else(|| (self.threads / 4).max(1))
+            .max(1)
+    }
+
     pub fn seqfile_paths(&self) -> obiread::PathIter {
         let paths: Vec<PathBuf> = if self.inputs.is_empty() {
             vec![PathBuf::from("-")]
@@ -121,13 +151,10 @@ pub struct PathWithSlot {
 
 pub enum PipelineData {
     Path(PathWithSlot),
-    RawChunk(Rope),
+    NucPage(NucPage),
-    NormChunk(Rope),
     Batch(Vec<RoutableSuperKmer>),
 }
 
-// SAFETY: Rope contains Cell<u8> which is !Sync, but pipeline ownership transfers
-// exclusively through channels — no item is ever shared across threads.
 unsafe impl Send for PipelineData {}
 unsafe impl Sync for PipelineData {}
 
@@ -148,18 +175,3 @@ pub fn throttle_paths(
     })
 }
 
-// ── I/O plumbing ──────────────────────────────────────────────────────────────
-
-pub fn open_chunks(path: PathBuf) -> io::Result<impl Iterator<Item = Rope>> {
-    let path_str = path
-        .to_str()
-        .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidInput, "non-UTF-8 path"))?;
-    let iter = obiread::read_sequence_chunks(path_str)?;
-    Ok(iter.filter_map(|r| match r {
-        Ok(rope) => Some(rope),
-        Err(e) => {
-            eprintln!("chunk read error: {e}");
-            None
-        }
-    }))
-}

src/obikmer/src/cmd/index.rs

@@ -152,16 +152,28 @@ pub(crate) fn resolve_approx_params(
 }
 
 pub fn run(args: IndexArgs) {
+    args.common.validate();
+
     let output = args.output.clone();
     let mut rep = Reporter::new();
 
     // ── Resolve evidence kind ────────────────────────────────────────────────
-    let evidence = if args.approx {
+    let (evidence, effective_kmer_size) = if args.approx {
         let (z, b, fp) = resolve_approx_params(args.findere_z, args.evidence_bits, args.fp);
-        info!("approximate evidence: b={b}, z={z}, fp={fp:.2e}");
+        let k = args.common.kmer_size;
-        IndexMode::Approx { b, z }
+        if z as usize >= k {
+            eprintln!(
+                "error: Findere z={z} must be < kmer-size={k} \
+                 (effective kmer size k−z+1 = {} ≤ 0)",
+                k as isize - z as isize + 1
+            );
+            std::process::exit(1);
+        }
+        let s = k - z as usize + 1;
+        info!("approximate evidence: b={b}, z={z}, fp={fp:.2e}, indexed kmer size={s}");
+        (IndexMode::Approx { b, z }, s)
     } else {
-        IndexMode::Exact
+        (IndexMode::Exact, args.common.kmer_size)
     };
 
     // ── Open or create the index ─────────────────────────────────────────────
@@ -186,7 +198,7 @@ pub fn run(args: IndexArgs) {
         }
         let block_bits = block_size_to_bits(args.block_size);
         let config = IndexConfig {
-            kmer_size:      args.common.kmer_size,
+            kmer_size:      effective_kmer_size,
             minimizer_size: args.common.minimizer_size,
             n_bits,
             with_counts:    args.with_counts,
@@ -220,7 +232,7 @@ pub fn run(args: IndexArgs) {
         let theta     = args.common.theta;
         let n_workers = args.common.threads.max(1);
 
-        let max_open = args.common.max_open_files.max(1);
+        let max_open = args.common.effective_max_open();
         scatter(idx.partition_mut(), args.common.seqfile_paths(), k, level_max, theta, n_workers, max_open, &mut rep);
 
         idx.mark_scattered().unwrap_or_else(|e| {

src/obikmer/src/cmd/query.rs

@@ -1,16 +1,30 @@
 use std::collections::HashMap;
 use std::io::{self, BufWriter, Write};
 use std::path::PathBuf;
+use std::sync::Arc;
 
 use clap::Args;
 use obikindex::KmerIndex;
 use obilayeredmap::IndexMode;
-use obiread::record::{SeqRecord, parse_chunk};
 use obiread::chunk::read_sequence_chunks;
+use obiread::record::{SeqRecord, parse_chunk};
+use obikrope::Rope;
 use obikseq::{RoutableSuperKmer, set_k, set_m};
 use obiskbuilder::SuperKmerIter;
 use tracing::info;
 
+// ── Pipeline data ─────────────────────────────────────────────────────────────
+
+enum QueryData {
+    Chunk(Rope),
+    Output(Vec<u8>),
+}
+
+// SAFETY: Rope contains Cell<u8> which is !Sync, but pipeline items are owned
+// exclusively through channels — no item is ever shared across threads.
+unsafe impl Send for QueryData {}
+unsafe impl Sync for QueryData {}
+
 // ── CLI ───────────────────────────────────────────────────────────────────────
 
 #[derive(Args)]
@@ -146,72 +160,153 @@ impl SeqAcc {
 // ── Findere z-window filter ───────────────────────────────────────────────────
 
 /// Apply the Findere z-window filter to per-kmer query results for one superkmer.
+/// Aggregate s-mer query results into k-mer answers using a Findere z-window.
 ///
-/// A k-mer at position i for genome g is confirmed only if it belongs to at least
+/// Input:  N s-mer results  (indexed kmer size s = k − z + 1).
-/// one run of z consecutive positions where all k-mers are present for g.
+/// Output: N − z + 1 k-mer results (user kmer size k).
-/// Unconfirmed positions are zeroed; positions whose entire row becomes zero are
-/// returned as `None`.
 ///
-/// When z <= 1 or the superkmer is shorter than z k-mers, results are returned
+/// For each genome g independently: k-mer at position i is confirmed iff all z values
-/// unchanged (short superkmers cannot satisfy the z-window constraint).
+/// results[i..i+z][g] are nonzero (None counts as zero for all genomes).
+/// Output values are taken from results[i]; genomes not confirmed are zeroed.
 fn apply_findere(
     results: &[Option<Box<[u32]>>],
     z: usize,
     n_genomes: usize,
 ) -> Vec<Option<Box<[u32]>>> {
     let n = results.len();
-    if z <= 1 || n < z {
+    if z <= 1 {
         return results.iter().map(|r| r.as_ref().map(|row| row.clone())).collect();
     }
+    if n < z {
+        return Vec::new();
+    }
 
-    let mut confirmed = vec![vec![false; n_genomes]; n];
+    let out_n = n - z + 1;
+    let mut confirmed = vec![vec![false; n_genomes]; out_n];
 
     for g in 0..n_genomes {
-        let present: Vec<bool> = results
+        let hit = |i: usize| results[i].as_ref().map_or(false, |r| r[g] > 0);
-            .iter()
-            .map(|r| r.as_ref().map_or(false, |row| row[g] > 0))
-            .collect();
 
-        let mut window_count = present[..z].iter().filter(|&&p| p).count();
+        let mut count: u32 = (0..z).filter(|&j| hit(j)).count() as u32;
-        if window_count == z {
+        if count == z as u32 { confirmed[0][g] = true; }
-            for c in confirmed[..z].iter_mut() {
+
-                c[g] = true;
+        for i in 1..out_n {
-            }
+            if hit(i - 1)     { count -= 1; }
+            if hit(i + z - 1) { count += 1; }
+            if count == z as u32 { confirmed[i][g] = true; }
+        }
+    }
+
+    (0..out_n).map(|i| {
+        let first = results[i].as_ref()?;
+        let mut row: Box<[u32]> = first.clone();
+        for g in 0..n_genomes {
+            if !confirmed[i][g] { row[g] = 0; }
+        }
+        if row.iter().any(|&v| v > 0) { Some(row) } else { None }
+    }).collect()
+}
+
+// ── process_chunk ─────────────────────────────────────────────────────────────
+
+fn process_chunk(
+    idx:               &KmerIndex,
+    rope:              Rope,
+    k:                 usize,
+    n_genomes:         usize,
+    n_partitions:      usize,
+    with_counts:       bool,
+    effective_z:       usize,
+    detail:            bool,
+    count_missing:     bool,
+    force_presence:    bool,
+    presence_threshold: u32,
+) -> Vec<u8> {
+    let records = parse_chunk(&rope, k);
+    if records.is_empty() {
+        return Vec::new();
+    }
+
+    let batch  = QueryBatch::from_records(records, k, 6, 0.7);
+    let n_seqs = batch.ids.len();
+
+    let mut accs: Vec<SeqAcc> =
+        (0..n_seqs).map(|_| SeqAcc::new(n_genomes)).collect();
+
+    let mut cov: Vec<Vec<Vec<u32>>> = if detail {
+        batch.n_kmers.iter()
+            .map(|&n| vec![vec![0u32; n as usize]; n_genomes])
+            .collect()
+    } else {
+        Vec::new()
+    };
+
+    let by_part = batch.split_by_partition(n_partitions);
+
+    for (part_idx, part_sks) in by_part.iter().enumerate() {
+        if part_sks.is_empty() {
+            continue;
         }
 
-        for j in 1..=(n - z) {
+        let kmer_results = idx
-            if present[j - 1]     { window_count -= 1; }
+            .partition()
-            if present[j + z - 1] { window_count += 1; }
+            .query_partition(part_idx, part_sks, k, n_genomes, with_counts)
-            if window_count == z {
+            .unwrap_or_else(|e| {
-                for c in confirmed[j..j + z].iter_mut() {
+                eprintln!("query error on partition {part_idx}: {e}");
-                    c[g] = true;
+                std::process::exit(1);
+            });
+
+        let presence  = force_presence || !with_counts;
+        let threshold = presence_threshold;
+
+        for (rsk, sk_kmer_results) in part_sks.iter().zip(kmer_results.iter()) {
+            let filtered = apply_findere(sk_kmer_results, effective_z, n_genomes);
+            let descs = batch.map.get(*rsk).expect("rsk must be in map");
+
+            for desc in descs {
+                let acc = &mut accs[desc.seq_idx as usize];
+
+                for (local_pos, hit) in filtered.iter().enumerate() {
+                    match hit {
+                        None => {
+                            if sk_kmer_results[local_pos].is_none() {
+                                acc.kmer_missing += 1;
+                            }
+                        }
+                        Some(row) => {
+                            acc.kmer_count += 1;
+                            for (g, &v) in row.iter().enumerate() {
+                                if v == 0 { continue; }
+                                let contribution = if presence {
+                                    u32::from(v >= threshold)
+                                } else {
+                                    v
+                                };
+                                acc.genome_totals[g] += contribution;
+                                if detail {
+                                    let abs_pos = desc.kmer_offset as usize + local_pos;
+                                    cov[desc.seq_idx as usize][g][abs_pos] += contribution;
+                                }
+                            }
+                        }
+                    }
                 }
             }
         }
     }
 
-    results.iter().enumerate().map(|(i, opt)| {
+    let mut buf = Vec::new();
-        let row = opt.as_ref()?;
+    emit_batch(&batch, &accs, idx.meta(), count_missing, detail, &cov, &mut buf);
-        let mut new_row: Box<[u32]> = row.clone();
+    buf
-        let mut any = false;
-        for g in 0..n_genomes {
-            if !confirmed[i][g] {
-                new_row[g] = 0;
-            } else {
-                any = true;
-            }
-        }
-        if any { Some(new_row) } else { None }
-    }).collect()
 }
 
 // ── Entry point ───────────────────────────────────────────────────────────────
 
 pub fn run(args: QueryArgs) {
-    let idx = KmerIndex::open(&args.index).unwrap_or_else(|e| {
+    let idx = Arc::new(KmerIndex::open(&args.index).unwrap_or_else(|e| {
         eprintln!("error opening index: {e}");
         std::process::exit(1);
-    });
+    }));
 
     set_k(idx.kmer_size());
     set_m(idx.minimizer_size());
@@ -220,6 +315,7 @@ pub fn run(args: QueryArgs) {
     let n_genomes    = idx.meta().genomes.len();
     let n_partitions = idx.n_partitions();
     let with_counts  = idx.meta().config.with_counts;
+    let n_workers    = args.threads.max(1);
 
     let effective_z: usize = args.findere_z.unwrap_or_else(|| {
         match idx.meta().config.evidence {
@@ -238,106 +334,48 @@ pub fn run(args: QueryArgs) {
         eprintln!("warning: --mismatch not yet implemented, ignored");
     }
 
+    let detail             = args.detail;
+    let count_missing      = args.count_missing;
+    let force_presence     = args.force_presence;
+    let presence_threshold = args.presence_threshold;
+
+    // Flat iterator over all Rope chunks from all input files.
+    // I/O runs in the source thread; chunk processing is parallelised by the pipe.
     let paths: Vec<PathBuf> = args.inputs.iter().map(PathBuf::from).collect();
+    let all_chunks = paths.into_iter().flat_map(|path| {
+        let path_str = path.to_str().unwrap_or("").to_owned();
+        match read_sequence_chunks(&path_str) {
+            Ok(iter) => Box::new(iter.filter_map(|r| match r {
+                Ok(rope) => Some(rope),
+                Err(e)   => { eprintln!("read error: {e}"); None }
+            })) as Box<dyn Iterator<Item = Rope> + Send>,
+            Err(e) => {
+                eprintln!("error opening {path_str}: {e}");
+                std::process::exit(1);
+            }
+        }
+    });
+
+    let pipe = obipipeline::make_pipe! {
+        QueryData : Rope => Vec<u8>,
+        | {
+            let idx = Arc::clone(&idx);
+            move |rope: Rope| {
+                process_chunk(
+                    &idx, rope, k, n_genomes, n_partitions, with_counts, effective_z,
+                    detail, count_missing, force_presence, presence_threshold,
+                )
+            }
+        } : Chunk => Output,
+    };
+
     let mut out = BufWriter::new(io::stdout());
-
+    for block in pipe.apply(all_chunks, n_workers, 2) {
-    for path in &paths {
+        if !block.is_empty() {
-        let chunks = read_sequence_chunks(path.to_str().unwrap_or(""))
+            out.write_all(&block).expect("write error");
-            .unwrap_or_else(|e| {
-                eprintln!("error opening {}: {e}", path.display());
-                std::process::exit(1);
-            });
-
-        for chunk_result in chunks {
-            let chunk = chunk_result.unwrap_or_else(|e| {
-                eprintln!("read error: {e}");
-                std::process::exit(1);
-            });
-
-            let records = parse_chunk(&chunk, k);
-            if records.is_empty() {
-                continue;
-            }
-
-            let batch  = QueryBatch::from_records(records, k, 6, 0.7);
-            let n_seqs = batch.ids.len();
-
-            let mut accs: Vec<SeqAcc> =
-                (0..n_seqs).map(|_| SeqAcc::new(n_genomes)).collect();
-
-            // [seq_idx][genome_idx][kmer_position] — allocated only with --detail
-            let mut cov: Vec<Vec<Vec<u32>>> = if args.detail {
-                batch.n_kmers.iter()
-                    .map(|&n| vec![vec![0u32; n as usize]; n_genomes])
-                    .collect()
-            } else {
-                Vec::new()
-            };
-
-            let by_part = batch.split_by_partition(n_partitions);
-
-            for (part_idx, part_sks) in by_part.iter().enumerate() {
-                if part_sks.is_empty() {
-                    continue;
-                }
-
-                let kmer_results = idx
-                    .partition()
-                    .query_partition(part_idx, part_sks, k, n_genomes, with_counts)
-                    .unwrap_or_else(|e| {
-                        eprintln!("query error on partition {part_idx}: {e}");
-                        std::process::exit(1);
-                    });
-
-                let presence  = args.force_presence || !with_counts;
-                let threshold = args.presence_threshold;
-
-                for (rsk, sk_kmer_results) in part_sks.iter().zip(kmer_results.iter()) {
-                    let filtered = apply_findere(sk_kmer_results, effective_z, n_genomes);
-                    let descs = batch.map.get(*rsk).expect("rsk must be in map");
-
-                    for desc in descs {
-                        let acc = &mut accs[desc.seq_idx as usize];
-
-                        for (local_pos, hit) in filtered.iter().enumerate() {
-                            match hit {
-                                None => {
-                                    // Only truly missing if the index also had no entry.
-                                    if sk_kmer_results[local_pos].is_none() {
-                                        acc.kmer_missing += 1;
-                                    }
-                                }
-                                Some(row) => {
-                                    acc.kmer_count += 1;
-                                    for (g, &v) in row.iter().enumerate() {
-                                        if v == 0 {
-                                            continue;
-                                        }
-                                        let contribution = if presence {
-                                            u32::from(v >= threshold)
-                                        } else {
-                                            v
-                                        };
-                                        acc.genome_totals[g] += contribution;
-                                        if args.detail {
-                                            let abs_pos = desc.kmer_offset as usize + local_pos;
-                                            cov[desc.seq_idx as usize][g][abs_pos] += contribution;
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-
-            emit_batch(
-                &batch, &accs, idx.meta(),
-                args.count_missing, args.detail, &cov,
-                &mut out,
-            );
         }
     }
+    out.flush().expect("flush error");
 }
 
 // ── Output ────────────────────────────────────────────────────────────────────

src/obikmer/src/cmd/superkmer.rs

@@ -4,7 +4,7 @@ use clap::Args;
 use obifastwrite::write_scatter;
 use obikseq::{RoutableSuperKmer, set_k, set_m};
 
-use crate::cli::{CommonArgs, PipelineData, PathWithSlot, open_chunks, partitions_to_bits, throttle_paths};
+use crate::cli::{CommonArgs, PipelineData, PathWithSlot, partitions_to_bits, throttle_paths};
 
 #[derive(Args)]
 pub struct SuperkmerArgs {
@@ -33,13 +33,15 @@ fn write_batch(
 // ── Entry point ───────────────────────────────────────────────────────────────
 
 pub fn run(args: SuperkmerArgs) {
+    args.common.validate();
+
     let k = args.common.kmer_size;
     let m = args.common.minimizer_size;
     let theta = args.common.theta;
     let level_max = args.common.level_max;
     let partition_bits = partitions_to_bits(args.common.partitions);
     let n_workers = args.common.threads.max(1);
-    let max_open = args.common.max_open_files.max(1);
+    let max_open = args.common.effective_max_open();
 
     set_k(k);
     set_m(m);
@@ -48,9 +50,14 @@ pub fn run(args: SuperkmerArgs) {
 
     let pipe = obipipeline::make_pipe! {
         PipelineData : PathWithSlot => Vec<RoutableSuperKmer>,
-        ||? { |pw: PathWithSlot| open_chunks(pw.path) }                                : Path     => RawChunk,
+        ||? {
-        |?  { move |rope| obiread::normalize_sequence_chunk(rope, k) }                 : RawChunk => NormChunk,
+            let k = k;
-        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }  : NormChunk => Batch,
+            move |pw: PathWithSlot| {
+                let path_str = pw.path.to_str().unwrap_or("").to_owned();
+                obiread::open_nuc_stream(&path_str, k)
+            }
+        } : Path => NucPage,
+        | { move |page| obiskbuilder::build_superkmers_page(page, k, level_max, theta) } : NucPage => Batch,
     };
 
     let mut out = BufWriter::new(io::stdout());

src/obikmer/src/steps/scatter.rs

@@ -1,30 +1,37 @@
 use std::path::PathBuf;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicU32, AtomicU64, Ordering};
 use std::sync::Arc;
 use std::time::{Duration, Instant};
 
 use indicatif::{ProgressBar, ProgressStyle};
+use obiread::NucPage;
 use obikpartitionner::KmerPartition;
-use obikrope::Rope;
 use obisys::{Reporter, Stage};
 use tracing::info;
 
-use crate::cli::{PipelineData, PathWithSlot, open_chunks, throttle_paths};
+use crate::cli::{PipelineData, PathWithSlot, throttle_paths};
 
 // ── Iterator that keeps the slot guard alive until the file is exhausted ──────
 
-struct GuardedIter<I> {
+struct GuardedIter {
-    inner:  I,
+    inner:       Box<dyn Iterator<Item = NucPage> + Send>,
-    _guard: Box<dyn Send + 'static>,
+    _guard:      Box<dyn Send + 'static>,
+    flat_active: Arc<AtomicU32>,
 }
 
-impl<I: Iterator<Item = Rope>> Iterator for GuardedIter<I> {
+impl Iterator for GuardedIter {
-    type Item = Rope;
+    type Item = NucPage;
-    fn next(&mut self) -> Option<Rope> {
+    fn next(&mut self) -> Option<NucPage> {
         self.inner.next()
     }
 }
 
+impl Drop for GuardedIter {
+    fn drop(&mut self) {
+        self.flat_active.fetch_sub(1, Ordering::Relaxed);
+    }
+}
+
 // ── scatter ───────────────────────────────────────────────────────────────────
 
 /// Run scatter: normalise → build superkmers → route to partition → close.
@@ -44,23 +51,36 @@ pub fn scatter(
     // Throttle in the source thread — never in a worker — to prevent deadlock.
     let throttled = throttle_paths(path_source, max_open);
 
-    let file_count = Arc::new(AtomicU64::new(0));
+    let file_count      = Arc::new(AtomicU64::new(0));
+    let flat_active     = Arc::new(AtomicU32::new(0));
+    let transform_active = Arc::new(AtomicU32::new(0));
 
     let t = Stage::start("scatter");
     let pipe = obipipeline::make_pipe! {
         PipelineData : PathWithSlot => Vec<RoutableSuperKmer>,
         ||? {
-            let file_count = Arc::clone(&file_count);
+            let file_count   = Arc::clone(&file_count);
+            let flat_active  = Arc::clone(&flat_active);
+            let k = k;
             move |pw: PathWithSlot| {
                 let PathWithSlot { path, _guard } = pw;
                 let n = file_count.fetch_add(1, Ordering::Relaxed) + 1;
                 info!("indexing [{}]: {}", n, path.display());
-                // _guard travels into GuardedIter; released when all chunks are read
+                let path_str = path.to_str().unwrap_or("").to_owned();
-                open_chunks(path).map(|iter| GuardedIter { inner: iter, _guard })
+                flat_active.fetch_add(1, Ordering::Relaxed);
+                obiread::open_nuc_stream(&path_str, k)
+                    .map(|iter| GuardedIter { inner: iter, _guard, flat_active: Arc::clone(&flat_active) })
             }
-        } : Path => RawChunk,
+        } : Path => NucPage,
-        |?  { move |rope| obiread::normalize_sequence_chunk(rope, k) }                 : RawChunk => NormChunk,
+        | {
-        |   { move |rope| obiskbuilder::build_superkmers(rope, k, level_max, theta) }  : NormChunk => Batch,
+            let transform_active = Arc::clone(&transform_active);
+            move |page| {
+                transform_active.fetch_add(1, Ordering::Relaxed);
+                let result = obiskbuilder::build_superkmers_page(page, k, level_max, theta);
+                transform_active.fetch_sub(1, Ordering::Relaxed);
+                result
+            }
+        } : NucPage => Batch,
     };
 
     let pb = ProgressBar::new_spinner();
@@ -93,7 +113,9 @@ pub fn scatter(
                 (format!("{:.0} Mbp", bp / 1e6), format!("{:.0} Mbp/s", ema_rate / 1e6))
             };
             let n_files = file_count.load(Ordering::Relaxed);
-            pb.set_message(format!("{count_str}  {rate_str}  {n_files} files"));
+            let r = flat_active.load(Ordering::Relaxed);
+            let c = transform_active.load(Ordering::Relaxed);
+            pb.set_message(format!("{count_str}  {rate_str}  {n_files} files  [R:{r} C:{c}]"));
         }
         kp.write_batch(batch).unwrap_or_else(|e| {
             eprintln!("error: {e}");

src/obiread/src/chunk.rs

@@ -191,111 +191,5 @@ pub fn fastq_chunks<R: Read>(source: R) -> SeqChunkIter<R> {
 }
 
 #[cfg(test)]
-mod tests {
+#[path = "tests/chunk.rs"]
-    use super::*;
+mod tests;
-    use crate::fasta::end_of_last_fasta_entry;
-    use crate::fastq::end_of_last_fastq_entry;
-
-    fn fasta_iter(data: &'static [u8], block_size: usize) -> SeqChunkIter<&'static [u8]> {
-        SeqChunkIter::new(data, block_size, end_of_last_fasta_entry, None)
-    }
-
-    fn fastq_iter(data: &'static [u8], block_size: usize) -> SeqChunkIter<&'static [u8]> {
-        SeqChunkIter::new(data, block_size, end_of_last_fastq_entry, None)
-    }
-
-    fn rope_to_vec(rope: &Rope) -> Vec<u8> {
-        rope.fw_cursor().collect()
-    }
-
-    // ── FASTA ─────────────────────────────────────────────────────────────────
-
-    #[test]
-    fn fasta_single_record_one_chunk() {
-        let data: &[u8] = b">s1\nACGT\n";
-        let chunks: Vec<_> = fasta_iter(data, 64).collect::<Result<_, _>>().unwrap();
-        assert_eq!(chunks.len(), 1);
-        assert_eq!(rope_to_vec(&chunks[0]), b">s1\nACGT\n");
-    }
-
-    #[test]
-    fn fasta_two_records_split_across_chunks() {
-        let data: &[u8] = b">s1\nACGT\n>s2\nTTTT\n";
-        let chunks: Vec<_> = fasta_iter(data, 10).collect::<Result<_, _>>().unwrap();
-        let all: Vec<u8> = chunks.iter().flat_map(|r| rope_to_vec(r)).collect();
-        assert_eq!(all, b">s1\nACGT\n>s2\nTTTT\n");
-    }
-
-    #[test]
-    fn fasta_each_chunk_ends_on_complete_record() {
-        let data: &[u8] = b">s1\nACGT\n>s2\nCCCC\n>s3\nGGGG\n>s4\nTTTT\n";
-        for block in [8, 12, 20, 100] {
-            let chunks: Vec<_> = fasta_iter(data, block).collect::<Result<_, _>>().unwrap();
-            for rope in &chunks {
-                let flat = rope_to_vec(rope);
-                assert_eq!(flat[0], b'>', "block={block}: chunk doesn't start with '>'");
-                assert_eq!(
-                    *flat.last().unwrap(),
-                    b'\n',
-                    "block={block}: chunk doesn't end with newline"
-                );
-            }
-        }
-    }
-
-    // ── FASTQ ─────────────────────────────────────────────────────────────────
-
-    fn make_fastq(records: &[(&[u8], &[u8])]) -> Vec<u8> {
-        let mut buf = Vec::new();
-        for (seq, qual) in records {
-            buf.extend_from_slice(b"@hdr\n");
-            buf.extend_from_slice(seq);
-            buf.push(b'\n');
-            buf.extend_from_slice(b"+\n");
-            buf.extend_from_slice(qual);
-            buf.push(b'\n');
-        }
-        buf
-    }
-
-    #[test]
-    fn fastq_single_record_one_chunk() {
-        let data = Box::leak(make_fastq(&[(b"ACGT", b"IIII")]).into_boxed_slice());
-        let chunks: Vec<_> = fastq_iter(data, 64).collect::<Result<_, _>>().unwrap();
-        assert_eq!(chunks.len(), 1);
-    }
-
-    #[test]
-    fn fastq_at_in_quality_handled() {
-        let data = Box::leak(
-            make_fastq(&[(b"ACGTACGT", b"@@@@IIII"), (b"TTTTTTTT", b"HHHHHHHH")])
-                .into_boxed_slice(),
-        );
-        let chunks: Vec<_> = fastq_iter(data, 16).collect::<Result<_, _>>().unwrap();
-        let all: Vec<u8> = chunks.iter().flat_map(|r| rope_to_vec(r)).collect();
-        assert_eq!(all, *data);
-    }
-
-    #[test]
-    fn fastq_each_chunk_starts_with_at() {
-        let data = Box::leak(
-            make_fastq(&[
-                (b"ACGT", b"IIII"),
-                (b"CCCC", b"JJJJ"),
-                (b"GGGG", b"KKKK"),
-                (b"TTTT", b"LLLL"),
-            ])
-            .into_boxed_slice(),
-        );
-        for block in [18, 30, 60] {
-            let chunks: Vec<_> = fastq_iter(data, block).collect::<Result<_, _>>().unwrap();
-            for rope in &chunks {
-                let first_byte = rope_to_vec(rope)[0];
-                assert_eq!(
-                    first_byte, b'@',
-                    "block={block}: chunk doesn't start with '@'"
-                );
-            }
-        }
-    }
-}

src/obiread/src/fasta.rs

@@ -35,71 +35,5 @@ pub fn end_of_last_fasta_entry(rope: &Rope) -> Option<usize> {
 }
 
 #[cfg(test)]
-mod tests {
+#[path = "tests/fasta.rs"]
-    use super::*;
+mod tests;
-
-    fn rope(data: &[u8]) -> Rope {
-        let mut r = Rope::new(None);
-        r.push(data.to_vec());
-        r
-    }
-
-    fn rope2(a: &[u8], b: &[u8]) -> Rope {
-        let mut r = Rope::new(None);
-        r.push(a.to_vec());
-        r.push(b.to_vec());
-        r
-    }
-
-    fn flat(r: &Rope) -> Vec<u8> {
-        r.fw_cursor().collect()
-    }
-
-    #[test]
-    fn single_entry_no_boundary() {
-        assert_eq!(end_of_last_fasta_entry(&rope(b">seq1\nACGT\n")), None);
-    }
-
-    #[test]
-    fn two_entries_cuts_at_second_header() {
-        let data = b">seq1\nACGT\n>seq2\nTTTT\n";
-        let r = rope(data);
-        let pos = end_of_last_fasta_entry(&r).unwrap();
-        assert_eq!(&flat(&r)[pos..], b">seq2\nTTTT\n");
-        assert_eq!(&flat(&r)[..pos], b">seq1\nACGT\n");
-    }
-
-    #[test]
-    fn three_entries_cuts_at_last_header() {
-        let data = b">s1\nAA\n>s2\nCC\n>s3\nGG\n";
-        let r = rope(data);
-        let pos = end_of_last_fasta_entry(&r).unwrap();
-        assert_eq!(&flat(&r)[pos..], b">s3\nGG\n");
-    }
-
-    #[test]
-    fn multiline_sequence() {
-        let data = b">s1\nACGT\nACGT\n>s2\nTTTT\n";
-        let r = rope(data);
-        let pos = end_of_last_fasta_entry(&r).unwrap();
-        assert_eq!(&flat(&r)[pos..], b">s2\nTTTT\n");
-    }
-
-    #[test]
-    fn crlf_line_endings() {
-        let data = b">s1\r\nACGT\r\n>s2\r\nTTTT\r\n";
-        let r = rope(data);
-        let pos = end_of_last_fasta_entry(&r).unwrap();
-        assert_eq!(&flat(&r)[pos..], b">s2\r\nTTTT\r\n");
-    }
-
-    #[test]
-    fn boundary_spans_two_blocks() {
-        let a = b">s1\nACGT\n";
-        let b = b">s2\nTTTT\n";
-        let r = rope2(a, b);
-        let all: Vec<u8> = flat(&r);
-        let pos = end_of_last_fasta_entry(&r).unwrap();
-        assert_eq!(&all[pos..], b">s2\nTTTT\n");
-    }
-}

src/obiread/src/fastq.rs

@@ -107,78 +107,5 @@ pub fn end_of_last_fastq_entry(rope: &Rope) -> Option<usize> {
 }
 
 #[cfg(test)]
-mod tests {
+#[path = "tests/fastq.rs"]
-    use super::*;
+mod tests;
-
-    fn rope(data: &[u8]) -> Rope {
-        let mut r = Rope::new(None);
-        r.push(data.to_vec());
-        r
-    }
-
-    fn make_fastq(records: &[(&[u8], &[u8])]) -> Vec<u8> {
-        let mut buf = Vec::new();
-        for (seq, qual) in records {
-            buf.extend_from_slice(b"@header\n");
-            buf.extend_from_slice(seq);
-            buf.push(b'\n');
-            buf.extend_from_slice(b"+\n");
-            buf.extend_from_slice(qual);
-            buf.push(b'\n');
-        }
-        buf
-    }
-
-    fn flat(r: &Rope) -> Vec<u8> {
-        r.fw_cursor().collect()
-    }
-
-    #[test]
-    fn single_record_no_boundary() {
-        let buf = make_fastq(&[(b"ACGT", b"IIII")]);
-        assert_eq!(end_of_last_fastq_entry(&rope(&buf)), None);
-    }
-
-    #[test]
-    fn two_records_cuts_at_second() {
-        let buf = make_fastq(&[(b"ACGT", b"IIII"), (b"TTTT", b"HHHH")]);
-        let r = rope(&buf);
-        let pos = end_of_last_fastq_entry(&r).unwrap();
-        assert_eq!(flat(&r)[pos], b'@');
-        assert_eq!(
-            &flat(&r)[pos..],
-            make_fastq(&[(b"TTTT", b"HHHH")]).as_slice()
-        );
-    }
-
-    #[test]
-    fn three_records_cuts_at_last() {
-        let buf = make_fastq(&[(b"ACGT", b"IIII"), (b"CCCC", b"JJJJ"), (b"GGGG", b"KKKK")]);
-        let r = rope(&buf);
-        let pos = end_of_last_fastq_entry(&r).unwrap();
-        assert_eq!(
-            &flat(&r)[pos..],
-            make_fastq(&[(b"GGGG", b"KKKK")]).as_slice()
-        );
-    }
-
-    #[test]
-    fn at_sign_in_quality_does_not_confuse() {
-        let buf = make_fastq(&[(b"ACGTACGT", b"@@@@IIII"), (b"TTTT", b"HHHH")]);
-        let r = rope(&buf);
-        let pos = end_of_last_fastq_entry(&r).unwrap();
-        assert_eq!(
-            &flat(&r)[pos..],
-            make_fastq(&[(b"TTTT", b"HHHH")]).as_slice()
-        );
-    }
-
-    #[test]
-    fn crlf_line_endings() {
-        let data = b"@h\r\nACGT\r\n+\r\nIIII\r\n@h\r\nTTTT\r\n+\r\nHHHH\r\n";
-        let r = rope(data);
-        let pos = end_of_last_fastq_entry(&r).unwrap();
-        assert_eq!(flat(&r)[pos], b'@');
-        assert_eq!(&flat(&r)[pos..], b"@h\r\nTTTT\r\n+\r\nHHHH\r\n");
-    }
-}

src/obiread/src/lib.rs

@@ -10,15 +10,19 @@ mod fasta;
 mod fastq;
 mod mimetype;
 pub mod normalize;
+mod nucstream;
 mod path_iterator;
 pub mod peakreader;
 pub mod record;
 pub mod xopen;
 
-pub use chunk::{SeqChunkIter, fasta_chunks, fastq_chunks,
+pub use chunk::{
-                read_fasta_chunks, read_fastq_chunks, read_sequence_chunks};
+    SeqChunkIter, fasta_chunks, fastq_chunks, read_fasta_chunks, read_fastq_chunks,
-pub use normalize::{normalize_fasta_chunk, normalize_fastq_chunk, normalize_sequence_chunk};
+    read_sequence_chunks,
+};
 pub use mimetype::MimeTypeGuesser;
+pub use normalize::{normalize_fasta_chunk, normalize_fastq_chunk, normalize_sequence_chunk};
+pub use nucstream::{NucPage, NucPageCursor, open_nuc_stream};
 pub use path_iterator::{PathIter, path_iter};
 pub use peakreader::PeekReader;
 pub use xopen::xopen;

src/obiread/src/mimetype.rs

@@ -9,6 +9,10 @@ use crate::peakreader::PeekReader;
 
 const BUF_SIZE: usize = 4096;
 
+fn is_gbff(buf: &[u8]) -> bool {
+    buf.starts_with(b"LOCUS ")
+}
+
 static RE_FASTA: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"^>[^ ]").unwrap());
 fn is_fasta(buf: &[u8]) -> bool {
     std::str::from_utf8(buf).map_or(false, |s| RE_FASTA.is_match(s))
@@ -30,6 +34,7 @@ fn is_text(buf: &[u8]) -> bool {
 // Most specific formats (fastq, fasta) come before the generic text/plain fallback.
 static INFER: LazyLock<Infer> = LazyLock::new(|| {
     let mut infer = Infer::new();
+    infer.add("text/gbff",  "gbff", is_gbff);
     infer.add("text/fastq", "fastq", is_fastq);
     infer.add("text/fasta", "fasta", is_fasta);
     infer.add("text/plain", "txt", is_text);

src/obiread/src/normalize.rs

@@ -215,239 +215,5 @@ fn is_acgt(upper: u8) -> bool {
 // ── tests ─────────────────────────────────────────────────────────────────────
 
 #[cfg(test)]
-mod tests {
+#[path = "tests/normalize.rs"]
-    use super::*;
+mod tests;
-
-    fn make_rope(data: &[u8]) -> Rope {
-        let mut r = Rope::new(None);
-        r.push(data.to_vec());
-        r
-    }
-
-    fn flat(r: Rope) -> Vec<u8> {
-        r.fw_cursor().collect()
-    }
-
-    fn run_fastq(data: &[u8], k: usize) -> Vec<u8> {
-        flat(normalize_fastq_chunk(make_rope(data), k))
-    }
-
-    fn run_fasta(data: &[u8], k: usize) -> Vec<u8> {
-        flat(normalize_fasta_chunk(make_rope(data), k))
-    }
-
-    fn make_fastq(records: &[&[u8]]) -> Vec<u8> {
-        let mut buf = Vec::new();
-        for seq in records {
-            buf.extend_from_slice(b"@hdr\n");
-            buf.extend_from_slice(seq);
-            buf.push(b'\n');
-            buf.extend_from_slice(b"+\n");
-            buf.extend_from_slice(&vec![b'I'; seq.len()]);
-            buf.push(b'\n');
-        }
-        buf
-    }
-
-    fn make_fasta(records: &[(&[u8], &[u8])]) -> Vec<u8> {
-        let mut buf = Vec::new();
-        for (id, seq) in records {
-            buf.push(b'>');
-            buf.extend_from_slice(id);
-            buf.push(b'\n');
-            buf.extend_from_slice(seq);
-            buf.push(b'\n');
-        }
-        buf
-    }
-
-    // ── FASTQ basic ──────────────────────────────────────────────────────────
-
-    #[test]
-    fn single_record_produces_seq_then_null() {
-        assert_eq!(run_fastq(&make_fastq(&[b"ACGTACGT"]), 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn two_records_concatenated() {
-        assert_eq!(
-            run_fastq(&make_fastq(&[b"ACGTACGT", b"TTTTTTTT"]), 4),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-
-    #[test]
-    fn lowercase_input_uppercased() {
-        assert_eq!(run_fastq(&make_fastq(&[b"acgtacgt"]), 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn mixed_case_uppercased() {
-        assert_eq!(run_fastq(&make_fastq(&[b"AcGtAcGt"]), 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn sequence_shorter_than_k_discarded() {
-        assert_eq!(run_fastq(&make_fastq(&[b"ACG"]), 4), b"");
-    }
-
-    #[test]
-    fn sequence_exactly_k_kept() {
-        assert_eq!(run_fastq(&make_fastq(&[b"ACGT"]), 4), b"ACGT\x00");
-    }
-
-    #[test]
-    fn short_record_among_valid_ones_discarded() {
-        assert_eq!(
-            run_fastq(&make_fastq(&[b"ACGTACGT", b"AC", b"TTTTTTTT"]), 4),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-
-    #[test]
-    fn ambiguous_splits_into_two_segments() {
-        assert_eq!(
-            run_fastq(&make_fastq(&[b"ACGTNACGT"]), 4),
-            b"ACGT\x00ACGT\x00"
-        );
-    }
-
-    #[test]
-    fn segment_after_ambiguous_too_short_discarded() {
-        assert_eq!(
-            run_fastq(&make_fastq(&[b"ACGTACGTNAC"]), 4),
-            b"ACGTACGT\x00"
-        );
-    }
-
-    #[test]
-    fn consecutive_ambiguous_produce_no_empty_segment() {
-        assert_eq!(
-            run_fastq(&make_fastq(&[b"ACGTNNNNACGT"]), 4),
-            b"ACGT\x00ACGT\x00"
-        );
-    }
-
-    #[test]
-    fn ambiguous_at_start_skipped() {
-        assert_eq!(run_fastq(&make_fastq(&[b"NNACGTACGT"]), 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn ambiguous_at_end_produces_no_trailing_empty() {
-        assert_eq!(run_fastq(&make_fastq(&[b"ACGTACGTNN"]), 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn crlf_handled() {
-        let data = b"@hdr\r\nACGTACGT\r\n+\r\nIIIIIIII\r\n";
-        assert_eq!(run_fastq(data, 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn multi_slice_rope() {
-        let data = make_fastq(&[b"ACGTACGT", b"TTTTTTTT"]);
-        let mid = data.len() / 2;
-        let mut rope = Rope::new(None);
-        rope.push(data[..mid].to_vec());
-        rope.push(data[mid..].to_vec());
-        assert_eq!(
-            flat(normalize_fastq_chunk(rope, 4)),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-
-    // ── FASTA ─────────────────────────────────────────────────────────────────
-
-    #[test]
-    fn fasta_single_record() {
-        assert_eq!(
-            run_fasta(&make_fasta(&[(b"s1", b"ACGTACGT")]), 4),
-            b"ACGTACGT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_two_records() {
-        assert_eq!(
-            run_fasta(
-                &make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"TTTTTTTT")]),
-                4
-            ),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_multiline_sequence_concatenated() {
-        assert_eq!(
-            run_fasta(b">s1\nACGT\nACGT\nACGT\n", 4),
-            b"ACGTACGTACGT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_lowercase_uppercased() {
-        assert_eq!(
-            run_fasta(&make_fasta(&[(b"s1", b"acgtacgt")]), 4),
-            b"ACGTACGT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_short_record_discarded() {
-        assert_eq!(run_fasta(&make_fasta(&[(b"s1", b"ACG")]), 4), b"");
-    }
-
-    #[test]
-    fn fasta_short_among_valid_discarded() {
-        assert_eq!(
-            run_fasta(
-                &make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"AC"), (b"s3", b"TTTTTTTT")]),
-                4
-            ),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_ambiguous_splits_segments() {
-        assert_eq!(run_fasta(b">s1\nACGTNACGT\n", 4), b"ACGT\x00ACGT\x00");
-    }
-
-    #[test]
-    fn fasta_ambiguous_across_line_boundary() {
-        assert_eq!(run_fasta(b">s1\nACGT\nNACGT\n", 4), b"ACGT\x00ACGT\x00");
-    }
-
-    #[test]
-    fn fasta_ambiguous_short_segment_discarded() {
-        assert_eq!(run_fasta(b">s1\nACGTACGTNAC\n", 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn fasta_no_trailing_newline() {
-        assert_eq!(run_fasta(b">s1\nACGTACGT", 4), b"ACGTACGT\x00");
-    }
-
-    #[test]
-    fn fasta_crlf_line_endings() {
-        assert_eq!(
-            run_fasta(b">s1\r\nACGT\r\nACGT\r\n>s2\r\nTTTT\r\n", 4),
-            b"ACGTACGT\x00TTTT\x00"
-        );
-    }
-
-    #[test]
-    fn fasta_multi_slice_rope() {
-        let data = make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"TTTTTTTT")]);
-        let mid = data.len() / 2;
-        let mut rope = Rope::new(None);
-        rope.push(data[..mid].to_vec());
-        rope.push(data[mid..].to_vec());
-        assert_eq!(
-            flat(normalize_fasta_chunk(rope, 4)),
-            b"ACGTACGT\x00TTTTTTTT\x00"
-        );
-    }
-}

src/obiread/src/nucstream.rs

@@ -0,0 +1,733 @@
+use std::io::{self, Read};
+use std::mem::ManuallyDrop;
+use std::sync::{Arc, Mutex};
+
+use crate::mimetype::MimeTypeGuesser;
+use crate::xopen::open_raw;
+
+pub const MAX_K: usize = 31;
+const PAGE_SIZE: usize = 65536;
+// overlap (MAX_K - 1) + page data (PAGE_SIZE) + 1 byte for the end-of-page terminating 0
+const BUF_SIZE: usize = MAX_K + PAGE_SIZE;
+
+// ─── OverlapState ─────────────────────────────────────────────────────────────
+
+pub(crate) struct OverlapState {
+    data: [u8; MAX_K],
+    len: usize,
+    k: usize,
+}
+
+impl OverlapState {
+    pub(crate) fn new(k: usize) -> Self {
+        assert!(k > 0 && k <= MAX_K);
+        Self {
+            data: [0u8; MAX_K],
+            len: 0,
+            k,
+        }
+    }
+}
+
+// ─── NucParser trait ──────────────────────────────────────────────────────────
+
+// Transforms a raw page into a compacted nucleotide stream in-place.
+//
+// Buffer layout on each call:
+//   buf[0..overlap_len()]           — overlap bytes copied by write_overlap()
+//   buf[overlap_len()..overlap_len()+n] — raw bytes just read from the source
+//
+// Returns the number of output bytes in buf[0..returned].
+pub(crate) trait NucParser {
+    // required: format-specific
+    fn new(k: usize) -> Self
+    where
+        Self: Sized;
+    fn overlap_state(&self) -> &OverlapState;
+    fn overlap_state_mut(&mut self) -> &mut OverlapState;
+    fn is_in_seq(&self) -> bool;
+    fn parse_inplace(&mut self, buf: &mut [u8], n: usize) -> usize;
+
+    // provided: format-independent overlap management
+    fn overlap_len(&self) -> usize {
+        self.overlap_state().len
+    }
+
+    fn write_overlap(&self, buf: &mut [u8]) {
+        let ol = &self.overlap_state();
+        buf[..ol.len].copy_from_slice(&ol.data[..ol.len]);
+    }
+
+    // Called at end of parse_inplace: saves overlap state and returns adjusted j.
+    // seq_start is the j-position where the last sequence started in this call's output.
+    fn save_overlap(&mut self, buf: &mut [u8], j: usize, seq_start: usize) -> usize {
+        if !self.is_in_seq() {
+            self.overlap_state_mut().len = 0;
+            return j;
+        }
+        let seq_len = j - seq_start;
+        let k = self.overlap_state().k;
+        if seq_len >= k {
+            // Sequence long enough: save last k-1 nucleotides, terminate with 0.
+            let ol = k - 1;
+            self.overlap_state_mut().data[..ol].copy_from_slice(&buf[j - ol..j]);
+            self.overlap_state_mut().len = ol;
+            // SAFETY: j <= total - 1 < BUF_SIZE = buf.len()
+            // (total = overlap_len + n <= (MAX_K-1) + PAGE_SIZE = BUF_SIZE - 1)
+            unsafe {
+                *buf.get_unchecked_mut(j) = 0;
+            }
+            j + 1
+        } else if seq_len > 0 {
+            // Short sequence (< k): save whole fragment, strip from output.
+            self.overlap_state_mut().data[..seq_len].copy_from_slice(&buf[seq_start..j]);
+            self.overlap_state_mut().len = seq_len;
+            seq_start
+        } else {
+            self.overlap_state_mut().len = 0;
+            j
+        }
+    }
+}
+
+// ─── FASTA parser ─────────────────────────────────────────────────────────────
+
+#[derive(Clone, Copy)]
+enum FastaState {
+    OutSeq,
+    InTitle,
+    InSeq,
+    InAmbiguous,
+}
+
+pub(crate) struct FastaParser {
+    state: FastaState,
+    overlap: OverlapState,
+}
+
+impl NucParser for FastaParser {
+    fn new(k: usize) -> Self {
+        Self {
+            state: FastaState::OutSeq,
+            overlap: OverlapState::new(k),
+        }
+    }
+
+    #[inline]
+    fn overlap_state(&self) -> &OverlapState {
+        &self.overlap
+    }
+
+    #[inline]
+    fn overlap_state_mut(&mut self) -> &mut OverlapState {
+        &mut self.overlap
+    }
+
+    #[inline]
+    fn is_in_seq(&self) -> bool {
+        matches!(self.state, FastaState::InSeq)
+    }
+
+    fn parse_inplace(&mut self, buf: &mut [u8], n: usize) -> usize {
+        let total = self.overlap.len + n;
+        let mut i = 0; // read index
+        let mut j = 0; // write index (invariant: j <= i always)
+        // j-position where the current sequence started in this call's output;
+        // meaningful only when state is InSeq.
+        let mut seq_start: usize = 0;
+
+        while i < total {
+            // SAFETY: i < total <= BUF_SIZE = buf.len()
+            let byte = unsafe { *buf.get_unchecked(i) };
+
+            match self.state {
+                FastaState::OutSeq => {
+                    if byte == b'>' {
+                        self.state = FastaState::InTitle;
+                    }
+                    i += 1;
+                }
+                FastaState::InTitle => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = FastaState::InSeq;
+                        seq_start = j;
+                    }
+                    i += 1;
+                }
+                FastaState::InSeq => {
+                    if byte == b'\n' || byte == b'\r' {
+                        i += 1;
+                        continue;
+                    }
+                    let nuc = byte & 0xDF; // to uppercase
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                        i += 1;
+                    } else if byte == b'>' {
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = FastaState::InTitle;
+                        i += 1;
+                    } else {
+                        // first ambiguous base: end current sequence if non-empty
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = FastaState::InAmbiguous;
+                        i += 1;
+                    }
+                }
+                FastaState::InAmbiguous => {
+                    if byte == b'\n' || byte == b'\r' {
+                        i += 1;
+                        continue;
+                    }
+                    if byte == b'>' {
+                        self.state = FastaState::InTitle;
+                        i += 1;
+                        continue;
+                    }
+                    let nuc = byte & 0xDF;
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        seq_start = j;
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                        self.state = FastaState::InSeq;
+                    }
+                    i += 1;
+                }
+            }
+        }
+
+        self.save_overlap(buf, j, seq_start)
+    }
+}
+
+// ─── FASTQ parser ─────────────────────────────────────────────────────────────
+
+#[derive(Clone, Copy)]
+enum FastqState {
+    OutSeq,
+    InTitle,
+    InSeq,
+    InAmbiguous,
+    InQualTitle,
+    InQual,
+}
+
+pub(crate) struct FastqParser {
+    state: FastqState,
+    overlap: OverlapState,
+}
+
+impl NucParser for FastqParser {
+    fn new(k: usize) -> Self {
+        Self {
+            state: FastqState::OutSeq,
+            overlap: OverlapState::new(k),
+        }
+    }
+
+    #[inline]
+    fn overlap_state(&self) -> &OverlapState {
+        &self.overlap
+    }
+
+    #[inline]
+    fn overlap_state_mut(&mut self) -> &mut OverlapState {
+        &mut self.overlap
+    }
+
+    #[inline]
+    fn is_in_seq(&self) -> bool {
+        matches!(self.state, FastqState::InSeq)
+    }
+
+    fn parse_inplace(&mut self, buf: &mut [u8], n: usize) -> usize {
+        let total = self.overlap.len + n;
+        let mut i = 0;
+        let mut j = 0;
+        let mut seq_start: usize = 0;
+
+        while i < total {
+            // SAFETY: i < total <= BUF_SIZE = buf.len()
+            let byte = unsafe { *buf.get_unchecked(i) };
+
+            match self.state {
+                FastqState::OutSeq => {
+                    if byte == b'@' {
+                        self.state = FastqState::InTitle;
+                    }
+                    i += 1;
+                }
+                FastqState::InTitle => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = FastqState::InSeq;
+                        seq_start = j;
+                    }
+                    i += 1;
+                }
+                FastqState::InSeq => {
+                    if byte == b'\n' || byte == b'\r' {
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = FastqState::InQualTitle;
+                        i += 1;
+                        continue;
+                    }
+                    let nuc = byte & 0xDF;
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                    } else {
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = FastqState::InAmbiguous;
+                    }
+                    i += 1;
+                }
+                FastqState::InAmbiguous => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = FastqState::InQualTitle;
+                        i += 1;
+                        continue;
+                    }
+                    let nuc = byte & 0xDF;
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        seq_start = j;
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                        self.state = FastqState::InSeq;
+                    }
+                    i += 1;
+                }
+                FastqState::InQualTitle => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = FastqState::InQual;
+                    }
+                    i += 1;
+                }
+                FastqState::InQual => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = FastqState::OutSeq;
+                    }
+                    i += 1;
+                }
+            }
+        }
+
+        self.save_overlap(buf, j, seq_start)
+    }
+}
+
+// ─── GenBank parser ───────────────────────────────────────────────────────────
+
+const ORIGIN_TAIL: &[u8] = b"RIGIN";
+
+#[derive(Clone, Copy)]
+enum GenbankState {
+    OutSeq,
+    MatchOrigin,
+    SkipOriginLine,
+    InSeq,
+    InSlash,
+    InAmbiguous,
+}
+
+pub(crate) struct GenbankParser {
+    state: GenbankState,
+    overlap: OverlapState,
+    keyword_pos: usize,
+    at_line_start: bool,
+}
+
+impl NucParser for GenbankParser {
+    fn new(k: usize) -> Self {
+        Self {
+            state: GenbankState::OutSeq,
+            overlap: OverlapState::new(k),
+            keyword_pos: 0,
+            at_line_start: true,
+        }
+    }
+
+    #[inline]
+    fn overlap_state(&self) -> &OverlapState {
+        &self.overlap
+    }
+
+    #[inline]
+    fn overlap_state_mut(&mut self) -> &mut OverlapState {
+        &mut self.overlap
+    }
+
+    #[inline]
+    fn is_in_seq(&self) -> bool {
+        matches!(self.state, GenbankState::InSeq)
+    }
+
+    fn parse_inplace(&mut self, buf: &mut [u8], n: usize) -> usize {
+        let total = self.overlap.len + n;
+        let mut i = 0;
+        let mut j = 0;
+        let mut seq_start: usize = 0;
+
+        while i < total {
+            // SAFETY: i < total <= BUF_SIZE = buf.len()
+            let byte = unsafe { *buf.get_unchecked(i) };
+
+            match self.state {
+                GenbankState::OutSeq => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.at_line_start = true;
+                    } else if self.at_line_start && byte == b'O' {
+                        self.state = GenbankState::MatchOrigin;
+                        self.keyword_pos = 1;
+                        self.at_line_start = false;
+                    } else {
+                        self.at_line_start = false;
+                    }
+                    i += 1;
+                }
+                GenbankState::MatchOrigin => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = GenbankState::OutSeq;
+                        self.at_line_start = true;
+                    } else if byte == ORIGIN_TAIL[self.keyword_pos - 1] {
+                        self.keyword_pos += 1;
+                        if self.keyword_pos == 6 {
+                            self.state = GenbankState::SkipOriginLine;
+                        }
+                    } else {
+                        self.state = GenbankState::OutSeq;
+                        self.at_line_start = false;
+                    }
+                    i += 1;
+                }
+                GenbankState::SkipOriginLine => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.state = GenbankState::InSeq;
+                        seq_start = j;
+                    }
+                    i += 1;
+                }
+                GenbankState::InSeq => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.at_line_start = true;
+                        i += 1;
+                        continue;
+                    }
+                    if self.at_line_start && byte == b'/' {
+                        self.state = GenbankState::InSlash;
+                        self.at_line_start = false;
+                        i += 1;
+                        continue;
+                    }
+                    self.at_line_start = false;
+                    let nuc = byte & 0xDF;
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                    } else if byte.is_ascii_digit() || byte == b' ' {
+                        // position numbers and spacing between groups: skip
+                    } else {
+                        // ambiguous base: end current sequence if non-empty
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = GenbankState::InAmbiguous;
+                    }
+                    i += 1;
+                }
+                GenbankState::InSlash => {
+                    if byte == b'/' {
+                        // confirmed "//": end of sequence record
+                        if j > seq_start {
+                            unsafe {
+                                *buf.get_unchecked_mut(j) = 0;
+                            }
+                            j += 1;
+                        }
+                        self.state = GenbankState::OutSeq;
+                        self.at_line_start = false;
+                    } else if byte == b'\n' || byte == b'\r' {
+                        // single '/' line: back to sequence
+                        self.state = GenbankState::InSeq;
+                        self.at_line_start = true;
+                    } else {
+                        // false positive: single '/' mid-line, resume sequence
+                        self.state = GenbankState::InSeq;
+                        self.at_line_start = false;
+                    }
+                    i += 1;
+                }
+                GenbankState::InAmbiguous => {
+                    if byte == b'\n' || byte == b'\r' {
+                        self.at_line_start = true;
+                        i += 1;
+                        continue;
+                    }
+                    if self.at_line_start && byte == b'/' {
+                        self.state = GenbankState::InSlash;
+                        self.at_line_start = false;
+                        i += 1;
+                        continue;
+                    }
+                    self.at_line_start = false;
+                    let nuc = byte & 0xDF;
+                    if nuc == b'A' || nuc == b'C' || nuc == b'G' || nuc == b'T' {
+                        seq_start = j;
+                        // SAFETY: j <= i < total <= BUF_SIZE = buf.len()
+                        unsafe {
+                            *buf.get_unchecked_mut(j) = nuc;
+                        }
+                        j += 1;
+                        self.state = GenbankState::InSeq;
+                    }
+                    // digits, spaces, other ambiguous codes: skip
+                    i += 1;
+                }
+            }
+        }
+
+        self.save_overlap(buf, j, seq_start)
+    }
+}
+
+// ─── NucPage ──────────────────────────────────────────────────────────────────
+
+/// Owned page of compacted nucleotides: uppercase A/C/G/T bytes separated by `0`
+/// at sequence boundaries. Automatically returns its buffer to the pool on drop.
+pub struct NucPage {
+    data: ManuallyDrop<Vec<u8>>,
+    len: usize,
+    pool: Arc<Mutex<Vec<Vec<u8>>>>,
+}
+
+impl std::ops::Deref for NucPage {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        &self.data[..self.len]
+    }
+}
+
+impl Drop for NucPage {
+    fn drop(&mut self) {
+        // SAFETY: data is never accessed after this point
+        let buf = unsafe { ManuallyDrop::take(&mut self.data) };
+        self.pool.lock().unwrap().push(buf);
+    }
+}
+
+// ─── NucPageCursor ────────────────────────────────────────────────────────────
+
+/// A forward cursor over the normalised bytes of a [`NucPage`].
+///
+/// Provides the `next_byte` / `rewind` interface consumed by
+/// [`obiskbuilder::SuperKmerStreamIter`].
+pub struct NucPageCursor<'a> {
+    data: &'a [u8],
+    pos: usize,
+}
+
+impl NucPageCursor<'_> {
+    /// Returns the next byte in the page, or `None` at end.
+    #[inline]
+    pub fn next_byte(&mut self) -> Option<u8> {
+        if self.pos < self.data.len() {
+            let b = self.data[self.pos];
+            self.pos += 1;
+            Some(b)
+        } else {
+            None
+        }
+    }
+
+    /// Steps the cursor back by `n` bytes.
+    ///
+    /// The caller guarantees that the last `n` bytes were all `ACGT`
+    /// (no `0x00` separators), so they are still in the page buffer.
+    #[inline]
+    pub fn rewind(&mut self, n: usize) {
+        self.pos -= n;
+    }
+
+    /// Total number of bytes in the underlying page.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Returns `true` if the page contains no bytes.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.data.is_empty()
+    }
+}
+
+impl NucPage {
+    /// Creates a forward cursor positioned at the start of this page.
+    pub fn cursor(&self) -> NucPageCursor<'_> {
+        NucPageCursor { data: self, pos: 0 }
+    }
+}
+
+// ─── NucStream ────────────────────────────────────────────────────────────────
+
+pub(crate) struct NucStream<R: Read, P: NucParser> {
+    reader: R,
+    parser: P,
+    pool: Arc<Mutex<Vec<Vec<u8>>>>,
+    eof: bool,
+}
+
+impl<R: Read, P: NucParser> NucStream<R, P> {
+    pub(crate) fn new(reader: R, k: usize) -> Self {
+        Self {
+            reader,
+            parser: P::new(k),
+            pool: Arc::new(Mutex::new(Vec::new())),
+            eof: false,
+        }
+    }
+
+    pub(crate) fn read_page(&mut self) -> Option<NucPage> {
+        loop {
+            if self.eof {
+                return None;
+            }
+            // take a buffer from the pool, or allocate fresh if all are in-flight
+            let mut buf = self
+                .pool
+                .lock()
+                .unwrap()
+                .pop()
+                .unwrap_or_else(|| vec![0u8; BUF_SIZE]);
+
+            let ol = self.parser.overlap_len();
+            self.parser.write_overlap(&mut buf[..ol]);
+            let n = self.reader.read(&mut buf[ol..ol + PAGE_SIZE]).unwrap_or(0);
+            if n == 0 {
+                self.eof = true;
+                if ol == 0 {
+                    self.pool.lock().unwrap().push(buf);
+                    return None;
+                }
+            }
+            let out_len = self.parser.parse_inplace(&mut buf, n);
+            if out_len > 0 {
+                return Some(NucPage {
+                    data: ManuallyDrop::new(buf),
+                    len: out_len,
+                    pool: Arc::clone(&self.pool),
+                });
+            }
+            // empty page (all headers/ambiguous): return buf to pool and loop
+            self.pool.lock().unwrap().push(buf);
+        }
+    }
+}
+
+impl<R: Read, P: NucParser> Iterator for NucStream<R, P> {
+    type Item = NucPage;
+    fn next(&mut self) -> Option<NucPage> {
+        self.read_page()
+    }
+}
+
+// ─── FastaNucStream ───────────────────────────────────────────────────────────
+
+pub(crate) type FastaNucStream<R> = NucStream<R, FastaParser>;
+pub(crate) type FastqNucStream<R> = NucStream<R, FastqParser>;
+pub(crate) type GenbankNucStream<R> = NucStream<R, GenbankParser>;
+
+// ─── AnyNucStream ─────────────────────────────────────────────────────────────
+
+pub(crate) enum AnyNucStream<R: Read> {
+    Fasta(FastaNucStream<R>),
+    Fastq(FastqNucStream<R>),
+    Genbank(GenbankNucStream<R>),
+}
+
+impl<R: Read> Iterator for AnyNucStream<R> {
+    type Item = NucPage;
+    fn next(&mut self) -> Option<NucPage> {
+        match self {
+            AnyNucStream::Fasta(s) => s.next(),
+            AnyNucStream::Fastq(s) => s.next(),
+            AnyNucStream::Genbank(s) => s.next(),
+        }
+    }
+}
+
+fn dispatch<R: Read>(
+    mut guesser: MimeTypeGuesser<R>,
+    k: usize,
+) -> Option<AnyNucStream<MimeTypeGuesser<R>>> {
+    match guesser.mime_type() {
+        Some("text/fasta") => Some(AnyNucStream::Fasta(NucStream::new(guesser, k))),
+        Some("text/fastq") => Some(AnyNucStream::Fastq(NucStream::new(guesser, k))),
+        Some("text/gbff") => Some(AnyNucStream::Genbank(NucStream::new(guesser, k))),
+        _ => None,
+    }
+}
+
+/// Wraps an already-open reader in a nucleotide stream, detecting its format.
+/// Returns `None` if the format is not recognised.
+pub(crate) fn nuc_stream<R: Read>(reader: R, k: usize) -> Option<AnyNucStream<MimeTypeGuesser<R>>> {
+    dispatch(MimeTypeGuesser::new(reader), k)
+}
+
+/// Opens a nucleotide stream from any source (file path, URL, or `-` for stdin),
+/// with transparent decompression and automatic format detection.
+///
+/// # Errors
+/// Returns an `io::Error` if the source cannot be opened, decompression fails,
+/// or the format is not recognised.
+pub fn open_nuc_stream(
+    source: &str,
+    k: usize,
+) -> io::Result<Box<dyn Iterator<Item = NucPage> + Send>> {
+    let reader = open_raw(source)?;
+    nuc_stream(reader, k)
+        .map(|s| Box::new(s) as Box<dyn Iterator<Item = NucPage> + Send>)
+        .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "unknown sequence format"))
+}
+
+#[cfg(test)]
+#[path = "tests/nucstream.rs"]
+mod tests;

src/obiread/src/path_iterator.rs

@@ -71,7 +71,7 @@ pub fn path_iter(paths: &[String]) -> PathIter {
     PathIter::new(path_bufs)
 }
 
-/// Returns true if the path ends with a fasta or fastq file extension.
+/// Returns true if the path ends with a recognised sequence file extension.
 fn is_fasta_or_fastq(path: &Path) -> bool {
     let name = path.file_name().and_then(|n| n.to_str()).unwrap_or("");
     name.ends_with(".fasta")
@@ -82,4 +82,10 @@ fn is_fasta_or_fastq(path: &Path) -> bool {
         || name.ends_with(".fa.gz")
         || name.ends_with(".fastq.gz")
         || name.ends_with(".fq.gz")
+        || name.ends_with(".gbff")
+        || name.ends_with(".gbk")
+        || name.ends_with(".gb")
+        || name.ends_with(".gbff.gz")
+        || name.ends_with(".gbk.gz")
+        || name.ends_with(".gb.gz")
 }

src/obiread/src/tests/chunk.rs

@@ -0,0 +1,106 @@
+use super::*;
+use crate::fasta::end_of_last_fasta_entry;
+use crate::fastq::end_of_last_fastq_entry;
+
+fn fasta_iter(data: &'static [u8], block_size: usize) -> SeqChunkIter<&'static [u8]> {
+    SeqChunkIter::new(data, block_size, end_of_last_fasta_entry, None)
+}
+
+fn fastq_iter(data: &'static [u8], block_size: usize) -> SeqChunkIter<&'static [u8]> {
+    SeqChunkIter::new(data, block_size, end_of_last_fastq_entry, None)
+}
+
+fn rope_to_vec(rope: &Rope) -> Vec<u8> {
+    rope.fw_cursor().collect()
+}
+
+// ── FASTA ─────────────────────────────────────────────────────────────────
+
+#[test]
+fn fasta_single_record_one_chunk() {
+    let data: &[u8] = b">s1\nACGT\n";
+    let chunks: Vec<_> = fasta_iter(data, 64).collect::<Result<_, _>>().unwrap();
+    assert_eq!(chunks.len(), 1);
+    assert_eq!(rope_to_vec(&chunks[0]), b">s1\nACGT\n");
+}
+
+#[test]
+fn fasta_two_records_split_across_chunks() {
+    let data: &[u8] = b">s1\nACGT\n>s2\nTTTT\n";
+    let chunks: Vec<_> = fasta_iter(data, 10).collect::<Result<_, _>>().unwrap();
+    let all: Vec<u8> = chunks.iter().flat_map(|r| rope_to_vec(r)).collect();
+    assert_eq!(all, b">s1\nACGT\n>s2\nTTTT\n");
+}
+
+#[test]
+fn fasta_each_chunk_ends_on_complete_record() {
+    let data: &[u8] = b">s1\nACGT\n>s2\nCCCC\n>s3\nGGGG\n>s4\nTTTT\n";
+    for block in [8, 12, 20, 100] {
+        let chunks: Vec<_> = fasta_iter(data, block).collect::<Result<_, _>>().unwrap();
+        for rope in &chunks {
+            let flat = rope_to_vec(rope);
+            assert_eq!(flat[0], b'>', "block={block}: chunk doesn't start with '>'");
+            assert_eq!(
+                *flat.last().unwrap(),
+                b'\n',
+                "block={block}: chunk doesn't end with newline"
+            );
+        }
+    }
+}
+
+// ── FASTQ ─────────────────────────────────────────────────────────────────
+
+fn make_fastq(records: &[(&[u8], &[u8])]) -> Vec<u8> {
+    let mut buf = Vec::new();
+    for (seq, qual) in records {
+        buf.extend_from_slice(b"@hdr\n");
+        buf.extend_from_slice(seq);
+        buf.push(b'\n');
+        buf.extend_from_slice(b"+\n");
+        buf.extend_from_slice(qual);
+        buf.push(b'\n');
+    }
+    buf
+}
+
+#[test]
+fn fastq_single_record_one_chunk() {
+    let data = Box::leak(make_fastq(&[(b"ACGT", b"IIII")]).into_boxed_slice());
+    let chunks: Vec<_> = fastq_iter(data, 64).collect::<Result<_, _>>().unwrap();
+    assert_eq!(chunks.len(), 1);
+}
+
+#[test]
+fn fastq_at_in_quality_handled() {
+    let data = Box::leak(
+        make_fastq(&[(b"ACGTACGT", b"@@@@IIII"), (b"TTTTTTTT", b"HHHHHHHH")])
+            .into_boxed_slice(),
+    );
+    let chunks: Vec<_> = fastq_iter(data, 16).collect::<Result<_, _>>().unwrap();
+    let all: Vec<u8> = chunks.iter().flat_map(|r| rope_to_vec(r)).collect();
+    assert_eq!(all, *data);
+}
+
+#[test]
+fn fastq_each_chunk_starts_with_at() {
+    let data = Box::leak(
+        make_fastq(&[
+            (b"ACGT", b"IIII"),
+            (b"CCCC", b"JJJJ"),
+            (b"GGGG", b"KKKK"),
+            (b"TTTT", b"LLLL"),
+        ])
+        .into_boxed_slice(),
+    );
+    for block in [18, 30, 60] {
+        let chunks: Vec<_> = fastq_iter(data, block).collect::<Result<_, _>>().unwrap();
+        for rope in &chunks {
+            let first_byte = rope_to_vec(rope)[0];
+            assert_eq!(
+                first_byte, b'@',
+                "block={block}: chunk doesn't start with '@'"
+            );
+        }
+    }
+}

src/obiread/src/tests/fasta.rs

@@ -0,0 +1,66 @@
+use super::*;
+
+fn rope(data: &[u8]) -> Rope {
+    let mut r = Rope::new(None);
+    r.push(data.to_vec());
+    r
+}
+
+fn rope2(a: &[u8], b: &[u8]) -> Rope {
+    let mut r = Rope::new(None);
+    r.push(a.to_vec());
+    r.push(b.to_vec());
+    r
+}
+
+fn flat(r: &Rope) -> Vec<u8> {
+    r.fw_cursor().collect()
+}
+
+#[test]
+fn single_entry_no_boundary() {
+    assert_eq!(end_of_last_fasta_entry(&rope(b">seq1\nACGT\n")), None);
+}
+
+#[test]
+fn two_entries_cuts_at_second_header() {
+    let data = b">seq1\nACGT\n>seq2\nTTTT\n";
+    let r = rope(data);
+    let pos = end_of_last_fasta_entry(&r).unwrap();
+    assert_eq!(&flat(&r)[pos..], b">seq2\nTTTT\n");
+    assert_eq!(&flat(&r)[..pos], b">seq1\nACGT\n");
+}
+
+#[test]
+fn three_entries_cuts_at_last_header() {
+    let data = b">s1\nAA\n>s2\nCC\n>s3\nGG\n";
+    let r = rope(data);
+    let pos = end_of_last_fasta_entry(&r).unwrap();
+    assert_eq!(&flat(&r)[pos..], b">s3\nGG\n");
+}
+
+#[test]
+fn multiline_sequence() {
+    let data = b">s1\nACGT\nACGT\n>s2\nTTTT\n";
+    let r = rope(data);
+    let pos = end_of_last_fasta_entry(&r).unwrap();
+    assert_eq!(&flat(&r)[pos..], b">s2\nTTTT\n");
+}
+
+#[test]
+fn crlf_line_endings() {
+    let data = b">s1\r\nACGT\r\n>s2\r\nTTTT\r\n";
+    let r = rope(data);
+    let pos = end_of_last_fasta_entry(&r).unwrap();
+    assert_eq!(&flat(&r)[pos..], b">s2\r\nTTTT\r\n");
+}
+
+#[test]
+fn boundary_spans_two_blocks() {
+    let a = b">s1\nACGT\n";
+    let b = b">s2\nTTTT\n";
+    let r = rope2(a, b);
+    let all: Vec<u8> = flat(&r);
+    let pos = end_of_last_fasta_entry(&r).unwrap();
+    assert_eq!(&all[pos..], b">s2\nTTTT\n");
+}

src/obiread/src/tests/fastq.rs

@@ -0,0 +1,73 @@
+use super::*;
+
+fn rope(data: &[u8]) -> Rope {
+    let mut r = Rope::new(None);
+    r.push(data.to_vec());
+    r
+}
+
+fn make_fastq(records: &[(&[u8], &[u8])]) -> Vec<u8> {
+    let mut buf = Vec::new();
+    for (seq, qual) in records {
+        buf.extend_from_slice(b"@header\n");
+        buf.extend_from_slice(seq);
+        buf.push(b'\n');
+        buf.extend_from_slice(b"+\n");
+        buf.extend_from_slice(qual);
+        buf.push(b'\n');
+    }
+    buf
+}
+
+fn flat(r: &Rope) -> Vec<u8> {
+    r.fw_cursor().collect()
+}
+
+#[test]
+fn single_record_no_boundary() {
+    let buf = make_fastq(&[(b"ACGT", b"IIII")]);
+    assert_eq!(end_of_last_fastq_entry(&rope(&buf)), None);
+}
+
+#[test]
+fn two_records_cuts_at_second() {
+    let buf = make_fastq(&[(b"ACGT", b"IIII"), (b"TTTT", b"HHHH")]);
+    let r = rope(&buf);
+    let pos = end_of_last_fastq_entry(&r).unwrap();
+    assert_eq!(flat(&r)[pos], b'@');
+    assert_eq!(
+        &flat(&r)[pos..],
+        make_fastq(&[(b"TTTT", b"HHHH")]).as_slice()
+    );
+}
+
+#[test]
+fn three_records_cuts_at_last() {
+    let buf = make_fastq(&[(b"ACGT", b"IIII"), (b"CCCC", b"JJJJ"), (b"GGGG", b"KKKK")]);
+    let r = rope(&buf);
+    let pos = end_of_last_fastq_entry(&r).unwrap();
+    assert_eq!(
+        &flat(&r)[pos..],
+        make_fastq(&[(b"GGGG", b"KKKK")]).as_slice()
+    );
+}
+
+#[test]
+fn at_sign_in_quality_does_not_confuse() {
+    let buf = make_fastq(&[(b"ACGTACGT", b"@@@@IIII"), (b"TTTT", b"HHHH")]);
+    let r = rope(&buf);
+    let pos = end_of_last_fastq_entry(&r).unwrap();
+    assert_eq!(
+        &flat(&r)[pos..],
+        make_fastq(&[(b"TTTT", b"HHHH")]).as_slice()
+    );
+}
+
+#[test]
+fn crlf_line_endings() {
+    let data = b"@h\r\nACGT\r\n+\r\nIIII\r\n@h\r\nTTTT\r\n+\r\nHHHH\r\n";
+    let r = rope(data);
+    let pos = end_of_last_fastq_entry(&r).unwrap();
+    assert_eq!(flat(&r)[pos], b'@');
+    assert_eq!(&flat(&r)[pos..], b"@h\r\nTTTT\r\n+\r\nHHHH\r\n");
+}

src/obiread/src/tests/normalize.rs

@@ -0,0 +1,234 @@
+use super::*;
+
+fn make_rope(data: &[u8]) -> Rope {
+    let mut r = Rope::new(None);
+    r.push(data.to_vec());
+    r
+}
+
+fn flat(r: Rope) -> Vec<u8> {
+    r.fw_cursor().collect()
+}
+
+fn run_fastq(data: &[u8], k: usize) -> Vec<u8> {
+    flat(normalize_fastq_chunk(make_rope(data), k))
+}
+
+fn run_fasta(data: &[u8], k: usize) -> Vec<u8> {
+    flat(normalize_fasta_chunk(make_rope(data), k))
+}
+
+fn make_fastq(records: &[&[u8]]) -> Vec<u8> {
+    let mut buf = Vec::new();
+    for seq in records {
+        buf.extend_from_slice(b"@hdr\n");
+        buf.extend_from_slice(seq);
+        buf.push(b'\n');
+        buf.extend_from_slice(b"+\n");
+        buf.extend_from_slice(&vec![b'I'; seq.len()]);
+        buf.push(b'\n');
+    }
+    buf
+}
+
+fn make_fasta(records: &[(&[u8], &[u8])]) -> Vec<u8> {
+    let mut buf = Vec::new();
+    for (id, seq) in records {
+        buf.push(b'>');
+        buf.extend_from_slice(id);
+        buf.push(b'\n');
+        buf.extend_from_slice(seq);
+        buf.push(b'\n');
+    }
+    buf
+}
+
+// ── FASTQ basic ──────────────────────────────────────────────────────────
+
+#[test]
+fn single_record_produces_seq_then_null() {
+    assert_eq!(run_fastq(&make_fastq(&[b"ACGTACGT"]), 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn two_records_concatenated() {
+    assert_eq!(
+        run_fastq(&make_fastq(&[b"ACGTACGT", b"TTTTTTTT"]), 4),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}
+
+#[test]
+fn lowercase_input_uppercased() {
+    assert_eq!(run_fastq(&make_fastq(&[b"acgtacgt"]), 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn mixed_case_uppercased() {
+    assert_eq!(run_fastq(&make_fastq(&[b"AcGtAcGt"]), 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn sequence_shorter_than_k_discarded() {
+    assert_eq!(run_fastq(&make_fastq(&[b"ACG"]), 4), b"");
+}
+
+#[test]
+fn sequence_exactly_k_kept() {
+    assert_eq!(run_fastq(&make_fastq(&[b"ACGT"]), 4), b"ACGT\x00");
+}
+
+#[test]
+fn short_record_among_valid_ones_discarded() {
+    assert_eq!(
+        run_fastq(&make_fastq(&[b"ACGTACGT", b"AC", b"TTTTTTTT"]), 4),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}
+
+#[test]
+fn ambiguous_splits_into_two_segments() {
+    assert_eq!(
+        run_fastq(&make_fastq(&[b"ACGTNACGT"]), 4),
+        b"ACGT\x00ACGT\x00"
+    );
+}
+
+#[test]
+fn segment_after_ambiguous_too_short_discarded() {
+    assert_eq!(
+        run_fastq(&make_fastq(&[b"ACGTACGTNAC"]), 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn consecutive_ambiguous_produce_no_empty_segment() {
+    assert_eq!(
+        run_fastq(&make_fastq(&[b"ACGTNNNNACGT"]), 4),
+        b"ACGT\x00ACGT\x00"
+    );
+}
+
+#[test]
+fn ambiguous_at_start_skipped() {
+    assert_eq!(run_fastq(&make_fastq(&[b"NNACGTACGT"]), 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn ambiguous_at_end_produces_no_trailing_empty() {
+    assert_eq!(run_fastq(&make_fastq(&[b"ACGTACGTNN"]), 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn crlf_handled() {
+    let data = b"@hdr\r\nACGTACGT\r\n+\r\nIIIIIIII\r\n";
+    assert_eq!(run_fastq(data, 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn multi_slice_rope() {
+    let data = make_fastq(&[b"ACGTACGT", b"TTTTTTTT"]);
+    let mid = data.len() / 2;
+    let mut rope = Rope::new(None);
+    rope.push(data[..mid].to_vec());
+    rope.push(data[mid..].to_vec());
+    assert_eq!(
+        flat(normalize_fastq_chunk(rope, 4)),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}
+
+// ── FASTA ─────────────────────────────────────────────────────────────────
+
+#[test]
+fn fasta_single_record() {
+    assert_eq!(
+        run_fasta(&make_fasta(&[(b"s1", b"ACGTACGT")]), 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fasta_two_records() {
+    assert_eq!(
+        run_fasta(
+            &make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"TTTTTTTT")]),
+            4
+        ),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}
+
+#[test]
+fn fasta_multiline_sequence_concatenated() {
+    assert_eq!(
+        run_fasta(b">s1\nACGT\nACGT\nACGT\n", 4),
+        b"ACGTACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fasta_lowercase_uppercased() {
+    assert_eq!(
+        run_fasta(&make_fasta(&[(b"s1", b"acgtacgt")]), 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fasta_short_record_discarded() {
+    assert_eq!(run_fasta(&make_fasta(&[(b"s1", b"ACG")]), 4), b"");
+}
+
+#[test]
+fn fasta_short_among_valid_discarded() {
+    assert_eq!(
+        run_fasta(
+            &make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"AC"), (b"s3", b"TTTTTTTT")]),
+            4
+        ),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}
+
+#[test]
+fn fasta_ambiguous_splits_segments() {
+    assert_eq!(run_fasta(b">s1\nACGTNACGT\n", 4), b"ACGT\x00ACGT\x00");
+}
+
+#[test]
+fn fasta_ambiguous_across_line_boundary() {
+    assert_eq!(run_fasta(b">s1\nACGT\nNACGT\n", 4), b"ACGT\x00ACGT\x00");
+}
+
+#[test]
+fn fasta_ambiguous_short_segment_discarded() {
+    assert_eq!(run_fasta(b">s1\nACGTACGTNAC\n", 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_no_trailing_newline() {
+    assert_eq!(run_fasta(b">s1\nACGTACGT", 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_crlf_line_endings() {
+    assert_eq!(
+        run_fasta(b">s1\r\nACGT\r\nACGT\r\n>s2\r\nTTTT\r\n", 4),
+        b"ACGTACGT\x00TTTT\x00"
+    );
+}
+
+#[test]
+fn fasta_multi_slice_rope() {
+    let data = make_fasta(&[(b"s1", b"ACGTACGT"), (b"s2", b"TTTTTTTT")]);
+    let mid = data.len() / 2;
+    let mut rope = Rope::new(None);
+    rope.push(data[..mid].to_vec());
+    rope.push(data[mid..].to_vec());
+    assert_eq!(
+        flat(normalize_fasta_chunk(rope, 4)),
+        b"ACGTACGT\x00TTTTTTTT\x00"
+    );
+}

src/obiread/src/tests/nucstream.rs

@@ -0,0 +1,267 @@
+use super::*;
+use std::io::Cursor;
+use std::ops::Deref;
+
+// ── helpers ───────────────────────────────────────────────────────────────
+
+fn run_fasta(data: &[u8], k: usize) -> Vec<u8> {
+    NucStream::<_, FastaParser>::new(Cursor::new(data.to_vec()), k)
+        .flat_map(|p| p.deref().to_vec())
+        .collect()
+}
+
+fn run_fastq(data: &[u8], k: usize) -> Vec<u8> {
+    NucStream::<_, FastqParser>::new(Cursor::new(data.to_vec()), k)
+        .flat_map(|p| p.deref().to_vec())
+        .collect()
+}
+
+fn run_genbank(data: &[u8], k: usize) -> Vec<u8> {
+    NucStream::<_, GenbankParser>::new(Cursor::new(data.to_vec()), k)
+        .flat_map(|p| p.deref().to_vec())
+        .collect()
+}
+
+fn pages_fasta(data: &[u8], k: usize) -> Vec<Vec<u8>> {
+    NucStream::<_, FastaParser>::new(Cursor::new(data.to_vec()), k)
+        .map(|p| p.deref().to_vec())
+        .collect()
+}
+
+// ── FastaParser ───────────────────────────────────────────────────────────
+
+#[test]
+fn fasta_single_sequence() {
+    assert_eq!(run_fasta(b">s1\nACGTACGT\n", 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_lowercase_uppercased() {
+    assert_eq!(run_fasta(b">s1\nacgtacgt\n", 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_multiline_sequence_concatenated() {
+    assert_eq!(run_fasta(b">s1\nACGT\nACGT\n", 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_two_sequences() {
+    let data = b">s1\nACGTACGT\n>s2\nTTTTTTTT\n";
+    assert_eq!(run_fasta(data, 4), b"ACGTACGT\x00TTTTTTTT\x00");
+}
+
+#[test]
+fn fasta_empty_input_yields_no_pages() {
+    assert_eq!(run_fasta(b"", 4), b"");
+}
+
+#[test]
+fn fasta_sequence_shorter_than_k_at_eof_discarded() {
+    // The 3-base fragment is saved as overlap and dropped at EOF (< k).
+    assert_eq!(run_fasta(b">s1\nACG\n", 4), b"");
+}
+
+#[test]
+fn fasta_ambiguous_splits_into_two_segments() {
+    assert_eq!(run_fasta(b">s1\nACGTNACGT\n", 4), b"ACGT\x00ACGT\x00");
+}
+
+#[test]
+fn fasta_short_segment_before_ambiguous_emitted() {
+    // "AC" (< k=4) before N is written with a separator — filtering by
+    // length is deferred to the superkmer builder, not done here.
+    assert_eq!(run_fasta(b">s1\nACNACGTACGT\n", 4), b"AC\x00ACGTACGT\x00");
+}
+
+#[test]
+fn fasta_ambiguous_at_start_skipped() {
+    assert_eq!(run_fasta(b">s1\nNNNACGTACGT\n", 4), b"ACGTACGT\x00");
+}
+
+// ── FastqParser ───────────────────────────────────────────────────────────
+
+#[test]
+fn fastq_single_record() {
+    assert_eq!(
+        run_fastq(b"@r1\nACGTACGT\n+\nIIIIIIII\n", 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fastq_lowercase_uppercased() {
+    assert_eq!(
+        run_fastq(b"@r1\nacgtacgt\n+\nIIIIIIII\n", 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fastq_quality_bytes_not_in_output() {
+    // '@' (Phred 31 = ASCII 64) in quality must not appear in output.
+    assert_eq!(
+        run_fastq(b"@r1\nACGTACGT\n+\n@@@@@@@@\n", 4),
+        b"ACGTACGT\x00"
+    );
+}
+
+#[test]
+fn fastq_two_records() {
+    let data = b"@r1\nACGTACGT\n+\nIIIIIIII\n@r2\nTTTTTTTT\n+\nIIIIIIII\n";
+    assert_eq!(run_fastq(data, 4), b"ACGTACGT\x00TTTTTTTT\x00");
+}
+
+#[test]
+fn fastq_ambiguous_splits_sequence() {
+    assert_eq!(
+        run_fastq(b"@r1\nACGTNACGT\n+\nIIIIIIIII\n", 4),
+        b"ACGT\x00ACGT\x00"
+    );
+}
+
+#[test]
+fn fastq_at_in_quality_line_not_a_record_start() {
+    // '@' in the quality line must not trigger a new record parse.
+    let data = b"@r1\nACGTACGT\n+\n@@@@@@@@\n@r2\nTTTTTTTT\n+\nIIIIIIII\n";
+    assert_eq!(run_fastq(data, 4), b"ACGTACGT\x00TTTTTTTT\x00");
+}
+
+// ── GenbankParser ─────────────────────────────────────────────────────────
+
+#[test]
+fn genbank_origin_to_slash() {
+    let data = b"LOCUS ...\nORIGIN\n        1 acgtacgt\n//\n";
+    assert_eq!(run_genbank(data, 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn genbank_position_numbers_and_spaces_skipped() {
+    let data = b"ORIGIN\n        1 acgt acgt\n//\n";
+    assert_eq!(run_genbank(data, 4), b"ACGTACGT\x00");
+}
+
+#[test]
+fn genbank_two_records() {
+    let data = b"ORIGIN\n        1 acgtacgt\n//\nLOCUS ...\nORIGIN\n        1 tttttttt\n//\n";
+    assert_eq!(run_genbank(data, 4), b"ACGTACGT\x00TTTTTTTT\x00");
+}
+
+#[test]
+fn genbank_ambiguous_splits_sequence() {
+    let data = b"ORIGIN\n        1 acgtnacgt\n//\n";
+    assert_eq!(run_genbank(data, 4), b"ACGT\x00ACGT\x00");
+}
+
+// ── NucPage ───────────────────────────────────────────────────────────────
+
+#[test]
+fn nuc_page_deref_correct_bytes() {
+    let page = NucStream::<_, FastaParser>::new(Cursor::new(b">s1\nACGT\n".to_vec()), 4)
+        .next()
+        .expect("page");
+    assert_eq!(page.deref(), b"ACGT\x00");
+}
+
+// ── NucPageCursor ─────────────────────────────────────────────────────────
+
+fn make_page(data: &[u8], k: usize) -> NucPage {
+    NucStream::<_, FastaParser>::new(Cursor::new(data.to_vec()), k)
+        .next()
+        .expect("at least one page")
+}
+
+#[test]
+fn cursor_reads_bytes_in_order() {
+    let page = make_page(b">s1\nACGTACGT\n", 4);
+    let mut cur = page.cursor();
+    assert_eq!(cur.next_byte(), Some(b'A'));
+    assert_eq!(cur.next_byte(), Some(b'C'));
+    assert_eq!(cur.next_byte(), Some(b'G'));
+    assert_eq!(cur.next_byte(), Some(b'T'));
+}
+
+#[test]
+fn cursor_rewind_rereads_bytes() {
+    let page = make_page(b">s1\nACGTACGT\n", 4);
+    let mut cur = page.cursor();
+    cur.next_byte(); // A
+    cur.next_byte(); // C
+    cur.rewind(1);
+    assert_eq!(cur.next_byte(), Some(b'C'));
+    cur.rewind(2);
+    assert_eq!(cur.next_byte(), Some(b'A'));
+}
+
+#[test]
+fn cursor_returns_none_at_end() {
+    // "ACGT\x00" = 5 bytes; consume all then expect None.
+    let page = make_page(b">s1\nACGT\n", 4);
+    let mut cur = page.cursor();
+    for _ in 0..5 {
+        cur.next_byte();
+    }
+    assert_eq!(cur.next_byte(), None);
+}
+
+#[test]
+fn cursor_len_matches_page_content() {
+    // "ACGTACGT\x00" = 9 bytes
+    let page = make_page(b">s1\nACGTACGT\n", 4);
+    let cur = page.cursor();
+    assert_eq!(cur.len(), 9);
+    assert!(!cur.is_empty());
+}
+
+// ── Overlap at page boundary ──────────────────────────────────────────────
+
+#[test]
+fn overlap_last_km1_bytes_prepended_to_next_page() {
+    const K: usize = 11;
+    // Sequence long enough to span two pages: PAGE_SIZE + K bytes.
+    // Pattern chosen so boundary bytes are unambiguous.
+    let seq: Vec<u8> = (0..PAGE_SIZE + K).map(|i| b"ACGT"[i % 4]).collect();
+    let mut input = b">seq\n".to_vec();
+    input.extend_from_slice(&seq);
+    input.push(b'\n');
+
+    let pages = pages_fasta(&input, K);
+    assert!(pages.len() >= 2, "need at least two pages");
+
+    let p1 = &pages[0];
+    let p2 = &pages[1];
+
+    // page1 must end with a \x00 separator (written by save_overlap)
+    assert_eq!(*p1.last().unwrap(), 0x00, "page1 must end with separator");
+
+    // last K-1 ACGT bytes of page1 == first K-1 bytes of page2
+    let ol = K - 1;
+    let p1_seq_end = &p1[p1.len() - 1 - ol..p1.len() - 1];
+    let p2_start = &p2[..ol];
+    assert_eq!(
+        p1_seq_end, p2_start,
+        "overlap bytes mismatch at page boundary"
+    );
+}
+
+// ── Pool ──────────────────────────────────────────────────────────────────
+
+#[test]
+fn pool_buffer_reused_after_drop() {
+    // Drop page1 so its buffer returns to the pool, then verify page2
+    // is produced correctly (no corruption, no panic).
+    const K: usize = 11;
+    let seq: Vec<u8> = vec![b'A'; PAGE_SIZE + K];
+    let mut input = b">seq\n".to_vec();
+    input.extend_from_slice(&seq);
+    input.push(b'\n');
+
+    let mut stream = NucStream::<_, FastaParser>::new(Cursor::new(input), K);
+    let page1 = stream.next().expect("page 1");
+    assert!(!page1.deref().is_empty());
+    drop(page1); // returns buffer to pool
+    let page2 = stream.next().expect("page 2");
+    assert!(!page2.deref().is_empty());
+    // page2 must still start with A's (overlap from page1)
+    assert_eq!(page2[0], b'A');
+}

src/obiread/src/xopen.rs

@@ -20,13 +20,13 @@ use std::io::{self, Read};
 
 /// Open any source for reading, with transparent decompression.
 ///
-/// Returns a `Box<dyn Read>` that yields uncompressed bytes regardless of
+/// Returns a `Box<dyn Read + Send>` that yields uncompressed bytes regardless
-/// whether the underlying source is plain text, gzip, bzip2, xz or zstd.
+/// of whether the underlying source is plain text, gzip, bzip2, xz or zstd.
 ///
 /// # Errors
 /// Returns an `io::Error` if the file cannot be opened, the URL cannot be
 /// fetched, or the compression header is malformed.
-pub fn xopen(source: &str) -> io::Result<MimeTypeGuesser<Box<dyn Read + Send>>> {
+pub(crate) fn open_raw(source: &str) -> io::Result<Box<dyn Read + Send>> {
     let raw: Box<dyn Read + Send> = match source {
         "-" => Box::new(io::stdin()),
         s if s.starts_with("http://") || s.starts_with("https://") => http_reader(s)?,
@@ -35,8 +35,15 @@ pub fn xopen(source: &str) -> io::Result<MimeTypeGuesser<Box<dyn Read + Send>>>
             Box::new(File::open(expanded.as_ref())?)
         }
     };
-    let decompressed = decompress(raw)?;
+    decompress(raw)
-    Ok(MimeTypeGuesser::new(decompressed))
+}
+
+/// Open any source for reading, with transparent decompression and MIME detection.
+///
+/// Wraps [`open_raw`] in a [`MimeTypeGuesser`] so callers can inspect the
+/// format before consuming the stream.
+pub fn xopen(source: &str) -> io::Result<MimeTypeGuesser<Box<dyn Read + Send>>> {
+    Ok(MimeTypeGuesser::new(open_raw(source)?))
 }
 
 // ── internal helpers ──────────────────────────────────────────────────────────

src/obiskbuilder/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2024"
 [dependencies]
 obikseq = { path = "../obikseq" }
 obikrope = { path = "../obikrope" }
+obiread = { path = "../obiread" }
 lazy_static = "1.5.0"
 
 [dev-dependencies]

src/obiskbuilder/src/lib.rs

@@ -6,6 +6,7 @@
 #![deny(missing_docs)]
 
 pub mod iter;
+pub mod stream_iter;
 mod scratch;
 
 pub(crate) mod encoding;
@@ -14,10 +15,23 @@ pub(crate) mod rolling_stat;
 
 pub use iter::SuperKmerIter;
 pub use scratch::SuperKmerScratch;
+pub use stream_iter::SuperKmerStreamIter;
 
+use obiread::NucPage;
 use obikrope::Rope;
 use obikseq::RoutableSuperKmer;
 
+/// Collect all super-kmers from a normalised [`NucPage`].
+pub fn build_superkmers_page(
+    page: NucPage,
+    k: usize,
+    level_max: usize,
+    theta: f64,
+) -> Vec<RoutableSuperKmer> {
+    let cursor = page.cursor();
+    SuperKmerStreamIter::new(cursor, k, level_max, theta).collect()
+}
+
 /// Collect all super-kmers from a normalised rope chunk.
 pub fn build_superkmers(
     rope: Rope,

src/obiskbuilder/src/stream_iter.rs

@@ -0,0 +1,129 @@
+//! Streaming superkmer iterator over a [`NucPageCursor`].
+
+use obiread::NucPageCursor;
+use obikseq::RoutableSuperKmer;
+use obikseq::kmer::Minimizer;
+
+use crate::rolling_stat::RollingStat;
+use crate::scratch::SuperKmerScratch;
+
+/// Streaming iterator over [`RoutableSuperKmer`] values from a [`NucPageCursor`].
+///
+/// Cut conditions (checked in order per nucleotide, once the k-mer window is full):
+///
+/// | Condition              | cursor rewind |
+/// |------------------------|---------------|
+/// | entropy(kmer) ≤ θ      | k−1           |
+/// | minimizer changed      | k             |
+/// | super-kmer length = 256| k             |
+pub struct SuperKmerStreamIter<'a> {
+    cursor:       NucPageCursor<'a>,
+    k:            usize,
+    theta:        f64,
+    scratch:      SuperKmerScratch,
+    stat:         RollingStat,
+    prev_min:     Option<Minimizer>,
+    prev_min_pos: usize,
+}
+
+impl<'a> SuperKmerStreamIter<'a> {
+    /// Build an iterator from a [`NucPageCursor`] over normalised sequence data.
+    pub fn new(cursor: NucPageCursor<'a>, k: usize, level_max: usize, theta: f64) -> Self {
+        Self {
+            cursor,
+            k,
+            theta,
+            scratch:      SuperKmerScratch::new(),
+            stat:         RollingStat::new(level_max),
+            prev_min:     None,
+            prev_min_pos: 0,
+        }
+    }
+
+    fn reset(&mut self) {
+        self.stat.reset();
+        self.scratch.reset();
+        self.prev_min = None;
+        self.prev_min_pos = 0;
+    }
+
+    fn try_emit(&mut self) -> Option<RoutableSuperKmer> {
+        if self.scratch.len() < self.k {
+            return None;
+        }
+        self.prev_min?;
+        Some(self.scratch.emit(self.prev_min_pos))
+    }
+}
+
+impl Iterator for SuperKmerStreamIter<'_> {
+    type Item = RoutableSuperKmer;
+
+    fn next(&mut self) -> Option<RoutableSuperKmer> {
+        loop {
+            let byte = match self.cursor.next_byte() {
+                None => {
+                    return self.try_emit();
+                }
+                Some(0x00) => {
+                    let result = self.try_emit();
+                    self.reset();
+                    if result.is_some() {
+                        return result;
+                    }
+                    continue;
+                }
+                Some(b) => b,
+            };
+
+            self.stat.push(byte);
+
+            if !self.stat.ready() {
+                self.scratch.push(byte);
+                continue;
+            }
+
+            // ── 1. Entropy check ─────────────────────────────────────────────
+            if self.stat.normalized_entropy().unwrap_or(1.0) < self.theta {
+                let result = self.try_emit();
+                self.cursor.rewind(self.k - 1);
+                self.reset();
+                if result.is_some() {
+                    return result;
+                }
+                continue;
+            }
+
+            let min     = self.stat.canonical_minimizer().unwrap();
+            let min_pos = self.stat.minimizer_position().unwrap_or(0);
+
+            // ── 2. Minimizer change ───────────────────────────────────────────
+            if let Some(prev) = self.prev_min {
+                if min != prev {
+                    let result = self.try_emit();
+                    self.cursor.rewind(self.k);
+                    self.reset();
+                    if result.is_some() {
+                        return result;
+                    }
+                    continue;
+                }
+            }
+
+            // ── 3. Super-kmer length cap ──────────────────────────────────────
+            if self.scratch.len() == 256 {
+                let result = self.try_emit();
+                self.cursor.rewind(self.k);
+                self.reset();
+                if result.is_some() {
+                    return result;
+                }
+                continue;
+            }
+
+            self.prev_min     = Some(min);
+            self.prev_min_pos = min_pos;
+            self.scratch.push(byte);
+        }
+    }
+}