diff --git a/go.mod b/go.mod
index 0647567..fd77a09 100644
--- a/go.mod
+++ b/go.mod
@@ -20,15 +20,28 @@ require (
 	scientificgo.org/special v0.0.0
 )
 
+require (
+	github.com/kr/pretty v0.2.1 // indirect
+	github.com/kr/text v0.1.0 // indirect
+)
+
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/dsnet/compress v0.0.1
+	github.com/gabriel-vasile/mimetype v1.4.2 // indirect
 	github.com/klauspost/compress v1.16.7 // indirect
 	github.com/mattn/go-runewidth v0.0.15 // indirect
 	github.com/mitchellh/colorstring v0.0.0-20190213212951-d06e56a500db // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rivo/uniseg v0.4.4 // indirect
 	github.com/shopspring/decimal v1.3.1 // indirect
+	github.com/ulikunitz/xz v0.5.11
+	github.com/yuin/goldmark v1.4.13 // indirect
+	golang.org/x/mod v0.12.0 // indirect
+	golang.org/x/net v0.14.0 // indirect
 	golang.org/x/sys v0.11.0 // indirect
 	golang.org/x/term v0.11.0 // indirect
+	golang.org/x/tools v0.12.1-0.20230815132531-74c255bcf846 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
 	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c // indirect
 )
diff --git a/go.sum b/go.sum
index 4ff6bda..41309d0 100644
--- a/go.sum
+++ b/go.sum
@@ -13,13 +13,25 @@ github.com/daichi-m/go18ds v1.12.1/go.mod h1:wc2dURUr8aMxxC4Mn5ObJGVM7uIKU8JagY4
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dsnet/compress v0.0.1 h1:PlZu0n3Tuv04TzpfPbrnI0HW/YwodEXDS+oPKahKF0Q=
+github.com/dsnet/compress v0.0.1/go.mod h1:Aw8dCMJ7RioblQeTqt88akK31OvO8Dhf5JflhBbQEHo=
+github.com/dsnet/golib v0.0.0-20171103203638-1ea166775780/go.mod h1:Lj+Z9rebOhdfkVLjJ8T6VcRQv3SXugXy999NBtR9aFY=
+github.com/gabriel-vasile/mimetype v1.4.2 h1:w5qFW6JKBz9Y393Y4q372O9A7cUSequkh1Q7OhCmWKU=
+github.com/gabriel-vasile/mimetype v1.4.2/go.mod h1:zApsH/mKG4w07erKIaJPFiX0Tsq9BFQgN3qGY5GnNgA=
 github.com/goccy/go-json v0.10.2 h1:CrxCmQqYDkv1z7lO7Wbh2HN93uovUHgrECaO5ZrCXAU=
 github.com/goccy/go-json v0.10.2/go.mod h1:6MelG93GURQebXPDq3khkgXZkazVtN9CRI+MGFi0w8I=
 github.com/k0kubun/go-ansi v0.0.0-20180517002512-3bf9e2903213/go.mod h1:vNUNkEQ1e29fT/6vq2aBdFsgNPmy8qMdSay1npru+Sw=
+github.com/klauspost/compress v1.4.1/go.mod h1:RyIbtBH6LamlWaDj8nUwkbUhJ87Yi3uG0guNDohfE1A=
 github.com/klauspost/compress v1.16.7 h1:2mk3MPGNzKyxErAw8YaohYh69+pa4sIQSC0fPGCFR9I=
 github.com/klauspost/compress v1.16.7/go.mod h1:ntbaceVETuRiXiv4DpjP66DpAtAGkEQskQzEyD//IeE=
+github.com/klauspost/cpuid v1.2.0/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
 github.com/klauspost/pgzip v1.2.6 h1:8RXeL5crjEUFnR2/Sn6GJNWtSQ3Dk8pq4CL3jvdDyjU=
 github.com/klauspost/pgzip v1.2.6/go.mod h1:Ch1tH69qFZu15pkjo5kYi6mth2Zzwzt50oCQKQE9RUs=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/mattn/go-isatty v0.0.17/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
 github.com/mattn/go-runewidth v0.0.14/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh153qUoGf23w=
 github.com/mattn/go-runewidth v0.0.15 h1:UNAjwbU9l54TA3KzvqLGxwWjHmMgBUVhBiTjelZgg3U=
@@ -45,8 +57,17 @@ github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5Cc
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/tevino/abool/v2 v2.1.0 h1:7w+Vf9f/5gmKT4m4qkayb33/92M+Um45F2BkHOR+L/c=
 github.com/tevino/abool/v2 v2.1.0/go.mod h1:+Lmlqk6bHDWHqN1cbxqhwEAwMPXgc8I1SDEamtseuXY=
+github.com/ulikunitz/xz v0.5.6/go.mod h1:2bypXElzHzzJZwzH67Y6wb67pO62Rzfn7BSiF4ABRW8=
+github.com/ulikunitz/xz v0.5.11 h1:kpFauv27b6ynzBNT/Xy+1k+fK4WswhN/6PN5WhFAGw8=
+github.com/ulikunitz/xz v0.5.11/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
+github.com/yuin/goldmark v1.4.13 h1:fVcFKWvrslecOb/tg+Cc05dkeYx540o0FuFt3nUVDoE=
+github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/exp v0.0.0-20230817173708-d852ddb80c63 h1:m64FZMko/V45gv0bNmrNYoDEq8U5YUhetc9cBWKS1TQ=
 golang.org/x/exp v0.0.0-20230817173708-d852ddb80c63/go.mod h1:0v4NqG35kSWCMzLaMeX+IQrlSnVE/bqGSyC2cz/9Le8=
+golang.org/x/mod v0.12.0 h1:rmsUpXtvNzj340zd98LZ4KntptpfRHwpFOHG188oHXc=
+golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/net v0.14.0 h1:BONx9s002vGdD9umnlX1Po8vOZmrgH34qlHcD1MfK14=
+golang.org/x/net v0.14.0/go.mod h1:PpSgVXXLK0OxS0F31C1/tv6XNguvCrnXIDrFMspZIUI=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -55,10 +76,14 @@ golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.6.0/go.mod h1:m6U89DPEgQRMq3DNkDClhWw02AUbt2daBVO4cn4Hv9U=
 golang.org/x/term v0.11.0 h1:F9tnn/DA/Im8nCwm+fX+1/eBwi4qFjRT++MhtVC4ZX0=
 golang.org/x/term v0.11.0/go.mod h1:zC9APTIj3jG3FdV/Ons+XE1riIZXG4aZ4GTHiPZJPIU=
+golang.org/x/tools v0.12.1-0.20230815132531-74c255bcf846 h1:Vve/L0v7CXXuxUmaMGIEK/dEeq7uiqb5qBgQrZzIE7E=
+golang.org/x/tools v0.12.1-0.20230815132531-74c255bcf846/go.mod h1:Sc0INKfu04TlqNoRA1hgpFZbhYXHPr4V5DzpSBTPqQM=
 gonum.org/v1/gonum v0.14.0 h1:2NiG67LD1tEH0D7kM+ps2V+fXmsAnpUeec7n8tcr4S0=
 gonum.org/v1/gonum v0.14.0/go.mod h1:AoWeoz0becf9QMWtE8iWXNXc27fK4fNeHNf/oMejGfU=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 scientificgo.org/special v0.0.0 h1:P6WJkECo6tgtvZAEfNXl+KEB9ReAatjKAeX8U07mjSc=
diff --git a/pkg/obiformats/ecopcr_read.go b/pkg/obiformats/ecopcr_read.go
index 1dae062..2b1ef0f 100644
--- a/pkg/obiformats/ecopcr_read.go
+++ b/pkg/obiformats/ecopcr_read.go
@@ -3,13 +3,14 @@ package obiformats
 import (
 	"encoding/csv"
 	"fmt"
-	gzip "github.com/klauspost/pgzip"
 	"io"
 	"os"
 	"path"
 	"strconv"
 	"strings"
 
+	gzip "github.com/klauspost/pgzip"
+
 	log "github.com/sirupsen/logrus"
 
 	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiiter"
@@ -209,7 +210,7 @@ func ReadEcoPCR(reader io.Reader, options ...WithOption) obiiter.IBioSequence {
 	}()
 
 	if opt.pointer.full_file_batch {
-		newIter = newIter.FullFileIterator()
+		newIter = newIter.CompleteFileIterator()
 	}
 
 	return newIter
diff --git a/pkg/obiformats/embl_read.go b/pkg/obiformats/embl_read.go
index 73db113..3b9f7c2 100644
--- a/pkg/obiformats/embl_read.go
+++ b/pkg/obiformats/embl_read.go
@@ -266,7 +266,7 @@ func ReadEMBL(reader io.Reader, options ...WithOption) obiiter.IBioSequence {
 	go _ReadFlatFileChunk(reader, entry_channel)
 
 	if opt.pointer.full_file_batch {
-		newIter = newIter.FullFileIterator()
+		newIter = newIter.CompleteFileIterator()
 	}
 
 	return newIter
diff --git a/pkg/obiformats/fastaseq_read.go b/pkg/obiformats/fastaseq_read.go
new file mode 100644
index 0000000..eb6e9cf
--- /dev/null
+++ b/pkg/obiformats/fastaseq_read.go
@@ -0,0 +1,322 @@
+package obiformats
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"path"
+
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiiter"
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obioptions"
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiseq"
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiutils"
+	"golang.org/x/exp/slices"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// lastSequenceCut extracts the up to the last sequence cut from a given buffer.
+//
+// It takes a parameter:
+//   - buffer []byte: the buffer to extract the sequence cut from.
+//
+// It returns two values:
+//   - []byte: the extracted sequences.
+//   - []byte: the remaining buffer after the sequence cut (the last sequence).
+func lastSequenceCut(buffer []byte) ([]byte, []byte) {
+	imax := len(buffer)
+	last := 0
+	state := 0
+	for i := imax - 1; i >= 0 && state < 2; i-- {
+		if state == 0 && buffer[i] == '>' {
+			state = 1
+			last = i
+		} else if state == 1 && (buffer[i] == '\r' || buffer[i] == '\n') {
+			state = 2
+		} else {
+			state = 0
+		}
+	}
+
+	if state == 2 {
+		return buffer[:last], bytes.Clone(buffer[last:])
+	}
+	return []byte{}, buffer
+}
+
+// firstSequenceCut cuts the input buffer at the first occurrence of a ">" character
+// following a sequence of "\r" or "\n" characters.
+//
+// It takes a byte slice as input, representing the buffer to be cut.
+// It returns two byte slices: the first slice contains the part of the buffer before the cut,
+// and the second slice contains the part of the buffer after the cut.
+func firstSequenceCut(buffer []byte) ([]byte, []byte) {
+	imax := len(buffer)
+	last := 0
+	state := 0
+	for i := 0; i < imax && state < 2; i++ {
+		if (state == 0 || state == 1) && (buffer[i] == '\r' || buffer[i] == '\n') {
+			state = 1
+		} else if (state == 1 || i == 0) && buffer[i] == '>' {
+			state = 2
+			last = i
+		} else {
+			state = 0
+		}
+	}
+
+	if state == 2 {
+		return bytes.Clone(buffer[:last]), buffer[last:]
+	}
+	return buffer, []byte{}
+
+}
+
+func fullSequenceCut(buffer []byte) ([]byte, []byte, []byte) {
+	before, buffer := firstSequenceCut(buffer)
+
+	if len(buffer) == 0 {
+		return before, []byte{}, []byte{}
+	}
+
+	buffer, after := lastSequenceCut(buffer)
+	return before, buffer, after
+}
+
+func Concatenate[S ~[]E, E any](s1, s2 S) S {
+	if len(s1) > 0 {
+		if len(s2) > 0 {
+			return append(s1[:len(s1):len(s1)], s2...)
+		}
+		return s1
+	}
+	return s2
+}
+
+type FastxChunk struct {
+	Bytes []byte
+	index int
+}
+
+func FastaChunkReader(r io.Reader, size int, cutHead bool) (chan FastxChunk, error) {
+	out := make(chan FastxChunk)
+	buff := make([]byte, size)
+
+	n, err := r.Read(buff)
+	if n > 0 && err == nil {
+		if n < size {
+			buff = buff[:n]
+		}
+
+		begin, buff := firstSequenceCut(buff)
+
+		if len(begin) > 0 && !cutHead {
+			return out, fmt.Errorf("begin is not empty : %s", string(begin))
+		}
+
+		go func(buff []byte) {
+			idx := 0
+			end := []byte{}
+
+			for err == nil && n > 0 {
+				// fmt.Println("============end=========================")
+				// fmt.Println(string(end))
+				// fmt.Println("------------buff------------------------")
+				// fmt.Println(string(buff))
+				buff = Concatenate(end, buff)
+				// fmt.Println("------------buff--pasted----------------")
+				// fmt.Println(string(buff))
+				buff, end = lastSequenceCut(buff)
+				// fmt.Println("----------------buff--cutted------------")
+				// fmt.Println(string(buff))
+				// fmt.Println("------------------end-------------------")
+				// fmt.Println(string(end))
+				// fmt.Println("========================================")
+				if len(buff) > 0 {
+					out <- FastxChunk{
+						Bytes: bytes.Clone(buff),
+						index: idx,
+					}
+					idx++
+				}
+
+				buff = slices.Grow(buff[:0], size)[0:size]
+				n, err = r.Read(buff)
+				if n < size {
+					buff = buff[:n]
+				}
+				// fmt.Printf("n = %d, err = %v\n", n, err)
+			}
+
+			if len(end) > 0 {
+				out <- FastxChunk{
+					Bytes: bytes.Clone(end),
+					index: idx,
+				}
+			}
+
+			close(out)
+		}(buff)
+	}
+
+	return out, nil
+}
+
+func ParseFastaChunk(source string, ch FastxChunk) *obiiter.BioSequenceBatch {
+	slice := make(obiseq.BioSequenceSlice, 0, obioptions.CLIBatchSize())
+
+	state := 0
+	start := 0
+	current := 0
+	var identifier string
+	var definition string
+
+	for i := 0; i < len(ch.Bytes); i++ {
+		C := ch.Bytes[i]
+		is_end_of_line := C == '\r' || C == '\n'
+		is_space := C == ' ' || C == '\t'
+		is_sep := is_space || is_end_of_line
+
+		switch state {
+		case 0:
+			if C == '>' {
+				// Beginning of sequence
+				state = 1
+			}
+		case 1:
+			if is_sep {
+				// No identifier -> ERROR
+				return nil
+			} else {
+				// Beginning of identifier
+				state = 2
+				start = i
+			}
+		case 2:
+			if is_sep {
+				// End of identifier
+				identifier = string(ch.Bytes[start:i])
+				state = 3
+			}
+		case 3:
+			if is_end_of_line {
+				// Definition empty
+				definition = ""
+				state = 5
+			} else if !is_space {
+				// Beginning of definition
+				start = i
+				state = 4
+			}
+		case 4:
+			if is_end_of_line {
+				definition = string(ch.Bytes[start:i])
+				state = 5
+
+			}
+		case 5:
+			if !is_end_of_line {
+				// Beginning of sequence
+				start = i
+				current = i + 1
+				state = 6
+			}
+		case 6:
+			if C == '>' {
+				// End of sequence
+				s := obiseq.NewBioSequence(identifier, bytes.Clone(ch.Bytes[start:current]), definition)
+				s.SetSource(source)
+				slice = append(slice, s)
+				state = 1
+
+			} else if !is_sep {
+				if C >= 'A' && C <= 'Z' {
+					C = C + 'a' - 'A'
+				}
+				// Removing white space from the sequence
+				if (C >= 'a' && C <= 'z') || C == '-' || C == '.' {
+					ch.Bytes[current] = C
+					current++
+				}
+			}
+		}
+	}
+
+	slice = append(slice, obiseq.NewBioSequence(identifier, bytes.Clone(ch.Bytes[start:current]), definition))
+	batch := obiiter.MakeBioSequenceBatch(ch.index, slice)
+	return &batch
+}
+
+func ReadFasta(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, error) {
+	opt := MakeOptions(options)
+	out := obiiter.MakeIBioSequence()
+
+	source := opt.Source()
+
+	nworker := obioptions.CLIReadParallelWorkers()
+	out.Add(nworker)
+
+	chkchan, err := FastaChunkReader(reader, 1024*500, false)
+
+	if err != nil {
+		return obiiter.NilIBioSequence, err
+	}
+
+	go func() {
+		out.WaitAndClose()
+	}()
+
+	parser := func() {
+		defer out.Done()
+		for chk := range chkchan {
+			seqs := ParseFastaChunk(source, chk)
+			if seqs != nil {
+				out.Push(*seqs)
+			}
+		}
+	}
+
+	for i := 0; i < nworker; i++ {
+		go parser()
+	}
+
+	newIter := out.SortBatches().Rebatch(opt.BatchSize())
+
+	log.Debugln("Full file batch mode : ", opt.FullFileBatch())
+	if opt.FullFileBatch() {
+		newIter = newIter.CompleteFileIterator()
+	}
+
+	annotParser := opt.ParseFastSeqHeader()
+
+	if annotParser != nil {
+		return IParseFastSeqHeaderBatch(newIter, options...), nil
+	}
+
+	return newIter, nil
+}
+
+func ReadFastaFromFile(filename string, options ...WithOption) (obiiter.IBioSequence, error) {
+	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
+
+	file, err := Ropen(filename)
+
+	if err != nil {
+		return obiiter.NilIBioSequence, err
+	}
+
+	return ReadFasta(file, options...)
+}
+
+func ReadFastaFromStdin(reader io.Reader, options ...WithOption) (obiiter.IBioSequence, error) {
+	options = append(options, OptionsSource(obiutils.RemoveAllExt("stdin")))
+	input, err := Buf(os.Stdin)
+
+	if err != nil {
+		log.Fatalf("open file error: %v", err)
+		return obiiter.NilIBioSequence, err
+	}
+
+	return ReadFasta(input, options...)
+}
diff --git a/pkg/obiformats/fastseq_read.go b/pkg/obiformats/fastseq_read.go
index e18a3b5..f1e4364 100644
--- a/pkg/obiformats/fastseq_read.go
+++ b/pkg/obiformats/fastseq_read.go
@@ -124,7 +124,7 @@ func ReadFastSeqFromFile(filename string, options ...WithOption) (obiiter.IBioSe
 
 	log.Debugln("Full file batch mode : ", opt.FullFileBatch())
 	if opt.FullFileBatch() {
-		newIter = newIter.FullFileIterator()
+		newIter = newIter.CompleteFileIterator()
 	}
 
 	parser := opt.ParseFastSeqHeader()
@@ -155,7 +155,7 @@ func ReadFastSeqFromStdin(options ...WithOption) obiiter.IBioSequence {
 
 	log.Debugln("Full file batch mode : ", opt.FullFileBatch())
 	if opt.FullFileBatch() {
-		newIter = newIter.FullFileIterator()
+		newIter = newIter.CompleteFileIterator()
 	}
 
 	parser := opt.ParseFastSeqHeader()
diff --git a/pkg/obiformats/genbank_read.go b/pkg/obiformats/genbank_read.go
index dabaa5a..40b3b1c 100644
--- a/pkg/obiformats/genbank_read.go
+++ b/pkg/obiformats/genbank_read.go
@@ -34,14 +34,14 @@ var _seqlenght_rx = regexp.MustCompile(" +([0-9]+) bp")
 func _ParseGenbankFile(source string,
 	input <-chan _FileChunk, out obiiter.IBioSequence,
 	chunck_order func() int) {
-    var err error
+	var err error
 	state := inHeader
 
 	for chunks := range input {
 		// log.Debugln("Chunk size", (chunks.raw.(*bytes.Buffer)).Len())
 		scanner := bufio.NewScanner(chunks.raw)
 		sequences := make(obiseq.BioSequenceSlice, 0, 100)
-		sumlength:=0
+		sumlength := 0
 		id := ""
 		lseq := -1
 		scientificName := ""
@@ -61,12 +61,12 @@ func _ParseGenbankFile(source string,
 			case strings.HasPrefix(line, "LOCUS       "):
 				state = inEntry
 				id = strings.SplitN(line[12:], " ", 2)[0]
-				match_length := _seqlenght_rx.FindStringSubmatch(line) 
+				match_length := _seqlenght_rx.FindStringSubmatch(line)
 				if len(match_length) > 0 {
-					lseq,err = strconv.Atoi(match_length[1])
+					lseq, err = strconv.Atoi(match_length[1])
 					if err != nil {
 						lseq = -1
-					}					
+					}
 				}
 				if lseq > 0 {
 					seqBytes = bytes.NewBuffer(obiseq.GetSlice(lseq + 20))
@@ -101,7 +101,7 @@ func _ParseGenbankFile(source string,
 				//	sequence.Len(), seqBytes.Len())
 
 				sequences = append(sequences, sequence)
-				sumlength+=sequence.Len()
+				sumlength += sequence.Len()
 
 				if len(sequences) == 100 || sumlength > 1e7 {
 					out.Push(obiiter.MakeBioSequenceBatch(chunck_order(), sequences))
@@ -137,7 +137,7 @@ func _ParseGenbankFile(source string,
 		if len(sequences) > 0 {
 			out.Push(obiiter.MakeBioSequenceBatch(chunck_order(), sequences))
 		}
-}
+	}
 
 	out.Done()
 
@@ -159,13 +159,13 @@ func ReadGenbank(reader io.Reader, options ...WithOption) obiiter.IBioSequence {
 
 	// for j := 0; j < opt.ParallelWorkers(); j++ {
 	for j := 0; j < nworkers; j++ {
-		go _ParseGenbankFile(opt.Source(), entry_channel, newIter,chunck_order)
+		go _ParseGenbankFile(opt.Source(), entry_channel, newIter, chunck_order)
 	}
 
 	go _ReadFlatFileChunk(reader, entry_channel)
 
 	if opt.pointer.full_file_batch {
-		newIter = newIter.FullFileIterator()
+		newIter = newIter.CompleteFileIterator()
 	}
 
 	return newIter
diff --git a/pkg/obiformats/options.go b/pkg/obiformats/options.go
index 6b1d72e..8c08687 100644
--- a/pkg/obiformats/options.go
+++ b/pkg/obiformats/options.go
@@ -1,6 +1,7 @@
 package obiformats
 
 import (
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obioptions"
 	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiseq"
 )
 
@@ -43,8 +44,8 @@ func MakeOptions(setters []WithOption) Options {
 		with_progress_bar:     false,
 		buffer_size:           2,
 		quality_shift:         33,
-		parallel_workers:      4,
-		batch_size:            5000,
+		parallel_workers:      obioptions.CLIReadParallelWorkers(),
+		batch_size:            obioptions.CLIBatchSize(),
 		full_file_batch:       false,
 		closefile:             false,
 		appendfile:            false,
diff --git a/pkg/obiformats/universal_read.go b/pkg/obiformats/universal_read.go
index f63b3fb..84ca323 100644
--- a/pkg/obiformats/universal_read.go
+++ b/pkg/obiformats/universal_read.go
@@ -4,12 +4,10 @@ import (
 	"bufio"
 	"bytes"
 	"io"
-	"os"
 	"path"
 	"regexp"
 
 	"github.com/gabriel-vasile/mimetype"
-	gzip "github.com/klauspost/pgzip"
 
 	log "github.com/sirupsen/logrus"
 
@@ -91,6 +89,36 @@ func OBIMimeTypeGuesser(stream io.Reader) (*mimetype.MIME, io.Reader, error) {
 	return mimeType, newReader, nil
 }
 
+// func ReadSequences(reader io.Reader,
+// 	options ...WithOption) (obiiter.IBioSequence, error) {
+
+// 	mime, reader, err := OBIMimeTypeGuesser(reader)
+
+// 	if err != nil {
+// 		return obiiter.NilIBioSequence, err
+// 	}
+
+// 	reader = bufio.NewReader(reader)
+
+// 	switch mime.String() {
+// 	case "text/fasta", "text/fastq":
+// 		file.Close()
+// 		is, err := ReadFastSeqFromFile(filename, options...)
+// 		return is, err
+// 	case "text/ecopcr2":
+// 		return ReadEcoPCR(reader, options...), nil
+// 	case "text/embl":
+// 		return ReadEMBL(reader, options...), nil
+// 	case "text/genbank":
+// 		return ReadGenbank(reader, options...), nil
+// 	default:
+// 		log.Fatalf("File %s has guessed format %s which is not yet implemented",
+// 			filename, mime.String())
+// 	}
+
+// 	return obiiter.NilIBioSequence, nil
+// }
+
 // ReadSequencesFromFile reads sequences from a file and returns an iterator of bio sequences and an error.
 //
 // Parameters:
@@ -102,32 +130,20 @@ func OBIMimeTypeGuesser(stream io.Reader) (*mimetype.MIME, io.Reader, error) {
 // - error: An error if any occurred during the reading process.
 func ReadSequencesFromFile(filename string,
 	options ...WithOption) (obiiter.IBioSequence, error) {
-	var file *os.File
+	var file *Reader
 	var reader io.Reader
-	var greader io.Reader
 	var err error
 
 	options = append(options, OptionsSource(obiutils.RemoveAllExt((path.Base(filename)))))
 
-	file, err = os.Open(filename)
+	file, err = Ropen(filename)
 
 	if err != nil {
 		log.Fatalf("open file error: %v", err)
 		return obiiter.NilIBioSequence, err
 	}
 
-	reader = file
-
-	// Test if the flux is compressed by gzip
-	greader, err = gzip.NewReader(reader)
-	if err != nil {
-		file.Seek(0, 0)
-	} else {
-		log.Debugf("File %s is gz compressed ", filename)
-		reader = greader
-	}
-
-	mime, reader, err := OBIMimeTypeGuesser(reader)
+	mime, reader, err := OBIMimeTypeGuesser(file)
 
 	if err != nil {
 		return obiiter.NilIBioSequence, err
@@ -136,10 +152,12 @@ func ReadSequencesFromFile(filename string,
 	reader = bufio.NewReader(reader)
 
 	switch mime.String() {
-	case "text/fasta", "text/fastq":
+	case "text/fastq":
 		file.Close()
 		is, err := ReadFastSeqFromFile(filename, options...)
 		return is, err
+	case "text/fasta":
+		return ReadFasta(reader, options...)
 	case "text/ecopcr2":
 		return ReadEcoPCR(reader, options...), nil
 	case "text/embl":
@@ -153,3 +171,9 @@ func ReadSequencesFromFile(filename string,
 
 	return obiiter.NilIBioSequence, nil
 }
+
+// func ReadSequencesFromStdin(options ...WithOption) obiiter.IBioSequence {
+
+// 	options = append(options, OptionsSource("stdin"))
+
+// }
diff --git a/pkg/obiformats/xopen.go b/pkg/obiformats/xopen.go
new file mode 100644
index 0000000..a74140f
--- /dev/null
+++ b/pkg/obiformats/xopen.go
@@ -0,0 +1,437 @@
+// This is an integration of the xopen package originally written by Brent Pedersen
+// (https://github.com/brentp/xopen).
+//
+// Here it can be considered as a fork of [Wei Shen](http://shenwei.me) the version :
+//
+//	https://github.com/shenwei356/xopen
+//
+// Package xopen makes it easy to get buffered readers and writers.
+// Ropen opens a (possibly gzipped) file/process/http site for buffered reading.
+// Wopen opens a (possibly gzipped) file for buffered writing.
+// Both will use gzip when appropriate and will user buffered IO.
+package obiformats
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"os/exec"
+	"os/user"
+	"path/filepath"
+	"strings"
+
+	"github.com/dsnet/compress/bzip2"
+	"github.com/klauspost/compress/zstd"
+	gzip "github.com/klauspost/pgzip"
+	"github.com/ulikunitz/xz"
+)
+
+// Level is the default compression level of gzip.
+// This value will be automatically adjusted to the default value of zstd or bzip2.
+var Level = gzip.DefaultCompression
+
+// ErrNoContent means nothing in the stream/file.
+var ErrNoContent = errors.New("xopen: no content")
+
+// ErrDirNotSupported means the path is a directory.
+var ErrDirNotSupported = errors.New("xopen: input is a directory")
+
+// IsGzip returns true buffered Reader has the gzip magic.
+func IsGzip(b *bufio.Reader) (bool, error) {
+	return CheckBytes(b, []byte{0x1f, 0x8b})
+}
+
+// IsXz returns true buffered Reader has the xz magic.
+func IsXz(b *bufio.Reader) (bool, error) {
+	return CheckBytes(b, []byte{0xfd, 0x37, 0x7a, 0x58, 0x5a, 0x00})
+}
+
+// IsZst returns true buffered Reader has the zstd magic.
+func IsZst(b *bufio.Reader) (bool, error) {
+	return CheckBytes(b, []byte{0x28, 0xB5, 0x2f, 0xfd})
+}
+
+// IsBzip2 returns true buffered Reader has the bzip2 magic.
+func IsBzip2(b *bufio.Reader) (bool, error) {
+	return CheckBytes(b, []byte{0x42, 0x5a, 0x68})
+}
+
+// IsStdin checks if we are getting data from stdin.
+func IsStdin() bool {
+	// http://stackoverflow.com/a/26567513
+	stat, err := os.Stdin.Stat()
+	if err != nil {
+		return false
+	}
+	return (stat.Mode() & os.ModeCharDevice) == 0
+}
+
+// ExpandUser expands ~/path and ~otheruser/path appropriately
+func ExpandUser(path string) (string, error) {
+	if len(path) == 0 || path[0] != '~' {
+		return path, nil
+	}
+	var u *user.User
+	var err error
+	if len(path) == 1 || path[1] == '/' {
+		u, err = user.Current()
+	} else {
+		name := strings.Split(path[1:], "/")[0]
+		u, err = user.Lookup(name)
+	}
+	if err != nil {
+		return "", err
+	}
+	home := u.HomeDir
+	path = home + "/" + path[1:]
+	return path, nil
+}
+
+// Exists checks if a local file exits
+func Exists(path string) bool {
+	path, perr := ExpandUser(path)
+	if perr != nil {
+		return false
+	}
+	_, err := os.Stat(path)
+	return err == nil
+}
+
+// CheckBytes peeks at a buffered stream and checks if the first read bytes match.
+func CheckBytes(b *bufio.Reader, buf []byte) (bool, error) {
+
+	m, err := b.Peek(len(buf))
+	if err != nil {
+		// return false, ErrNoContent
+		return false, err // EOF
+	}
+	for i := range buf {
+		if m[i] != buf[i] {
+			return false, nil
+		}
+	}
+	return true, nil
+}
+
+// Reader is returned by Ropen
+type Reader struct {
+	*bufio.Reader
+	rdr io.Reader
+	gz  io.ReadCloser
+}
+
+// Close the associated files.
+func (r *Reader) Close() error {
+	var err error
+	if r.gz != nil {
+		err = r.gz.Close()
+		if err != nil {
+			return err
+		}
+	}
+	if c, ok := r.rdr.(io.ReadCloser); ok {
+		err = c.Close()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Writer is returned by Wopen
+type Writer struct {
+	*bufio.Writer
+	wtr *os.File
+	gz  *gzip.Writer
+	xw  *xz.Writer
+	zw  *zstd.Encoder
+	bz2 *bzip2.Writer
+}
+
+// Close the associated files.
+func (w *Writer) Close() error {
+	var err error
+	err = w.Flush()
+	if err != nil {
+		return err
+	}
+
+	if w.gz != nil {
+		err = w.gz.Close()
+		if err != nil {
+			return err
+		}
+	}
+	if w.xw != nil {
+		err = w.xw.Close()
+		if err != nil {
+			return err
+		}
+	}
+	if w.zw != nil {
+		err = w.zw.Close()
+		if err != nil {
+			return err
+		}
+	}
+	if w.bz2 != nil {
+		err = w.bz2.Close()
+		if err != nil {
+			return err
+		}
+	}
+	return w.wtr.Close()
+}
+
+// Flush the writer.
+func (w *Writer) Flush() error {
+	var err error
+	err = w.Writer.Flush()
+	if err != nil {
+		return err
+	}
+
+	if w.gz != nil {
+		err = w.gz.Flush()
+		if err != nil {
+			return err
+		}
+	}
+	if w.zw != nil {
+		err = w.zw.Flush()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+var bufSize = 65536
+
+// Buf returns a buffered reader from an io.Reader
+// If f == "-", then it will attempt to read from os.Stdin.
+// If the file is gzipped, it will be read as such.
+func Buf(r io.Reader) (*Reader, error) {
+	b := bufio.NewReaderSize(r, bufSize)
+	var rd io.Reader
+	var rdr io.ReadCloser
+
+	if is, err := IsGzip(b); err != nil {
+		// check BOM
+		t, _, err := b.ReadRune() // no content
+		if err != nil {
+			return nil, ErrNoContent
+		}
+		if t != '\uFEFF' {
+			b.UnreadRune()
+		}
+		return &Reader{b, r, rdr}, nil // non-gzip file with content less than 2 bytes
+	} else if is {
+		rdr, err = gzip.NewReader(b)
+		if err != nil {
+			return nil, err
+		}
+		b = bufio.NewReaderSize(rdr, bufSize)
+	} else if is, err := IsZst(b); err != nil {
+		// check BOM
+		t, _, err := b.ReadRune() // no content
+		if err != nil {
+			return nil, ErrNoContent
+		}
+		if t != '\uFEFF' {
+			b.UnreadRune()
+		}
+		return &Reader{b, r, rdr}, nil // non-gzip/zst file with content less than 4 bytes
+	} else if is {
+		rd, err = zstd.NewReader(b)
+		if err != nil {
+			return nil, err
+		}
+		b = bufio.NewReaderSize(rd, bufSize)
+	} else if is, err := IsXz(b); err != nil {
+		// check BOM
+		t, _, err := b.ReadRune() // no content
+		if err != nil {
+			return nil, ErrNoContent
+		}
+		if t != '\uFEFF' {
+			b.UnreadRune()
+		}
+		return &Reader{b, r, rdr}, nil // non-gzip/zst/xz file with content less than 6 bytes
+	} else if is {
+		rd, err = xz.NewReader(b)
+		if err != nil {
+			return nil, err
+		}
+		b = bufio.NewReaderSize(rd, bufSize)
+	} else if is, err := IsBzip2(b); err != nil {
+		// check BOM
+		t, _, err := b.ReadRune() // no content
+		if err != nil {
+			return nil, ErrNoContent
+		}
+		if t != '\uFEFF' {
+			b.UnreadRune()
+		}
+		return &Reader{b, r, rdr}, nil // non-gzip/zst/xz file with content less than 6 bytes
+	} else if is {
+		rd, err = bzip2.NewReader(b, &bzip2.ReaderConfig{})
+		if err != nil {
+			return nil, err
+		}
+		b = bufio.NewReaderSize(rd, bufSize)
+	}
+
+	// other files with content >= 6 bytes
+
+	// check BOM
+	t, _, err := b.ReadRune()
+	if err != nil {
+		return nil, ErrNoContent
+	}
+	if t != '\uFEFF' {
+		b.UnreadRune()
+	}
+	return &Reader{b, r, rdr}, nil
+}
+
+// XReader returns a reader from a url string or a file.
+func XReader(f string) (io.Reader, error) {
+	if strings.HasPrefix(f, "http://") || strings.HasPrefix(f, "https://") {
+		var rsp *http.Response
+		rsp, err := http.Get(f)
+		if err != nil {
+			return nil, err
+		}
+		if rsp.StatusCode != 200 {
+			return nil, fmt.Errorf("http error downloading %s. status: %s", f, rsp.Status)
+		}
+		rdr := rsp.Body
+		return rdr, nil
+	}
+	f, err := ExpandUser(f)
+	if err != nil {
+		return nil, err
+	}
+
+	fi, err := os.Stat(f)
+	if err != nil {
+		return nil, err
+	}
+	if fi.IsDir() {
+		return nil, ErrDirNotSupported
+	}
+
+	return os.Open(f)
+}
+
+// Ropen opens a buffered reader.
+func Ropen(f string) (*Reader, error) {
+	var err error
+	var rdr io.Reader
+	if f == "-" {
+		if !IsStdin() {
+			return nil, errors.New("stdin not detected")
+		}
+		b, err := Buf(os.Stdin)
+		return b, err
+	} else if f[0] == '|' {
+		// TODO: use csv to handle quoted file names.
+		cmdStrs := strings.Split(f[1:], " ")
+		var cmd *exec.Cmd
+		if len(cmdStrs) == 2 {
+			cmd = exec.Command(cmdStrs[0], cmdStrs[1:]...)
+		} else {
+			cmd = exec.Command(cmdStrs[0])
+		}
+		rdr, err = cmd.StdoutPipe()
+		if err != nil {
+			return nil, err
+		}
+		err = cmd.Start()
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		rdr, err = XReader(f)
+	}
+	if err != nil {
+		return nil, err
+	}
+	b, err := Buf(rdr)
+	return b, err
+}
+
+// Wopen opens a buffered reader.
+// If f == "-", then stdout will be used.
+// If f endswith ".gz", then the output will be gzipped.
+// If f endswith ".xz", then the output will be zx-compressed.
+// If f endswith ".zst", then the output will be zstd-compressed.
+// If f endswith ".bz2", then the output will be bzip2-compressed.
+func Wopen(f string) (*Writer, error) {
+	return WopenFile(f, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+}
+
+// WopenFile opens a buffered reader.
+// If f == "-", then stdout will be used.
+// If f endswith ".gz", then the output will be gzipped.
+// If f endswith ".xz", then the output will be zx-compressed.
+// If f endswith ".bz2", then the output will be bzip2-compressed.
+func WopenFile(f string, flag int, perm os.FileMode) (*Writer, error) {
+	var wtr *os.File
+	if f == "-" {
+		wtr = os.Stdout
+	} else {
+		dir := filepath.Dir(f)
+		fi, err := os.Stat(dir)
+		if err == nil && !fi.IsDir() {
+			return nil, fmt.Errorf("can not write file into a non-directory path: %s", dir)
+		}
+		if os.IsNotExist(err) {
+			os.MkdirAll(dir, 0755)
+		}
+		wtr, err = os.OpenFile(f, flag, perm)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	f2 := strings.ToLower(f)
+	if strings.HasSuffix(f2, ".gz") {
+		gz, err := gzip.NewWriterLevel(wtr, Level)
+		if err != nil {
+			err = errors.New(fmt.Sprintf("xopen: %s", err))
+		}
+		return &Writer{bufio.NewWriterSize(gz, bufSize), wtr, gz, nil, nil, nil}, err
+	}
+	if strings.HasSuffix(f2, ".xz") {
+		xw, err := xz.NewWriter(wtr)
+		return &Writer{bufio.NewWriterSize(xw, bufSize), wtr, nil, xw, nil, nil}, err
+	}
+	if strings.HasSuffix(f2, ".zst") {
+		level := Level
+		if level == gzip.DefaultCompression {
+			level = 2
+		}
+		zw, err := zstd.NewWriter(wtr, zstd.WithEncoderLevel(zstd.EncoderLevel(level)))
+		if err != nil {
+			err = errors.New(fmt.Sprintf("xopen: zstd: %s", err))
+		}
+		return &Writer{bufio.NewWriterSize(zw, bufSize), wtr, nil, nil, zw, nil}, err
+	}
+	if strings.HasSuffix(f2, ".bz2") {
+		level := Level
+		if level == gzip.DefaultCompression {
+			level = 6
+		}
+		bz2, err := bzip2.NewWriter(wtr, &bzip2.WriterConfig{Level: level})
+		if err != nil {
+			err = errors.New(fmt.Sprintf("xopen: %s", err))
+		}
+		return &Writer{bufio.NewWriterSize(bz2, bufSize), wtr, nil, nil, nil, bz2}, err
+	}
+	return &Writer{bufio.NewWriterSize(wtr, bufSize), wtr, nil, nil, nil, nil}, nil
+}
diff --git a/pkg/obiformats/xopen_test.go b/pkg/obiformats/xopen_test.go
new file mode 100644
index 0000000..b40ec11
--- /dev/null
+++ b/pkg/obiformats/xopen_test.go
@@ -0,0 +1,148 @@
+package obiformats
+
+import (
+	"bufio"
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"testing"
+
+	. "gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type XopenTest struct{}
+
+var _ = Suite(&XopenTest{})
+
+func gzFromString(s string) string {
+	var c bytes.Buffer
+	gz := gzip.NewWriter(&c)
+	gz.Write([]byte(s))
+	return c.String()
+}
+
+var gzTests = []struct {
+	isGz bool
+	data string
+}{
+	{false, "asdf"},
+	{true, gzFromString("asdf")},
+}
+
+func (s *XopenTest) TestIsGzip(c *C) {
+	for _, t := range gzTests {
+		isGz, err := IsGzip(bufio.NewReader(strings.NewReader(t.data)))
+		c.Assert(err, IsNil)
+		c.Assert(t.isGz, Equals, isGz)
+	}
+}
+
+func (s *XopenTest) TestIsStdin(c *C) {
+	r := IsStdin()
+	c.Assert(r, Equals, false)
+}
+
+func (s *XopenTest) TestRopen(c *C) {
+	rdr, err := Ropen("-")
+	c.Assert(err, ErrorMatches, "stdin not detected")
+	c.Assert(rdr, IsNil)
+}
+
+func (s *XopenTest) TestWopen(c *C) {
+	for _, f := range []string{"t.gz", "t"} {
+		testString := "ASDF1234"
+		wtr, err := Wopen(f)
+		c.Assert(err, IsNil)
+		_, err = os.Stat(f)
+		c.Assert(err, IsNil)
+		c.Assert(wtr.wtr, NotNil)
+		fmt.Fprintf(wtr, testString)
+		wtr.Close()
+
+		rdr, err := Ropen(f)
+		c.Assert(err, IsNil)
+
+		str, err := rdr.ReadString(99)
+		c.Assert(str, Equals, testString)
+		c.Assert(err, Equals, io.EOF)
+		str, err = rdr.ReadString(99)
+		c.Assert(str, Equals, "")
+
+		rdr.Close()
+		os.Remove(f)
+	}
+}
+
+var httpTests = []struct {
+	url         string
+	expectError bool
+}{
+	{"https://raw.githubusercontent.com/brentp/xopen/master/README.md", false},
+	{"http://raw.githubusercontent.com/brentp/xopen/master/README.md", false},
+	{"http://raw.githubusercontent.com/brentp/xopen/master/BAD.md", true},
+}
+
+func (s *XopenTest) TestReadHttp(c *C) {
+	for _, t := range httpTests {
+		rdr, err := Ropen(t.url)
+		if !t.expectError {
+			c.Assert(err, IsNil)
+			v, err := rdr.ReadString(byte('\n'))
+			c.Assert(err, IsNil)
+			c.Assert(len(v), Not(Equals), 0)
+		} else {
+			c.Assert(err, ErrorMatches, ".* 404 Not Found")
+		}
+	}
+}
+
+func (s *XopenTest) TestReadProcess(c *C) {
+	for _, cmd := range []string{"|ls -lh", "|ls", "|ls -lh xopen_test.go"} {
+		rdr, err := Ropen(cmd)
+		c.Assert(err, IsNil)
+		b := make([]byte, 1000)
+		_, err = rdr.Read(b)
+		if err != io.EOF {
+			c.Assert(err, IsNil)
+		}
+		lines := strings.Split(string(b), "\n")
+		has := false
+		for _, line := range lines {
+			if strings.Contains(line, "xopen_test.go") {
+				has = true
+			}
+		}
+		c.Assert(has, Equals, true)
+	}
+}
+
+func (s *XopenTest) TestOpenStdout(c *C) {
+	w, err := Wopen("-")
+	c.Assert(err, IsNil)
+	c.Assert(w.wtr, Equals, os.Stdout)
+}
+
+func (s *XopenTest) TestOpenBadFile(c *C) {
+	r, err := Ropen("XXXXXXXXXXXXXXXXXXXXXXX")
+	c.Assert(r, IsNil)
+	c.Assert(err, ErrorMatches, ".*no such file.*")
+}
+
+func (s *XopenTest) TestExists(c *C) {
+	c.Assert(Exists("xopen.go"), Equals, true)
+	c.Assert(Exists("____xx"), Equals, false)
+}
+
+func (s *XopenTest) TestUser(c *C) {
+	c.Assert(Exists("~"), Equals, true)
+}
+
+func (s *XopenTest) TestExpand(c *C) {
+	_, err := ExpandUser("~baduser66")
+	c.Assert(err, Not(IsNil))
+}
diff --git a/pkg/obiiter/batchiterator.go b/pkg/obiiter/batchiterator.go
index 927f46c..f6901ec 100644
--- a/pkg/obiiter/batchiterator.go
+++ b/pkg/obiiter/batchiterator.go
@@ -461,7 +461,7 @@ func (iterator IBioSequence) Recycle() {
 		// iterator.Get()
 		batch := iterator.Get()
 		log.Debugln("Recycling batch #", batch.Order())
-		recycled+=batch.Len()
+		recycled += batch.Len()
 		batch.Recycle(true)
 	}
 	log.Debugf("End of the recycling of %d Bioseq objects", recycled)
@@ -679,7 +679,7 @@ func (iterator IBioSequence) Load() obiseq.BioSequenceSlice {
 	chunck := obiseq.MakeBioSequenceSlice()
 	for iterator.Next() {
 		b := iterator.Get()
-		log.Debugf("append %d sequences",b.Len())
+		log.Debugf("append %d sequences", b.Len())
 		chunck = append(chunck, b.Slice()...)
 		b.Recycle(false)
 	}
@@ -687,7 +687,14 @@ func (iterator IBioSequence) Load() obiseq.BioSequenceSlice {
 	return chunck
 }
 
-func (iterator IBioSequence) FullFileIterator() IBioSequence {
+// CompleteFileIterator generates a new iterator for reading a complete file.
+//
+// This iterator reads all the remaining sequences in the file, and returns them as a
+// single obiseq.BioSequenceSlice.
+//
+// The function takes no parameters.
+// It returns an IBioSequence object.
+func (iterator IBioSequence) CompleteFileIterator() IBioSequence {
 
 	newIter := MakeIBioSequence()
 	log.Debug("Stream is read in full file mode")
@@ -700,7 +707,7 @@ func (iterator IBioSequence) FullFileIterator() IBioSequence {
 
 	go func() {
 		slice := iterator.Load()
-		log.Printf("A batch of  %d sequence is read",len(slice))
+		log.Printf("A batch of  %d sequence is read", len(slice))
 		if len(slice) > 0 {
 			newIter.Push(MakeBioSequenceBatch(0, slice))
 		}
@@ -716,7 +723,6 @@ func (iterator IBioSequence) FullFileIterator() IBioSequence {
 
 // It takes a slice of BioSequence objects, and returns an iterator that will return batches of
 // BioSequence objects
-
 func IBatchOver(data obiseq.BioSequenceSlice,
 	size int, sizes ...int) IBioSequence {
 
diff --git a/pkg/obiseq/biosequence.go b/pkg/obiseq/biosequence.go
index e25f3d4..69b4f20 100644
--- a/pkg/obiseq/biosequence.go
+++ b/pkg/obiseq/biosequence.go
@@ -203,77 +203,135 @@ func (s *BioSequence) Len() int {
 	return len(s.sequence)
 }
 
-// Checking if the BioSequence has quality scores.
+// HasQualities checks if the BioSequence has sequence qualitiy scores.
+//
+// This function does not have any parameters.
+// It returns a boolean value indicating whether the BioSequence has qualities.
 func (s *BioSequence) HasQualities() bool {
 	return len(s.qualities) > 0
 }
 
-// Returning the qualities of the sequence.
+// Qualities returns the sequence quality scores of the BioSequence.
+//
+// It checks if the BioSequence has qualities. If it does, it returns the qualities
+// stored in the BioSequence struct. Otherwise, it creates and returns default
+// qualities based on the length of the sequence.
+//
+// Returns:
+//   - Quality: The quality of the BioSequence.
 func (s *BioSequence) Qualities() Quality {
 	if s.HasQualities() {
 		return s.qualities
-	} else {
-		return __make_default_qualities__(len(s.sequence))
 	}
+	return __make_default_qualities__(len(s.sequence))
 }
 
+// Features returns the feature string of the BioSequence.
+//
+//	The feature string contains the EMBL/GenBank not parsed feature table
+//
+// as extracted from the flat file.
+//
+// No parameters.
+// Returns a string.
 func (s *BioSequence) Features() string {
 	return string(s.feature)
 }
 
-// Checking if the BioSequence has annotations.
+// HasAnnotation checks if the BioSequence has any annotations.
+//
+// It does not take any parameters.
+// It returns a boolean value indicating whether the BioSequence has any annotations.
 func (s *BioSequence) HasAnnotation() bool {
 	return len(s.annotations) > 0
 }
 
-// Returning the annotations of the BioSequence.
+// Annotations returns the Annotation object associated with the BioSequence.
+//
+// This function does not take any parameters.
+// It returns an Annotation object.
 func (s *BioSequence) Annotations() Annotation {
-
 	if s.annotations == nil {
 		s.annotations = GetAnnotation()
 	}
-
 	return s.annotations
 }
 
+// AnnotationsLock locks the annotation of the BioSequence.
+//
+// This function acquires a lock on the annotation of the BioSequence,
+// preventing concurrent access to it.
 func (s *BioSequence) AnnotationsLock() {
 	s.annot_lock.Lock()
 }
 
+// AnnotationsUnlock unlocks the annotations mutex in the BioSequence struct.
+//
+// No parameters.
+// No return types.
 func (s *BioSequence) AnnotationsUnlock() {
 	s.annot_lock.Unlock()
 }
 
-// Checking if the BioSequence has a source.
+// HasSource checks if the BioSequence has a source.
+//
+// The source is the filename without directory name and extension from where the sequence was read.
+//
+// No parameters.
+// Returns a boolean value indicating whether the BioSequence has a source or not.
 func (s *BioSequence) HasSource() bool {
 	return len(s.source) > 0
 }
 
+// Source returns the source of the BioSequence.
+//
+// The source is the filename without directory name and extension from where the sequence was read.
+//
+// This function does not take any parameters.
+// It returns a string.
 func (s *BioSequence) Source() string {
 	return s.source
 }
 
-// Returning the MD5 hash of the sequence.
+// MD5 calculates the MD5 hash of the BioSequence.
+//
+// No parameters.
+// Returns [16]byte, the MD5 hash of the BioSequence.
 func (s *BioSequence) MD5() [16]byte {
 	return md5.Sum(s.sequence)
 }
 
-// Setting the id of the BioSequence.
+// SetId sets the id of the BioSequence.
+//
+// Parameters:
+// - id: the new id for the BioSequence.
+//
+// No return value.
 func (s *BioSequence) SetId(id string) {
 	s.id = id
 }
 
-// Setting the definition of the sequence.
+// SetDefinition sets the definition of the BioSequence.
+//
+// It takes a string parameter 'definition' and assigns it to the 'definition' field of the BioSequence struct.
 func (s *BioSequence) SetDefinition(definition string) {
 	s.definition = definition
 }
 
-// Setting the source of the sequence.
+// SetSource sets the source of the BioSequence.
+//
+// Parameter:
+// - source: a string representing the filename without directory name and extension from where the sequence was read.
 func (s *BioSequence) SetSource(source string) {
 	s.source = source
 }
 
-// Setting the features of the BioSequence.
+// SetFeatures sets the feature of the BioSequence.
+//
+// Parameters:
+// - feature: a byte slice representing the feature to be set.
+//
+// No return value.
 func (s *BioSequence) SetFeatures(feature []byte) {
 	if cap(s.feature) >= 300 {
 		RecycleSlice(&s.feature)
diff --git a/pkg/obiseq/biosequence_test.go b/pkg/obiseq/biosequence_test.go
index 9311b7e..4089a18 100644
--- a/pkg/obiseq/biosequence_test.go
+++ b/pkg/obiseq/biosequence_test.go
@@ -328,6 +328,225 @@ func TestBioSequence_Len(t *testing.T) {
 	}
 }
 
+// TestHasQualities tests the HasQualities method of the BioSequence struct.
+//
+// It includes two test cases:
+//
+//  1. Test case 1: BioSequence with empty qualities slice
+//     - Creates a BioSequence instance with an empty qualities slice.
+//     - Expects false as the result of calling the HasQualities method on the BioSequence instance.
+//
+//  2. Test case 2: BioSequence with non-empty qualities slice
+//     - Creates a BioSequence instance with a non-empty qualities slice.
+//     - Expects true as the result of calling the HasQualities method on the BioSequence instance.
+//
+// No parameters are required.
+// No return types are specified.
+func TestHasQualities(t *testing.T) {
+	// Test case 1: BioSequence with empty qualities slice
+	seq1 := NewBioSequence("", []byte(""), "")
+	seq1.qualities = []byte{}
+	if seq1.HasQualities() != false {
+		t.Errorf("Test case 1 failed: expected false, got true")
+	}
+
+	// Test case 2: BioSequence with non-empty qualities slice
+	seq2 := NewBioSequence("", []byte(""), "")
+	seq2.qualities = []byte{20, 30, 40}
+	if seq2.HasQualities() != true {
+		t.Errorf("Test case 2 failed: expected true, got false")
+	}
+}
+
+// TestQualities tests the Qualities method of the BioSequence struct.
+//
+// It creates a BioSequence with a given sequence and qualities and sets them.
+// Then it compares the returned qualities with the expected ones.
+// If the qualities are not equal, it fails the test case.
+//
+// Test case 1: BioSequence has qualities
+// - sequence: []byte("ATCG")
+// - qualities: Quality{10, 20, 30, 40}
+// - expected: Quality{10, 20, 30, 40}
+//
+// Test case 2: BioSequence does not have qualities
+// - sequence: []byte("ATCG")
+// - qualities: nil
+// - expected: defaultQualities
+//
+// Parameters:
+// - t: *testing.T - the testing struct for running test cases and reporting failures.
+//
+// Return type:
+// None
+func TestQualities(t *testing.T) {
+	// Test case: BioSequence has qualities
+	sequence := []byte("ATCG")
+	qualities := Quality{10, 20, 30, 40}
+	bioSeq := NewBioSequence("ABC123", sequence, "Test Sequence")
+	bioSeq.SetQualities(qualities)
+
+	result := bioSeq.Qualities()
+	expected := qualities
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("Test case failed: BioSequence has qualities")
+	}
+
+	// Test case: BioSequence does not have qualities
+	defaultQualities := __make_default_qualities__(len(sequence))
+	bioSeq = NewBioSequence("ABC123", sequence, "Test Sequence")
+	bioSeq.SetQualities(nil)
+
+	result = bioSeq.Qualities()
+	expected = defaultQualities
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("Test case failed: BioSequence does not have qualities")
+	}
+}
+
+// TestBioSequence_Features tests the Features function of the BioSequence struct.
+//
+// It first tests the case when the feature string is empty. It creates a new BioSequence
+// with an empty feature string and an empty byte slice. It expects an empty string as
+// the result of calling the Features function on this BioSequence. If the result does
+// not match the expected value, it prints an error message.
+//
+// It then tests the case when the feature string is non-empty. It creates a new BioSequence
+// with an empty feature string and an empty byte slice. It sets the feature string to
+// "test sequence" and expects "test sequence" as the result of calling the Features function
+// on this BioSequence. If the result does not match the expected value, it prints an error message.
+func TestBioSequence_Features(t *testing.T) {
+	// Testing empty feature string
+	seq := NewBioSequence("", []byte(""), "")
+	expected := ""
+	if got := seq.Features(); got != expected {
+		t.Errorf("Expected %q, but got %q", expected, got)
+	}
+
+	// Testing non-empty feature string
+	seq = NewBioSequence("", []byte(""), "")
+	seq.feature = []byte("test sequence")
+	expected = "test sequence"
+	if got := seq.Features(); got != expected {
+		t.Errorf("Expected %q, but got %q", expected, got)
+	}
+}
+
+// TestHasAnnotation is a unit test function that tests the HasAnnotation method of the BioSequence struct.
+//
+// This function tests the behavior of the HasAnnotation method in different scenarios:
+// - Test case: BioSequence with no annotations.
+// - Test case: BioSequence with one annotation.
+// - Test case: BioSequence with multiple annotations.
+//
+// The function verifies that the HasAnnotation method returns the expected boolean value for each test case.
+// It uses the *testing.T parameter to report any test failures.
+//
+// No parameters.
+// No return values.
+func TestHasAnnotation(t *testing.T) {
+	// Test case: BioSequence with no annotations
+	seq := BioSequence{}
+	expected := false
+	if got := seq.HasAnnotation(); got != expected {
+		t.Errorf("Expected %v, but got %v", expected, got)
+	}
+
+	// Test case: BioSequence with one annotation
+	seq = BioSequence{annotations: map[string]interface{}{"annotation1": "value1"}}
+	expected = true
+	if got := seq.HasAnnotation(); got != expected {
+		t.Errorf("Expected %v, but got %v", expected, got)
+	}
+
+	// Test case: BioSequence with multiple annotations
+	seq = BioSequence{
+		annotations: map[string]interface{}{
+			"annotation1": "value1",
+			"annotation2": "value2",
+		},
+	}
+	expected = true
+	if got := seq.HasAnnotation(); got != expected {
+		t.Errorf("Expected %v, but got %v", expected, got)
+	}
+}
+
+// TestBioSequenceAnnotations tests the Annotations method of the BioSequence struct.
+//
+// It verifies the behavior of the method when the `annotations` field of the BioSequence struct is nil and when it is not nil.
+// The method should return the expected annotation values and fail the test if the returned annotations do not match the expected ones.
+// The test cases cover both scenarios to ensure the correctness of the method.
+func TestBioSequenceAnnotations(t *testing.T) {
+	s := &BioSequence{}
+
+	// Test case 1: Annotations is nil
+	s.annotations = nil
+	expected := GetAnnotation()
+	actual := s.Annotations()
+	if !reflect.DeepEqual(expected, actual) {
+		t.Errorf("Test case 1 failed: Expected %v, but got %v", expected, actual)
+	}
+
+	// Test case 2: Annotations is not nil
+	s.annotations = Annotation{}
+	expected = s.annotations
+	actual = s.Annotations()
+	if !reflect.DeepEqual(expected, actual) {
+		t.Errorf("Test case 2 failed: Expected %v, but got %v", expected, actual)
+	}
+}
+
+func TestAnnotationsLock(t *testing.T) {
+	// Test case 1: Lock the annotation of an empty BioSequence
+	seq := NewEmptyBioSequence(0)
+	seq.AnnotationsLock()
+
+	// Test case 2: Lock the annotation of a BioSequence with existing annotations
+	seq2 := NewEmptyBioSequence(0)
+	seq2.annotations = map[string]interface{}{
+		"key1": "value1",
+		"key2": "value2",
+	}
+	seq2.AnnotationsLock()
+}
+
+// TestBioSequence_MD5 tests the MD5 function of the BioSequence struct.
+//
+// It includes two test cases: one for an empty sequence and one for a non-empty sequence.
+// Each test case creates a BioSequence instance with a specific sequence and compares the MD5 result with the expected value.
+// If the result does not match the expected value, an error is reported using the t.Errorf function.
+// The expected MD5 values are hardcoded in the test cases.
+func TestBioSequence_MD5(t *testing.T) {
+	// Test case 1: Empty sequence
+	{
+		s := &BioSequence{sequence: []byte("")}
+		expected := [16]byte{
+			0xd4, 0x1d, 0x8c, 0xd9, 0x8f, 0x00, 0xb2, 0x04,
+			0xe9, 0x80, 0x09, 0x98, 0xec, 0xf8, 0x42, 0x7e,
+		}
+		result := s.MD5()
+		if result != expected {
+			t.Errorf("Test case 1 failed. Expected: %v, got: %v", expected, result)
+		}
+	}
+
+	// Test case 2: Non-empty sequence
+	{
+		s := &BioSequence{sequence: []byte("ACGT")}
+		expected := [16]byte{
+			0xf1, 0xf8, 0xf4, 0xbf, 0x41, 0x3b, 0x16, 0xad,
+			0x13, 0x57, 0x22, 0xaa, 0x45, 0x91, 0x04, 0x3e,
+		}
+		result := s.MD5()
+		if result != expected {
+			t.Errorf("Test case 2 failed. Expected: %v, got: %v", expected, result)
+		}
+	}
+}
+
 // TestBioSequence_Composition tests the Composition method of the BioSequence struct.
 //
 // It tests the method with three different test cases:
diff --git a/pkg/obiseq/biosequenceslice.go b/pkg/obiseq/biosequenceslice.go
index 3337512..1ae2ee7 100644
--- a/pkg/obiseq/biosequenceslice.go
+++ b/pkg/obiseq/biosequenceslice.go
@@ -1,8 +1,10 @@
 package obiseq
 
 import (
-	log "github.com/sirupsen/logrus"
 	"sync"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/exp/slices"
 )
 
 // BioSequenceSlice represents a collection or a set of BioSequence.
@@ -18,22 +20,39 @@ var _BioSequenceSlicePool = sync.Pool{
 	},
 }
 
-// > This function returns a pointer to a new `BioSequenceSlice` object
+// NewBioSequenceSlice returns a new BioSequenceSlice with the specified size.
+//
+// The size parameter is optional. If provided, the returned slice will be
+// resized accordingly.
+//
+// Returns a pointer to the newly created BioSequenceSlice.
 func NewBioSequenceSlice(size ...int) *BioSequenceSlice {
 	slice := _BioSequenceSlicePool.Get().(*BioSequenceSlice)
 	if len(size) > 0 {
 		s := size[0]
 		slice = slice.InsureCapacity(s)
-		(*slice)=(*slice)[0:s]
+		(*slice) = (*slice)[0:s]
 	}
 	return slice
 }
 
-// `MakeBioSequenceSlice()` returns a pointer to a new `BioSequenceSlice` struct
+// MakeBioSequenceSlice creates a new BioSequenceSlice with the specified size(s).
+//
+// Parameters:
+// - size: The size(s) of the BioSequenceSlice to create (optional).
+//
+// Return:
+// A new BioSequenceSlice with the specified size(s).
 func MakeBioSequenceSlice(size ...int) BioSequenceSlice {
 	return *NewBioSequenceSlice(size...)
 }
 
+// Recycle cleans up the BioSequenceSlice by recycling its elements and resetting its length.
+//
+// If including_seq is true, each element of the BioSequenceSlice is recycled using the Recycle method,
+// and then set to nil. If including_seq is false, each element is simply set to nil.
+//
+// The function does not return anything.
 func (s *BioSequenceSlice) Recycle(including_seq bool) {
 	if s == nil {
 		log.Panicln("Trying too recycle a nil pointer")
@@ -42,60 +61,113 @@ func (s *BioSequenceSlice) Recycle(including_seq bool) {
 	// Code added to potentially limit memory leaks
 	if including_seq {
 		for i := range *s {
-			(*s)[i] .Recycle()
+			(*s)[i].Recycle()
 			(*s)[i] = nil
 		}
-	
+
 	} else {
 		for i := range *s {
 			(*s)[i] = nil
-		}	
+		}
 	}
 
 	*s = (*s)[:0]
 	_BioSequenceSlicePool.Put(s)
 }
 
-// Making sure that the slice has enough capacity to hold the number of elements that are being added
-// to it.
+// InsureCapacity ensures that the BioSequenceSlice has a minimum capacity
+//
+// It takes an integer `capacity` as a parameter, which represents the desired minimum capacity of the BioSequenceSlice.
+// It returns a pointer to the BioSequenceSlice.
 func (s *BioSequenceSlice) InsureCapacity(capacity int) *BioSequenceSlice {
 	var c int
 	if s != nil {
-		c = cap(*s)	
+		c = cap(*s)
 	} else {
 		c = 0
 	}
 
-	if c < capacity {
-		sl := make(BioSequenceSlice, 0,capacity)
-		s = &sl
-	}
+	*s = slices.Grow[BioSequenceSlice](*s, capacity-c)
 
 	return s
 }
 
-// Appending the sequence to the slice.
+// Push appends a BioSequence to the BioSequenceSlice.
+//
+// It takes a pointer to a BioSequenceSlice and a BioSequence as parameters.
+// It does not return anything.
 func (s *BioSequenceSlice) Push(sequence *BioSequence) {
 	*s = append(*s, sequence)
 }
 
-// Returning the last element of the slice and removing it from the slice.
+// Pop returns and removes the last element from the BioSequenceSlice.
+//
+// It does not take any parameters.
+// It returns *BioSequence, the last element of the slice.
 func (s *BioSequenceSlice) Pop() *BioSequence {
-	_s := (*s)[len(*s)-1]
-	(*s)[len(*s)-1] = nil
-	*s = (*s)[:len(*s)-1]
-	return _s
+	// Get the length of the slice
+	length := len(*s)
+
+	// If the slice is empty, return nil
+	if length == 0 {
+		return nil
+	}
+
+	// Get the last element of the slice
+	lastElement := (*s)[length-1]
+
+	// Set the last element to nil
+	(*s)[length-1] = nil
+
+	// Remove the last element from the slice
+	*s = (*s)[:length-1]
+
+	// Return the last element
+	return lastElement
 }
 
-// Returning the first element of the slice and removing it from the slice.
+// Pop0 returns and removes the first element of the BioSequenceSlice.
+//
+// It does not take any parameters.
+// It returns a pointer to a BioSequence object.
 func (s *BioSequenceSlice) Pop0() *BioSequence {
-	_s := (*s)[0]
+	if len(*s) == 0 {
+		return nil
+	}
+	firstElement := (*s)[0]
 	(*s)[0] = nil
 	*s = (*s)[1:]
-	return _s
+	return firstElement
 }
 
-// Test that a slice of sequences contains at least a sequence.
+// NotEmpty checks if the BioSequenceSlice is not empty.
+//
+// No parameters.
+// Returns a boolean value indicating if the BioSequenceSlice is not empty.
 func (s BioSequenceSlice) NotEmpty() bool {
 	return len(s) > 0
 }
+
+// Len returns the length of the BioSequenceSlice.
+//
+// It has no parameters.
+// It returns an integer.
+func (s BioSequenceSlice) Len() int {
+	return len(s)
+}
+
+// Size returns the total size of the BioSequenceSlice.
+//
+// It calculates the size by iterating over each BioSequence in the slice
+// and summing up their lengths.
+//
+// Returns an integer representing the total size of the BioSequenceSlice.
+func (s BioSequenceSlice) Size() int {
+	size := 0
+
+	for _, s := range s {
+		size += s.Len()
+	}
+
+	return size
+}