Involved Source Files Package gzip implements reading and writing of gzip format compressed files,
as specified in RFC 1952.gzip.go
Code Examples
package main
import (
"bytes"
"compress/gzip"
"fmt"
"io"
"log"
"os"
"time"
)
func main() {
var buf bytes.Buffer
zw := gzip.NewWriter(&buf)
var files = []struct {
name string
comment string
modTime time.Time
data string
}{
{"file-1.txt", "file-header-1", time.Date(2006, time.February, 1, 3, 4, 5, 0, time.UTC), "Hello Gophers - 1"},
{"file-2.txt", "file-header-2", time.Date(2007, time.March, 2, 4, 5, 6, 1, time.UTC), "Hello Gophers - 2"},
}
for _, file := range files {
zw.Name = file.name
zw.Comment = file.comment
zw.ModTime = file.modTime
if _, err := zw.Write([]byte(file.data)); err != nil {
log.Fatal(err)
}
if err := zw.Close(); err != nil {
log.Fatal(err)
}
zw.Reset(&buf)
}
zr, err := gzip.NewReader(&buf)
if err != nil {
log.Fatal(err)
}
for {
zr.Multistream(false)
fmt.Printf("Name: %s\nComment: %s\nModTime: %s\n\n", zr.Name, zr.Comment, zr.ModTime.UTC())
if _, err := io.Copy(os.Stdout, zr); err != nil {
log.Fatal(err)
}
fmt.Print("\n\n")
err = zr.Reset(&buf)
if err == io.EOF {
break
}
if err != nil {
log.Fatal(err)
}
}
if err := zr.Close(); err != nil {
log.Fatal(err)
}
}
package main
import (
"compress/gzip"
"io"
"log"
"net/http"
"net/http/httptest"
"os"
"strings"
)
func main() {
// This is an example of writing a compressing reader.
// This can be useful for an HTTP client body, as shown.
const testdata = "the data to be compressed"
// This HTTP handler is just for testing purposes.
handler := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
zr, err := gzip.NewReader(req.Body)
if err != nil {
log.Fatal(err)
}
// Just output the data for the example.
if _, err := io.Copy(os.Stdout, zr); err != nil {
log.Fatal(err)
}
})
ts := httptest.NewServer(handler)
defer ts.Close()
// The remainder is the example code.
// The data we want to compress, as an io.Reader
dataReader := strings.NewReader(testdata)
// bodyReader is the body of the HTTP request, as an io.Reader.
// httpWriter is the body of the HTTP request, as an io.Writer.
bodyReader, httpWriter := io.Pipe()
// Make sure that bodyReader is always closed, so that the
// goroutine below will always exit.
defer bodyReader.Close()
// gzipWriter compresses data to httpWriter.
gzipWriter := gzip.NewWriter(httpWriter)
// errch collects any errors from the writing goroutine.
errch := make(chan error, 1)
go func() {
defer close(errch)
sentErr := false
sendErr := func(err error) {
if !sentErr {
errch <- err
sentErr = true
}
}
// Copy our data to gzipWriter, which compresses it to
// gzipWriter, which feeds it to bodyReader.
if _, err := io.Copy(gzipWriter, dataReader); err != nil && err != io.ErrClosedPipe {
sendErr(err)
}
if err := gzipWriter.Close(); err != nil && err != io.ErrClosedPipe {
sendErr(err)
}
if err := httpWriter.Close(); err != nil && err != io.ErrClosedPipe {
sendErr(err)
}
}()
// Send an HTTP request to the test server.
req, err := http.NewRequest("PUT", ts.URL, bodyReader)
if err != nil {
log.Fatal(err)
}
// Note that passing req to http.Client.Do promises that it
// will close the body, in this case bodyReader.
resp, err := ts.Client().Do(req)
if err != nil {
log.Fatal(err)
}
// Check whether there was an error compressing the data.
if err := <-errch; err != nil {
log.Fatal(err)
}
// For this example we don't care about the response.
resp.Body.Close()
}
package main
import (
"bytes"
"compress/gzip"
"fmt"
"io"
"log"
"os"
"time"
)
func main() {
var buf bytes.Buffer
zw := gzip.NewWriter(&buf)
// Setting the Header fields is optional.
zw.Name = "a-new-hope.txt"
zw.Comment = "an epic space opera by George Lucas"
zw.ModTime = time.Date(1977, time.May, 25, 0, 0, 0, 0, time.UTC)
_, err := zw.Write([]byte("A long time ago in a galaxy far, far away..."))
if err != nil {
log.Fatal(err)
}
if err := zw.Close(); err != nil {
log.Fatal(err)
}
zr, err := gzip.NewReader(&buf)
if err != nil {
log.Fatal(err)
}
fmt.Printf("Name: %s\nComment: %s\nModTime: %s\n\n", zr.Name, zr.Comment, zr.ModTime.UTC())
if _, err := io.Copy(os.Stdout, zr); err != nil {
log.Fatal(err)
}
if err := zr.Close(); err != nil {
log.Fatal(err)
}
}
Package-Level Type Names (total 3)
/* sort by: | */
The gzip file stores a header giving metadata about the compressed file.
That header is exposed as the fields of the [Writer] and [Reader] structs.
Strings must be UTF-8 encoded and may only contain Unicode code points
U+0001 through U+00FF, due to limitations of the GZIP file format. // comment // "extra data" // modification time // file name // operating system type
A Reader is an [io.Reader] that can be read to retrieve
uncompressed data from a gzip-format compressed file.
In general, a gzip file can be a concatenation of gzip files,
each with its own header. Reads from the Reader
return the concatenation of the uncompressed data of each.
Only the first header is recorded in the Reader fields.
Gzip files store a length and checksum of the uncompressed data.
The Reader will return an [ErrChecksum] when [Reader.Read]
reaches the end of the uncompressed data if it does not
have the expected length or checksum. Clients should treat data
returned by [Reader.Read] as tentative until they receive the [io.EOF]
marking the end of the data. // valid after NewReader or Reader.Reset // comment // "extra data" // modification time // file name // operating system type Close closes the [Reader]. It does not close the underlying reader.
In order for the GZIP checksum to be verified, the reader must be
fully consumed until the [io.EOF]. Multistream controls whether the reader supports multistream files.
If enabled (the default), the [Reader] expects the input to be a sequence
of individually gzipped data streams, each with its own header and
trailer, ending at EOF. The effect is that the concatenation of a sequence
of gzipped files is treated as equivalent to the gzip of the concatenation
of the sequence. This is standard behavior for gzip readers.
Calling Multistream(false) disables this behavior; disabling the behavior
can be useful when reading file formats that distinguish individual gzip
data streams or mix gzip data streams with other data streams.
In this mode, when the [Reader] reaches the end of the data stream,
[Reader.Read] returns [io.EOF]. The underlying reader must implement [io.ByteReader]
in order to be left positioned just after the gzip stream.
To start the next stream, call z.Reset(r) followed by z.Multistream(false).
If there is no next stream, z.Reset(r) will return [io.EOF]. Read implements [io.Reader], reading uncompressed bytes from its underlying reader. Reset discards the [Reader] z's state and makes it equivalent to the
result of its original state from [NewReader], but reading from r instead.
This permits reusing a [Reader] rather than allocating a new one.
*Reader : io.Closer
*Reader : io.ReadCloser
*Reader : io.Reader
func NewReader(r io.Reader) (*Reader, error)
A Writer is an [io.WriteCloser].
Writes to a Writer are compressed and written to w. // written at first call to Write, Flush, or Close // comment // "extra data" // modification time // file name // operating system type Close closes the [Writer] by flushing any unwritten data to the underlying
[io.Writer] and writing the GZIP footer.
It does not close the underlying [io.Writer]. Flush flushes any pending compressed data to the underlying writer.
It is useful mainly in compressed network protocols, to ensure that
a remote reader has enough data to reconstruct a packet. Flush does
not return until the data has been written. If the underlying
writer returns an error, Flush returns that error.
In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH. Reset discards the [Writer] z's state and makes it equivalent to the
result of its original state from [NewWriter] or [NewWriterLevel], but
writing to w instead. This permits reusing a [Writer] rather than
allocating a new one. Write writes a compressed form of p to the underlying [io.Writer]. The
compressed bytes are not necessarily flushed until the [Writer] is closed.
*Writer : internal/bisect.Writer
*Writer : io.Closer
*Writer : io.WriteCloser
*Writer : io.Writer
func NewWriter(w io.Writer) *Writer
func NewWriterLevel(w io.Writer, level int) (*Writer, error)
Package-Level Functions (total 3)
NewReader creates a new [Reader] reading the given reader.
If r does not also implement [io.ByteReader],
the decompressor may read more data than necessary from r.
It is the caller's responsibility to call [Reader.Close] when done.
The Reader.[Header] fields will be valid in the [Reader] returned.
NewWriter returns a new [Writer].
Writes to the returned writer are compressed and written to w.
It is the caller's responsibility to call Close on the [Writer] when done.
Writes may be buffered and not flushed until Close.
Callers that wish to set the fields in Writer.[Header] must do so before
the first call to Write, Flush, or Close.
ErrChecksum is returned when reading GZIP data that has an invalid checksum.
ErrHeader is returned when reading GZIP data that has an invalid header.
Package-Level Constants (total 5)
These constants are copied from the [flate] package, so that code that imports
[compress/gzip] does not also have to import [compress/flate].
These constants are copied from the [flate] package, so that code that imports
[compress/gzip] does not also have to import [compress/flate].
These constants are copied from the [flate] package, so that code that imports
[compress/gzip] does not also have to import [compress/flate].
These constants are copied from the [flate] package, so that code that imports
[compress/gzip] does not also have to import [compress/flate].
These constants are copied from the [flate] package, so that code that imports
[compress/gzip] does not also have to import [compress/flate].
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