package gzip

Import Path
	compress/gzip (on go.dev)

Dependency Relation
	imports 8 packages, and imported by 3 packages

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 [io.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 Close on the [Reader] 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.
NewWriterLevel is like [NewWriter] but specifies the compression level instead of assuming [DefaultCompression]. The compression level can be [DefaultCompression], [NoCompression], [HuffmanOnly] or any integer value between [BestSpeed] and [BestCompression] inclusive. The error returned will be nil if the level is valid.
Package-Level Variables (total 2)
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".