package flate

Import Path
	compress/flate (on go.dev)

Dependency Relation
	imports 9 packages, and imported by 3 packages


Involved Source Files

	    deflate.go
	    deflatefast.go
	    dict_decoder.go
	    huffman_bit_writer.go
	    huffman_code.go
	
		Package flate implements the DEFLATE compressed data format, described in
		RFC 1951.  The gzip and zlib packages implement access to DEFLATE-based file
		formats.

	    token.go


Code Examples

	
		package main
		
		import (
			"bytes"
			"compress/flate"
			"fmt"
			"io"
			"log"
			"os"
			"strings"
		)
		
		func main() {
			// The dictionary is a string of bytes. When compressing some input data,
			// the compressor will attempt to substitute substrings with matches found
			// in the dictionary. As such, the dictionary should only contain substrings
			// that are expected to be found in the actual data stream.
			const dict = `<?xml version="1.0"?>` + `<book>` + `<data>` + `<meta name="` + `" content="`
		
			// The data to compress should (but is not required to) contain frequent
			// substrings that match those in the dictionary.
			const data = `<?xml version="1.0"?>
		<book>
			<meta name="title" content="The Go Programming Language"/>
			<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
			<meta name="published" content="2015-10-26"/>
			<meta name="isbn" content="978-0134190440"/>
			<data>...</data>
		</book>
		`
		
			var b bytes.Buffer
		
			// Compress the data using the specially crafted dictionary.
			zw, err := flate.NewWriterDict(&b, flate.DefaultCompression, []byte(dict))
			if err != nil {
				log.Fatal(err)
			}
			if _, err := io.Copy(zw, strings.NewReader(data)); err != nil {
				log.Fatal(err)
			}
			if err := zw.Close(); err != nil {
				log.Fatal(err)
			}
		
			// The decompressor must use the same dictionary as the compressor.
			// Otherwise, the input may appear as corrupted.
			fmt.Println("Decompressed output using the dictionary:")
			zr := flate.NewReaderDict(bytes.NewReader(b.Bytes()), []byte(dict))
			if _, err := io.Copy(os.Stdout, zr); err != nil {
				log.Fatal(err)
			}
			if err := zr.Close(); err != nil {
				log.Fatal(err)
			}
		
			fmt.Println()
		
			// Substitute all of the bytes in the dictionary with a '#' to visually
			// demonstrate the approximate effectiveness of using a preset dictionary.
			fmt.Println("Substrings matched by the dictionary are marked with #:")
			hashDict := []byte(dict)
			for i := range hashDict {
				hashDict[i] = '#'
			}
			zr = flate.NewReaderDict(&b, hashDict)
			if _, err := io.Copy(os.Stdout, zr); err != nil {
				log.Fatal(err)
			}
			if err := zr.Close(); err != nil {
				log.Fatal(err)
			}
		
		}

	
		package main
		
		import (
			"bytes"
			"compress/flate"
			"io"
			"log"
			"os"
			"strings"
		)
		
		func main() {
			proverbs := []string{
				"Don't communicate by sharing memory, share memory by communicating.\n",
				"Concurrency is not parallelism.\n",
				"The bigger the interface, the weaker the abstraction.\n",
				"Documentation is for users.\n",
			}
		
			var r strings.Reader
			var b bytes.Buffer
			buf := make([]byte, 32<<10)
		
			zw, err := flate.NewWriter(nil, flate.DefaultCompression)
			if err != nil {
				log.Fatal(err)
			}
			zr := flate.NewReader(nil)
		
			for _, s := range proverbs {
				r.Reset(s)
				b.Reset()
		
				// Reset the compressor and encode from some input stream.
				zw.Reset(&b)
				if _, err := io.CopyBuffer(zw, &r, buf); err != nil {
					log.Fatal(err)
				}
				if err := zw.Close(); err != nil {
					log.Fatal(err)
				}
		
				// Reset the decompressor and decode to some output stream.
				if err := zr.(flate.Resetter).Reset(&b, nil); err != nil {
					log.Fatal(err)
				}
				if _, err := io.CopyBuffer(os.Stdout, zr, buf); err != nil {
					log.Fatal(err)
				}
				if err := zr.Close(); err != nil {
					log.Fatal(err)
				}
			}
		
		}

	
		package main
		
		import (
			"compress/flate"
			"fmt"
			"io"
			"log"
			"strings"
			"sync"
		)
		
		func main() {
			var wg sync.WaitGroup
			defer wg.Wait()
		
			// Use io.Pipe to simulate a network connection.
			// A real network application should take care to properly close the
			// underlying connection.
			rp, wp := io.Pipe()
		
			// Start a goroutine to act as the transmitter.
			wg.Add(1)
			go func() {
				defer wg.Done()
		
				zw, err := flate.NewWriter(wp, flate.BestSpeed)
				if err != nil {
					log.Fatal(err)
				}
		
				b := make([]byte, 256)
				for _, m := range strings.Fields("A long time ago in a galaxy far, far away...") {
					// We use a simple framing format where the first byte is the
					// message length, followed the message itself.
					b[0] = uint8(copy(b[1:], m))
		
					if _, err := zw.Write(b[:1+len(m)]); err != nil {
						log.Fatal(err)
					}
		
					// Flush ensures that the receiver can read all data sent so far.
					if err := zw.Flush(); err != nil {
						log.Fatal(err)
					}
				}
		
				if err := zw.Close(); err != nil {
					log.Fatal(err)
				}
			}()
		
			// Start a goroutine to act as the receiver.
			wg.Add(1)
			go func() {
				defer wg.Done()
		
				zr := flate.NewReader(rp)
		
				b := make([]byte, 256)
				for {
					// Read the message length.
					// This is guaranteed to return for every corresponding
					// Flush and Close on the transmitter side.
					if _, err := io.ReadFull(zr, b[:1]); err != nil {
						if err == io.EOF {
							break // The transmitter closed the stream
						}
						log.Fatal(err)
					}
		
					// Read the message content.
					n := int(b[0])
					if _, err := io.ReadFull(zr, b[:n]); err != nil {
						log.Fatal(err)
					}
		
					fmt.Printf("Received %d bytes: %s\n", n, b[:n])
				}
				fmt.Println()
		
				if err := zr.Close(); err != nil {
					log.Fatal(err)
				}
			}()
		
		}




Package-Level Type Names (total 7)


	/* sort by:  |  */
	
		A CorruptInputError reports the presence of corrupt input at a given offset.

		
			( CorruptInputError) Error() string
		
			 CorruptInputError : error


	
		An InternalError reports an error in the flate code itself.

		
			( InternalError) Error() string
		
			 InternalError : error


	
		The actual read interface needed by [NewReader].
		If the passed in io.Reader does not also have ReadByte,
		the [NewReader] will introduce its own buffering.

		
			( Reader) Read(p []byte) (n int, err error)
			( Reader) ReadByte() (byte, error)
		
			*bufio.Reader
			 bufio.ReadWriter
			*bytes.Buffer
			*bytes.Reader
			 image/jpeg.Reader (interface)
			*internal/zstd.Reader
			*strings.Reader
		
			 Reader : image/jpeg.Reader
			 Reader : io.ByteReader
			 Reader : io.Reader


	
		A ReadError reports an error encountered while reading input.
		
		Deprecated: No longer returned.

		
			
				// error returned by underlying Read

			
				// byte offset where error occurred

		
			(*ReadError) Error() string
		
			*ReadError : error


	
		Resetter resets a ReadCloser returned by [NewReader] or [NewReaderDict]
		to switch to a new underlying [Reader]. This permits reusing a ReadCloser
		instead of allocating a new one.

		
			
				Reset discards any buffered data and resets the Resetter as if it was
				newly initialized with the given reader.

		
			 compress/zlib.Resetter (interface)
		
			 Resetter : compress/zlib.Resetter


	
		A WriteError reports an error encountered while writing output.
		
		Deprecated: No longer returned.

		
			
				// error returned by underlying Read

			
				// byte offset where error occurred

		
			(*WriteError) Error() string
		
			*WriteError : error


	
		A Writer takes data written to it and writes the compressed
		form of that data to an underlying writer (see [NewWriter]).

		
			
				Close flushes and closes the writer.

			
				Flush flushes any pending 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.
				Calling Flush when there is no pending data still causes the [Writer]
				to emit a sync marker of at least 4 bytes.
				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's state and makes it equivalent to
				the result of [NewWriter] or [NewWriterDict] called with dst
				and w's level and dictionary.

			
				Write writes data to w, which will eventually write the
				compressed form of data to its underlying writer.

		
			*Writer : internal/bisect.Writer
			*Writer : io.Closer
			*Writer : io.WriteCloser
			*Writer : io.Writer
		
			func NewWriter(w io.Writer, level int) (*Writer, error)
			func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error)




Package-Level Functions (total 4)


	
		NewReader returns a new ReadCloser that can be used
		to read the uncompressed version of r.
		If r does not also implement [io.ByteReader],
		the decompressor may read more data than necessary from r.
		The reader returns [io.EOF] after the final block in the DEFLATE stream has
		been encountered. Any trailing data after the final block is ignored.
		
		The [io.ReadCloser] returned by NewReader also implements [Resetter].


	
		NewReaderDict is like [NewReader] but initializes the reader
		with a preset dictionary. The returned [Reader] behaves as if
		the uncompressed data stream started with the given dictionary,
		which has already been read. NewReaderDict is typically used
		to read data compressed by NewWriterDict.
		
		The ReadCloser returned by NewReaderDict also implements [Resetter].


	
		NewWriter returns a new [Writer] compressing data at the given level.
		Following zlib, levels range from 1 ([BestSpeed]) to 9 ([BestCompression]);
		higher levels typically run slower but compress more. Level 0
		([NoCompression]) does not attempt any compression; it only adds the
		necessary DEFLATE framing.
		Level -1 ([DefaultCompression]) uses the default compression level.
		Level -2 ([HuffmanOnly]) will use Huffman compression only, giving
		a very fast compression for all types of input, but sacrificing considerable
		compression efficiency.
		
		If level is in the range [-2, 9] then the error returned will be nil.
		Otherwise the error returned will be non-nil.


	
		NewWriterDict is like [NewWriter] but initializes the new
		[Writer] with a preset dictionary. The returned [Writer] behaves
		as if the dictionary had been written to it without producing
		any compressed output. The compressed data written to w
		can only be decompressed by a [Reader] initialized with the
		same dictionary.




Package-Level Constants (total 5)


	const BestCompression = 9
	const BestSpeed = 1
	const DefaultCompression = -1
	
		HuffmanOnly disables Lempel-Ziv match searching and only performs Huffman
		entropy encoding. This mode is useful in compressing data that has
		already been compressed with an LZ style algorithm (e.g. Snappy or LZ4)
		that lacks an entropy encoder. Compression gains are achieved when
		certain bytes in the input stream occur more frequently than others.
		
		Note that HuffmanOnly produces a compressed output that is
		RFC 1951 compliant. That is, any valid DEFLATE decompressor will
		continue to be able to decompress this output.


	const NoCompression = 0