mirror of
https://github.com/mjl-/mox.git
synced 2025-06-30 15:28:15 +03:00
f40f94670e
to compress the entire IMAP connection. tested with thunderbird, meli, k9, ios mail. the initial implementation had interoperability issues with some of these clients: if they write the deflate stream and flush in "partial mode", the go stdlib flate reader does not return any data (until there is an explicit zero-length "sync flush" block, or until the history/sliding window is full), blocking progress, resulting in clients closing the seemingly stuck connection after considering the connection timed out. this includes a coy of the flate package with a new reader that returns partially flushed blocks earlier. this also adds imap trace logging to imapclient.Conn, which was useful for debugging.
694 lines
18 KiB
Go
694 lines
18 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package flate
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import (
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"io"
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)
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const (
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// The largest offset code.
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offsetCodeCount = 30
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// The special code used to mark the end of a block.
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endBlockMarker = 256
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// The first length code.
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lengthCodesStart = 257
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// The number of codegen codes.
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codegenCodeCount = 19
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badCode = 255
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// bufferFlushSize indicates the buffer size
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// after which bytes are flushed to the writer.
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// Should preferably be a multiple of 6, since
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// we accumulate 6 bytes between writes to the buffer.
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bufferFlushSize = 240
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// bufferSize is the actual output byte buffer size.
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// It must have additional headroom for a flush
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// which can contain up to 8 bytes.
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bufferSize = bufferFlushSize + 8
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)
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// The number of extra bits needed by length code X - LENGTH_CODES_START.
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var lengthExtraBits = []int8{
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/* 257 */ 0, 0, 0,
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/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
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/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
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/* 280 */ 4, 5, 5, 5, 5, 0,
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}
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// The length indicated by length code X - LENGTH_CODES_START.
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var lengthBase = []uint32{
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0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
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12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
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64, 80, 96, 112, 128, 160, 192, 224, 255,
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}
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// offset code word extra bits.
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var offsetExtraBits = []int8{
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0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
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4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
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9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
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}
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var offsetBase = []uint32{
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0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
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0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
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0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
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0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
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0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
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0x001800, 0x002000, 0x003000, 0x004000, 0x006000,
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}
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// The odd order in which the codegen code sizes are written.
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var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
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type huffmanBitWriter struct {
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// writer is the underlying writer.
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// Do not use it directly; use the write method, which ensures
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// that Write errors are sticky.
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writer io.Writer
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// Data waiting to be written is bytes[0:nbytes]
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// and then the low nbits of bits. Data is always written
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// sequentially into the bytes array.
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bits uint64
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nbits uint
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bytes [bufferSize]byte
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codegenFreq [codegenCodeCount]int32
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nbytes int
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literalFreq []int32
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offsetFreq []int32
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codegen []uint8
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literalEncoding *huffmanEncoder
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offsetEncoding *huffmanEncoder
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codegenEncoding *huffmanEncoder
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err error
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}
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func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
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return &huffmanBitWriter{
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writer: w,
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literalFreq: make([]int32, maxNumLit),
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offsetFreq: make([]int32, offsetCodeCount),
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codegen: make([]uint8, maxNumLit+offsetCodeCount+1),
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literalEncoding: newHuffmanEncoder(maxNumLit),
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codegenEncoding: newHuffmanEncoder(codegenCodeCount),
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offsetEncoding: newHuffmanEncoder(offsetCodeCount),
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}
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}
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func (w *huffmanBitWriter) reset(writer io.Writer) {
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w.writer = writer
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w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
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}
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func (w *huffmanBitWriter) flush() {
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if w.err != nil {
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w.nbits = 0
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return
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}
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n := w.nbytes
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for w.nbits != 0 {
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w.bytes[n] = byte(w.bits)
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w.bits >>= 8
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if w.nbits > 8 { // Avoid underflow
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w.nbits -= 8
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} else {
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w.nbits = 0
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}
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n++
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}
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w.bits = 0
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w.write(w.bytes[:n])
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w.nbytes = 0
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}
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func (w *huffmanBitWriter) write(b []byte) {
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if w.err != nil {
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return
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}
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_, w.err = w.writer.Write(b)
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}
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func (w *huffmanBitWriter) writeBits(b int32, nb uint) {
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if w.err != nil {
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return
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}
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w.bits |= uint64(b) << w.nbits
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w.nbits += nb
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if w.nbits >= 48 {
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bits := w.bits
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w.bits >>= 48
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w.nbits -= 48
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n := w.nbytes
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bytes := w.bytes[n : n+6]
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bytes[0] = byte(bits)
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bytes[1] = byte(bits >> 8)
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bytes[2] = byte(bits >> 16)
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bytes[3] = byte(bits >> 24)
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bytes[4] = byte(bits >> 32)
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bytes[5] = byte(bits >> 40)
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n += 6
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if n >= bufferFlushSize {
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w.write(w.bytes[:n])
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n = 0
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}
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w.nbytes = n
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}
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}
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func (w *huffmanBitWriter) writeBytes(bytes []byte) {
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if w.err != nil {
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return
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}
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n := w.nbytes
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if w.nbits&7 != 0 {
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w.err = InternalError("writeBytes with unfinished bits")
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return
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}
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for w.nbits != 0 {
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w.bytes[n] = byte(w.bits)
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w.bits >>= 8
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w.nbits -= 8
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n++
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}
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if n != 0 {
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w.write(w.bytes[:n])
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}
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w.nbytes = 0
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w.write(bytes)
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}
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// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
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// the literal and offset lengths arrays (which are concatenated into a single
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// array). This method generates that run-length encoding.
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//
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// The result is written into the codegen array, and the frequencies
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// of each code is written into the codegenFreq array.
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// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
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// information. Code badCode is an end marker
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//
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// numLiterals The number of literals in literalEncoding
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// numOffsets The number of offsets in offsetEncoding
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// litenc, offenc The literal and offset encoder to use
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func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litEnc, offEnc *huffmanEncoder) {
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clear(w.codegenFreq[:])
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// Note that we are using codegen both as a temporary variable for holding
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// a copy of the frequencies, and as the place where we put the result.
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// This is fine because the output is always shorter than the input used
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// so far.
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codegen := w.codegen // cache
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// Copy the concatenated code sizes to codegen. Put a marker at the end.
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cgnl := codegen[:numLiterals]
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for i := range cgnl {
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cgnl[i] = uint8(litEnc.codes[i].len)
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}
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cgnl = codegen[numLiterals : numLiterals+numOffsets]
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for i := range cgnl {
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cgnl[i] = uint8(offEnc.codes[i].len)
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}
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codegen[numLiterals+numOffsets] = badCode
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size := codegen[0]
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count := 1
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outIndex := 0
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for inIndex := 1; size != badCode; inIndex++ {
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// INVARIANT: We have seen "count" copies of size that have not yet
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// had output generated for them.
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nextSize := codegen[inIndex]
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if nextSize == size {
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count++
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continue
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}
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// We need to generate codegen indicating "count" of size.
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if size != 0 {
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codegen[outIndex] = size
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outIndex++
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w.codegenFreq[size]++
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count--
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for count >= 3 {
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n := 6
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if n > count {
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n = count
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}
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codegen[outIndex] = 16
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outIndex++
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codegen[outIndex] = uint8(n - 3)
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outIndex++
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w.codegenFreq[16]++
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count -= n
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}
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} else {
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for count >= 11 {
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n := 138
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if n > count {
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n = count
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}
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codegen[outIndex] = 18
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outIndex++
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codegen[outIndex] = uint8(n - 11)
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outIndex++
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w.codegenFreq[18]++
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count -= n
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}
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if count >= 3 {
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// count >= 3 && count <= 10
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codegen[outIndex] = 17
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outIndex++
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codegen[outIndex] = uint8(count - 3)
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outIndex++
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w.codegenFreq[17]++
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count = 0
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}
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}
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count--
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for ; count >= 0; count-- {
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codegen[outIndex] = size
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outIndex++
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w.codegenFreq[size]++
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}
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// Set up invariant for next time through the loop.
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size = nextSize
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count = 1
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}
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// Marker indicating the end of the codegen.
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codegen[outIndex] = badCode
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}
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// dynamicSize returns the size of dynamically encoded data in bits.
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func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
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numCodegens = len(w.codegenFreq)
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for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
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numCodegens--
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}
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header := 3 + 5 + 5 + 4 + (3 * numCodegens) +
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w.codegenEncoding.bitLength(w.codegenFreq[:]) +
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int(w.codegenFreq[16])*2 +
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int(w.codegenFreq[17])*3 +
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int(w.codegenFreq[18])*7
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size = header +
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litEnc.bitLength(w.literalFreq) +
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offEnc.bitLength(w.offsetFreq) +
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extraBits
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return size, numCodegens
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}
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// fixedSize returns the size of dynamically encoded data in bits.
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func (w *huffmanBitWriter) fixedSize(extraBits int) int {
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return 3 +
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fixedLiteralEncoding.bitLength(w.literalFreq) +
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fixedOffsetEncoding.bitLength(w.offsetFreq) +
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extraBits
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}
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// storedSize calculates the stored size, including header.
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// The function returns the size in bits and whether the block
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// fits inside a single block.
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func (w *huffmanBitWriter) storedSize(in []byte) (int, bool) {
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if in == nil {
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return 0, false
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}
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if len(in) <= maxStoreBlockSize {
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return (len(in) + 5) * 8, true
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}
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return 0, false
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}
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func (w *huffmanBitWriter) writeCode(c hcode) {
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if w.err != nil {
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return
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}
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w.bits |= uint64(c.code) << w.nbits
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w.nbits += uint(c.len)
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if w.nbits >= 48 {
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bits := w.bits
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w.bits >>= 48
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w.nbits -= 48
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n := w.nbytes
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bytes := w.bytes[n : n+6]
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bytes[0] = byte(bits)
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bytes[1] = byte(bits >> 8)
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bytes[2] = byte(bits >> 16)
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bytes[3] = byte(bits >> 24)
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bytes[4] = byte(bits >> 32)
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bytes[5] = byte(bits >> 40)
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n += 6
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if n >= bufferFlushSize {
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w.write(w.bytes[:n])
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n = 0
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}
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w.nbytes = n
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}
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}
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// Write the header of a dynamic Huffman block to the output stream.
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//
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// numLiterals The number of literals specified in codegen
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// numOffsets The number of offsets specified in codegen
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// numCodegens The number of codegens used in codegen
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func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
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if w.err != nil {
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return
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}
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var firstBits int32 = 4
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if isEof {
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firstBits = 5
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}
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w.writeBits(firstBits, 3)
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w.writeBits(int32(numLiterals-257), 5)
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w.writeBits(int32(numOffsets-1), 5)
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w.writeBits(int32(numCodegens-4), 4)
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for i := 0; i < numCodegens; i++ {
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value := uint(w.codegenEncoding.codes[codegenOrder[i]].len)
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w.writeBits(int32(value), 3)
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}
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i := 0
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for {
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var codeWord int = int(w.codegen[i])
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i++
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if codeWord == badCode {
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break
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}
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w.writeCode(w.codegenEncoding.codes[uint32(codeWord)])
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switch codeWord {
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case 16:
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w.writeBits(int32(w.codegen[i]), 2)
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i++
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case 17:
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w.writeBits(int32(w.codegen[i]), 3)
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i++
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case 18:
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w.writeBits(int32(w.codegen[i]), 7)
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i++
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}
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}
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}
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func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
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if w.err != nil {
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return
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}
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var flag int32
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if isEof {
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flag = 1
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}
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w.writeBits(flag, 3)
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w.flush()
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w.writeBits(int32(length), 16)
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w.writeBits(int32(^uint16(length)), 16)
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}
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func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
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if w.err != nil {
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return
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}
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// Indicate that we are a fixed Huffman block
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var value int32 = 2
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if isEof {
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value = 3
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}
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w.writeBits(value, 3)
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}
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// writeBlock will write a block of tokens with the smallest encoding.
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// The original input can be supplied, and if the huffman encoded data
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// is larger than the original bytes, the data will be written as a
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// stored block.
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// If the input is nil, the tokens will always be Huffman encoded.
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func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
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if w.err != nil {
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return
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}
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tokens = append(tokens, endBlockMarker)
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numLiterals, numOffsets := w.indexTokens(tokens)
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var extraBits int
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storedSize, storable := w.storedSize(input)
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if storable {
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// We only bother calculating the costs of the extra bits required by
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// the length of offset fields (which will be the same for both fixed
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// and dynamic encoding), if we need to compare those two encodings
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// against stored encoding.
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for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
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// First eight length codes have extra size = 0.
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extraBits += int(w.literalFreq[lengthCode]) * int(lengthExtraBits[lengthCode-lengthCodesStart])
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}
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for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
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// First four offset codes have extra size = 0.
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extraBits += int(w.offsetFreq[offsetCode]) * int(offsetExtraBits[offsetCode])
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}
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}
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// Figure out smallest code.
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// Fixed Huffman baseline.
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var literalEncoding = fixedLiteralEncoding
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var offsetEncoding = fixedOffsetEncoding
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var size = w.fixedSize(extraBits)
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// Dynamic Huffman?
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var numCodegens int
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// Generate codegen and codegenFrequencies, which indicates how to encode
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// the literalEncoding and the offsetEncoding.
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w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
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w.codegenEncoding.generate(w.codegenFreq[:], 7)
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dynamicSize, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, extraBits)
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if dynamicSize < size {
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size = dynamicSize
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literalEncoding = w.literalEncoding
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offsetEncoding = w.offsetEncoding
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}
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// Stored bytes?
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if storable && storedSize < size {
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w.writeStoredHeader(len(input), eof)
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w.writeBytes(input)
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return
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}
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// Huffman.
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if literalEncoding == fixedLiteralEncoding {
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w.writeFixedHeader(eof)
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} else {
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w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
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}
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// Write the tokens.
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w.writeTokens(tokens, literalEncoding.codes, offsetEncoding.codes)
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}
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// writeBlockDynamic encodes a block using a dynamic Huffman table.
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// This should be used if the symbols used have a disproportionate
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// histogram distribution.
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// If input is supplied and the compression savings are below 1/16th of the
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// input size the block is stored.
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func (w *huffmanBitWriter) writeBlockDynamic(tokens []token, eof bool, input []byte) {
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if w.err != nil {
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return
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}
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tokens = append(tokens, endBlockMarker)
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numLiterals, numOffsets := w.indexTokens(tokens)
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// Generate codegen and codegenFrequencies, which indicates how to encode
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// the literalEncoding and the offsetEncoding.
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w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
|
|
w.codegenEncoding.generate(w.codegenFreq[:], 7)
|
|
size, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, 0)
|
|
|
|
// Store bytes, if we don't get a reasonable improvement.
|
|
if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
// Write Huffman table.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
|
|
// Write the tokens.
|
|
w.writeTokens(tokens, w.literalEncoding.codes, w.offsetEncoding.codes)
|
|
}
|
|
|
|
// indexTokens indexes a slice of tokens, and updates
|
|
// literalFreq and offsetFreq, and generates literalEncoding
|
|
// and offsetEncoding.
|
|
// The number of literal and offset tokens is returned.
|
|
func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
|
|
clear(w.literalFreq)
|
|
clear(w.offsetFreq)
|
|
|
|
for _, t := range tokens {
|
|
if t < matchType {
|
|
w.literalFreq[t.literal()]++
|
|
continue
|
|
}
|
|
length := t.length()
|
|
offset := t.offset()
|
|
w.literalFreq[lengthCodesStart+lengthCode(length)]++
|
|
w.offsetFreq[offsetCode(offset)]++
|
|
}
|
|
|
|
// get the number of literals
|
|
numLiterals = len(w.literalFreq)
|
|
for w.literalFreq[numLiterals-1] == 0 {
|
|
numLiterals--
|
|
}
|
|
// get the number of offsets
|
|
numOffsets = len(w.offsetFreq)
|
|
for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
|
|
numOffsets--
|
|
}
|
|
if numOffsets == 0 {
|
|
// We haven't found a single match. If we want to go with the dynamic encoding,
|
|
// we should count at least one offset to be sure that the offset huffman tree could be encoded.
|
|
w.offsetFreq[0] = 1
|
|
numOffsets = 1
|
|
}
|
|
w.literalEncoding.generate(w.literalFreq, 15)
|
|
w.offsetEncoding.generate(w.offsetFreq, 15)
|
|
return
|
|
}
|
|
|
|
// writeTokens writes a slice of tokens to the output.
|
|
// codes for literal and offset encoding must be supplied.
|
|
func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
for _, t := range tokens {
|
|
if t < matchType {
|
|
w.writeCode(leCodes[t.literal()])
|
|
continue
|
|
}
|
|
// Write the length
|
|
length := t.length()
|
|
lengthCode := lengthCode(length)
|
|
w.writeCode(leCodes[lengthCode+lengthCodesStart])
|
|
extraLengthBits := uint(lengthExtraBits[lengthCode])
|
|
if extraLengthBits > 0 {
|
|
extraLength := int32(length - lengthBase[lengthCode])
|
|
w.writeBits(extraLength, extraLengthBits)
|
|
}
|
|
// Write the offset
|
|
offset := t.offset()
|
|
offsetCode := offsetCode(offset)
|
|
w.writeCode(oeCodes[offsetCode])
|
|
extraOffsetBits := uint(offsetExtraBits[offsetCode])
|
|
if extraOffsetBits > 0 {
|
|
extraOffset := int32(offset - offsetBase[offsetCode])
|
|
w.writeBits(extraOffset, extraOffsetBits)
|
|
}
|
|
}
|
|
}
|
|
|
|
// huffOffset is a static offset encoder used for huffman only encoding.
|
|
// It can be reused since we will not be encoding offset values.
|
|
var huffOffset *huffmanEncoder
|
|
|
|
func init() {
|
|
offsetFreq := make([]int32, offsetCodeCount)
|
|
offsetFreq[0] = 1
|
|
huffOffset = newHuffmanEncoder(offsetCodeCount)
|
|
huffOffset.generate(offsetFreq, 15)
|
|
}
|
|
|
|
// writeBlockHuff encodes a block of bytes as either
|
|
// Huffman encoded literals or uncompressed bytes if the
|
|
// results only gains very little from compression.
|
|
func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
|
|
if w.err != nil {
|
|
return
|
|
}
|
|
|
|
// Clear histogram
|
|
clear(w.literalFreq)
|
|
|
|
// Add everything as literals
|
|
histogram(input, w.literalFreq)
|
|
|
|
w.literalFreq[endBlockMarker] = 1
|
|
|
|
const numLiterals = endBlockMarker + 1
|
|
w.offsetFreq[0] = 1
|
|
const numOffsets = 1
|
|
|
|
w.literalEncoding.generate(w.literalFreq, 15)
|
|
|
|
// Figure out smallest code.
|
|
// Always use dynamic Huffman or Store
|
|
var numCodegens int
|
|
|
|
// Generate codegen and codegenFrequencies, which indicates how to encode
|
|
// the literalEncoding and the offsetEncoding.
|
|
w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
|
|
w.codegenEncoding.generate(w.codegenFreq[:], 7)
|
|
size, numCodegens := w.dynamicSize(w.literalEncoding, huffOffset, 0)
|
|
|
|
// Store bytes, if we don't get a reasonable improvement.
|
|
if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
|
|
w.writeStoredHeader(len(input), eof)
|
|
w.writeBytes(input)
|
|
return
|
|
}
|
|
|
|
// Huffman.
|
|
w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
|
|
encoding := w.literalEncoding.codes[:257]
|
|
n := w.nbytes
|
|
for _, t := range input {
|
|
// Bitwriting inlined, ~30% speedup
|
|
c := encoding[t]
|
|
w.bits |= uint64(c.code) << w.nbits
|
|
w.nbits += uint(c.len)
|
|
if w.nbits < 48 {
|
|
continue
|
|
}
|
|
// Store 6 bytes
|
|
bits := w.bits
|
|
w.bits >>= 48
|
|
w.nbits -= 48
|
|
bytes := w.bytes[n : n+6]
|
|
bytes[0] = byte(bits)
|
|
bytes[1] = byte(bits >> 8)
|
|
bytes[2] = byte(bits >> 16)
|
|
bytes[3] = byte(bits >> 24)
|
|
bytes[4] = byte(bits >> 32)
|
|
bytes[5] = byte(bits >> 40)
|
|
n += 6
|
|
if n < bufferFlushSize {
|
|
continue
|
|
}
|
|
w.write(w.bytes[:n])
|
|
if w.err != nil {
|
|
return // Return early in the event of write failures
|
|
}
|
|
n = 0
|
|
}
|
|
w.nbytes = n
|
|
w.writeCode(encoding[endBlockMarker])
|
|
}
|
|
|
|
// histogram accumulates a histogram of b in h.
|
|
//
|
|
// len(h) must be >= 256, and h's elements must be all zeroes.
|
|
func histogram(b []byte, h []int32) {
|
|
h = h[:256]
|
|
for _, t := range b {
|
|
h[t]++
|
|
}
|
|
}
|