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Diffstat (limited to 'internal/zlib/writer.go')
| -rw-r--r-- | internal/zlib/writer.go | 228 |
1 files changed, 0 insertions, 228 deletions
diff --git a/internal/zlib/writer.go b/internal/zlib/writer.go deleted file mode 100644 index 81c57f55..00000000 --- a/internal/zlib/writer.go +++ /dev/null @@ -1,228 +0,0 @@ -// Copyright 2009 The Go Authors. All rights reserved. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE file. - -package zlib - -import ( - "compress/flate" - "encoding/binary" - "fmt" - "hash" - "io" - "sync" - - "codeberg.org/lindenii/furgit/internal/adler32" -) - -// These constants are copied from the [flate] package, so that code that imports -// [compress/zlib] does not also have to import [compress/flate]. -const ( - NoCompression = flate.NoCompression - BestSpeed = flate.BestSpeed - BestCompression = flate.BestCompression - DefaultCompression = flate.DefaultCompression - HuffmanOnly = flate.HuffmanOnly -) - -// A Writer takes data written to it and writes the compressed -// form of that data to an underlying writer (see [NewWriter]). -type Writer struct { - w io.Writer - level int - dict []byte - compressor *flate.Writer - digest hash.Hash32 - err error - scratch [4]byte - wroteHeader bool -} - -var writerPool = sync.Pool{ - New: func() any { - return new(Writer) - }, -} - -// NewWriter creates 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. -func NewWriter(w io.Writer) *Writer { - z, _ := NewWriterLevelDict(w, DefaultCompression, nil) - return z -} - -// 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. -func NewWriterLevel(w io.Writer, level int) (*Writer, error) { - return NewWriterLevelDict(w, level, nil) -} - -// NewWriterLevelDict is like [NewWriterLevel] but specifies a dictionary to -// compress with. -// -// The dictionary may be nil. If not, its contents should not be modified until -// the Writer is closed. -func NewWriterLevelDict(w io.Writer, level int, dict []byte) (*Writer, error) { - if level < HuffmanOnly || level > BestCompression { - return nil, fmt.Errorf("zlib: invalid compression level: %d", level) - } - v := writerPool.Get() - z, ok := v.(*Writer) - if !ok { - panic("zlib: pool returned unexpected type") - } - - // flate.Writer can only be Reset with the same level/dictionary mode. - // Reuse it only when the configuration is unchanged and dictionary-free. - reuseCompressor := z.compressor != nil && z.level == level && z.dict == nil && dict == nil - if !reuseCompressor { - z.compressor = nil - } - if z.digest != nil { - z.digest.Reset() - } - - *z = Writer{ - w: w, - level: level, - dict: dict, - compressor: z.compressor, - digest: z.digest, - } - if z.compressor != nil { - z.compressor.Reset(w) - } - return z, nil -} - -// Reset clears the state of the [Writer] z such that it is equivalent to its -// initial state from [NewWriterLevel] or [NewWriterLevelDict], but instead writing -// to w. -func (z *Writer) Reset(w io.Writer) { - z.w = w - // z.level and z.dict left unchanged. - if z.compressor != nil { - z.compressor.Reset(w) - } - if z.digest != nil { - z.digest.Reset() - } - z.err = nil - z.scratch = [4]byte{} - z.wroteHeader = false -} - -// writeHeader writes the ZLIB header. -func (z *Writer) writeHeader() (err error) { - z.wroteHeader = true - // ZLIB has a two-byte header (as documented in RFC 1950). - // The first four bits is the CINFO (compression info), which is 7 for the default deflate window size. - // The next four bits is the CM (compression method), which is 8 for deflate. - z.scratch[0] = 0x78 - // The next two bits is the FLEVEL (compression level). The four values are: - // 0=fastest, 1=fast, 2=default, 3=best. - // The next bit, FDICT, is set if a dictionary is given. - // The final five FCHECK bits form a mod-31 checksum. - switch z.level { - case -2, 0, 1: - z.scratch[1] = 0 << 6 - case 2, 3, 4, 5: - z.scratch[1] = 1 << 6 - case 6, -1: - z.scratch[1] = 2 << 6 - case 7, 8, 9: - z.scratch[1] = 3 << 6 - default: - panic("unreachable") - } - if z.dict != nil { - z.scratch[1] |= 1 << 5 - } - z.scratch[1] += uint8(31 - binary.BigEndian.Uint16(z.scratch[:2])%31) - if _, err = z.w.Write(z.scratch[0:2]); err != nil { - return err - } - if z.dict != nil { - // The next four bytes are the Adler-32 checksum of the dictionary. - binary.BigEndian.PutUint32(z.scratch[:], adler32.Checksum(z.dict)) - if _, err = z.w.Write(z.scratch[0:4]); err != nil { - return err - } - } - if z.compressor == nil { - // Initialize deflater unless the Writer is being reused - // after a Reset call. - z.compressor, err = flate.NewWriterDict(z.w, z.level, z.dict) - if err != nil { - return err - } - z.digest = adler32.New() - } - return nil -} - -// Write writes a compressed form of p to the underlying [io.Writer]. The -// compressed bytes are not necessarily flushed until the [Writer] is closed or -// explicitly flushed. -func (z *Writer) Write(p []byte) (n int, err error) { - if !z.wroteHeader { - z.err = z.writeHeader() - } - if z.err != nil { - return 0, z.err - } - if len(p) == 0 { - return 0, nil - } - n, err = z.compressor.Write(p) - if err != nil { - z.err = err - return - } - z.digest.Write(p) - return -} - -// Flush flushes the Writer to its underlying [io.Writer]. -func (z *Writer) Flush() error { - if !z.wroteHeader { - z.err = z.writeHeader() - } - if z.err != nil { - return z.err - } - z.err = z.compressor.Flush() - return z.err -} - -// Close closes the Writer, flushing any unwritten data to the underlying -// [io.Writer], but does not close the underlying io.Writer. -func (z *Writer) Close() error { - if !z.wroteHeader { - z.err = z.writeHeader() - } - if z.err != nil { - return z.err - } - z.err = z.compressor.Close() - if z.err != nil { - return z.err - } - checksum := z.digest.Sum32() - // ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952). - binary.BigEndian.PutUint32(z.scratch[:], checksum) - _, z.err = z.w.Write(z.scratch[0:4]) - if z.err != nil { - return z.err - } - - writerPool.Put(z) - return nil -} |