Switch back to internal zlib for loose objects too

Still marginally less overhead due to pooling

3 files changed, 419 insertions, 0 deletions

diff --git a/internal/zlib/LICENSE b/internal/zlib/LICENSE
new file mode 100644
index 00000000..2a7cf70d
--- /dev/null
+++ b/internal/zlib/LICENSE
@@ -0,0 +1,27 @@
+Copyright 2009 The Go Authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google LLC nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/internal/zlib/reader.go b/internal/zlib/reader.go
new file mode 100644
index 00000000..7602890b
--- /dev/null
+++ b/internal/zlib/reader.go
@@ -0,0 +1,198 @@
+// 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 implements reading and writing of zlib format compressed data,
+as specified in RFC 1950.
+
+This package differs from the standard library's compress/zlib package
+in that it pools readers to reduce allocations. Writers are unchanged.
+
+Note that closing the reader causes it to be returned to a pool for
+reuse. Therefore, the caller must not retain references to the
+reader after closing it; in the standard library's compress/zlib package,
+it is legal to Reset a closed reader and continue using it; that is
+not allowed here, so there is simply no Resetter interface.
+
+The implementation provides filters that uncompress during reading
+and compress during writing.  For example, to write compressed data
+to a buffer:
+
+	var b bytes.Buffer
+	w := zlib.NewWriter(&b)
+	w.Write([]byte("hello, world\n"))
+	w.Close()
+
+and to read that data back:
+
+	r, err := zlib.NewReader(&b)
+	io.Copy(os.Stdout, r)
+	r.Close()
+*/
+package zlib
+
+import (
+	"bufio"
+	"compress/flate"
+	"encoding/binary"
+	"errors"
+	"hash"
+	"io"
+	"sync"
+
+	"git.sr.ht/~runxiyu/furgit/internal/adler32"
+)
+
+const (
+	zlibDeflate   = 8
+	zlibMaxWindow = 7
+)
+
+var (
+	// ErrChecksum is returned when reading ZLIB data that has an invalid checksum.
+	ErrChecksum = errors.New("zlib: invalid checksum")
+	// ErrDictionary is returned when reading ZLIB data that has an invalid dictionary.
+	ErrDictionary = errors.New("zlib: invalid dictionary")
+	// ErrHeader is returned when reading ZLIB data that has an invalid header.
+	ErrHeader = errors.New("zlib: invalid header")
+)
+
+var pool = sync.Pool{
+	New: func() any {
+		r := new(reader)
+		return r
+	},
+}
+
+type reader struct {
+	r            flate.Reader
+	decompressor io.ReadCloser
+	digest       hash.Hash32
+	err          error
+	scratch      [4]byte
+}
+
+// NewReader creates a new ReadCloser.
+// Reads from the returned ReadCloser read and decompress data from r.
+// If r does not implement [io.ByteReader], the decompressor may read more
+// data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser when done.
+func NewReader(r io.Reader) (io.ReadCloser, error) {
+	return NewReaderDict(r, nil)
+}
+
+// NewReaderDict is like [NewReader] but uses a preset dictionary.
+// NewReaderDict ignores the dictionary if the compressed data does not refer to it.
+// If the compressed data refers to a different dictionary, NewReaderDict returns [ErrDictionary].
+func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error) {
+	v := pool.Get()
+	z, ok := v.(*reader)
+	if !ok {
+		panic("zlib: pool returned unexpected type")
+	}
+	err := z.Reset(r, dict)
+	if err != nil {
+		return nil, err
+	}
+	return z, nil
+}
+
+func (z *reader) Read(p []byte) (int, error) {
+	if z.err != nil {
+		return 0, z.err
+	}
+
+	var n int
+	n, z.err = z.decompressor.Read(p)
+	z.digest.Write(p[0:n])
+	if z.err != io.EOF {
+		// In the normal case we return here.
+		return n, z.err
+	}
+
+	// Finished file; check checksum.
+	if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		z.err = err
+		return n, z.err
+	}
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	checksum := binary.BigEndian.Uint32(z.scratch[:4])
+	if checksum != z.digest.Sum32() {
+		z.err = ErrChecksum
+		return n, z.err
+	}
+	return n, io.EOF
+}
+
+// Calling Close does not close the wrapped [io.Reader] originally passed to [NewReader].
+// In order for the ZLIB checksum to be verified, the reader must be
+// fully consumed until the [io.EOF].
+func (z *reader) Close() error {
+	if z.err != nil && z.err != io.EOF {
+		return z.err
+	}
+	z.err = z.decompressor.Close()
+	if z.err != nil {
+		return z.err
+	}
+
+	pool.Put(z)
+	return nil
+}
+
+func (z *reader) Reset(r io.Reader, dict []byte) error {
+	*z = reader{decompressor: z.decompressor}
+	if fr, ok := r.(flate.Reader); ok {
+		z.r = fr
+	} else {
+		z.r = bufio.NewReader(r)
+	}
+
+	// Read the header (RFC 1950 section 2.2.).
+	_, z.err = io.ReadFull(z.r, z.scratch[0:2])
+	if z.err != nil {
+		if z.err == io.EOF {
+			z.err = io.ErrUnexpectedEOF
+		}
+		return z.err
+	}
+	h := binary.BigEndian.Uint16(z.scratch[:2])
+	if (z.scratch[0]&0x0f != zlibDeflate) || (z.scratch[0]>>4 > zlibMaxWindow) || (h%31 != 0) {
+		z.err = ErrHeader
+		return z.err
+	}
+	haveDict := z.scratch[1]&0x20 != 0
+	if haveDict {
+		_, z.err = io.ReadFull(z.r, z.scratch[0:4])
+		if z.err != nil {
+			if z.err == io.EOF {
+				z.err = io.ErrUnexpectedEOF
+			}
+			return z.err
+		}
+		checksum := binary.BigEndian.Uint32(z.scratch[:4])
+		if checksum != adler32.Checksum(dict) {
+			z.err = ErrDictionary
+			return z.err
+		}
+	}
+
+	if z.decompressor == nil {
+		if haveDict {
+			z.decompressor = flate.NewReaderDict(z.r, dict)
+		} else {
+			z.decompressor = flate.NewReader(z.r)
+		}
+	} else {
+		z.err = z.decompressor.(flate.Resetter).Reset(z.r, dict)
+		if z.err != nil {
+			return z.err
+		}
+	}
+	z.digest = adler32.New()
+	return nil
+}
diff --git a/internal/zlib/writer.go b/internal/zlib/writer.go
new file mode 100644
index 00000000..65e96809
--- /dev/null
+++ b/internal/zlib/writer.go
@@ -0,0 +1,194 @@
+// 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"
+
+	"git.sr.ht/~runxiyu/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
+}
+
+// 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)
+	}
+	return &Writer{
+		w:     w,
+		level: level,
+		dict:  dict,
+	}, 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])
+	return z.err
+}