internal/compress: Import flate and such from klauspost/compress

1 files changed, 92 insertions, 0 deletions

diff --git a/internal/compress/zlib/reader_reset.go b/internal/compress/zlib/reader_reset.go
new file mode 100644
index 00000000..f374111c
--- /dev/null
+++ b/internal/compress/zlib/reader_reset.go
@@ -0,0 +1,92 @@
+// 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 (
+	"bufio"
+	"encoding/binary"
+	"errors"
+	"io"
+
+	"codeberg.org/lindenii/furgit/internal/adler32"
+	"codeberg.org/lindenii/furgit/internal/compress/flate"
+)
+
+// reset resets receiver to read a new zlib stream.
+func (z *Reader) reset(r io.Reader, dict []byte) error {
+	*z = Reader{decompressor: z.decompressor}
+
+	var input flate.Reader
+	if fr, ok := r.(flate.Reader); ok {
+		input = fr
+	} else {
+		input = bufio.NewReader(r)
+	}
+
+	z.counter = &countingFlateReader{inner: input}
+	z.r = z.counter
+
+	// Read the header (RFC 1950 section 2.2.).
+	_, z.err = io.ReadFull(z.r, z.scratch[0:2])
+	if z.err != nil {
+		if errors.Is(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 errors.Is(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 {
+		resetter, ok := z.decompressor.(flate.Resetter)
+		if !ok {
+			panic("zlib: pooled decompressor does not implement flate.Resetter")
+		}
+
+		z.err = resetter.Reset(z.r, dict)
+		if z.err != nil {
+			return z.err
+		}
+
+		z.digest = adler32.New()
+
+		return nil
+	}
+
+	if haveDict {
+		z.decompressor = flate.NewReaderDict(z.r, dict)
+	} else {
+		z.decompressor = flate.NewReader(z.r)
+	}
+
+	z.digest = adler32.New()
+
+	return nil
+}