compress/bzip2: support concatenated files

While we're here, add a test for the same functionality in gzip,
which was already implemented, and add bzip2 CRC checks.

Fixes #5772.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/12387044

src/pkg/compress/bzip2/bzip2.go

@@ -23,6 +23,9 @@ func (s StructuralError) Error() string {
 // A reader decompresses bzip2 compressed data.
 type reader struct {
 	br           bitReader
+	fileCRC      uint32
+	blockCRC     uint32
+	wantBlockCRC uint32
 	setupDone    bool // true if we have parsed the bzip2 header.
 	blockSize    int  // blockSize in bytes, i.e. 900 * 1024.
 	eof          bool
@@ -50,13 +53,15 @@ const bzip2BlockMagic = 0x314159265359
 const bzip2FinalMagic = 0x177245385090
 
 // setup parses the bzip2 header.
-func (bz2 *reader) setup() error {
+func (bz2 *reader) setup(needMagic bool) error {
 	br := &bz2.br
 
+	if needMagic {
 		magic := br.ReadBits(16)
 		if magic != bzip2FileMagic {
 			return StructuralError("bad magic value")
 		}
+	}
 
 	t := br.ReadBits(8)
 	if t != 'h' {
@@ -68,8 +73,11 @@ func (bz2 *reader) setup() error {
 		return StructuralError("invalid compression level")
 	}
 
+	bz2.fileCRC = 0
 	bz2.blockSize = 100 * 1024 * (int(level) - '0')
+	if bz2.blockSize > len(bz2.tt) {
 		bz2.tt = make([]uint32, bz2.blockSize)
+	}
 	return nil
 }
 
@@ -79,7 +87,7 @@ func (bz2 *reader) Read(buf []byte) (n int, err error) {
 	}
 
 	if !bz2.setupDone {
-		err = bz2.setup()
+		err = bz2.setup(true)
 		brErr := bz2.br.Err()
 		if brErr != nil {
 			err = brErr
@@ -98,14 +106,14 @@ func (bz2 *reader) Read(buf []byte) (n int, err error) {
 	return
 }
 
-func (bz2 *reader) read(buf []byte) (n int, err error) {
+func (bz2 *reader) readFromBlock(buf []byte) int {
 	// bzip2 is a block based compressor, except that it has a run-length
 	// preprocessing step. The block based nature means that we can
 	// preallocate fixed-size buffers and reuse them. However, the RLE
 	// preprocessing would require allocating huge buffers to store the
 	// maximum expansion. Thus we process blocks all at once, except for
 	// the RLE which we decompress as required.
-
+	n := 0
 	for (bz2.repeats > 0 || bz2.preRLEUsed < len(bz2.preRLE)) && n < len(buf) {
 		// We have RLE data pending.
 
@@ -148,34 +156,87 @@ func (bz2 *reader) read(buf []byte) (n int, err error) {
 		n++
 	}
 
+	return n
+}
+
+func (bz2 *reader) read(buf []byte) (int, error) {
+	for {
+		n := bz2.readFromBlock(buf)
 		if n > 0 {
-		return
+			bz2.blockCRC = updateCRC(bz2.blockCRC, buf[:n])
+			return n, nil
 		}
 
-	// No RLE data is pending so we need to read a block.
+		// End of block. Check CRC.
+		if bz2.blockCRC != bz2.wantBlockCRC {
+			bz2.br.err = StructuralError("block checksum mismatch")
+			return 0, bz2.br.err
+		}
 
+		// Find next block.
 		br := &bz2.br
-	magic := br.ReadBits64(48)
-	if magic == bzip2FinalMagic {
-		br.ReadBits64(32) // ignored CRC
-		bz2.eof = true
-		return 0, io.EOF
-	} else if magic != bzip2BlockMagic {
+		switch br.ReadBits64(48) {
+		default:
 			return 0, StructuralError("bad magic value found")
-	}
 
-	err = bz2.readBlock()
+		case bzip2BlockMagic:
+			// Start of block.
+			err := bz2.readBlock()
 			if err != nil {
 				return 0, err
 			}
 
-	return bz2.read(buf)
+		case bzip2FinalMagic:
+			// Check end-of-file CRC.
+			wantFileCRC := uint32(br.ReadBits64(32))
+			if br.err != nil {
+				return 0, br.err
+			}
+			if bz2.fileCRC != wantFileCRC {
+				br.err = StructuralError("file checksum mismatch")
+				return 0, br.err
+			}
+
+			// Skip ahead to byte boundary.
+			// Is there a file concatenated to this one?
+			// It would start with BZ.
+			if br.bits%8 != 0 {
+				br.ReadBits(br.bits % 8)
+			}
+			b, err := br.r.ReadByte()
+			if err == io.EOF {
+				br.err = io.EOF
+				bz2.eof = true
+				return 0, io.EOF
+			}
+			if err != nil {
+				br.err = err
+				return 0, err
+			}
+			z, err := br.r.ReadByte()
+			if err != nil {
+				if err == io.EOF {
+					err = io.ErrUnexpectedEOF
+				}
+				br.err = err
+				return 0, err
+			}
+			if b != 'B' || z != 'Z' {
+				return 0, StructuralError("bad magic value in continuation file")
+			}
+			if err := bz2.setup(false); err != nil {
+				return 0, err
+			}
+		}
+	}
 }
 
 // readBlock reads a bzip2 block. The magic number should already have been consumed.
 func (bz2 *reader) readBlock() (err error) {
 	br := &bz2.br
-	br.ReadBits64(32) // skip checksum. TODO: check it if we can figure out what it is.
+	bz2.wantBlockCRC = uint32(br.ReadBits64(32)) // skip checksum. TODO: check it if we can figure out what it is.
+	bz2.blockCRC = 0
+	bz2.fileCRC = (bz2.fileCRC<<1 | bz2.fileCRC>>31) ^ bz2.wantBlockCRC
 	randomized := br.ReadBits(1)
 	if randomized != 0 {
 		return StructuralError("deprecated randomized files")
@@ -391,3 +452,33 @@ func inverseBWT(tt []uint32, origPtr uint, c []uint) uint32 {
 
 	return tt[origPtr] >> 8
 }
+
+// This is a standard CRC32 like in hash/crc32 except that all the shifts are reversed,
+// causing the bits in the input to be processed in the reverse of the usual order.
+
+var crctab [256]uint32
+
+func init() {
+	const poly = 0x04C11DB7
+	for i := range crctab {
+		crc := uint32(i) << 24
+		for j := 0; j < 8; j++ {
+			if crc&0x80000000 != 0 {
+				crc = (crc << 1) ^ poly
+			} else {
+				crc <<= 1
+			}
+		}
+		crctab[i] = crc
+	}
+}
+
+// updateCRC updates the crc value to incorporate the data in b.
+// The initial value is 0.
+func updateCRC(val uint32, b []byte) uint32 {
+	crc := ^val
+	for _, v := range b {
+		crc = crctab[byte(crc>>24)^v] ^ (crc << 8)
+	}
+	return ^crc
+}

src/pkg/compress/bzip2/bzip2_test.go

@@ -63,6 +63,19 @@ func TestHelloWorldBZ2(t *testing.T) {
 	}
 }
 
+func TestConcat(t *testing.T) {
+	out, err := decompressHex(helloWorldBZ2Hex + helloWorldBZ2Hex)
+	if err != nil {
+		t.Errorf("error from Read: %s", err)
+		return
+	}
+
+	hello2 := bytes.Repeat(helloWorld, 2)
+	if !bytes.Equal(hello2, out) {
+		t.Errorf("got %x, want %x", out, hello2)
+	}
+}
+
 func testZeros(t *testing.T, inHex string, n int) {
 	out, err := decompressHex(inHex)
 	if err != nil {

src/pkg/compress/gzip/gzip_test.go

@@ -197,3 +197,20 @@ func TestWriterFlush(t *testing.T) {
 		t.Fatal("Flush didn't flush any data")
 	}
 }
+
+// Multiple gzip files concatenated form a valid gzip file.
+func TestConcat(t *testing.T) {
+	var buf bytes.Buffer
+	w := NewWriter(&buf)
+	w.Write([]byte("hello "))
+	w.Close()
+	w = NewWriter(&buf)
+	w.Write([]byte("world\n"))
+	w.Close()
+
+	r, err := NewReader(&buf)
+	data, err := ioutil.ReadAll(r)
+	if string(data) != "hello world\n" || err != nil {
+		t.Fatalf("ReadAll = %q, %v, want %q, nil", data, err, "hello world")
+	}
+}