archive/zip: more efficient reader and bug fix

Fixes #2090.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/4815068

src/pkg/archive/zip/reader.go

@@ -6,7 +6,6 @@ package zip
 
 import (
 	"bufio"
-	"bytes"
 	"compress/flate"
 	"hash"
 	"hash/crc32"
@@ -37,8 +36,7 @@ type File struct {
 	FileHeader
 	zipr         io.ReaderAt
 	zipsize      int64
-	headerOffset uint32
-	bodyOffset   int64
+	headerOffset int64
 }
 
 func (f *File) hasDataDescriptor() bool {
@@ -90,12 +88,12 @@ func (z *Reader) init(r io.ReaderAt, size int64) os.Error {
 
 	// The count of files inside a zip is truncated to fit in a uint16.
 	// Gloss over this by reading headers until we encounter
-	// a bad one, and then only report a FormatError if
+	// a bad one, and then only report a FormatError or UnexpectedEOF if
 	// the file count modulo 65536 is incorrect.
 	for {
 		f := &File{zipr: r, zipsize: size}
-		err := readDirectoryHeader(f, buf)
-		if err == FormatError {
+		err = readDirectoryHeader(f, buf)
+		if err == FormatError || err == io.ErrUnexpectedEOF {
 			break
 		}
 		if err != nil {
@@ -104,9 +102,10 @@ func (z *Reader) init(r io.ReaderAt, size int64) os.Error {
 		z.File = append(z.File, f)
 	}
 	if uint16(len(z.File)) != end.directoryRecords {
-		return FormatError
+		// Return the readDirectoryHeader error if we read
+		// the wrong number of directory entries.
+		return err
 	}
-
 	return nil
 }
 
@@ -116,26 +115,18 @@ func (rc *ReadCloser) Close() os.Error {
 }
 
 // Open returns a ReadCloser that provides access to the File's contents.
+// It is safe to Open and Read from files concurrently.
 func (f *File) Open() (rc io.ReadCloser, err os.Error) {
-	off := int64(f.headerOffset)
-	size := int64(f.CompressedSize)
-	if f.bodyOffset == 0 {
-		r := io.NewSectionReader(f.zipr, off, f.zipsize-off)
-		if err = readFileHeader(f, r); err != nil {
-			return
-		}
-		if f.bodyOffset, err = r.Seek(0, os.SEEK_CUR); err != nil {
-			return
-		}
-		if size == 0 {
-			size = int64(f.CompressedSize)
-		}
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return
 	}
-	if f.hasDataDescriptor() && size == 0 {
+	size := int64(f.CompressedSize)
+	if size == 0 && f.hasDataDescriptor() {
 		// permit SectionReader to see the rest of the file
-		size = f.zipsize - (off + f.bodyOffset)
+		size = f.zipsize - (f.headerOffset + bodyOffset)
 	}
-	r := io.NewSectionReader(f.zipr, off+f.bodyOffset, size)
+	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
 	switch f.Method {
 	case Store: // (no compression)
 		rc = ioutil.NopCloser(r)
@@ -176,75 +167,99 @@ func (r *checksumReader) Read(b []byte) (n int, err os.Error) {
 
 func (r *checksumReader) Close() os.Error { return r.rc.Close() }
 
-func readFileHeader(f *File, r io.Reader) (err os.Error) {
-	defer recoverError(&err)
-	var (
-		signature      uint32
-		filenameLength uint16
-		extraLength    uint16
-	)
-	read(r, &signature)
-	if signature != fileHeaderSignature {
+func readFileHeader(f *File, r io.Reader) os.Error {
+	var b [fileHeaderLen]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return err
+	}
+	c := binary.LittleEndian
+	if sig := c.Uint32(b[:4]); sig != fileHeaderSignature {
 		return FormatError
 	}
-	read(r, &f.ReaderVersion)
-	read(r, &f.Flags)
-	read(r, &f.Method)
-	read(r, &f.ModifiedTime)
-	read(r, &f.ModifiedDate)
-	read(r, &f.CRC32)
-	read(r, &f.CompressedSize)
-	read(r, &f.UncompressedSize)
-	read(r, &filenameLength)
-	read(r, &extraLength)
-	f.Name = string(readByteSlice(r, filenameLength))
-	f.Extra = readByteSlice(r, extraLength)
-	return
+	f.ReaderVersion = c.Uint16(b[4:6])
+	f.Flags = c.Uint16(b[6:8])
+	f.Method = c.Uint16(b[8:10])
+	f.ModifiedTime = c.Uint16(b[10:12])
+	f.ModifiedDate = c.Uint16(b[12:14])
+	f.CRC32 = c.Uint32(b[14:18])
+	f.CompressedSize = c.Uint32(b[18:22])
+	f.UncompressedSize = c.Uint32(b[22:26])
+	filenameLen := int(c.Uint16(b[26:28]))
+	extraLen := int(c.Uint16(b[28:30]))
+	d := make([]byte, filenameLen+extraLen)
+	if _, err := io.ReadFull(r, d); err != nil {
+		return err
+	}
+	f.Name = string(d[:filenameLen])
+	f.Extra = d[filenameLen:]
+	return nil
 }
 
-func readDirectoryHeader(f *File, r io.Reader) (err os.Error) {
-	defer recoverError(&err)
-	var (
-		signature          uint32
-		filenameLength     uint16
-		extraLength        uint16
-		commentLength      uint16
-		startDiskNumber    uint16 // unused
-		internalAttributes uint16 // unused
-		externalAttributes uint32 // unused
-	)
-	read(r, &signature)
-	if signature != directoryHeaderSignature {
+// findBodyOffset does the minimum work to verify the file has a header
+// and returns the file body offset.
+func (f *File) findBodyOffset() (int64, os.Error) {
+	r := io.NewSectionReader(f.zipr, f.headerOffset, f.zipsize-f.headerOffset)
+	var b [fileHeaderLen]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return 0, err
+	}
+	c := binary.LittleEndian
+	if sig := c.Uint32(b[:4]); sig != fileHeaderSignature {
+		return 0, FormatError
+	}
+	filenameLen := int(c.Uint16(b[26:28]))
+	extraLen := int(c.Uint16(b[28:30]))
+	return int64(fileHeaderLen + filenameLen + extraLen), nil
+}
+
+// readDirectoryHeader attempts to read a directory header from r.
+// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
+// and FormatError if it doesn't find a valid header signature.
+func readDirectoryHeader(f *File, r io.Reader) os.Error {
+	var b [directoryHeaderLen]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return err
+	}
+	c := binary.LittleEndian
+	if sig := c.Uint32(b[:4]); sig != directoryHeaderSignature {
 		return FormatError
 	}
-	read(r, &f.CreatorVersion)
-	read(r, &f.ReaderVersion)
-	read(r, &f.Flags)
-	read(r, &f.Method)
-	read(r, &f.ModifiedTime)
-	read(r, &f.ModifiedDate)
-	read(r, &f.CRC32)
-	read(r, &f.CompressedSize)
-	read(r, &f.UncompressedSize)
-	read(r, &filenameLength)
-	read(r, &extraLength)
-	read(r, &commentLength)
-	read(r, &startDiskNumber)
-	read(r, &internalAttributes)
-	read(r, &externalAttributes)
-	read(r, &f.headerOffset)
-	f.Name = string(readByteSlice(r, filenameLength))
-	f.Extra = readByteSlice(r, extraLength)
-	f.Comment = string(readByteSlice(r, commentLength))
-	return
+	f.CreatorVersion = c.Uint16(b[4:6])
+	f.ReaderVersion = c.Uint16(b[6:8])
+	f.Flags = c.Uint16(b[8:10])
+	f.Method = c.Uint16(b[10:12])
+	f.ModifiedTime = c.Uint16(b[12:14])
+	f.ModifiedDate = c.Uint16(b[14:16])
+	f.CRC32 = c.Uint32(b[16:20])
+	f.CompressedSize = c.Uint32(b[20:24])
+	f.UncompressedSize = c.Uint32(b[24:28])
+	filenameLen := int(c.Uint16(b[28:30]))
+	extraLen := int(c.Uint16(b[30:32]))
+	commentLen := int(c.Uint16(b[32:34]))
+	// startDiskNumber := c.Uint16(b[34:36])    // Unused
+	// internalAttributes := c.Uint16(b[36:38]) // Unused
+	// externalAttributes := c.Uint32(b[38:42]) // Unused
+	f.headerOffset = int64(c.Uint32(b[42:46]))
+	d := make([]byte, filenameLen+extraLen+commentLen)
+	if _, err := io.ReadFull(r, d); err != nil {
+		return err
+	}
+	f.Name = string(d[:filenameLen])
+	f.Extra = d[filenameLen : filenameLen+extraLen]
+	f.Comment = string(d[filenameLen+extraLen:])
+	return nil
 }
 
-func readDataDescriptor(r io.Reader, f *File) (err os.Error) {
-	defer recoverError(&err)
-	read(r, &f.CRC32)
-	read(r, &f.CompressedSize)
-	read(r, &f.UncompressedSize)
-	return
+func readDataDescriptor(r io.Reader, f *File) os.Error {
+	var b [dataDescriptorLen]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return err
+	}
+	c := binary.LittleEndian
+	f.CRC32 = c.Uint32(b[:4])
+	f.CompressedSize = c.Uint32(b[4:8])
+	f.UncompressedSize = c.Uint32(b[8:12])
+	return nil
 }
 
 func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err os.Error) {
@@ -268,48 +283,29 @@ func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err os.Erro
 	}
 
 	// read header into struct
-	defer recoverError(&err)
-	br := bytes.NewBuffer(b[4:]) // skip over signature
+	c := binary.LittleEndian
 	d := new(directoryEnd)
-	read(br, &d.diskNbr)
-	read(br, &d.dirDiskNbr)
-	read(br, &d.dirRecordsThisDisk)
-	read(br, &d.directoryRecords)
-	read(br, &d.directorySize)
-	read(br, &d.directoryOffset)
-	read(br, &d.commentLen)
-	d.comment = string(readByteSlice(br, d.commentLen))
+	d.diskNbr = c.Uint16(b[4:6])
+	d.dirDiskNbr = c.Uint16(b[6:8])
+	d.dirRecordsThisDisk = c.Uint16(b[8:10])
+	d.directoryRecords = c.Uint16(b[10:12])
+	d.directorySize = c.Uint32(b[12:16])
+	d.directoryOffset = c.Uint32(b[16:20])
+	d.commentLen = c.Uint16(b[20:22])
+	d.comment = string(b[22 : 22+int(d.commentLen)])
 	return d, nil
 }
 
 func findSignatureInBlock(b []byte) int {
-	const minSize = 4 + 2 + 2 + 2 + 2 + 4 + 4 + 2 // fixed part of header
-	for i := len(b) - minSize; i >= 0; i-- {
+	for i := len(b) - directoryEndLen; i >= 0; i-- {
 		// defined from directoryEndSignature in struct.go
 		if b[i] == 'P' && b[i+1] == 'K' && b[i+2] == 0x05 && b[i+3] == 0x06 {
 			// n is length of comment
-			n := int(b[i+minSize-2]) | int(b[i+minSize-1])<<8
-			if n+minSize+i == len(b) {
+			n := int(b[i+directoryEndLen-2]) | int(b[i+directoryEndLen-1])<<8
+			if n+directoryEndLen+i == len(b) {
 				return i
 			}
 		}
 	}
 	return -1
 }
-
-func read(r io.Reader, data interface{}) {
-	if err := binary.Read(r, binary.LittleEndian, data); err != nil {
-		panic(err)
-	}
-}
-
-func readByteSlice(r io.Reader, l uint16) []byte {
-	b := make([]byte, l)
-	if l == 0 {
-		return b
-	}
-	if _, err := io.ReadFull(r, b); err != nil {
-		panic(err)
-	}
-	return b
-}

src/pkg/archive/zip/reader_test.go

@@ -162,6 +162,8 @@ func readTestFile(t *testing.T, ft ZipTestFile, f *File) {
 		t.Errorf("%s: mtime=%s (%d); want %s (%d)", f.Name, time.SecondsToUTC(got), got, mtime, want)
 	}
 
+	size0 := f.UncompressedSize
+
 	var b bytes.Buffer
 	r, err := f.Open()
 	if err != nil {
@@ -169,6 +171,10 @@ func readTestFile(t *testing.T, ft ZipTestFile, f *File) {
 		return
 	}
 
+	if size1 := f.UncompressedSize; size0 != size1 {
+		t.Errorf("file %q changed f.UncompressedSize from %d to %d", f.Name, size0, size1)
+	}
+
 	_, err = io.Copy(&b, r)
 	if err != nil {
 		t.Error(err)

src/pkg/archive/zip/struct.go

@@ -24,6 +24,9 @@ const (
 	fileHeaderSignature      = 0x04034b50
 	directoryHeaderSignature = 0x02014b50
 	directoryEndSignature    = 0x06054b50
+	fileHeaderLen            = 30 // + filename + extra
+	directoryHeaderLen       = 46 // + filename + extra + comment
+	directoryEndLen          = 22 // + comment
 	dataDescriptorLen        = 12
 )