package packfile
import (
"bytes"
"compress/zlib"
"encoding/binary"
"fmt"
"io"
"gopkg.in/src-d/go-git.v4/core"
)
var (
// ErrEmptyPackfile is returned by ReadHeader when no data is found in the packfile
ErrEmptyPackfile = NewError("empty packfile")
// ErrBadSignature is returned by ReadHeader when the signature in the packfile is incorrect.
ErrBadSignature = NewError("malformed pack file signature")
// ErrUnsupportedVersion is returned by ReadHeader when the packfile version is
// different than VersionSupported.
ErrUnsupportedVersion = NewError("unsupported packfile version")
)
const (
// VersionSupported is the packfile version supported by this parser.
VersionSupported = 2
)
// A Parser is a collection of functions to read and process data form a packfile.
// Values from this type are not zero-value safe. See the NewParser function bellow.
type Parser struct {
ReadRecaller
ObjectFactory func() core.Object
}
// NewParser returns a new Parser that reads from the packfile represented by r.
func NewParser(r ReadRecaller) *Parser {
return &Parser{ReadRecaller: r}
}
// ReadInt32 reads 4 bytes and returns them as a Big Endian int32.
func (p Parser) readInt32() (uint32, error) {
var v uint32
if err := binary.Read(p, binary.BigEndian, &v); err != nil {
return 0, err
}
return v, nil
}
// ReadSignature reads an returns the signature field in the packfile.
func (p *Parser) ReadSignature() ([]byte, error) {
var sig = make([]byte, 4)
if _, err := io.ReadFull(p, sig); err != nil {
return []byte{}, err
}
return sig, nil
}
// IsValidSignature returns if sig is a valid packfile signature.
func (p Parser) IsValidSignature(sig []byte) bool {
return bytes.Equal(sig, []byte{'P', 'A', 'C', 'K'})
}
// ReadVersion reads and returns the version field of a packfile.
func (p *Parser) ReadVersion() (uint32, error) {
return p.readInt32()
}
// IsSupportedVersion returns whether version v is supported by the parser.
// The current supported version is VersionSupported, defined above.
func (p *Parser) IsSupportedVersion(v uint32) bool {
return v == VersionSupported
}
// ReadCount reads and returns the count of objects field of a packfile.
func (p *Parser) ReadCount() (uint32, error) {
return p.readInt32()
}
// ReadHeader reads the whole packfile header (signature, version and
// object count). It returns the object count and performs checks on the
// validity of the signature and the version fields.
func (p Parser) ReadHeader() (uint32, error) {
sig, err := p.ReadSignature()
if err != nil {
if err == io.EOF {
return 0, ErrEmptyPackfile
}
return 0, err
}
if !p.IsValidSignature(sig) {
return 0, ErrBadSignature
}
ver, err := p.ReadVersion()
if err != nil {
return 0, err
}
if !p.IsSupportedVersion(ver) {
return 0, ErrUnsupportedVersion.AddDetails("%d", ver)
}
count, err := p.ReadCount()
if err != nil {
return 0, err
}
return count, nil
}
// ReadObjectTypeAndLength reads and returns the object type and the
// length field from an object entry in a packfile.
func (p Parser) ReadObjectTypeAndLength() (core.ObjectType, int64, error) {
t, c, err := p.readType()
if err != nil {
return t, 0, err
}
l, err := p.readLength(c)
return t, l, err
}
func (p Parser) readType() (core.ObjectType, byte, error) {
var c byte
var err error
if c, err = p.ReadByte(); err != nil {
return core.ObjectType(0), 0, err
}
typ := parseType(c)
return typ, c, nil
}
var (
maskContinue = uint8(128) // 1000 0000
maskType = uint8(112) // 0111 0000
maskFirstLength = uint8(15) // 0000 1111
firstLengthBits = uint8(4) // the first byte has 4 bits to store the length
maskLength = uint8(127) // 0111 1111
lengthBits = uint8(7) // subsequent bytes has 7 bits to store the length
)
func parseType(b byte) core.ObjectType {
return core.ObjectType((b & maskType) >> firstLengthBits)
}
// the length is codified in the last 4 bits of the first byte and in
// the last 7 bits of subsequent bytes. Last byte has a 0 MSB.
func (p Parser) readLength(first byte) (int64, error) {
length := int64(first & maskFirstLength)
c := first
shift := firstLengthBits
var err error
for moreBytesInLength(c) {
if c, err = p.ReadByte(); err != nil {
return 0, err
}
length += int64(c&maskLength) << shift
shift += lengthBits
}
return length, nil
}
func moreBytesInLength(c byte) bool {
return c&maskContinue > 0
}
// ReadObject reads and returns a git object from an object entry in the packfile.
// Non-deltified and deltified objects are supported.
func (p Parser) FillObject(obj core.Object) error {
start, err := p.Offset()
if err != nil {
return err
}
t, l, err := p.ReadObjectTypeAndLength()
if err != nil {
return err
}
obj.SetSize(l)
switch t {
case core.CommitObject, core.TreeObject, core.BlobObject, core.TagObject:
obj.SetType(t)
err = p.ReadNonDeltaObjectContent(obj)
case core.REFDeltaObject:
err = p.ReadREFDeltaObjectContent(obj)
case core.OFSDeltaObject:
err = p.ReadOFSDeltaObjectContent(obj, start)
default:
err = ErrInvalidObject.AddDetails("tag %q", t)
}
return err
}
// ReadNonDeltaObjectContent reads and returns a non-deltified object
// from it zlib stream in an object entry in the packfile.
func (p Parser) ReadNonDeltaObjectContent(obj core.Object) error {
w, err := obj.Writer()
if err != nil {
return err
}
return p.inflate(w)
}
func (p Parser) inflate(w io.Writer) (err error) {
zr, err := zlib.NewReader(p)
if err != nil {
if err != zlib.ErrHeader {
return fmt.Errorf("zlib reading error: %s", err)
}
}
defer func() {
closeErr := zr.Close()
if err == nil {
err = closeErr
}
}()
_, err = io.Copy(w, zr)
return err
}
// ReadREFDeltaObjectContent reads and returns an object specified by a
// REF-Delta entry in the packfile, form the hash onwards.
func (p Parser) ReadREFDeltaObjectContent(obj core.Object) error {
refHash, err := p.ReadHash()
if err != nil {
return err
}
base, err := p.RecallByHash(refHash)
if err != nil {
return err
}
obj.SetType(base.Type())
if err := p.ReadAndApplyDelta(obj, base); err != nil {
return err
}
return nil
}
// ReadHash reads a hash.
func (p Parser) ReadHash() (core.Hash, error) {
var h core.Hash
if _, err := io.ReadFull(p, h[:]); err != nil {
return core.ZeroHash, err
}
return h, nil
}
// ReadAndSolveDelta reads and returns the base patched with the contents
// of a zlib compressed diff data in the delta portion of an object
// entry in the packfile.
func (p Parser) ReadAndApplyDelta(target, base core.Object) error {
buf := bytes.NewBuffer(nil)
if err := p.inflate(buf); err != nil {
return err
}
return ApplyDelta(target, base, buf.Bytes())
}
// ReadOFSDeltaObjectContent reads an returns an object specified by an
// OFS-delta entry in the packfile from it negative offset onwards. The
// start parameter is the offset of this particular object entry (the
// current offset minus the already processed type and length).
func (p Parser) ReadOFSDeltaObjectContent(obj core.Object, start int64) error {
jump, err := p.ReadNegativeOffset()
if err != nil {
return err
}
base, err := p.RecallByOffset(start + jump)
if err != nil {
return err
}
obj.SetType(base.Type())
if err := p.ReadAndApplyDelta(obj, base); err != nil {
return err
}
return nil
}
// ReadNegativeOffset reads and returns an offset from a OFS DELTA
// object entry in a packfile. OFS DELTA offsets are specified in Git
// VLQ special format:
//
// Ordinary VLQ has some redundancies, example: the number 358 can be
// encoded as the 2-octet VLQ 0x8166 or the 3-octet VLQ 0x808166 or the
// 4-octet VLQ 0x80808166 and so forth.
//
// To avoid these redundancies, the VLQ format used in Git removes this
// prepending redundancy and extends the representable range of shorter
// VLQs by adding an offset to VLQs of 2 or more octets in such a way
// that the lowest possible value for such an (N+1)-octet VLQ becomes
// exactly one more than the maximum possible value for an N-octet VLQ.
// In particular, since a 1-octet VLQ can store a maximum value of 127,
// the minimum 2-octet VLQ (0x8000) is assigned the value 128 instead of
// 0. Conversely, the maximum value of such a 2-octet VLQ (0xff7f) is
// 16511 instead of just 16383. Similarly, the minimum 3-octet VLQ
// (0x808000) has a value of 16512 instead of zero, which means
// that the maximum 3-octet VLQ (0xffff7f) is 2113663 instead of
// just 2097151. And so forth.
//
// This is how the offset is saved in C:
//
// dheader[pos] = ofs & 127;
// while (ofs >>= 7)
// dheader[--pos] = 128 | (--ofs & 127);
//
func (p Parser) ReadNegativeOffset() (int64, error) {
var c byte
var err error
if c, err = p.ReadByte(); err != nil {
return 0, err
}
var offset = int64(c & maskLength)
for moreBytesInLength(c) {
offset++
if c, err = p.ReadByte(); err != nil {
return 0, err
}
offset = (offset << lengthBits) + int64(c&maskLength)
}
return -offset, nil
}
