package advrefs
import (
"bytes"
"encoding/hex"
"errors"
"fmt"
"io"
"gopkg.in/src-d/go-git.v4/core"
"gopkg.in/src-d/go-git.v4/formats/packp/pktline"
)
// A Decoder reads and decodes AdvRef values from an input stream.
type Decoder struct {
s *pktline.Scanner // a pkt-line scanner from the input stream
line []byte // current pkt-line contents, use parser.nextLine() to make it advance
nLine int // current pkt-line number for debugging, begins at 1
hash core.Hash // last hash read
err error // sticky error, use the parser.error() method to fill this out
data *AdvRefs // parsed data is stored here
}
// ErrEmpty is returned by Decode when there was no advertised-message at all
var ErrEmpty = errors.New("empty advertised-ref message")
// NewDecoder returns a new decoder that reads from r.
//
// Will not read more data from r than necessary.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{
s: pktline.NewScanner(r),
}
}
// Decode reads the next advertised-refs message form its input and
// stores it in the value pointed to by v.
func (d *Decoder) Decode(v *AdvRefs) error {
d.data = v
for state := decodePrefix; state != nil; {
state = state(d)
}
return d.err
}
type decoderStateFn func(*Decoder) decoderStateFn
// fills out the parser stiky error
func (d *Decoder) error(format string, a ...interface{}) {
d.err = fmt.Errorf("pkt-line %d: %s", d.nLine,
fmt.Sprintf(format, a...))
}
// Reads a new pkt-line from the scanner, makes its payload available as
// p.line and increments p.nLine. A successful invocation returns true,
// otherwise, false is returned and the sticky error is filled out
// accordingly. Trims eols at the end of the payloads.
func (d *Decoder) nextLine() bool {
d.nLine++
if !d.s.Scan() {
if d.err = d.s.Err(); d.err != nil {
return false
}
if d.nLine == 1 {
d.err = ErrEmpty
return false
}
d.error("EOF")
return false
}
d.line = d.s.Bytes()
d.line = bytes.TrimSuffix(d.line, eol)
return true
}
// The HTTP smart prefix is often followed by a flush-pkt.
func decodePrefix(d *Decoder) decoderStateFn {
if ok := d.nextLine(); !ok {
return nil
}
if isPrefix(d.line) {
tmp := make([]byte, len(d.line))
copy(tmp, d.line)
d.data.Prefix = append(d.data.Prefix, tmp)
if ok := d.nextLine(); !ok {
return nil
}
}
if isFlush(d.line) {
d.data.Prefix = append(d.data.Prefix, pktline.Flush)
if ok := d.nextLine(); !ok {
return nil
}
}
return decodeFirstHash
}
func isPrefix(payload []byte) bool {
return payload[0] == '#'
}
func isFlush(payload []byte) bool {
return len(payload) == 0
}
// If the first hash is zero, then a no-refs is comming. Otherwise, a
// list-of-refs is comming, and the hash will be followed by the first
// advertised ref.
func decodeFirstHash(p *Decoder) decoderStateFn {
if len(p.line) < hashSize {
p.error("cannot read hash, pkt-line too short")
return nil
}
if _, err := hex.Decode(p.hash[:], p.line[:hashSize]); err != nil {
p.error("invalid hash text: %s", err)
return nil
}
p.line = p.line[hashSize:]
if p.hash.IsZero() {
return decodeSkipNoRefs
}
return decodeFirstRef
}
// Skips SP "capabilities^{}" NUL
func decodeSkipNoRefs(p *Decoder) decoderStateFn {
if len(p.line) < len(noHeadMark) {
p.error("too short zero-id ref")
return nil
}
if !bytes.HasPrefix(p.line, noHeadMark) {
p.error("malformed zero-id ref")
return nil
}
p.line = p.line[len(noHeadMark):]
return decodeCaps
}
// decode the refname, expectes SP refname NULL
func decodeFirstRef(l *Decoder) decoderStateFn {
if len(l.line) < 3 {
l.error("line too short after hash")
return nil
}
if !bytes.HasPrefix(l.line, sp) {
l.error("no space after hash")
return nil
}
l.line = l.line[1:]
chunks := bytes.SplitN(l.line, null, 2)
if len(chunks) < 2 {
l.error("NULL not found")
return nil
}
ref := chunks[0]
l.line = chunks[1]
if bytes.Equal(ref, []byte(head)) {
l.data.Head = &l.hash
} else {
l.data.References[string(ref)] = l.hash
}
return decodeCaps
}
func decodeCaps(p *Decoder) decoderStateFn {
if len(p.line) == 0 {
return decodeOtherRefs
}
for _, c := range bytes.Split(p.line, sp) {
name, values := readCapability(c)
p.data.Capabilities.Add(name, values...)
}
return decodeOtherRefs
}
// Capabilities are a single string or a name=value.
// Even though we are only going to read at moust 1 value, we return
// a slice of values, as Capability.Add receives that.
func readCapability(data []byte) (name string, values []string) {
pair := bytes.SplitN(data, []byte{'='}, 2)
if len(pair) == 2 {
values = append(values, string(pair[1]))
}
return string(pair[0]), values
}
// The refs are either tips (obj-id SP refname) or a peeled (obj-id SP refname^{}).
// If there are no refs, then there might be a shallow or flush-ptk.
func decodeOtherRefs(p *Decoder) decoderStateFn {
if ok := p.nextLine(); !ok {
return nil
}
if bytes.HasPrefix(p.line, shallow) {
return decodeShallow
}
if len(p.line) == 0 {
return nil
}
saveTo := p.data.References
if bytes.HasSuffix(p.line, peeled) {
p.line = bytes.TrimSuffix(p.line, peeled)
saveTo = p.data.Peeled
}
ref, hash, err := readRef(p.line)
if err != nil {
p.error("%s", err)
return nil
}
saveTo[ref] = hash
return decodeOtherRefs
}
// Reads a ref-name
func readRef(data []byte) (string, core.Hash, error) {
chunks := bytes.Split(data, sp)
switch {
case len(chunks) == 1:
return "", core.ZeroHash, fmt.Errorf("malformed ref data: no space was found")
case len(chunks) > 2:
return "", core.ZeroHash, fmt.Errorf("malformed ref data: more than one space found")
default:
return string(chunks[1]), core.NewHash(string(chunks[0])), nil
}
}
// Keeps reading shallows until a flush-pkt is found
func decodeShallow(p *Decoder) decoderStateFn {
if !bytes.HasPrefix(p.line, shallow) {
p.error("malformed shallow prefix, found %q... instead", p.line[:len(shallow)])
return nil
}
p.line = bytes.TrimPrefix(p.line, shallow)
if len(p.line) != hashSize {
p.error(fmt.Sprintf(
"malformed shallow hash: wrong length, expected 40 bytes, read %d bytes",
len(p.line)))
return nil
}
text := p.line[:hashSize]
var h core.Hash
if _, err := hex.Decode(h[:], text); err != nil {
p.error("invalid hash text: %s", err)
return nil
}
p.data.Shallows = append(p.data.Shallows, h)
if ok := p.nextLine(); !ok {
return nil
}
if len(p.line) == 0 {
return nil // succesfull parse of the advertised-refs message
}
return decodeShallow
}
