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// pktline provides support for the pkt-line format described in gitprotocol-common(5).
package pktline
import (
"errors"
"io"
)
const (
maxPacketSize = 65520
maxPacketDataLen = maxPacketSize - 4
)
var (
ErrInvalidHeader = errors.New("pktline: invalid header")
ErrPacketTooLarge = errors.New("pktline: packet too large")
ErrBufferTooSmall = errors.New("pktline: buffer too small")
)
type Status uint8
const (
StatusEOF Status = iota
StatusData
StatusFlush
StatusDelim
StatusResponseEnd
)
// ReadLine reads a single pkt-line from r into buf.
// It returns the payload slice, number of payload bytes, and a status.
func ReadLine(r io.Reader, buf []byte) ([]byte, int, Status, error) {
if r == nil {
return nil, 0, StatusEOF, ErrInvalidHeader
}
var header [4]byte
if _, err := io.ReadFull(r, header[:]); err != nil {
if errors.Is(err, io.EOF) {
return nil, 0, StatusEOF, io.EOF
}
if errors.Is(err, io.ErrUnexpectedEOF) {
return nil, 0, StatusEOF, io.ErrUnexpectedEOF
}
return nil, 0, StatusEOF, err
}
n, err := parseHeader(header[:])
if err != nil {
return nil, 0, StatusEOF, err
}
switch n {
case 0:
return nil, 0, StatusFlush, nil
case 1:
return nil, 0, StatusDelim, nil
case 2:
return nil, 0, StatusResponseEnd, nil
}
if n < 4 {
return nil, 0, StatusEOF, ErrInvalidHeader
}
n -= 4
if n > maxPacketDataLen {
return nil, 0, StatusEOF, ErrPacketTooLarge
}
if n > len(buf) {
return nil, 0, StatusEOF, ErrBufferTooSmall
}
if _, err := io.ReadFull(r, buf[:n]); err != nil {
if errors.Is(err, io.ErrUnexpectedEOF) {
return nil, 0, StatusEOF, io.ErrUnexpectedEOF
}
return nil, 0, StatusEOF, err
}
return buf[:n], n, StatusData, nil
}
// WriteLine writes a single pkt-line with data as its payload.
func WriteLine(w io.Writer, data []byte) error {
if w == nil {
return ErrInvalidHeader
}
if len(data) > maxPacketDataLen {
return ErrPacketTooLarge
}
var header [4]byte
setHeader(header[:], len(data)+4)
if _, err := w.Write(header[:]); err != nil {
return err
}
if len(data) == 0 {
return nil
}
_, err := w.Write(data)
return err
}
// Flush writes a flush-pkt ("0000").
func Flush(w io.Writer) error {
return writeLiteral(w, "0000")
}
// Delim writes a delim-pkt ("0001").
func Delim(w io.Writer) error {
return writeLiteral(w, "0001")
}
// ResponseEnd writes a response-end pkt ("0002").
func ResponseEnd(w io.Writer) error {
return writeLiteral(w, "0002")
}
func writeLiteral(w io.Writer, s string) error {
if w == nil {
return ErrInvalidHeader
}
_, err := io.WriteString(w, s)
return err
}
func parseHeader(b []byte) (int, error) {
if len(b) < 4 {
return 0, ErrInvalidHeader
}
v0, ok := hexVal(b[0])
if !ok {
return 0, ErrInvalidHeader
}
v1, ok := hexVal(b[1])
if !ok {
return 0, ErrInvalidHeader
}
v2, ok := hexVal(b[2])
if !ok {
return 0, ErrInvalidHeader
}
v3, ok := hexVal(b[3])
if !ok {
return 0, ErrInvalidHeader
}
return (v0 << 12) | (v1 << 8) | (v2 << 4) | v3, nil
}
func setHeader(buf []byte, size int) {
const hex = "0123456789abcdef"
buf[0] = hex[(size>>12)&0x0f]
buf[1] = hex[(size>>8)&0x0f]
buf[2] = hex[(size>>4)&0x0f]
buf[3] = hex[size&0x0f]
}
// IIRC strconv.ParseUint, encoding/hex.Decode, etc., allocate memory.
func hexVal(b byte) (int, bool) {
switch {
case b >= '0' && b <= '9':
return int(b - '0'), true
case b >= 'a' && b <= 'f':
return int(b-'a') + 10, true
case b >= 'A' && b <= 'F':
return int(b-'A') + 10, true
default:
return 0, false
}
}
|
