package pktline import ( "errors" "io" "github.com/go-git/go-git/v5/utils/trace" ) const ( lenSize = 4 ) // ErrInvalidPktLen is returned by Err() when an invalid pkt-len is found. var ErrInvalidPktLen = errors.New("invalid pkt-len found") // Scanner provides a convenient interface for reading the payloads of a // series of pkt-lines. It takes an io.Reader providing the source, // which then can be tokenized through repeated calls to the Scan // method. // // After each Scan call, the Bytes method will return the payload of the // corresponding pkt-line on a shared buffer, which will be 65516 bytes // or smaller. Flush pkt-lines are represented by empty byte slices. // // Scanning stops at EOF or the first I/O error. type Scanner struct { r io.Reader // The reader provided by the client err error // Sticky error payload []byte // Last pkt-payload len [lenSize]byte // Last pkt-len } // NewScanner returns a new Scanner to read from r. func NewScanner(r io.Reader) *Scanner { return &Scanner{ r: r, } } // Err returns the first error encountered by the Scanner. func (s *Scanner) Err() error { return s.err } // Scan advances the Scanner to the next pkt-line, whose payload will // then be available through the Bytes method. Scanning stops at EOF // or the first I/O error. After Scan returns false, the Err method // will return any error that occurred during scanning, except that if // it was io.EOF, Err will return nil. func (s *Scanner) Scan() bool { var l int l, s.err = s.readPayloadLen() if s.err == io.EOF { s.err = nil return false } if s.err != nil { return false } if cap(s.payload) < l { s.payload = make([]byte, 0, l) } if _, s.err = io.ReadFull(s.r, s.payload[:l]); s.err != nil { return false } s.payload = s.payload[:l] trace.Packet.Printf("packet: < %04x %s", l, s.payload) return true } // Bytes returns the most recent payload generated by a call to Scan. // The underlying array may point to data that will be overwritten by a // subsequent call to Scan. It does no allocation. func (s *Scanner) Bytes() []byte { return s.payload } // Method readPayloadLen returns the payload length by reading the // pkt-len and subtracting the pkt-len size. func (s *Scanner) readPayloadLen() (int, error) { if _, err := io.ReadFull(s.r, s.len[:]); err != nil { if err == io.ErrUnexpectedEOF { return 0, ErrInvalidPktLen } return 0, err } n, err := hexDecode(s.len) if err != nil { return 0, err } switch { case n == 0: return 0, nil case n <= lenSize: return 0, ErrInvalidPktLen case n > OversizePayloadMax+lenSize: return 0, ErrInvalidPktLen default: return n - lenSize, nil } } // Turns the hexadecimal representation of a number in a byte slice into // a number. This function substitute strconv.ParseUint(string(buf), 16, // 16) and/or hex.Decode, to avoid generating new strings, thus helping the // GC. func hexDecode(buf [lenSize]byte) (int, error) { var ret int for i := 0; i < lenSize; i++ { n, err := asciiHexToByte(buf[i]) if err != nil { return 0, ErrInvalidPktLen } ret = 16*ret + int(n) } return ret, nil } // turns the hexadecimal ascii representation of a byte into its // numerical value. Example: from 'b' to 11 (0xb). func asciiHexToByte(b byte) (byte, error) { switch { case b >= '0' && b <= '9': return b - '0', nil case b >= 'a' && b <= 'f': return b - 'a' + 10, nil default: return 0, ErrInvalidPktLen } }