Merge pull request #52 from damoye/master

More robust SOCKS handshaking.

Author: riobard

socks/socks.go

@@ -43,9 +43,6 @@ const (
 // MaxAddrLen is the maximum size of SOCKS address in bytes.
 const MaxAddrLen = 1 + 1 + 255 + 2
 
-// MaxReqLen is the maximum size of SOCKS request in bytes.
-const MaxReqLen = 1 + 1 + 1 + MaxAddrLen
-
 // Addr represents a SOCKS address as defined in RFC 1928 section 5.
 type Addr []byte
 
@@ -68,9 +65,10 @@ func (a Addr) String() string {
 	return net.JoinHostPort(host, port)
 }
 
-// ReadAddr reads just enough bytes from r to get a valid Addr.
-func ReadAddr(r io.Reader) (Addr, error) {
-	b := make([]byte, MaxAddrLen)
+func readAddr(r io.Reader, b []byte) (Addr, error) {
+	if len(b) < MaxAddrLen {
+		return nil, io.ErrShortBuffer
+	}
 	_, err := io.ReadFull(r, b[:1]) // read 1st byte for address type
 	if err != nil {
 		return nil, err
@@ -95,6 +93,11 @@ func ReadAddr(r io.Reader) (Addr, error) {
 	return nil, ErrAddressNotSupported
 }
 
+// ReadAddr reads just enough bytes from r to get a valid Addr.
+func ReadAddr(r io.Reader) (Addr, error) {
+	return readAddr(r, make([]byte, MaxAddrLen))
+}
+
 // SplitAddr slices a SOCKS address from beginning of b. Returns nil if failed.
 func SplitAddr(b []byte) Addr {
 	addrLen := 1
@@ -163,29 +166,32 @@ func ParseAddr(s string) Addr {
 
 // Handshake fast-tracks SOCKS initialization to get target address to connect.
 func Handshake(rw io.ReadWriter) (Addr, error) {
-	// Read RFC 1928 section 4 for request and reply structure and sizes
-	buf := make([]byte, MaxReqLen)
-
-	_, err := rw.Read(buf) // SOCKS version and auth methods
-	if err != nil {
+	// Read RFC 1928 for request and reply structure and sizes.
+	buf := make([]byte, MaxAddrLen)
+	// read VER, NMETHODS, METHODS
+	if _, err := io.ReadFull(rw, buf[:2]); err != nil {
 		return nil, err
 	}
-
-	_, err = rw.Write([]byte{5, 0}) // SOCKS v5, no auth required
-	if err != nil {
+	nmethods := buf[1]
+	if _, err := io.ReadFull(rw, buf[:nmethods]); err != nil {
 		return nil, err
 	}
-
-	n, err := rw.Read(buf) // SOCKS request: VER, CMD, RSV, Addr
-	if err != nil {
+	// write VER METHOD
+	if _, err := rw.Write([]byte{5, 0}); err != nil {
+		return nil, err
+	}
+	// read VER CMD RSV ATYP DST.ADDR DST.PORT
+	if _, err := io.ReadFull(rw, buf[:3]); err != nil {
 		return nil, err
 	}
-	buf = buf[:n]
-
 	if buf[1] != CmdConnect {
 		return nil, ErrCommandNotSupported
 	}
-
-	_, err = rw.Write([]byte{5, 0, 0, 1, 0, 0, 0, 0, 0, 0}) // SOCKS v5, reply succeeded
-	return buf[3:], err                                     // skip VER, CMD, RSV fields
+	addr, err := readAddr(rw, buf)
+	if err != nil {
+		return nil, err
+	}
+	// write VER REP RSV ATYP BND.ADDR BND.PORT
+	_, err = rw.Write([]byte{5, 0, 0, 1, 0, 0, 0, 0, 0, 0})
+	return addr, err
 }