Fix buffering in version negotiation

The service-side version negotiation had a buffer overread that would
cause remotely triggerable panic.

Refactor that code to resolve that issue, follow the spec more exactly,
and avoid reading more data from the socket than is used for version
negotiation, in case clients write optimistically.

ricochet.go

@@ -8,6 +8,7 @@ import (
 	"github.com/s-rah/go-ricochet/contact"
 	"github.com/s-rah/go-ricochet/control"
 	"github.com/s-rah/go-ricochet/utils"
+	"io"
 	"log"
 	"net"
 	"strconv"
@@ -327,52 +328,55 @@ func (r *Ricochet) processConnection(oc *OpenConnection, service RicochetService
 	}
 }
 
-// negotiateVersion Perform version negotiation with the connected host.
+// Perform version negotiation on the connection, and create an OpenConnection if successful
 func (r *Ricochet) negotiateVersion(conn net.Conn, outbound bool) (*OpenConnection, error) {
-	version := make([]byte, 4)
-	version[0] = 0x49
-	version[1] = 0x4D
-	version[2] = 0x01
-	version[3] = 0x01
+	versions := []byte{0x49, 0x4D, 0x01, 0x01}
 
-	// If this was initiated by us then we need to initiate the version info.
+	// Outbound side of the connection sends a list of supported versions
 	if outbound {
-		// Send Version String
-
-		conn.Write(version)
-		res, err := r.rni.Recv(conn)
-
-		if len(res) != 1 || err != nil {
-			return nil, errors.New("Failed Version Negotiating")
-		}
-
-		if res[0] != 1 {
-			return nil, errors.New("Failed Version Negotiating - Invalid Version ")
-		}
-	} else {
-		// Do Version Negotiation
-
-		buf := make([]byte, 10)
-		n, err := conn.Read(buf)
-		if err != nil && n >= 4 {
+		if n, err := conn.Write(versions); err != nil || n < len(versions) {
 			return nil, err
 		}
 
-		if buf[0] == version[0] && buf[1] == version[1] {
-			foundVersion := false
-			if buf[2] >= 1 {
-				for i := 3; i < n; i++ {
-					if buf[i] == 0x01 {
-						conn.Write([]byte{0x01})
-						foundVersion = true
+		res := make([]byte, 1)
+		if _, err := io.ReadAtLeast(conn, res, len(res)); err != nil {
+			return nil, err
 		}
-				}
-			}
-			if !foundVersion {
-				return nil, errors.New("Failed Version Negotiating - No Available Version")
+
+		if res[0] != 0x01 {
+			return nil, errors.New("unsupported protocol version")
 		}
 	} else {
-			return nil, errors.New("Failed Version Negotiating - Invalid Version Header")
+		// Read version response header
+		header := make([]byte, 3)
+		if _, err := io.ReadAtLeast(conn, header, len(header)); err != nil {
+			return nil, err
+		}
+
+		if header[0] != versions[0] || header[1] != versions[1] || header[2] < 1 {
+			return nil, errors.New("invalid protocol response")
+		}
+
+		// Read list of supported versions (which is header[2] bytes long)
+		versionList := make([]byte, header[2])
+		if _, err := io.ReadAtLeast(conn, versionList, len(versionList)); err != nil {
+			return nil, err
+		}
+
+		selectedVersion := byte(0xff)
+		for _, v := range versionList {
+			if v == 0x01 {
+				selectedVersion = v
+				break
+			}
+		}
+
+		if n, err := conn.Write([]byte{selectedVersion}); err != nil || n < 1 {
+			return nil, err
+		}
+
+		if selectedVersion == 0xff {
+			return nil, errors.New("no supported protocol version")
 		}
 	}