zmq4: extend ZMTP greeting tests for various version cases

Updates go-zeromq#56.

protocol.go

@@ -108,9 +108,7 @@ func (g *greeting) read(r io.Reader) error {
 		return xerrors.Errorf("invalid ZMTP signature footer: %w", errGreeting)
 	}
 
-	// FIXME(sbinet): handle version negotiations as per
-	// https://rfc.zeromq.org/spec:23/ZMTP/#version-negotiation
-	if g.Version != defaultVersion {
+	if !g.validate(defaultVersion) {
 		return xerrors.Errorf(
 			"invalid ZMTP version (got=%v, want=%v): %w",
 			g.Version, defaultVersion, errGreeting,
@@ -148,6 +146,24 @@ func (g *greeting) marshal() []byte {
 	return buf[:]
 }
 
+func (g *greeting) validate(ref [2]uint8) bool {
+	switch {
+	case g.Version == ref:
+		return true
+	case g.Version[0] > ref[0] ||
+		g.Version[0] == ref[0] && g.Version[1] > ref[1]:
+		// accept higher protocol values
+		return true
+	case g.Version[0] < ref[0] ||
+		g.Version[0] == ref[0] && g.Version[1] < ref[1]:
+		// FIXME(sbinet): handle version negotiations as per
+		// https://rfc.zeromq.org/spec:23/ZMTP/#version-negotiation
+		return false
+	default:
+		return false
+	}
+}
+
 const (
 	sysSockType = "Socket-Type"
 	sysSockID   = "Identity"

protocol_test.go

@@ -79,11 +79,43 @@ func TestGreeting(t *testing.T) {
 			want: xerrors.Errorf("invalid ZMTP signature footer: %w", errGreeting),
 		},
 		{
-			name: "invalid-version", // FIXME(sbinet): adapt for when/if we support multiple ZMTP versions
+			name: "higher-major-version",
 			data: func() []byte {
 				w := new(bytes.Buffer)
 				g := greeting{
-					Version: [2]uint8{1, 1},
+					Version: [2]uint8{defaultVersion[0] + 1, defaultVersion[1]},
+				}
+				g.Sig.Header = sigHeader
+				g.Sig.Footer = sigFooter
+				err := g.write(w)
+				if err != nil {
+					t.Fatalf("could not marshal greeting: %+v", err)
+				}
+				return w.Bytes()
+			}(),
+		},
+		{
+			name: "higher-minor-version",
+			data: func() []byte {
+				w := new(bytes.Buffer)
+				g := greeting{
+					Version: [2]uint8{defaultVersion[0], defaultVersion[1] + 1},
+				}
+				g.Sig.Header = sigHeader
+				g.Sig.Footer = sigFooter
+				err := g.write(w)
+				if err != nil {
+					t.Fatalf("could not marshal greeting: %+v", err)
+				}
+				return w.Bytes()
+			}(),
+		},
+		{
+			name: "smaller-major-version", // FIXME(sbinet): adapt for when/if we support multiple ZMTP versions
+			data: func() []byte {
+				w := new(bytes.Buffer)
+				g := greeting{
+					Version: [2]uint8{defaultVersion[0] - 1, defaultVersion[1]},
 				}
 				g.Sig.Header = sigHeader
 				g.Sig.Footer = sigFooter
@@ -94,7 +126,7 @@ func TestGreeting(t *testing.T) {
 				return w.Bytes()
 			}(),
 			want: xerrors.Errorf("invalid ZMTP version (got=%v, want=%v): %w",
-				[2]uint{1, 1},
+				[2]uint8{defaultVersion[0] - 1, defaultVersion[1]},
 				defaultVersion,
 				errGreeting,
 			),