task 80: fix protocol compatibility parsing

2 files changed, 51 insertions, 4 deletions

diff --git a/internal/server/handlers/protocol_codec.go b/internal/server/handlers/protocol_codec.go
index 192cc81..58c78c0 100644
--- a/internal/server/handlers/protocol_codec.go
+++ b/internal/server/handlers/protocol_codec.go
@@ -29,16 +29,16 @@ func (c protocolCodec) handleProtocolVersion(args []string) ([]string, int, stri
 	}
 
 	if args[1] != protocol.ProtocolCompat {
-		clientCompat, _ := strconv.Atoi(args[1])
-		serverCompat, _ := strconv.Atoi(protocol.ProtocolCompat)
-		if clientCompat <= 3 {
+		clientMajor, clientMinor := parseProtocolCompat(args[1])
+		serverMajor, serverMinor := parseProtocolCompat(protocol.ProtocolCompat)
+		if clientMajor <= 3 {
 			// Protocol version 3 or lower expect a newline as message separator
 			// One day (after 2 major versions) this exception may be removed!
 			add = "\n"
 		}
 
 		toUpdate := "client"
-		if clientCompat > serverCompat {
+		if clientMajor > serverMajor || (clientMajor == serverMajor && clientMinor > serverMinor) {
 			toUpdate = "server"
 		}
 		err := fmt.Errorf("the DTail server protocol version '%s' does not match "+
@@ -50,6 +50,21 @@ func (c protocolCodec) handleProtocolVersion(args []string) ([]string, int, stri
 	return args[2:], argc - 2, add, nil
 }
 
+func parseProtocolCompat(version string) (int, int) {
+	major := 0
+	minor := 0
+
+	parts := strings.SplitN(version, ".", 2)
+	if len(parts) > 0 {
+		major, _ = strconv.Atoi(parts[0])
+	}
+	if len(parts) == 2 {
+		minor, _ = strconv.Atoi(parts[1])
+	}
+
+	return major, minor
+}
+
 func (c protocolCodec) handleBase64(args []string, argc int) ([]string, int, error) {
 	err := errors.New("unable to decode client message, DTail server and client " +
 		"versions may not be compatible")
diff --git a/internal/server/handlers/protocol_codec_test.go b/internal/server/handlers/protocol_codec_test.go
new file mode 100644
index 0000000..a182d18
--- /dev/null
+++ b/internal/server/handlers/protocol_codec_test.go
@@ -0,0 +1,32 @@
+package handlers
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/mimecast/dtail/internal/protocol"
+)
+
+func TestHandleProtocolVersionUsesSemanticCompatComparison(t *testing.T) {
+	codec := newProtocolCodec(nil)
+
+	args, argc, add, err := codec.handleProtocolVersion([]string{"protocol", "4", "tail", "payload"})
+	if err == nil {
+		t.Fatal("expected protocol mismatch error")
+	}
+	if argc != 4 {
+		t.Fatalf("unexpected argc: got %d want 4", argc)
+	}
+	if len(args) != 4 || args[0] != "protocol" || args[1] != "4" {
+		t.Fatalf("unexpected args returned: %#v", args)
+	}
+	if add != "" {
+		t.Fatalf("unexpected message separator: %q", add)
+	}
+	if !strings.Contains(err.Error(), "please update DTail client") {
+		t.Fatalf("expected client update guidance, got %q", err)
+	}
+	if !strings.Contains(err.Error(), protocol.ProtocolCompat) {
+		t.Fatalf("expected error to mention server protocol version, got %q", err)
+	}
+}