Base for better conflict resolution

conflict_test.go

@@ -0,0 +1,23 @@
+// Copyright (C) 2015 The Protocol Authors.
+
+package protocol
+
+import "testing"
+
+func TestWinsConflict(t *testing.T) {
+	testcases := [][2]FileInfo{
+		// The first should always win over the second
+		{{Modified: 42}, {Modified: 41}},
+		{{Modified: 41}, {Modified: 42, Flags: FlagDeleted}},
+		{{Modified: 41, Version: Vector{{42, 2}, {43, 1}}}, {Modified: 41, Version: Vector{{42, 1}, {43, 2}}}},
+	}
+
+	for _, tc := range testcases {
+		if !tc[0].WinsConflict(tc[1]) {
+			t.Errorf("%v should win over %v", tc[0], tc[1])
+		}
+		if tc[1].WinsConflict(tc[0]) {
+			t.Errorf("%v should not win over %v", tc[1], tc[0])
+		}
+	}
+}

message.go

@@ -58,6 +58,31 @@ func (f FileInfo) HasPermissionBits() bool {
 	return f.Flags&FlagNoPermBits == 0
 }
 
+// WinsConflict returns true if "f" is the one to choose when it is in
+// conflict with "other".
+func (f FileInfo) WinsConflict(other FileInfo) bool {
+	// If a modification is in conflict with a delete, we pick the
+	// modification.
+	if !f.IsDeleted() && other.IsDeleted() {
+		return true
+	}
+	if f.IsDeleted() && !other.IsDeleted() {
+		return false
+	}
+
+	// The one with the newer modification time wins.
+	if f.Modified > other.Modified {
+		return true
+	}
+	if f.Modified < other.Modified {
+		return false
+	}
+
+	// The modification times were equal. Use the device ID in the version
+	// vector as tie breaker.
+	return f.Version.Compare(other.Version) == ConcurrentGreater
+}
+
 type BlockInfo struct {
 	Offset int64 // noencode (cache only)
 	Size   int32