From cfc9776baefd28210239e958c68ce4d9b7230b4f Mon Sep 17 00:00:00 2001
From: Jakob Borg <jakob@nym.se>
Date: Thu, 9 Apr 2015 12:53:13 +0200
Subject: [PATCH] Check for short ID conflict at startup

---
 cmd/syncthing/main.go      | 19 +++++++++++++++++++
 cmd/syncthing/main_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/cmd/syncthing/main.go b/cmd/syncthing/main.go
index 14fa8660a..c2ea0a088 100644
--- a/cmd/syncthing/main.go
+++ b/cmd/syncthing/main.go
@@ -435,6 +435,10 @@ func syncthingMain() {
 		cfg.Save()
 	}
 
+	if err := checkShortIDs(cfg); err != nil {
+		l.Fatalln("Short device IDs are in conflict. Unlucky!\n  Regenerate the device ID of one if the following:\n  ", err)
+	}
+
 	if len(profiler) > 0 {
 		go func() {
 			l.Debugln("Starting profiler on", profiler)
@@ -1031,3 +1035,18 @@ func cleanConfigDirectory() {
 		}
 	}
 }
+
+// checkShortIDs verifies that the configuration won't result in duplicate
+// short ID:s; that is, that the devices in the cluster all have unique
+// initial 64 bits.
+func checkShortIDs(cfg *config.Wrapper) error {
+	exists := make(map[uint64]protocol.DeviceID)
+	for deviceID := range cfg.Devices() {
+		shortID := deviceID.Short()
+		if otherID, ok := exists[shortID]; ok {
+			return fmt.Errorf("%v in conflict with %v", deviceID, otherID)
+		}
+		exists[shortID] = deviceID
+	}
+	return nil
+}
diff --git a/cmd/syncthing/main_test.go b/cmd/syncthing/main_test.go
index a3ef5ee7a..b64a10274 100644
--- a/cmd/syncthing/main_test.go
+++ b/cmd/syncthing/main_test.go
@@ -140,3 +140,27 @@ func TestFolderErrors(t *testing.T) {
 		t.Error("Unexpected error", cfg.Folders()["folder"].Invalid)
 	}
 }
+
+func TestShortIDCheck(t *testing.T) {
+	cfg := config.Wrap("/tmp/test", config.Configuration{
+		Devices: []config.DeviceConfiguration{
+			{DeviceID: protocol.DeviceID{8, 16, 24, 32, 40, 48, 56, 0, 0}},
+			{DeviceID: protocol.DeviceID{8, 16, 24, 32, 40, 48, 56, 1, 1}}, // first 56 bits same, differ in the first 64 bits
+		},
+	})
+
+	if err := checkShortIDs(cfg); err != nil {
+		t.Error("Unexpected error:", err)
+	}
+
+	cfg = config.Wrap("/tmp/test", config.Configuration{
+		Devices: []config.DeviceConfiguration{
+			{DeviceID: protocol.DeviceID{8, 16, 24, 32, 40, 48, 56, 64, 0}},
+			{DeviceID: protocol.DeviceID{8, 16, 24, 32, 40, 48, 56, 64, 1}}, // first 64 bits same
+		},
+	})
+
+	if err := checkShortIDs(cfg); err == nil {
+		t.Error("Should have gotten an error")
+	}
+}