packer/plugin: detect invalid versions

CHANGELOG.md

@@ -15,6 +15,7 @@ IMPROVEMENTS:
 
 * core: User variables can now be used for integer, boolean, etc.
   values. [GH-418]
+* core: Plugins made with incompatible versions will no longer load.
 * builder/amazon/all: Interrupts work while waiting for AMI to be ready.
 * provisioner/shell: Script line-endings are automatically converted to
   Unix-style line-endings. Can be disabled by setting "binary" to "true".

packer/plugin/client.go

@@ -317,10 +317,24 @@ func (c *Client) Start() (address string, err error) {
 		err = errors.New("timeout while waiting for plugin to start")
 	case <-exitCh:
 		err = errors.New("plugin exited before we could connect")
-	case line := <-linesCh:
-		// Trim the address and reset the err since we were able
-		// to read some sort of address.
-		c.address = strings.TrimSpace(string(line))
+	case lineBytes := <-linesCh:
+		// Trim the line and split by "|" in order to get the parts of
+		// the output.
+		line := strings.TrimSpace(string(lineBytes))
+		parts := strings.SplitN(line, "|", 2)
+		if len(parts) < 2 {
+			err = fmt.Errorf("Unrecognized remote plugin message: %s", line)
+			return
+		}
+
+		// Test the API version
+		if parts[0] != APIVersion {
+			err = fmt.Errorf("Incompatible API version with plugin. "+
+				"Plugin version: %s, Ours: %s", parts[0], APIVersion)
+			return
+		}
+
+		c.address = parts[1]
 		address = c.address
 	}
 

packer/plugin/client_test.go

@@ -37,6 +37,21 @@ func TestClient(t *testing.T) {
 	}
 }
 
+func TestClientStart_badVersion(t *testing.T) {
+	config := &ClientConfig{
+		Cmd:          helperProcess("bad-version"),
+		StartTimeout: 50 * time.Millisecond,
+	}
+
+	c := NewClient(config)
+	defer c.Kill()
+
+	_, err := c.Start()
+	if err == nil {
+		t.Fatal("err should not be nil")
+	}
+}
+
 func TestClient_Start_Timeout(t *testing.T) {
 	config := &ClientConfig{
 		Cmd:          helperProcess("start-timeout"),

packer/plugin/plugin.go

@@ -30,6 +30,11 @@ var Interrupts int32 = 0
 const MagicCookieKey = "PACKER_PLUGIN_MAGIC_COOKIE"
 const MagicCookieValue = "d602bf8f470bc67ca7faa0386276bbdd4330efaf76d1a219cb4d6991ca9872b2"
 
+// The APIVersion is outputted along with the RPC address. The plugin
+// client validates this API version and will show an error if it doesn't
+// know how to speak it.
+const APIVersion = "1"
+
 // This serves a single RPC connection on the given RPC server on
 // a random port.
 func serve(server *rpc.Server) (err error) {
@@ -77,7 +82,7 @@ func serve(server *rpc.Server) (err error) {
 
 	// Output the address to stdout
 	log.Printf("Plugin address: %s\n", address)
-	fmt.Println(address)
+	fmt.Printf("%s|%s\n", APIVersion, address)
 	os.Stdout.Sync()
 
 	// Accept a connection

packer/plugin/plugin_test.go

@@ -50,6 +50,9 @@ func TestHelperProcess(*testing.T) {
 
 	cmd, args := args[0], args[1:]
 	switch cmd {
+	case "bad-version":
+		fmt.Printf("%s1|:1234\n", APIVersion)
+		<-make(chan int)
 	case "builder":
 		ServeBuilder(new(helperBuilder))
 	case "command":
@@ -59,7 +62,7 @@ func TestHelperProcess(*testing.T) {
 	case "invalid-rpc-address":
 		fmt.Println("lolinvalid")
 	case "mock":
-		fmt.Println(":1234")
+		fmt.Printf("%s|:1234\n", APIVersion)
 		<-make(chan int)
 	case "post-processor":
 		ServePostProcessor(new(helperPostProcessor))
@@ -69,11 +72,11 @@ func TestHelperProcess(*testing.T) {
 		time.Sleep(1 * time.Minute)
 		os.Exit(1)
 	case "stderr":
-		fmt.Println(":1234")
+		fmt.Printf("%s|:1234\n", APIVersion)
 		log.Println("HELLO")
 		log.Println("WORLD")
 	case "stdin":
-		fmt.Println(":1234")
+		fmt.Printf("%s|:1234\n", APIVersion)
 		data := make([]byte, 5)
 		if _, err := os.Stdin.Read(data); err != nil {
 			log.Printf("stdin read error: %s", err)