removing more constants

client.go

@@ -43,15 +43,11 @@ type Client struct {
 // plugin client. After being used to initialize a plugin client,
 // that configuration must not be modified again.
 type ClientConfig struct {
-	// Plugins are the plugins that support being dispensed. This should
-	// match the server side. If it doesn't, the ProtocolVersion should
-	// be incremented.
-	Plugins map[string]Plugin
+	// HandshakeConfig is the configuration that must match servers.
+	HandshakeConfig
 
-	// ProtocolVersion is the version that the client expects the
-	// server to be speaking at a protocol layer. This should be set
-	// and match the plugin side.
-	ProtocolVersion uint
+	// Plugins are the plugins that can be consumed.
+	Plugins map[string]Plugin
 
 	// The unstarted subprocess for starting the plugin.
 	Cmd *exec.Cmd
@@ -238,7 +234,7 @@ func (c *Client) Start() (addr net.Addr, err error) {
 	c.doneLogging = make(chan struct{})
 
 	env := []string{
-		fmt.Sprintf("%s=%s", MagicCookieKey, MagicCookieValue),
+		fmt.Sprintf("%s=%s", c.config.MagicCookieKey, c.config.MagicCookieValue),
 		fmt.Sprintf("PLUGIN_MIN_PORT=%d", c.config.MinPort),
 		fmt.Sprintf("PLUGIN_MAX_PORT=%d", c.config.MaxPort),
 	}

client_test.go

@@ -11,7 +11,7 @@ import (
 
 func TestClient(t *testing.T) {
 	process := helperProcess("mock")
-	c := NewClient(&ClientConfig{Cmd: process, ProtocolVersion: testAPIVersion})
+	c := NewClient(&ClientConfig{Cmd: process, HandshakeConfig: testHandshake})
 	defer c.Kill()
 
 	// Test that it parses the proper address
@@ -45,7 +45,7 @@ func TestClientStart_badVersion(t *testing.T) {
 	config := &ClientConfig{
 		Cmd:             helperProcess("bad-version"),
 		StartTimeout:    50 * time.Millisecond,
-		ProtocolVersion: testAPIVersion,
+		HandshakeConfig: testHandshake,
 	}
 
 	c := NewClient(config)
@@ -61,7 +61,7 @@ func TestClient_Start_Timeout(t *testing.T) {
 	config := &ClientConfig{
 		Cmd:             helperProcess("start-timeout"),
 		StartTimeout:    50 * time.Millisecond,
-		ProtocolVersion: testAPIVersion,
+		HandshakeConfig: testHandshake,
 	}
 
 	c := NewClient(config)
@@ -79,7 +79,7 @@ func TestClient_Stderr(t *testing.T) {
 	c := NewClient(&ClientConfig{
 		Cmd:             process,
 		Stderr:          stderr,
-		ProtocolVersion: testAPIVersion,
+		HandshakeConfig: testHandshake,
 	})
 	defer c.Kill()
 
@@ -126,7 +126,7 @@ func TestClient_Stdin(t *testing.T) {
 	os.Stdin = tf
 
 	process := helperProcess("stdin")
-	c := NewClient(&ClientConfig{Cmd: process, ProtocolVersion: testAPIVersion})
+	c := NewClient(&ClientConfig{Cmd: process, HandshakeConfig: testHandshake})
 	defer c.Kill()
 
 	_, err = c.Start()

plugin_test.go

@@ -11,7 +11,11 @@ import (
 )
 
 // testAPIVersion is the ProtocolVersion we use for testing.
-const testAPIVersion uint = 1
+var testHandshake = HandshakeConfig{
+	ProtocolVersion:  1,
+	MagicCookieKey:   "TEST_MAGIC_COOKIE",
+	MagicCookieValue: "test",
+}
 
 // testInterface is the test interface we use for plugins.
 type testInterface interface {
@@ -102,22 +106,22 @@ func TestHelperProcess(*testing.T) {
 	cmd, args := args[0], args[1:]
 	switch cmd {
 	case "bad-version":
-		fmt.Printf("%d1|tcp|:1234\n", testAPIVersion)
+		fmt.Printf("%d1|tcp|:1234\n", testHandshake.ProtocolVersion)
 		<-make(chan int)
 	case "invalid-rpc-address":
 		fmt.Println("lolinvalid")
 	case "mock":
-		fmt.Printf("%d|tcp|:1234\n", testAPIVersion)
+		fmt.Printf("%d|tcp|:1234\n", testHandshake.ProtocolVersion)
 		<-make(chan int)
 	case "start-timeout":
 		time.Sleep(1 * time.Minute)
 		os.Exit(1)
 	case "stderr":
-		fmt.Printf("%d|tcp|:1234\n", testAPIVersion)
+		fmt.Printf("%d|tcp|:1234\n", testHandshake.ProtocolVersion)
 		log.Println("HELLO")
 		log.Println("WORLD")
 	case "stdin":
-		fmt.Printf("%d|tcp|:1234\n", testAPIVersion)
+		fmt.Printf("%d|tcp|:1234\n", testHandshake.ProtocolVersion)
 		data := make([]byte, 5)
 		if _, err := os.Stdin.Read(data); err != nil {
 			log.Printf("stdin read error: %s", err)

server.go

@@ -13,21 +13,33 @@ import (
 	"sync/atomic"
 )
 
-// The "magic cookie" is used to verify that the user intended to
-// actually run this binary. If this cookie isn't present as an
-// environmental variable, then we bail out early with an error.
-const MagicCookieKey = "OTTO_PLUGIN_MAGIC_COOKIE"
-const MagicCookieValue = "11aab7ff21cb9ff7b0e9975d53f17a8dab571eac9b5ff0191730046698f07b7f"
+// HandshakeConfig is the configuration used by client and servers to
+// handshake before starting a plugin connection. This is embedded by
+// both ServeConfig and ClientConfig.
+//
+// In practice, the plugin host creates a HandshakeConfig that is exported
+// and plugins then can easily consume it.
+type HandshakeConfig struct {
+	// ProtocolVersion is the version that clients must match on to
+	// agree they can communicate. This should match the ProtocolVersion
+	// set on ClientConfig when using a plugin.
+	ProtocolVersion uint
+
+	// MagicCookieKey and value are used as a very basic verification
+	// that a plugin is intended to be launched. This is not a security
+	// measure, just a UX feature. If the magic cookie doesn't match,
+	// we show human-friendly output.
+	MagicCookieKey   string
+	MagicCookieValue string
+}
 
 // ServeConfig configures what sorts of plugins are served.
 type ServeConfig struct {
+	// HandshakeConfig is the configuration that must match clients.
+	HandshakeConfig
+
 	// Plugins are the plugins that are served.
 	Plugins map[string]Plugin
-
-	// ProtocolVersion is the version that clients must match on to
-	// agree they can communicate. This should match the ProtocolVersion
-	// set on ClientConfig when using a plugin.
-	ProtocolVersion uint
 }
 
 // Serve serves the plugins given by ServeConfig.
@@ -36,7 +48,7 @@ type ServeConfig struct {
 // errors will be outputted to the log.
 func Serve(opts *ServeConfig) {
 	// First check the cookie
-	if os.Getenv(MagicCookieKey) != MagicCookieValue {
+	if os.Getenv(opts.MagicCookieKey) != opts.MagicCookieValue {
 		fmt.Fprintf(os.Stderr,
 			"This binary is a plugin. These are not meant to be executed directly.\n"+
 				"Please execute the program that consumes these plugins, which will\n"+