packer/rpc: Support Cache interface

packer/cache.go

@@ -14,7 +14,7 @@ type Cache interface {
 	// the lock is held.
 	//
 	// The cache will block and wait for the lock.
-	Lock(string) (string, error)
+	Lock(string) string
 
 	// Unlock will unlock a certain cache key. Be very careful that this
 	// is only called once per lock obtained.
@@ -38,12 +38,12 @@ type FileCache struct {
 	rw       map[string]*sync.RWMutex
 }
 
-func (f *FileCache) Lock(key string) (string, error) {
+func (f *FileCache) Lock(key string) string {
 	hashKey := f.hashKey(key)
 	rw := f.rwLock(hashKey)
 	rw.Lock()
 
-	return filepath.Join(f.CacheDir, hashKey), nil
+	return filepath.Join(f.CacheDir, hashKey)
 }
 
 func (f *FileCache) Unlock(key string) {

packer/cache_test.go

@@ -22,11 +22,7 @@ func TestFileCache(t *testing.T) {
 	defer os.RemoveAll(cacheDir)
 
 	cache := &FileCache{CacheDir: cacheDir}
-	path, err := cache.Lock("foo")
-	if err != nil {
-		t.Fatalf("error locking: %s", err)
-	}
-
+	path := cache.Lock("foo")
 	err = ioutil.WriteFile(path, []byte("data"), 0666)
 	if err != nil {
 		t.Fatalf("error writing: %s", err)

packer/rpc/cache.go

@@ -0,0 +1,77 @@
+package rpc
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"net/rpc"
+)
+
+// An implementation of packer.Cache where the cache is actually executed
+// over an RPC connection.
+type cache struct {
+	client *rpc.Client
+}
+
+// CacheServer wraps a packer.Cache implementation and makes it exportable
+// as part of a Golang RPC server.
+type CacheServer struct {
+	cache packer.Cache
+}
+
+func Cache(client *rpc.Client) *cache {
+	return &cache{client}
+}
+
+type CacheRLockResponse struct {
+	Path   string
+	Exists bool
+}
+
+func (c *cache) Lock(key string) (result string) {
+	if err := c.client.Call("Cache.Lock", key, &result); err != nil {
+		panic(err)
+	}
+
+	return
+}
+
+func (c *cache) RLock(key string) (string, bool) {
+	var result CacheRLockResponse
+	if err := c.client.Call("Cache.RLock", key, &result); err != nil {
+		panic(err)
+	}
+
+	return result.Path, result.Exists
+}
+
+func (c *cache) Unlock(key string) {
+	if err := c.client.Call("Cache.Unlock", key, new(interface{})); err != nil {
+		panic(err)
+	}
+}
+
+func (c *cache) RUnlock(key string) {
+	if err := c.client.Call("Cache.RUnlock", key, new(interface{})); err != nil {
+		panic(err)
+	}
+}
+
+func (c *CacheServer) Lock(key string, result *string) error {
+	*result = c.cache.Lock(key)
+	return nil
+}
+
+func (c *CacheServer) Unlock(key string, result *interface{}) error {
+	c.cache.Unlock(key)
+	return nil
+}
+
+func (c *CacheServer) RLock(key string, result *CacheRLockResponse) error {
+	path, exists := c.cache.RLock(key)
+	*result = CacheRLockResponse{path, exists}
+	return nil
+}
+
+func (c *CacheServer) RUnlock(key string, result *interface{}) error {
+	c.cache.RUnlock(key)
+	return nil
+}

packer/rpc/cache_test.go

@@ -0,0 +1,86 @@
+package rpc
+
+import (
+	"cgl.tideland.biz/asserts"
+	"github.com/mitchellh/packer/packer"
+	"net/rpc"
+	"testing"
+)
+
+type testCache struct {
+	lockCalled    bool
+	lockKey       string
+	unlockCalled  bool
+	unlockKey     string
+	rlockCalled   bool
+	rlockKey      string
+	runlockCalled bool
+	runlockKey    string
+}
+
+func (t *testCache) Lock(key string) string {
+	t.lockCalled = true
+	t.lockKey = key
+	return "foo"
+}
+
+func (t *testCache) RLock(key string) (string, bool) {
+	t.rlockCalled = true
+	t.rlockKey = key
+	return "foo", true
+}
+
+func (t *testCache) Unlock(key string) {
+	t.unlockCalled = true
+	t.unlockKey = key
+}
+
+func (t *testCache) RUnlock(key string) {
+	t.runlockCalled = true
+	t.runlockKey = key
+}
+
+func TestCache_Implements(t *testing.T) {
+	var raw interface{}
+	raw = Cache(nil)
+	if _, ok := raw.(packer.Cache); !ok {
+		t.Fatal("Cache must be a cache.")
+	}
+}
+
+func TestCacheRPC(t *testing.T) {
+	assert := asserts.NewTestingAsserts(t, true)
+
+	// Create the interface to test
+	c := new(testCache)
+
+	// Start the server
+	server := rpc.NewServer()
+	RegisterCache(server, c)
+	address := serveSingleConn(server)
+
+	// Create the client over RPC and run some methods to verify it works
+	rpcClient, err := rpc.Dial("tcp", address)
+	assert.Nil(err, "should be able to connect")
+	client := Cache(rpcClient)
+
+	// Test Lock
+	client.Lock("foo")
+	assert.True(c.lockCalled, "should be called")
+	assert.Equal(c.lockKey, "foo", "should have proper key")
+
+	// Test Unlock
+	client.Unlock("foo")
+	assert.True(c.unlockCalled, "should be called")
+	assert.Equal(c.unlockKey, "foo", "should have proper key")
+
+	// Test RLock
+	client.RLock("foo")
+	assert.True(c.rlockCalled, "should be called")
+	assert.Equal(c.rlockKey, "foo", "should have proper key")
+
+	// Test RUnlock
+	client.RUnlock("foo")
+	assert.True(c.runlockCalled, "should be called")
+	assert.Equal(c.runlockKey, "foo", "should have proper key")
+}

packer/rpc/server.go

@@ -23,6 +23,12 @@ func RegisterBuilder(s *rpc.Server, b packer.Builder) {
 	s.RegisterName("Builder", &BuilderServer{b})
 }
 
+// Registers the appropriate endpoint on an RPC server to serve a
+// Packer Cache.
+func RegisterCache(s *rpc.Server, c packer.Cache) {
+	s.RegisterName("Cache", &CacheServer{c})
+}
+
 // Registers the appropriate endpoint on an RPC server to serve a
 // Packer Command.
 func RegisterCommand(s *rpc.Server, c packer.Command) {