Moving error handlers to the cache implementations.

cache.go

@@ -12,9 +12,9 @@ import (
 // Cache represents a token cacher.
 type Cache interface {
 	// Read reads a cache token from the specified file.
-	Read() (token *Token, err error)
+	Read() (token *Token)
 	// Write writes a token to the specified file.
-	Write(token *Token) (err error)
+	Write(token *Token)
 }
 
 // NewFileCache creates a new file cache.
@@ -24,25 +24,29 @@ func NewFileCache(filename string) *FileCache {
 
 // FileCache represents a file based token cacher.
 type FileCache struct {
-	filename string
+	filename         string
+	ErrorHandlerFunc func(error)
 }
 
 // Read reads a cache token from the specified file.
-func (f *FileCache) Read() (token *Token, err error) {
+func (f *FileCache) Read() (token *Token) {
 	data, err := ioutil.ReadFile(f.filename)
-	if err != nil {
+	if err == nil {
-		return nil, err
+		err = json.Unmarshal(data, token)
 	}
-	token = &Token{}
+	if f.ErrorHandlerFunc != nil {
-	err = json.Unmarshal(data, &token)
+		f.ErrorHandlerFunc(err)
-	return token, err
+	}
+	return
 }
 
 // Write writes a token to the specified file.
-func (f *FileCache) Write(token *Token) error {
+func (f *FileCache) Write(token *Token) {
 	data, err := json.Marshal(token)
-	if err != nil {
+	if err == nil {
-		return err
+		err = ioutil.WriteFile(f.filename, data, 0644)
+	}
+	if f.ErrorHandlerFunc != nil {
+		f.ErrorHandlerFunc(err)
 	}
-	return ioutil.WriteFile(f.filename, data, 0644)
 }

cache_test.go

@@ -0,0 +1,27 @@
+// Copyright 2014 The oauth2 Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package oauth2
+
+import (
+	"os"
+	"testing"
+)
+
+func TestFileCacheErrorHandling(t *testing.T) {
+	var lastErr error
+	fileCache := NewFileCache("/path/that/doesnt/exist")
+	fileCache.ErrorHandlerFunc = func(err error) {
+		lastErr = err
+	}
+	fileCache.Read()
+	if !os.IsNotExist(lastErr) {
+		t.Fatalf("Read should have invoked the error handling func with os.ErrNotExist, but read err is %v", lastErr)
+	}
+	lastErr = nil
+	fileCache.Write(&Token{})
+	if !os.IsNotExist(lastErr) {
+		t.Fatalf("Write should have invoked the error handling func with os.ErrNotExist, but read err is %v", lastErr)
+	}
+}

oauth2.go

@@ -64,6 +64,7 @@ type TokenFetcher interface {
 	// If the implementation doesn't know how to retrieve a new token,
 	// it returns an error.
 	FetchToken(existing *Token) (*Token, error)
+	// Cache returns the Cache implementation to read/persist user tokens.
 	Cache() Cache
 }
 

transport.go

@@ -98,7 +98,7 @@ func (t *authorizedTransport) RoundTrip(req *http.Request) (resp *http.Response,
 
 	if token == nil && cache != nil {
 		// Try to read from cache initially
-		token, _ := cache.Read()
+		token = cache.Read()
 	}
 	if token == nil || token.Expired() {
 		// Check if the token is refreshable.