Added a mutex around backend varible for concurrent reads

Makefile

@@ -1,7 +1,7 @@
 all: test bench vet check-gofmt
 
 bench:
-	go test -bench . -run "Benchmark" ./form
+	go test -race -bench . -run "Benchmark" ./form
 
 build:
 	go build ./...
@@ -10,7 +10,7 @@ check-gofmt:
 	scripts/check_gofmt.sh
 
 test:
-	go test ./...
+	go test -race ./...
 
 vet:
 	go vet ./...

error_test.go

@@ -22,7 +22,7 @@ func TestErrorResponse(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	SetBackend("api", BackendConfiguration{
+	SetBackend("api", &BackendConfiguration{
 		APIBackend,
 		ts.URL,
 		&http.Client{},

stripe.go

@@ -14,6 +14,7 @@ import (
 	"os/exec"
 	"runtime"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/stripe/stripe-go/form"
@@ -101,6 +102,7 @@ const (
 // Backends are the currently supported endpoints.
 type Backends struct {
 	API, Uploads Backend
+	mu           sync.RWMutex
 }
 
 // stripeClientUserAgent contains information about the current runtime which
@@ -157,31 +159,41 @@ func SetHTTPClient(client *http.Client) {
 // should only need to use this for testing purposes or on App Engine.
 func NewBackends(httpClient *http.Client) *Backends {
 	return &Backends{
-		API: BackendConfiguration{
+		API: &BackendConfiguration{
 			APIBackend, APIURL, httpClient},
-		Uploads: BackendConfiguration{
+		Uploads: &BackendConfiguration{
 			UploadsBackend, UploadsURL, httpClient},
 	}
 }
 
 // GetBackend returns the currently used backend in the binding.
 func GetBackend(backend SupportedBackend) Backend {
-	var ret Backend
 	switch backend {
 	case APIBackend:
-		if backends.API == nil {
-			backends.API = BackendConfiguration{backend, apiURL, httpClient}
+		backends.mu.RLock()
+		ret := backends.API
+		backends.mu.RUnlock()
+		if ret != nil {
+			return ret
 		}
-
-		ret = backends.API
+		backends.mu.Lock()
+		defer backends.mu.Unlock()
+		backends.API = &BackendConfiguration{backend, apiURL, httpClient}
+		return backends.API
 	case UploadsBackend:
-		if backends.Uploads == nil {
-			backends.Uploads = BackendConfiguration{backend, uploadsURL, httpClient}
+		backends.mu.RLock()
+		ret := backends.Uploads
+		backends.mu.RUnlock()
+		if ret != nil {
+			return ret
 		}
-		ret = backends.Uploads
+		backends.mu.Lock()
+		defer backends.mu.Unlock()
+		backends.Uploads = &BackendConfiguration{backend, uploadsURL, httpClient}
+		return backends.Uploads
 	}
 
-	return ret
+	return nil
 }
 
 // SetBackend sets the backend used in the binding.
@@ -195,7 +207,7 @@ func SetBackend(backend SupportedBackend, b Backend) {
 }
 
 // Call is the Backend.Call implementation for invoking Stripe APIs.
-func (s BackendConfiguration) Call(method, path, key string, form *form.Values, params *Params, v interface{}) error {
+func (s *BackendConfiguration) Call(method, path, key string, form *form.Values, params *Params, v interface{}) error {
 	var body io.Reader
 	if form != nil && !form.Empty() {
 		data := form.Encode()
@@ -219,7 +231,7 @@ func (s BackendConfiguration) Call(method, path, key string, form *form.Values,
 }
 
 // CallMultipart is the Backend.CallMultipart implementation for invoking Stripe APIs.
-func (s BackendConfiguration) CallMultipart(method, path, key, boundary string, body io.Reader, params *Params, v interface{}) error {
+func (s *BackendConfiguration) CallMultipart(method, path, key, boundary string, body io.Reader, params *Params, v interface{}) error {
 	contentType := "multipart/form-data; boundary=" + boundary
 
 	req, err := s.NewRequest(method, path, key, contentType, body, params)

stripe_test.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"regexp"
 	"runtime"
+	"sync"
 	"testing"
 
 	assert "github.com/stretchr/testify/require"
@@ -22,6 +23,25 @@ func TestCheckinUseBearerAuth(t *testing.T) {
 	assert.Equal(t, "Bearer "+key, req.Header.Get("Authorization"))
 }
 
+// TestMultipleAPICalls will fail the test run if a race condition is thrown while running multople NewRequest calls.
+func TestMultipleAPICalls(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+			key := "apiKey"
+
+			req, err := c.NewRequest("", "", key, "", nil, nil)
+			assert.NoError(t, err)
+
+			assert.Equal(t, "Bearer "+key, req.Header.Get("Authorization"))
+		}()
+	}
+	wg.Wait()
+}
+
 func TestIdempotencyKey(t *testing.T) {
 	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 	p := &stripe.Params{IdempotencyKey: "idempotency-key"}

testing/testing.go

@@ -55,7 +55,7 @@ func init() {
 	}
 
 	stripe.Key = "sk_test_myTestKey"
-	stripe.SetBackend("api", stripe.BackendConfiguration{
+	stripe.SetBackend("api", &stripe.BackendConfiguration{
 		Type:       stripe.APIBackend,
 		URL:        "http://localhost:" + port + "/v1",
 		HTTPClient: &http.Client{},