From e98c3509c65c13550f11fb751953d42c161eaedc Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Sat, 14 Oct 2017 12:03:25 -0700
Subject: [PATCH 1/8] Moved mutex to BackendConfiguration

---
 Makefile       |  4 ++--
 error_test.go  |  4 +---
 stripe.go      | 22 +++++++++++-----------
 stripe_test.go | 20 ++++++++++++++++++++
 4 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/Makefile b/Makefile
index 79b9ba3ecf..4f3332ea0d 100644
--- a/Makefile
+++ b/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 ./...
diff --git a/error_test.go b/error_test.go
index 427aab772e..23be3f089f 100644
--- a/error_test.go
+++ b/error_test.go
@@ -23,9 +23,7 @@ func TestErrorResponse(t *testing.T) {
 	defer ts.Close()
 
 	SetBackend("api", BackendConfiguration{
-		APIBackend,
-		ts.URL,
-		&http.Client{},
+		Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
 	})
 
 	err := GetBackend(APIBackend).Call("GET", "/v1/account", "sk_test_badKey", nil, nil, nil)
diff --git a/stripe.go b/stripe.go
index 4a63e2edb4..e7a6758227 100644
--- a/stripe.go
+++ b/stripe.go
@@ -76,6 +76,7 @@ type Backend interface {
 
 // BackendConfiguration is the internal implementation for making HTTP calls to Stripe.
 type BackendConfiguration struct {
+	sync.Mutex
 	Type       SupportedBackend
 	URL        string
 	HTTPClient *http.Client
@@ -101,7 +102,6 @@ const (
 
 // Backends are the currently supported endpoints.
 type Backends struct {
-	mu           sync.Mutex
 	API, Uploads Backend
 }
 
@@ -160,28 +160,27 @@ func SetHTTPClient(client *http.Client) {
 func NewBackends(httpClient *http.Client) *Backends {
 	return &Backends{
 		API: BackendConfiguration{
-			APIBackend, APIURL, httpClient},
+			Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
 		Uploads: BackendConfiguration{
-			UploadsBackend, UploadsURL, httpClient},
+			Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
 	}
 }
 
 // GetBackend returns the currently used backend in the binding.
 func GetBackend(backend SupportedBackend) Backend {
 	var ret Backend
-	backends.mu.Lock()
-	defer backends.mu.Unlock()
-
 	switch backend {
 	case APIBackend:
 		if backends.API == nil {
-			backends.API = BackendConfiguration{backend, apiURL, httpClient}
+			backends.API = BackendConfiguration{
+				Type: backend, URL: apiURL, HTTPClient: httpClient}
 		}
 
 		ret = backends.API
 	case UploadsBackend:
 		if backends.Uploads == nil {
-			backends.Uploads = BackendConfiguration{backend, uploadsURL, httpClient}
+			backends.Uploads = BackendConfiguration{
+				Type: backend, URL: uploadsURL, HTTPClient: httpClient}
 		}
 		ret = backends.Uploads
 	}
@@ -191,9 +190,6 @@ func GetBackend(backend SupportedBackend) Backend {
 
 // SetBackend sets the backend used in the binding.
 func SetBackend(backend SupportedBackend, b Backend) {
-	backends.mu.Lock()
-	defer backends.mu.Unlock()
-
 	switch backend {
 	case APIBackend:
 		backends.API = b
@@ -245,6 +241,8 @@ func (s BackendConfiguration) CallMultipart(method, path, key, boundary string,
 // NewRequest is used by Call to generate an http.Request. It handles encoding
 // parameters and attaching the appropriate headers.
 func (s *BackendConfiguration) NewRequest(method, path, key, contentType string, body io.Reader, params *Params) (*http.Request, error) {
+	s.Lock()
+	defer s.Unlock()
 	if !strings.HasPrefix(path, "/") {
 		path = "/" + path
 	}
@@ -300,6 +298,8 @@ func (s *BackendConfiguration) NewRequest(method, path, key, contentType string,
 // the backend's HTTP client to execute the request and unmarshals the response
 // into v. It also handles unmarshaling errors returned by the API.
 func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
+	s.Lock()
+	defer s.Unlock()
 	if LogLevel > 1 {
 		Logger.Printf("Requesting %v %v%v\n", req.Method, req.URL.Host, req.URL.Path)
 	}
diff --git a/stripe_test.go b/stripe_test.go
index b88e546dea..9f77cc2d7e 100644
--- a/stripe_test.go
+++ b/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"}

From e611f43699ce1070cdba6085ec0289cd98e90b61 Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 06:51:58 -0700
Subject: [PATCH 2/8] Added exported mutex to solve go-vet and pass CI.

---
 error_test.go |  3 ++-
 stripe.go     | 18 +++++++++---------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/error_test.go b/error_test.go
index 23be3f089f..defcabf14a 100644
--- a/error_test.go
+++ b/error_test.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"sync"
 	"testing"
 
 	assert "github.com/stretchr/testify/require"
@@ -23,7 +24,7 @@ func TestErrorResponse(t *testing.T) {
 	defer ts.Close()
 
 	SetBackend("api", BackendConfiguration{
-		Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
+		Mutex: &sync.Mutex{}, Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
 	})
 
 	err := GetBackend(APIBackend).Call("GET", "/v1/account", "sk_test_badKey", nil, nil, nil)
diff --git a/stripe.go b/stripe.go
index e7a6758227..407e9edf86 100644
--- a/stripe.go
+++ b/stripe.go
@@ -76,7 +76,7 @@ type Backend interface {
 
 // BackendConfiguration is the internal implementation for making HTTP calls to Stripe.
 type BackendConfiguration struct {
-	sync.Mutex
+	Mutex      *sync.Mutex
 	Type       SupportedBackend
 	URL        string
 	HTTPClient *http.Client
@@ -160,9 +160,9 @@ func SetHTTPClient(client *http.Client) {
 func NewBackends(httpClient *http.Client) *Backends {
 	return &Backends{
 		API: BackendConfiguration{
-			Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
+			Mutex: &sync.Mutex{}, Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
 		Uploads: BackendConfiguration{
-			Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
+			Mutex: &sync.Mutex{}, Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
 	}
 }
 
@@ -173,14 +173,14 @@ func GetBackend(backend SupportedBackend) Backend {
 	case APIBackend:
 		if backends.API == nil {
 			backends.API = BackendConfiguration{
-				Type: backend, URL: apiURL, HTTPClient: httpClient}
+				Mutex: &sync.Mutex{}, Type: backend, URL: apiURL, HTTPClient: httpClient}
 		}
 
 		ret = backends.API
 	case UploadsBackend:
 		if backends.Uploads == nil {
 			backends.Uploads = BackendConfiguration{
-				Type: backend, URL: uploadsURL, HTTPClient: httpClient}
+				Mutex: &sync.Mutex{}, Type: backend, URL: uploadsURL, HTTPClient: httpClient}
 		}
 		ret = backends.Uploads
 	}
@@ -241,8 +241,8 @@ func (s BackendConfiguration) CallMultipart(method, path, key, boundary string,
 // NewRequest is used by Call to generate an http.Request. It handles encoding
 // parameters and attaching the appropriate headers.
 func (s *BackendConfiguration) NewRequest(method, path, key, contentType string, body io.Reader, params *Params) (*http.Request, error) {
-	s.Lock()
-	defer s.Unlock()
+	s.Mutex.Lock()
+	defer s.Mutex.Unlock()
 	if !strings.HasPrefix(path, "/") {
 		path = "/" + path
 	}
@@ -298,8 +298,8 @@ func (s *BackendConfiguration) NewRequest(method, path, key, contentType string,
 // the backend's HTTP client to execute the request and unmarshals the response
 // into v. It also handles unmarshaling errors returned by the API.
 func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
-	s.Lock()
-	defer s.Unlock()
+	s.Mutex.Lock()
+	defer s.Mutex.Unlock()
 	if LogLevel > 1 {
 		Logger.Printf("Requesting %v %v%v\n", req.Method, req.URL.Host, req.URL.Path)
 	}

From 58e3196279f72a94a6eaa7f99882f9292b22e12e Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 07:04:39 -0700
Subject: [PATCH 3/8] Updated tests and stripe.go, not sure how this was
 passing locally. Did not update branch when switching environments

---
 stripe_test.go     | 18 +++++++++---------
 testing/testing.go |  2 ++
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/stripe_test.go b/stripe_test.go
index 9f77cc2d7e..fc0bd4fcf0 100644
--- a/stripe_test.go
+++ b/stripe_test.go
@@ -14,7 +14,7 @@ import (
 )
 
 func TestCheckinUseBearerAuth(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 	key := "apiKey"
 
 	req, err := c.NewRequest("", "", key, "", nil, nil)
@@ -30,7 +30,7 @@ func TestMultipleAPICalls(t *testing.T) {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+			c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 			key := "apiKey"
 
 			req, err := c.NewRequest("", "", key, "", nil, nil)
@@ -43,7 +43,7 @@ func TestMultipleAPICalls(t *testing.T) {
 }
 
 func TestIdempotencyKey(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 	p := &stripe.Params{IdempotencyKey: "idempotency-key"}
 
 	req, err := c.NewRequest("", "", "", "", nil, p)
@@ -53,7 +53,7 @@ func TestIdempotencyKey(t *testing.T) {
 }
 
 func TestStripeAccount(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 	p := &stripe.Params{StripeAccount: TestMerchantID}
 
 	req, err := c.NewRequest("", "", "", "", nil, p)
@@ -72,7 +72,7 @@ func TestStripeAccount(t *testing.T) {
 }
 
 func TestUserAgent(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -94,7 +94,7 @@ func TestUserAgentWithAppInfo(t *testing.T) {
 	stripe.SetAppInfo(appInfo)
 	defer stripe.SetAppInfo(nil)
 
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -108,7 +108,7 @@ func TestUserAgentWithAppInfo(t *testing.T) {
 }
 
 func TestStripeClientUserAgent(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -142,7 +142,7 @@ func TestStripeClientUserAgentWithAppInfo(t *testing.T) {
 	stripe.SetAppInfo(appInfo)
 	defer stripe.SetAppInfo(nil)
 
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -161,7 +161,7 @@ func TestStripeClientUserAgentWithAppInfo(t *testing.T) {
 }
 
 func TestResponseToError(t *testing.T) {
-	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
 
 	// A test response that includes a status code and request ID.
 	res := &http.Response{
diff --git a/testing/testing.go b/testing/testing.go
index 55dc955fbb..880da2cdac 100644
--- a/testing/testing.go
+++ b/testing/testing.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"sync"
 
 	stripe "github.com/stripe/stripe-go"
 	"github.com/stripe/stripe-go/form"
@@ -56,6 +57,7 @@ func init() {
 
 	stripe.Key = "sk_test_myTestKey"
 	stripe.SetBackend("api", stripe.BackendConfiguration{
+		Mutex:      &sync.Mutex{},
 		Type:       stripe.APIBackend,
 		URL:        "http://localhost:" + port + "/v1",
 		HTTPClient: &http.Client{},

From 453a5bb728b4edb86dbb39a25305cf7666fa2801 Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 10:50:48 -0700
Subject: [PATCH 4/8] Changed method receiver to pointer, removing the need for
 a mutex address

---
 error_test.go  |  5 ++---
 stripe.go      | 30 +++++++++++++++---------------
 stripe_test.go | 18 +++++++++---------
 3 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/error_test.go b/error_test.go
index defcabf14a..919a6137cc 100644
--- a/error_test.go
+++ b/error_test.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"sync"
 	"testing"
 
 	assert "github.com/stretchr/testify/require"
@@ -23,8 +22,8 @@ func TestErrorResponse(t *testing.T) {
 	}))
 	defer ts.Close()
 
-	SetBackend("api", BackendConfiguration{
-		Mutex: &sync.Mutex{}, Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
+	SetBackend("api", &BackendConfiguration{
+		Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
 	})
 
 	err := GetBackend(APIBackend).Call("GET", "/v1/account", "sk_test_badKey", nil, nil, nil)
diff --git a/stripe.go b/stripe.go
index 407e9edf86..7a8d40592b 100644
--- a/stripe.go
+++ b/stripe.go
@@ -76,10 +76,10 @@ type Backend interface {
 
 // BackendConfiguration is the internal implementation for making HTTP calls to Stripe.
 type BackendConfiguration struct {
-	Mutex      *sync.Mutex
 	Type       SupportedBackend
 	URL        string
 	HTTPClient *http.Client
+	sync.Mutex
 }
 
 // SupportedBackend is an enumeration of supported Stripe endpoints.
@@ -159,10 +159,10 @@ 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{
-			Mutex: &sync.Mutex{}, Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
-		Uploads: BackendConfiguration{
-			Mutex: &sync.Mutex{}, Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
+		API: &BackendConfiguration{
+			Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
+		Uploads: &BackendConfiguration{
+			Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
 	}
 }
 
@@ -172,15 +172,15 @@ func GetBackend(backend SupportedBackend) Backend {
 	switch backend {
 	case APIBackend:
 		if backends.API == nil {
-			backends.API = BackendConfiguration{
-				Mutex: &sync.Mutex{}, Type: backend, URL: apiURL, HTTPClient: httpClient}
+			backends.API = &BackendConfiguration{
+				Type: backend, URL: apiURL, HTTPClient: httpClient}
 		}
 
 		ret = backends.API
 	case UploadsBackend:
 		if backends.Uploads == nil {
-			backends.Uploads = BackendConfiguration{
-				Mutex: &sync.Mutex{}, Type: backend, URL: uploadsURL, HTTPClient: httpClient}
+			backends.Uploads = &BackendConfiguration{
+				Type: backend, URL: uploadsURL, HTTPClient: httpClient}
 		}
 		ret = backends.Uploads
 	}
@@ -199,7 +199,7 @@ 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()
@@ -223,7 +223,7 @@ 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)
@@ -241,8 +241,8 @@ func (s BackendConfiguration) CallMultipart(method, path, key, boundary string,
 // NewRequest is used by Call to generate an http.Request. It handles encoding
 // parameters and attaching the appropriate headers.
 func (s *BackendConfiguration) NewRequest(method, path, key, contentType string, body io.Reader, params *Params) (*http.Request, error) {
-	s.Mutex.Lock()
-	defer s.Mutex.Unlock()
+	s.Lock()
+	defer s.Unlock()
 	if !strings.HasPrefix(path, "/") {
 		path = "/" + path
 	}
@@ -298,8 +298,8 @@ func (s *BackendConfiguration) NewRequest(method, path, key, contentType string,
 // the backend's HTTP client to execute the request and unmarshals the response
 // into v. It also handles unmarshaling errors returned by the API.
 func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
-	s.Mutex.Lock()
-	defer s.Mutex.Unlock()
+	s.Lock()
+	defer s.Unlock()
 	if LogLevel > 1 {
 		Logger.Printf("Requesting %v %v%v\n", req.Method, req.URL.Host, req.URL.Path)
 	}
diff --git a/stripe_test.go b/stripe_test.go
index fc0bd4fcf0..9f77cc2d7e 100644
--- a/stripe_test.go
+++ b/stripe_test.go
@@ -14,7 +14,7 @@ import (
 )
 
 func TestCheckinUseBearerAuth(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 	key := "apiKey"
 
 	req, err := c.NewRequest("", "", key, "", nil, nil)
@@ -30,7 +30,7 @@ func TestMultipleAPICalls(t *testing.T) {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+			c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 			key := "apiKey"
 
 			req, err := c.NewRequest("", "", key, "", nil, nil)
@@ -43,7 +43,7 @@ func TestMultipleAPICalls(t *testing.T) {
 }
 
 func TestIdempotencyKey(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 	p := &stripe.Params{IdempotencyKey: "idempotency-key"}
 
 	req, err := c.NewRequest("", "", "", "", nil, p)
@@ -53,7 +53,7 @@ func TestIdempotencyKey(t *testing.T) {
 }
 
 func TestStripeAccount(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 	p := &stripe.Params{StripeAccount: TestMerchantID}
 
 	req, err := c.NewRequest("", "", "", "", nil, p)
@@ -72,7 +72,7 @@ func TestStripeAccount(t *testing.T) {
 }
 
 func TestUserAgent(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -94,7 +94,7 @@ func TestUserAgentWithAppInfo(t *testing.T) {
 	stripe.SetAppInfo(appInfo)
 	defer stripe.SetAppInfo(nil)
 
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -108,7 +108,7 @@ func TestUserAgentWithAppInfo(t *testing.T) {
 }
 
 func TestStripeClientUserAgent(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -142,7 +142,7 @@ func TestStripeClientUserAgentWithAppInfo(t *testing.T) {
 	stripe.SetAppInfo(appInfo)
 	defer stripe.SetAppInfo(nil)
 
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 
 	req, err := c.NewRequest("", "", "", "", nil, nil)
 	assert.NoError(t, err)
@@ -161,7 +161,7 @@ func TestStripeClientUserAgentWithAppInfo(t *testing.T) {
 }
 
 func TestResponseToError(t *testing.T) {
-	c := &stripe.BackendConfiguration{Mutex: &sync.Mutex{}, URL: stripe.APIURL}
+	c := &stripe.BackendConfiguration{URL: stripe.APIURL}
 
 	// A test response that includes a status code and request ID.
 	res := &http.Response{

From 5935c86521d15714334a8843d69b39599014a2fe Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 10:59:00 -0700
Subject: [PATCH 5/8] Updated testing BackendConfig -- no idea why this passes
 with 'make' locally

---
 testing/testing.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/testing/testing.go b/testing/testing.go
index 880da2cdac..e7447846e1 100644
--- a/testing/testing.go
+++ b/testing/testing.go
@@ -56,7 +56,7 @@ func init() {
 	}
 
 	stripe.Key = "sk_test_myTestKey"
-	stripe.SetBackend("api", stripe.BackendConfiguration{
+	stripe.SetBackend("api", &stripe.BackendConfiguration{
 		Mutex:      &sync.Mutex{},
 		Type:       stripe.APIBackend,
 		URL:        "http://localhost:" + port + "/v1",

From 745a98f73e18571b999411ce8fd4aec16c3f7608 Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 11:02:11 -0700
Subject: [PATCH 6/8] Removed mutex.

---
 testing/testing.go | 2 --
 1 file changed, 2 deletions(-)

diff --git a/testing/testing.go b/testing/testing.go
index e7447846e1..3fcecc5e51 100644
--- a/testing/testing.go
+++ b/testing/testing.go
@@ -6,7 +6,6 @@ import (
 	"os"
 	"strconv"
 	"strings"
-	"sync"
 
 	stripe "github.com/stripe/stripe-go"
 	"github.com/stripe/stripe-go/form"
@@ -57,7 +56,6 @@ func init() {
 
 	stripe.Key = "sk_test_myTestKey"
 	stripe.SetBackend("api", &stripe.BackendConfiguration{
-		Mutex:      &sync.Mutex{},
 		Type:       stripe.APIBackend,
 		URL:        "http://localhost:" + port + "/v1",
 		HTTPClient: &http.Client{},

From ab5be532db7841c33c7a38926613a4f0e31b6da4 Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 13:42:01 -0700
Subject: [PATCH 7/8] Named mutex

---
 stripe.go | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/stripe.go b/stripe.go
index 7a8d40592b..6cb6a4cbe6 100644
--- a/stripe.go
+++ b/stripe.go
@@ -76,10 +76,10 @@ type Backend interface {
 
 // BackendConfiguration is the internal implementation for making HTTP calls to Stripe.
 type BackendConfiguration struct {
+	mu         sync.Mutex
 	Type       SupportedBackend
 	URL        string
 	HTTPClient *http.Client
-	sync.Mutex
 }
 
 // SupportedBackend is an enumeration of supported Stripe endpoints.
@@ -241,8 +241,8 @@ func (s *BackendConfiguration) CallMultipart(method, path, key, boundary string,
 // NewRequest is used by Call to generate an http.Request. It handles encoding
 // parameters and attaching the appropriate headers.
 func (s *BackendConfiguration) NewRequest(method, path, key, contentType string, body io.Reader, params *Params) (*http.Request, error) {
-	s.Lock()
-	defer s.Unlock()
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	if !strings.HasPrefix(path, "/") {
 		path = "/" + path
 	}
@@ -298,8 +298,8 @@ func (s *BackendConfiguration) NewRequest(method, path, key, contentType string,
 // the backend's HTTP client to execute the request and unmarshals the response
 // into v. It also handles unmarshaling errors returned by the API.
 func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
-	s.Lock()
-	defer s.Unlock()
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	if LogLevel > 1 {
 		Logger.Printf("Requesting %v %v%v\n", req.Method, req.URL.Host, req.URL.Path)
 	}

From a8ae95163f86b133d1a7f7bae4390ee2486d04b5 Mon Sep 17 00:00:00 2001
From: Nathan Hyland <nathan.hyland@gmail.com>
Date: Mon, 16 Oct 2017 16:50:50 -0700
Subject: [PATCH 8/8] Updated with PR comments

---
 Makefile      |  4 ++--
 error_test.go |  4 +++-
 stripe.go     | 40 ++++++++++++++++++++++------------------
 3 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/Makefile b/Makefile
index 4f3332ea0d..c2cadaed60 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 all: test bench vet check-gofmt
 
 bench:
-	go test --race -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 --race ./...
+	go test -race ./...
 
 vet:
 	go vet ./...
diff --git a/error_test.go b/error_test.go
index 919a6137cc..693579e4c5 100644
--- a/error_test.go
+++ b/error_test.go
@@ -23,7 +23,9 @@ func TestErrorResponse(t *testing.T) {
 	defer ts.Close()
 
 	SetBackend("api", &BackendConfiguration{
-		Type: APIBackend, URL: ts.URL, HTTPClient: &http.Client{},
+		APIBackend,
+		ts.URL,
+		&http.Client{},
 	})
 
 	err := GetBackend(APIBackend).Call("GET", "/v1/account", "sk_test_badKey", nil, nil, nil)
diff --git a/stripe.go b/stripe.go
index 6cb6a4cbe6..8a6f731fb8 100644
--- a/stripe.go
+++ b/stripe.go
@@ -76,7 +76,6 @@ type Backend interface {
 
 // BackendConfiguration is the internal implementation for making HTTP calls to Stripe.
 type BackendConfiguration struct {
-	mu         sync.Mutex
 	Type       SupportedBackend
 	URL        string
 	HTTPClient *http.Client
@@ -103,6 +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
@@ -160,32 +160,40 @@ func SetHTTPClient(client *http.Client) {
 func NewBackends(httpClient *http.Client) *Backends {
 	return &Backends{
 		API: &BackendConfiguration{
-			Type: APIBackend, URL: APIURL, HTTPClient: httpClient},
+			APIBackend, APIURL, httpClient},
 		Uploads: &BackendConfiguration{
-			Type: UploadsBackend, URL: UploadsURL, HTTPClient: httpClient},
+			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{
-				Type: backend, URL: apiURL, HTTPClient: 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{
-				Type: backend, URL: uploadsURL, HTTPClient: 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.
@@ -241,8 +249,6 @@ func (s *BackendConfiguration) CallMultipart(method, path, key, boundary string,
 // NewRequest is used by Call to generate an http.Request. It handles encoding
 // parameters and attaching the appropriate headers.
 func (s *BackendConfiguration) NewRequest(method, path, key, contentType string, body io.Reader, params *Params) (*http.Request, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
 	if !strings.HasPrefix(path, "/") {
 		path = "/" + path
 	}
@@ -298,8 +304,6 @@ func (s *BackendConfiguration) NewRequest(method, path, key, contentType string,
 // the backend's HTTP client to execute the request and unmarshals the response
 // into v. It also handles unmarshaling errors returned by the API.
 func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
 	if LogLevel > 1 {
 		Logger.Printf("Requesting %v %v%v\n", req.Method, req.URL.Host, req.URL.Path)
 	}