api: uses context from net/http

This commit removes the now unnecessary CancelableTransport and rely on
the net/http context support.

api/client.go

@@ -23,19 +23,10 @@ import (
 	"path"
 	"strings"
 	"time"
-
-	"golang.org/x/net/context/ctxhttp"
 )
 
-// CancelableTransport is like net.Transport but provides
-// per-request cancelation functionality.
-type CancelableTransport interface {
-	http.RoundTripper
-	CancelRequest(req *http.Request)
-}
-
-// DefaultTransport is used if no Transport is set in Config.
-var DefaultTransport CancelableTransport = &http.Transport{
+// DefaultRoundTripper is used if no RoundTripper is set in Config.
+var DefaultRoundTripper http.RoundTripper = &http.Transport{
 	Proxy: http.ProxyFromEnvironment,
 	Dial: (&net.Dialer{
 		Timeout:   30 * time.Second,
@@ -49,16 +40,16 @@ type Config struct {
 	// The address of the Prometheus to connect to.
 	Address string
 
-	// Transport is used by the Client to drive HTTP requests. If not
-	// provided, DefaultTransport will be used.
-	Transport CancelableTransport
+	// RoundTripper is used by the Client to drive HTTP requests. If not
+	// provided, DefaultRoundTripper will be used.
+	RoundTripper http.RoundTripper
 }
 
-func (cfg *Config) transport() CancelableTransport {
-	if cfg.Transport == nil {
-		return DefaultTransport
+func (cfg *Config) roundTripper() http.RoundTripper {
+	if cfg.RoundTripper == nil {
+		return DefaultRoundTripper
 	}
-	return cfg.Transport
+	return cfg.RoundTripper
 }
 
 // Client is the interface for an API client.
@@ -79,13 +70,13 @@ func New(cfg Config) (Client, error) {
 
 	return &httpClient{
 		endpoint: u,
-		transport: cfg.transport(),
+		client:   http.Client{Transport: cfg.roundTripper()},
 	}, nil
 }
 
 type httpClient struct {
 	endpoint *url.URL
-	transport CancelableTransport
+	client   http.Client
 }
 
 func (c *httpClient) URL(ep string, args map[string]string) *url.URL {
@@ -103,8 +94,10 @@ func (c *httpClient) URL(ep string, args map[string]string) *url.URL {
 }
 
 func (c *httpClient) Do(ctx context.Context, req *http.Request) (*http.Response, []byte, error) {
-	resp, err := ctxhttp.Do(ctx, &http.Client{Transport: c.transport}, req)
-
+	if ctx != nil {
+		req = req.WithContext(ctx)
+	}
+	resp, err := c.client.Do(req)
 	defer func() {
 		if resp != nil {
 			resp.Body.Close()

api/client_test.go

@@ -14,14 +14,15 @@
 package api
 
 import (
+	"net/http"
 	"net/url"
 	"testing"
 )
 
 func TestConfig(t *testing.T) {
 	c := Config{}
-	if c.transport() != DefaultTransport {
-		t.Fatalf("expected default transport for nil Transport field")
+	if c.roundTripper() != DefaultRoundTripper {
+		t.Fatalf("expected default roundtripper for nil RoundTripper field")
 	}
 }
 
@@ -100,7 +101,7 @@ func TestClientURL(t *testing.T) {
 
 		hclient := &httpClient{
 			endpoint: ep,
-			transport: DefaultTransport,
+			client:   http.Client{Transport: DefaultRoundTripper},
 		}
 
 		u := hclient.URL(test.endpoint, test.args)