Reimplement HUB_TEST_HOST support using a custom http.Transport

In testing, we want to redirect all requests to a local test server
pretending to be GitHub API, but we want them to preserve their original
"Host" header. A good place to do that transparently is the `RoundTrip`
method that handles every request for this http.Client instance.

github/client.go

@@ -463,23 +463,10 @@ func (client *Client) newOctokitClient(auth octokit.AuthMethod) *octokit.Client
 		host = client.Host.Host
 	}
 	host = normalizeHost(host)
+	apiHostURL := client.absolute(host)
 
-	apiHost := host
-	hubTestHost := os.Getenv("HUB_TEST_HOST")
-	if hubTestHost != "" {
-		apiHost = hubTestHost
-	}
-
-	hostURL := client.absolute(host)
-	apiHostURL := client.absolute(apiHost)
-
-	httpClient := newHttpClient(os.Getenv("HUB_VERBOSE") != "")
+	httpClient := newHttpClient(os.Getenv("HUB_TEST_HOST"), os.Getenv("HUB_VERBOSE") != "")
 	c := octokit.NewClientWith(apiHostURL.String(), UserAgent, auth, httpClient)
-	if hubTestHost != "" {
-		// if it's in test, make sure host name is in the header
-		c.Header.Set("Host", host)
-		c.Header.Set("X-Original-Scheme", hostURL.Scheme)
-	}
 
 	return c
 }

github/client_test.go

@@ -3,7 +3,6 @@ package github
 import (
 	"fmt"
 	"net/http"
-	"os"
 	"testing"
 
 	"github.com/bmizerany/assert"
@@ -22,13 +21,6 @@ func TestClient_newOctokitClient(t *testing.T) {
 	c = NewClient("http://github.corporate.com")
 	cc = c.newOctokitClient(nil)
 	assert.Equal(t, "http://github.corporate.com", cc.Endpoint.String())
-
-	os.Setenv("HUB_TEST_HOST", "http://127.0.0.1")
-	defer os.Setenv("HUB_TEST_HOST", "")
-	c = NewClient("github.corporate.com")
-	cc = c.newOctokitClient(nil)
-	assert.Equal(t, "http://127.0.0.1", cc.Endpoint.String())
-	assert.Equal(t, "github.corporate.com", cc.Header.Get("Host"))
 }
 
 func TestClient_FormatError(t *testing.T) {

github/http.go

@@ -15,8 +15,9 @@ import (
 )
 
 type verboseTransport struct {
-	Transport *http.Transport
-	Verbose   bool
+	Transport   *http.Transport
+	Verbose     bool
+	OverrideURL *url.URL
 }
 
 func (t *verboseTransport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
@@ -24,6 +25,13 @@ func (t *verboseTransport) RoundTrip(req *http.Request) (resp *http.Response, er
 		t.dumpRequest(req)
 	}
 
+	if t.OverrideURL != nil {
+		req = cloneRequest(req)
+		req.Header.Set("X-Original-Scheme", req.URL.Scheme)
+		req.URL.Scheme = t.OverrideURL.Scheme
+		req.URL.Host = t.OverrideURL.Host
+	}
+
 	resp, err = t.Transport.RoundTrip(req)
 
 	if err == nil && t.Verbose {
@@ -33,8 +41,19 @@ func (t *verboseTransport) RoundTrip(req *http.Request) (resp *http.Response, er
 	return
 }
 
+func cloneRequest(req *http.Request) *http.Request {
+	dup := new(http.Request)
+	*dup = *req
+	dup.URL, _ = url.Parse(req.URL.String())
+	dup.Header = make(http.Header)
+	for k, s := range req.Header {
+		dup.Header[k] = s
+	}
+	return dup
+}
+
 func (t *verboseTransport) dumpRequest(req *http.Request) {
-	info := fmt.Sprintf("> %s %s://%s%s", req.Method, req.Header.Get("X-Original-Scheme"), req.Host, req.URL.Path)
+	info := fmt.Sprintf("> %s %s://%s%s", req.Method, req.URL.Scheme, req.Host, req.URL.Path)
 	t.verbosePrintln(info)
 	t.dumpHeaders(req.Header, ">")
 	body := t.dumpBody(req.Body)
@@ -100,10 +119,15 @@ func (t *verboseTransport) verbosePrintln(msg string) {
 	fmt.Fprintln(os.Stderr, msg)
 }
 
-func newHttpClient(verbose bool) *http.Client {
+func newHttpClient(testHost string, verbose bool) *http.Client {
+	var testURL *url.URL
+	if testHost != "" {
+		testURL, _ = url.Parse(testHost)
+	}
 	tr := &verboseTransport{
-		Transport: &http.Transport{Proxy: proxyFromEnvironment},
-		Verbose:   verbose,
+		Transport:   &http.Transport{Proxy: proxyFromEnvironment},
+		Verbose:     verbose,
+		OverrideURL: testURL,
 	}
 	return &http.Client{Transport: tr}
 }