http: expose Client's Transport

This is again an intentionally minimal change.

The plan is to keep Client's zero value be a usable
client, with optional fields being added over time
(e.g. cookie manager, redirect policy, auth)

R=rsc
CC=golang-dev
https://golang.org/cl/4239044

src/pkg/http/client.go

@@ -16,10 +16,11 @@ import (
 	"strings"
 )
 
-// A Client is an HTTP client.
-// It is not yet possible to create custom Clients; use DefaultClient.
+// A Client is an HTTP client. Its zero value (DefaultClient) is a usable client
+// that uses DefaultTransport.
+// Client is not yet very configurable.
 type Client struct {
-	transport ClientTransport // if nil, DefaultTransport is used
+	Transport ClientTransport // if nil, DefaultTransport is used
 }
 
 // DefaultClient is the default Client and is used by Get, Head, and Post.
@@ -87,15 +88,15 @@ func matchNoProxy(addr string) bool {
 // Do sends an HTTP request and returns an HTTP response, following
 // policy (e.g. redirects, cookies, auth) as configured on the client.
 //
-// Callers should close resp.Body when done reading it.
+// Callers should close resp.Body when done reading from it.
 //
 // Generally Get, Post, or PostForm will be used instead of Do.
 func (c *Client) Do(req *Request) (resp *Response, err os.Error) {
-	return send(req, c.transport)
+	return send(req, c.Transport)
 }
 
 
-// send issues an HTTP request.  Caller should close resp.Body when done reading it.
+// send issues an HTTP request.  Caller should close resp.Body when done reading from it.
 //
 // TODO: support persistent connections (multiple requests on a single connection).
 // send() method is nonpublic because, when we refactor the code for persistent
@@ -103,6 +104,10 @@ func (c *Client) Do(req *Request) (resp *Response, err os.Error) {
 func send(req *Request, t ClientTransport) (resp *Response, err os.Error) {
 	if t == nil {
 		t = DefaultTransport
+		if t == nil {
+			err = os.NewError("no http.Client.Transport or http.DefaultTransport")
+			return
+		}
 	}
 	info := req.URL.RawUserinfo
 	if len(info) > 0 {
@@ -138,7 +143,7 @@ func shouldRedirect(statusCode int) bool {
 // finalURL is the URL from which the response was fetched -- identical to the
 // input URL unless redirects were followed.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 //
 // Get is a convenience wrapper around DefaultClient.Get.
 func Get(url string) (r *Response, finalURL string, err os.Error) {
@@ -156,7 +161,7 @@ func Get(url string) (r *Response, finalURL string, err os.Error) {
 // finalURL is the URL from which the response was fetched -- identical to the
 // input URL unless redirects were followed.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 func (c *Client) Get(url string) (r *Response, finalURL string, err os.Error) {
 	// TODO: if/when we add cookie support, the redirected request shouldn't
 	// necessarily supply the same cookies as the original.
@@ -183,7 +188,7 @@ func (c *Client) Get(url string) (r *Response, finalURL string, err os.Error) {
 			break
 		}
 		url = req.URL.String()
-		if r, err = send(&req, c.transport); err != nil {
+		if r, err = send(&req, c.Transport); err != nil {
 			break
 		}
 		if shouldRedirect(r.StatusCode) {
@@ -205,7 +210,7 @@ func (c *Client) Get(url string) (r *Response, finalURL string, err os.Error) {
 
 // Post issues a POST to the specified URL.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 //
 // Post is a wrapper around DefaultClient.Post
 func Post(url string, bodyType string, body io.Reader) (r *Response, err os.Error) {
@@ -214,7 +219,7 @@ func Post(url string, bodyType string, body io.Reader) (r *Response, err os.Erro
 
 // Post issues a POST to the specified URL.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 func (c *Client) Post(url string, bodyType string, body io.Reader) (r *Response, err os.Error) {
 	var req Request
 	req.Method = "POST"
@@ -232,13 +237,13 @@ func (c *Client) Post(url string, bodyType string, body io.Reader) (r *Response,
 		return nil, err
 	}
 
-	return send(&req, c.transport)
+	return send(&req, c.Transport)
 }
 
 // PostForm issues a POST to the specified URL, 
 // with data's keys and values urlencoded as the request body.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 //
 // PostForm is a wrapper around DefaultClient.PostForm
 func PostForm(url string, data map[string]string) (r *Response, err os.Error) {
@@ -248,7 +253,7 @@ func PostForm(url string, data map[string]string) (r *Response, err os.Error) {
 // PostForm issues a POST to the specified URL, 
 // with data's keys and values urlencoded as the request body.
 //
-// Caller should close r.Body when done reading it.
+// Caller should close r.Body when done reading from it.
 func (c *Client) PostForm(url string, data map[string]string) (r *Response, err os.Error) {
 	var req Request
 	req.Method = "POST"
@@ -268,7 +273,7 @@ func (c *Client) PostForm(url string, data map[string]string) (r *Response, err
 		return nil, err
 	}
 
-	return send(&req, c.transport)
+	return send(&req, c.Transport)
 }
 
 // TODO: remove this function when PostForm takes a multimap.
@@ -294,7 +299,7 @@ func (c *Client) Head(url string) (r *Response, err os.Error) {
 	if req.URL, err = ParseURL(url); err != nil {
 		return
 	}
-	return send(&req, c.transport)
+	return send(&req, c.Transport)
 }
 
 type nopCloser struct {

src/pkg/http/client_test.go

@@ -51,7 +51,7 @@ func (t *recordingTransport) Do(req *Request) (resp *Response, err os.Error) {
 
 func TestGetRequestFormat(t *testing.T) {
 	tr := &recordingTransport{}
-	client := &Client{transport: tr}
+	client := &Client{Transport: tr}
 	url := "http://dummy.faketld/"
 	client.Get(url) // Note: doesn't hit network
 	if tr.req.Method != "GET" {