net/http/client.go: fix cookie handling on (*Client) Do()

Fix the problem with no cookie handling when sending
other than GET or HEAD request through
(*Client) Do(*Request) (*Resposne, error).
https://code.google.com/p/go/issues/detail?id=3985

Adds a function (*Client) send(*Request) (*Reponse, error):
- sets cookies from CookieJar to request,
- sends request
- parses a reply cookies and updates CookieJar

Fixes #3985

R=bradfitz
CC=gobot, golang-dev
https://golang.org/cl/6653049

src/pkg/net/http/client.go

@@ -87,6 +87,22 @@ type readClose struct {
 	io.Closer
 }
 
+func (c *Client) send(req *Request) (*Response, error) {
+	if c.Jar != nil {
+		for _, cookie := range c.Jar.Cookies(req.URL) {
+			req.AddCookie(cookie)
+		}
+	}
+	resp, err := send(req, c.Transport)
+	if err != nil {
+		return nil, err
+	}
+	if c.Jar != nil {
+		c.Jar.SetCookies(req.URL, resp.Cookies())
+	}
+	return resp, err
+}
+
 // Do sends an HTTP request and returns an HTTP response, following
 // policy (e.g. redirects, cookies, auth) as configured on the client.
 //
@@ -106,7 +122,7 @@ func (c *Client) Do(req *Request) (resp *Response, err error) {
 	if req.Method == "GET" || req.Method == "HEAD" {
 		return c.doFollowingRedirects(req)
 	}
-	return send(req, c.Transport)
+	return c.send(req)
 }
 
 // send issues an HTTP request.
@@ -215,11 +231,6 @@ func (c *Client) doFollowingRedirects(ireq *Request) (resp *Response, err error)
 		return nil, errors.New("http: nil Request.URL")
 	}
 
-	jar := c.Jar
-	if jar == nil {
-		jar = blackHoleJar{}
-	}
-
 	req := ireq
 	urlStr := "" // next relative or absolute URL to fetch (after first request)
 	redirectFailed := false
@@ -247,16 +258,10 @@ func (c *Client) doFollowingRedirects(ireq *Request) (resp *Response, err error)
 			}
 		}
 
-		for _, cookie := range jar.Cookies(req.URL) {
-			req.AddCookie(cookie)
-		}
 		urlStr = req.URL.String()
-		if resp, err = send(req, c.Transport); err != nil {
+		if resp, err = c.send(req); err != nil {
 			break
 		}
-		if c := resp.Cookies(); len(c) > 0 {
-			jar.SetCookies(req.URL, c)
-		}
 
 		if shouldRedirect(resp.StatusCode) {
 			resp.Body.Close()
@@ -316,16 +321,7 @@ func (c *Client) Post(url string, bodyType string, body io.Reader) (resp *Respon
 		return nil, err
 	}
 	req.Header.Set("Content-Type", bodyType)
-	if c.Jar != nil {
-		for _, cookie := range c.Jar.Cookies(req.URL) {
-			req.AddCookie(cookie)
-		}
-	}
-	resp, err = send(req, c.Transport)
-	if err == nil && c.Jar != nil {
-		c.Jar.SetCookies(req.URL, resp.Cookies())
-	}
-	return
+	return c.send(req)
 }
 
 // PostForm issues a POST to the specified URL, with data's keys and

src/pkg/net/http/client_test.go

@@ -285,6 +285,10 @@ func TestClientSendsCookieFromJar(t *testing.T) {
 	req, _ := NewRequest("GET", us, nil)
 	client.Do(req) // Note: doesn't hit network
 	matchReturnedCookies(t, expectedCookies, tr.req.Cookies())
+
+	req, _ = NewRequest("POST", us, nil)
+	client.Do(req) // Note: doesn't hit network
+	matchReturnedCookies(t, expectedCookies, tr.req.Cookies())
 }
 
 // Just enough correctness for our redirect tests. Uses the URL.Host as the

src/pkg/net/http/jar.go

@@ -23,8 +23,3 @@ type CookieJar interface {
 	// restrictions such as in RFC 6265.
 	Cookies(u *url.URL) []*Cookie
 }
-
-type blackHoleJar struct{}
-
-func (blackHoleJar) SetCookies(u *url.URL, cookies []*Cookie) {}
-func (blackHoleJar) Cookies(u *url.URL) []*Cookie             { return nil }