net/http: follow certain redirects after POST requests

Fixes #4145

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6923055

src/pkg/net/http/client.go

@@ -120,7 +120,10 @@ func (c *Client) send(req *Request) (*Response, error) {
 // Generally Get, Post, or PostForm will be used instead of Do.
 func (c *Client) Do(req *Request) (resp *Response, err error) {
 	if req.Method == "GET" || req.Method == "HEAD" {
-		return c.doFollowingRedirects(req)
+		return c.doFollowingRedirects(req, shouldRedirectGet)
+	}
+	if req.Method == "POST" || req.Method == "PUT" {
+		return c.doFollowingRedirects(req, shouldRedirectPost)
 	}
 	return c.send(req)
 }
@@ -166,7 +169,7 @@ func send(req *Request, t RoundTripper) (resp *Response, err error) {
 
 // True if the specified HTTP status code is one for which the Get utility should
 // automatically redirect.
-func shouldRedirect(statusCode int) bool {
+func shouldRedirectGet(statusCode int) bool {
 	switch statusCode {
 	case StatusMovedPermanently, StatusFound, StatusSeeOther, StatusTemporaryRedirect:
 		return true
@@ -174,6 +177,16 @@ func shouldRedirect(statusCode int) bool {
 	return false
 }
 
+// True if the specified HTTP status code is one for which the Post utility should
+// automatically redirect.
+func shouldRedirectPost(statusCode int) bool {
+	switch statusCode {
+	case StatusFound, StatusSeeOther:
+		return true
+	}
+	return false
+}
+
 // Get issues a GET to the specified URL.  If the response is one of the following
 // redirect codes, Get follows the redirect, up to a maximum of 10 redirects:
 //
@@ -214,10 +227,10 @@ func (c *Client) Get(url string) (resp *Response, err error) {
 	if err != nil {
 		return nil, err
 	}
-	return c.doFollowingRedirects(req)
+	return c.doFollowingRedirects(req, shouldRedirectGet)
 }
 
-func (c *Client) doFollowingRedirects(ireq *Request) (resp *Response, err error) {
+func (c *Client) doFollowingRedirects(ireq *Request, shouldRedirect func(int) bool) (resp *Response, err error) {
 	// TODO: if/when we add cookie support, the redirected request shouldn't
 	// necessarily supply the same cookies as the original.
 	var base *url.URL
@@ -238,6 +251,9 @@ func (c *Client) doFollowingRedirects(ireq *Request) (resp *Response, err error)
 		if redirect != 0 {
 			req = new(Request)
 			req.Method = ireq.Method
+			if ireq.Method == "POST" || ireq.Method == "PUT" {
+				req.Method = "GET"
+			}
 			req.Header = make(Header)
 			req.URL, err = base.Parse(urlStr)
 			if err != nil {
@@ -321,7 +337,7 @@ func (c *Client) Post(url string, bodyType string, body io.Reader) (resp *Respon
 		return nil, err
 	}
 	req.Header.Set("Content-Type", bodyType)
-	return c.send(req)
+	return c.doFollowingRedirects(req, shouldRedirectPost)
 }
 
 // PostForm issues a POST to the specified URL, with data's keys and
@@ -371,5 +387,5 @@ func (c *Client) Head(url string) (resp *Response, err error) {
 	if err != nil {
 		return nil, err
 	}
-	return c.doFollowingRedirects(req)
+	return c.doFollowingRedirects(req, shouldRedirectGet)
 }

src/pkg/net/http/client_test.go

@@ -7,6 +7,7 @@
 package http_test
 
 import (
+	"bytes"
 	"crypto/tls"
 	"crypto/x509"
 	"errors"
@@ -246,6 +247,52 @@ func TestRedirects(t *testing.T) {
 	}
 }
 
+func TestPostRedirects(t *testing.T) {
+	var log struct {
+		sync.Mutex
+		bytes.Buffer
+	}
+	var ts *httptest.Server
+	ts = httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		log.Lock()
+		fmt.Fprintf(&log.Buffer, "%s %s ", r.Method, r.RequestURI)
+		log.Unlock()
+		if v := r.URL.Query().Get("code"); v != "" {
+			code, _ := strconv.Atoi(v)
+			if code/100 == 3 {
+				w.Header().Set("Location", ts.URL)
+			}
+			w.WriteHeader(code)
+		}
+	}))
+	tests := []struct {
+		suffix string
+		want   int // response code
+	}{
+		{"/", 200},
+		{"/?code=301", 301},
+		{"/?code=302", 200},
+		{"/?code=303", 200},
+		{"/?code=404", 404},
+	}
+	for _, tt := range tests {
+		res, err := Post(ts.URL+tt.suffix, "text/plain", strings.NewReader("Some content"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if res.StatusCode != tt.want {
+			t.Errorf("POST %s: status code = %d; want %d", tt.suffix, res.StatusCode, tt.want)
+		}
+	}
+	log.Lock()
+	got := log.String()
+	log.Unlock()
+	want := "POST / POST /?code=301 POST /?code=302 GET / POST /?code=303 GET / POST /?code=404 "
+	if got != want {
+		t.Errorf("Log differs.\n Got: %q\nWant: %q", got, want)
+	}
+}
+
 var expectedCookies = []*Cookie{
 	{Name: "ChocolateChip", Value: "tasty"},
 	{Name: "First", Value: "Hit"},