net/http: fix redirect logic to handle mutations of cookies

In the situation where the Client.Jar is set and the Request.Header
has cookies manually inserted, the redirect logic needs to be
able to apply changes to cookies from "Set-Cookie" headers to both
the Jar and the manually inserted Header cookies.

Since Header cookies lack information about the original domain
and path, the logic in this CL simply removes cookies from the
initial Header if any subsequent "Set-Cookie" matches. Thus,
in the event of cookie conflicts, the logic preserves the behavior
prior to change made in golang.org/cl/28930.

Fixes #17494
Updates #4800

Change-Id: I645194d9f97ff4d95bd07ca36de1d6cdf2f32429
Reviewed-on: https://go-review.googlesource.com/31435Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/client.go

@@ -18,6 +18,7 @@ import (
 	"io/ioutil"
 	"log"
 	"net/url"
+	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -444,10 +445,10 @@ func (c *Client) doFollowingRedirects(req *Request, shouldRedirect func(int) boo
 	}
 
 	var (
-		deadline = c.deadline()
-		reqs     []*Request
-		resp     *Response
-		ireqhdr  = req.Header.clone()
+		deadline    = c.deadline()
+		reqs        []*Request
+		resp        *Response
+		copyHeaders = c.makeHeadersCopier(req)
 	)
 	uerr := func(err error) error {
 		req.closeBody()
@@ -495,17 +496,13 @@ func (c *Client) doFollowingRedirects(req *Request, shouldRedirect func(int) boo
 				req.Method = "GET"
 				req.Body = nil // TODO: fix this when 307/308 support happens
 			}
-			// Copy the initial request's Header values
-			// (at least the safe ones).  Do this before
-			// setting the Referer, in case the user set
-			// Referer on their first request. If they
-			// really want to override, they can do it in
+
+			// Copy original headers before setting the Referer,
+			// in case the user set Referer on their first request.
+			// If they really want to override, they can do it in
 			// their CheckRedirect func.
-			for k, vv := range ireqhdr {
-				if shouldCopyHeaderOnRedirect(k, ireq.URL, u) {
-					req.Header[k] = vv
-				}
-			}
+			copyHeaders(req)
+
 			// Add the Referer header from the most recent
 			// request URL to the new one, if it's not https->http:
 			if ref := refererForURL(reqs[len(reqs)-1].URL, req.URL); ref != "" {
@@ -561,6 +558,70 @@ func (c *Client) doFollowingRedirects(req *Request, shouldRedirect func(int) boo
 	}
 }
 
+// makeHeadersCopier makes a function that copies headers from the
+// initial Request, ireq. For every redirect, this function must be called
+// so that it can copy headers into the upcoming Request.
+func (c *Client) makeHeadersCopier(ireq *Request) func(*Request) {
+	// The headers to copy are from the very initial request.
+	// We use a closured callback to keep a reference to these original headers.
+	var (
+		ireqhdr  = ireq.Header.clone()
+		icookies map[string][]*Cookie
+	)
+	if c.Jar != nil && ireq.Header.Get("Cookie") != "" {
+		icookies = make(map[string][]*Cookie)
+		for _, c := range ireq.Cookies() {
+			icookies[c.Name] = append(icookies[c.Name], c)
+		}
+	}
+
+	preq := ireq // The previous request
+	return func(req *Request) {
+		// If Jar is present and there was some initial cookies provided
+		// via the request header, then we may need to alter the initial
+		// cookies as we follow redirects since each redirect may end up
+		// modifying a pre-existing cookie.
+		//
+		// Since cookies already set in the request header do not contain
+		// information about the original domain and path, the logic below
+		// assumes any new set cookies override the original cookie
+		// regardless of domain or path.
+		//
+		// See https://golang.org/issue/17494
+		if c.Jar != nil && icookies != nil {
+			var changed bool
+			resp := req.Response // The response that caused the upcoming redirect
+			for _, c := range resp.Cookies() {
+				if _, ok := icookies[c.Name]; ok {
+					delete(icookies, c.Name)
+					changed = true
+				}
+			}
+			if changed {
+				ireqhdr.Del("Cookie")
+				var ss []string
+				for _, cs := range icookies {
+					for _, c := range cs {
+						ss = append(ss, c.Name+"="+c.Value)
+					}
+				}
+				sort.Strings(ss) // Ensure deterministic headers
+				ireqhdr.Set("Cookie", strings.Join(ss, "; "))
+			}
+		}
+
+		// Copy the initial request's Header values
+		// (at least the safe ones).
+		for k, vv := range ireqhdr {
+			if shouldCopyHeaderOnRedirect(k, preq.URL, req.URL) {
+				req.Header[k] = vv
+			}
+		}
+
+		preq = req // Update previous Request with the current request
+	}
+}
+
 func defaultCheckRedirect(req *Request, via []*Request) error {
 	if len(via) >= 10 {
 		return errors.New("stopped after 10 redirects")
@@ -625,7 +686,7 @@ func (c *Client) PostForm(url string, data url.Values) (resp *Response, err erro
 	return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
 }
 
-// Head issues a HEAD to the specified URL.  If the response is one of
+// Head issues a HEAD to the specified URL. If the response is one of
 // the following redirect codes, Head follows the redirect, up to a
 // maximum of 10 redirects:
 //
@@ -639,7 +700,7 @@ func Head(url string) (resp *Response, err error) {
 	return DefaultClient.Head(url)
 }
 
-// Head issues a HEAD to the specified URL.  If the response is one of the
+// Head issues a HEAD to the specified URL. If the response is one of the
 // following redirect codes, Head follows the redirect after calling the
 // Client's CheckRedirect function:
 //

src/net/http/client_test.go

@@ -19,6 +19,7 @@ import (
 	"log"
 	"net"
 	. "net/http"
+	"net/http/cookiejar"
 	"net/http/httptest"
 	"net/url"
 	"reflect"
@@ -1296,6 +1297,101 @@ func TestClientCopyHeadersOnRedirect(t *testing.T) {
 	}
 }
 
+// Issue 17494: cookies should be altered when Client follows redirects.
+func TestClientAltersCookiesOnRedirect(t *testing.T) {
+	cookieMap := func(cs []*Cookie) map[string][]string {
+		m := make(map[string][]string)
+		for _, c := range cs {
+			m[c.Name] = append(m[c.Name], c.Value)
+		}
+		return m
+	}
+
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		var want map[string][]string
+		got := cookieMap(r.Cookies())
+
+		c, _ := r.Cookie("Cycle")
+		switch c.Value {
+		case "0":
+			want = map[string][]string{
+				"Cookie1": []string{"OldValue1a", "OldValue1b"},
+				"Cookie2": []string{"OldValue2"},
+				"Cookie3": []string{"OldValue3a", "OldValue3b"},
+				"Cookie4": []string{"OldValue4"},
+				"Cycle":   []string{"0"},
+			}
+			SetCookie(w, &Cookie{Name: "Cycle", Value: "1", Path: "/"})
+			SetCookie(w, &Cookie{Name: "Cookie2", Path: "/", MaxAge: -1}) // Delete cookie from Header
+			Redirect(w, r, "/", StatusFound)
+		case "1":
+			want = map[string][]string{
+				"Cookie1": []string{"OldValue1a", "OldValue1b"},
+				"Cookie3": []string{"OldValue3a", "OldValue3b"},
+				"Cookie4": []string{"OldValue4"},
+				"Cycle":   []string{"1"},
+			}
+			SetCookie(w, &Cookie{Name: "Cycle", Value: "2", Path: "/"})
+			SetCookie(w, &Cookie{Name: "Cookie3", Value: "NewValue3", Path: "/"}) // Modify cookie in Header
+			SetCookie(w, &Cookie{Name: "Cookie4", Value: "NewValue4", Path: "/"}) // Modify cookie in Jar
+			Redirect(w, r, "/", StatusFound)
+		case "2":
+			want = map[string][]string{
+				"Cookie1": []string{"OldValue1a", "OldValue1b"},
+				"Cookie3": []string{"NewValue3"},
+				"Cookie4": []string{"NewValue4"},
+				"Cycle":   []string{"2"},
+			}
+			SetCookie(w, &Cookie{Name: "Cycle", Value: "3", Path: "/"})
+			SetCookie(w, &Cookie{Name: "Cookie5", Value: "NewValue5", Path: "/"}) // Insert cookie into Jar
+			Redirect(w, r, "/", StatusFound)
+		case "3":
+			want = map[string][]string{
+				"Cookie1": []string{"OldValue1a", "OldValue1b"},
+				"Cookie3": []string{"NewValue3"},
+				"Cookie4": []string{"NewValue4"},
+				"Cookie5": []string{"NewValue5"},
+				"Cycle":   []string{"3"},
+			}
+			// Don't redirect to ensure the loop ends.
+		default:
+			t.Errorf("unexpected redirect cycle")
+			return
+		}
+
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("redirect %s, Cookie = %v, want %v", c.Value, got, want)
+		}
+	}))
+	defer ts.Close()
+
+	tr := &Transport{}
+	defer tr.CloseIdleConnections()
+	jar, _ := cookiejar.New(nil)
+	c := &Client{
+		Transport: tr,
+		Jar:       jar,
+	}
+
+	u, _ := url.Parse(ts.URL)
+	req, _ := NewRequest("GET", ts.URL, nil)
+	req.AddCookie(&Cookie{Name: "Cookie1", Value: "OldValue1a"})
+	req.AddCookie(&Cookie{Name: "Cookie1", Value: "OldValue1b"})
+	req.AddCookie(&Cookie{Name: "Cookie2", Value: "OldValue2"})
+	req.AddCookie(&Cookie{Name: "Cookie3", Value: "OldValue3a"})
+	req.AddCookie(&Cookie{Name: "Cookie3", Value: "OldValue3b"})
+	jar.SetCookies(u, []*Cookie{&Cookie{Name: "Cookie4", Value: "OldValue4", Path: "/"}})
+	jar.SetCookies(u, []*Cookie{&Cookie{Name: "Cycle", Value: "0", Path: "/"}})
+	res, err := c.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	if res.StatusCode != 200 {
+		t.Fatal(res.Status)
+	}
+}
+
 // Part of Issue 4800
 func TestShouldCopyHeaderOnRedirect(t *testing.T) {
 	tests := []struct {