http: add Location method to Response

Fixes #2300

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5117041

src/pkg/http/response.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"url"
 )
 
 var respExcludeHeader = map[string]bool{
@@ -77,6 +78,23 @@ func (r *Response) Cookies() []*Cookie {
 	return readSetCookies(r.Header)
 }
 
+var ErrNoLocation = os.NewError("http: no Location header in response")
+
+// Location returns the URL of the response's "Location" header,
+// if present.  Relative redirects are resolved relative to
+// the Response's Request.  ErrNoLocation is returned if no
+// Location header is present.
+func (r *Response) Location() (*url.URL, os.Error) {
+	lv := r.Header.Get("Location")
+	if lv == "" {
+		return nil, ErrNoLocation
+	}
+	if r.Request != nil && r.Request.URL != nil {
+		return r.Request.URL.Parse(lv)
+	}
+	return url.Parse(lv)
+}
+
 // ReadResponse reads and returns an HTTP response from r.  The
 // req parameter specifies the Request that corresponds to
 // this Response.  Clients must call resp.Body.Close when finished

src/pkg/http/response_test.go

@@ -15,6 +15,7 @@ import (
 	"io/ioutil"
 	"reflect"
 	"testing"
+	"url"
 )
 
 type respTest struct {
@@ -395,3 +396,52 @@ func diff(t *testing.T, prefix string, have, want interface{}) {
 		}
 	}
 }
+
+type responseLocationTest struct {
+	location string // Response's Location header or ""
+	requrl   string // Response.Request.URL or ""
+	want     string
+	wantErr  os.Error
+}
+
+var responseLocationTests = []responseLocationTest{
+	{"/foo", "http://bar.com/baz", "http://bar.com/foo", nil},
+	{"http://foo.com/", "http://bar.com/baz", "http://foo.com/", nil},
+	{"", "http://bar.com/baz", "", ErrNoLocation},
+}
+
+func TestLocationResponse(t *testing.T) {
+	for i, tt := range responseLocationTests {
+		res := new(Response)
+		res.Header = make(Header)
+		res.Header.Set("Location", tt.location)
+		if tt.requrl != "" {
+			res.Request = &Request{}
+			var err os.Error
+			res.Request.URL, err = url.Parse(tt.requrl)
+			if err != nil {
+				t.Fatalf("bad test URL %q: %v", tt.requrl, err)
+			}
+		}
+
+		got, err := res.Location()
+		if tt.wantErr != nil {
+			if err == nil {
+				t.Errorf("%d. err=nil; want %q", i, tt.wantErr)
+				continue
+			}
+			if g, e := err.String(), tt.wantErr.String(); g != e {
+				t.Errorf("%d. err=%q; want %q", i, g, e)
+				continue
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("%d. err=%q", i, err)
+			continue
+		}
+		if g, e := got.String(), tt.want; g != e {
+			t.Errorf("%d. Location=%q; want %q", i, g, e)
+		}
+	}
+}