Make sure both the x-etags are always set

httpcache.go

@@ -101,6 +101,10 @@ type Transport struct {
 	// An empty string signals that this request should not be cached.
 	CacheKey func(req *http.Request) string
 
+	// AlwaysUseCachedResponse is an optional func that when it returns true
+	// a successful response from the cache will be returned without connecting to the server.
+	AlwaysUseCachedResponse func(req *http.Request, key string) bool
+
 	// Around is an optional func.
 	// If set, the Transport will call Around at the start of RoundTrip
 	// and defer the returned func until the end of RoundTrip.
@@ -141,6 +145,9 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 	var cachedResp *http.Response
 	if cacheable {
 		cachedResp, err = t.cachedResponse(req)
+		if err == nil && cachedResp != nil && t.AlwaysUseCachedResponse != nil && t.AlwaysUseCachedResponse(req, cacheKey) {
+			return cachedResp, nil
+		}
 	} else {
 		// Need to invalidate an existing value
 		t.Cache.Delete(cacheKey)
@@ -242,7 +249,11 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 			if t.EnableETagPair {
 				if etag := resp.Header.Get("etag"); etag != "" {
 					resp.Header.Set(XETag1, etag)
-					resp.Header.Set(XETag2, cachedXEtag)
+					etag2 := cachedXEtag
+					if etag2 == "" {
+						etag2 = etag
+					}
+					resp.Header.Set(XETag2, etag2)
 				} else {
 					etagHash = md5.New()
 					r = struct {
@@ -261,8 +272,11 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 					if etagHash != nil {
 						md5Str := hex.EncodeToString(etagHash.Sum(nil))
 						resp.Header.Set(XETag1, md5Str)
-						resp.Header.Set(XETag2, cachedXEtag)
-
+						etag2 := cachedXEtag
+						if etag2 == "" {
+							etag2 = md5Str
+						}
+						resp.Header.Set(XETag2, etag2)
 					}
 					resp := *resp
 					resp.Body = io.NopCloser(r)

httpcache_test.go

@@ -224,7 +224,7 @@ func TestEnableETagPair(t *testing.T) {
 		_, resp := doMethod(t, "GET", "/etag", nil)
 		c.Assert(resp.StatusCode, qt.Equals, http.StatusOK)
 		c.Assert(resp.Header.Get(XETag1), qt.Equals, "124567")
-		c.Assert(resp.Header.Get(XETag2), qt.Equals, "")
+		c.Assert(resp.Header.Get(XETag2), qt.Equals, "124567")
 	}
 	{
 		_, resp := doMethod(t, "GET", "/etag", nil)
@@ -238,7 +238,7 @@ func TestEnableETagPair(t *testing.T) {
 		_, resp := doMethod(t, "GET", "/helloheaderasbody", map[string]string{"Hello": "world1"})
 		c.Assert(resp.StatusCode, qt.Equals, http.StatusOK)
 		c.Assert(resp.Header.Get(XETag1), qt.Equals, "48b21a691481958c34cc165011bdb9bc")
-		c.Assert(resp.Header.Get(XETag2), qt.Equals, "")
+		c.Assert(resp.Header.Get(XETag2), qt.Equals, "48b21a691481958c34cc165011bdb9bc")
 	}
 	{
 		_, resp := doMethod(t, "GET", "/helloheaderasbody", map[string]string{"Hello": "world2"})
@@ -248,6 +248,27 @@ func TestEnableETagPair(t *testing.T) {
 	}
 }
 
+func TestAlwaysUseCachedResponse(t *testing.T) {
+	resetTest()
+	c := qt.New(t)
+	s.transport.AlwaysUseCachedResponse = func(req *http.Request, key string) bool {
+		return req.Header.Get("Hello") == "world2"
+	}
+
+	{
+		s, _ := doMethod(t, "GET", "/helloheaderasbody", map[string]string{"Hello": "world1"})
+		c.Assert(s, qt.Equals, "world1")
+	}
+	{
+		s, _ := doMethod(t, "GET", "/helloheaderasbody", map[string]string{"Hello": "world2"})
+		c.Assert(s, qt.Equals, "world1")
+	}
+	{
+		s, _ := doMethod(t, "GET", "/helloheaderasbody", map[string]string{"Hello": "world3"})
+		c.Assert(s, qt.Equals, "world3")
+	}
+}
+
 func TestAround(t *testing.T) {
 	resetTest()
 	c := qt.New(t)