store: reword panic message and add test to check httputil client has…

… CheckRedirect defined

Signed-off-by: Zeyad Gouda <[email protected]>

httputil/client_test.go

@@ -100,6 +100,12 @@ func (s *clientSuite) TestClientProxyTakesUserAgent(c *check.C) {
 	c.Assert(called, check.Equals, true)
 }
 
+func (s *clientSuite) TestClientCheckRedirect(c *check.C) {
+	cli := httputil.NewHTTPClient(&httputil.ClientOptions{})
+	c.Assert(cli, check.NotNil)
+	c.Assert(cli.CheckRedirect, check.NotNil)
+}
+
 var privKey, _ = rsa.GenerateKey(rand.Reader, 768)
 
 // see crypto/tls/generate_cert.go

store/store_download.go

@@ -474,7 +474,7 @@ func downloadImpl(ctx context.Context, name, sha3_384, downloadURL string, user
 		cli := s.newHTTPClient(nil)
 		oldCheckRedirect := cli.CheckRedirect
 		if oldCheckRedirect == nil {
-			panic("internal error: CheckRedirect cannot be nil")
+			panic("internal error: the httputil.NewHTTPClient-produced http.Client must have CheckRedirect defined")
 		}
 		cli.CheckRedirect = func(req *http.Request, via []*http.Request) error {
 			// remove user/device auth headers from being sent in "CDN" redirects

store/store_download_test.go

@@ -1006,7 +1006,7 @@ func (s *storeDownloadSuite) TestDownloadNoCheckRedirectPanic(c *C) {
 	downloadFunc := func() {
 		s.store.Download(s.ctx, "foo", targetFn, &snap.DownloadInfo{}, nil, nil, nil)
 	}
-	c.Assert(downloadFunc, PanicMatches, "internal error: CheckRedirect cannot be nil")
+	c.Assert(downloadFunc, PanicMatches, "internal error: the httputil.NewHTTPClient-produced http.Client must have CheckRedirect defined")
 }
 
 func (s *storeDownloadSuite) TestDownloadInfiniteRedirect(c *C) {