httpcli: Content-Length as obj type indicator

For higher level clients using ResponseClassAuto (e.g. scheduler
callers) infer the response object type based on the Content-Length
header in the HTTP response. Streaming responses using recordio will not
have sent a Content-Length header, whereas "singleton" JSON object
responses will have one.

api/v1/lib/httpcli/http.go

@@ -299,13 +299,21 @@ func validateSuccessfulResponse(codec encoding.Codec, res *http.Response, rc cli
 	return nil
 }
 
-func newSourceFactory(rc client.ResponseClass) encoding.SourceFactoryFunc {
+func newSourceFactory(rc client.ResponseClass, knownLen bool) encoding.SourceFactoryFunc {
 	switch rc {
 	case client.ResponseClassNoData:
 		return nil
 	case client.ResponseClassSingleton:
 		return encoding.SourceReader
-	case client.ResponseClassStreaming, client.ResponseClassAuto:
+	case client.ResponseClassStreaming:
+		return recordIOSourceFactory
+	case client.ResponseClassAuto:
+		// Some operations return the same content-type header (json) but actually
+		// return different content types (recordio vs singleton json obj).
+		// Check the content-length header to distinguish between these cases.
+		if knownLen {
+			return encoding.SourceReader
+		}
 		return recordIOSourceFactory
 	default:
 		panic(fmt.Sprintf("unsupported response-class: %q", rc))
@@ -344,7 +352,7 @@ func (c *Client) HandleResponse(res *http.Response, rc client.ResponseClass, err
 	case http.StatusOK:
 		debug.Log("request OK, decoding response")
 
-		sf := newSourceFactory(rc)
+		sf := newSourceFactory(rc, res.ContentLength > -1)
 		if sf == nil {
 			if rc != client.ResponseClassNoData {
 				panic("nil Source for response that expected data")

api/v1/lib/httpcli/http_test.go

@@ -50,23 +50,25 @@ func TestPrepareForResponse(t *testing.T) {
 
 func TestNewSourceFactory(t *testing.T) {
 	for ti, tc := range []struct {
-		rc         client.ResponseClass
-		wantsNil   bool
-		wantsPanic bool
+		rc          client.ResponseClass
+		knownLength bool
+		wantsNil    bool
+		wantsPanic  bool
 	}{
-		{client.ResponseClass(-1), false, true},
-		{client.ResponseClassNoData, true, false},
-		{client.ResponseClassAuto, false, false},
-		{client.ResponseClassSingleton, false, false},
-		{client.ResponseClassStreaming, false, false},
+		{client.ResponseClass(-1), false, false, true},
+		{client.ResponseClassNoData, false, true, false},
+		{client.ResponseClassAuto, false, false, false},
+		{client.ResponseClassAuto, true, false, false},
+		{client.ResponseClassSingleton, false, false, false},
+		{client.ResponseClassStreaming, false, false, false},
 	} {
 		f := func() encoding.SourceFactoryFunc {
 			defer func() {
 				if x := recover(); (x != nil) != tc.wantsPanic {
 					panic(x)
 				}
 			}()
-			return newSourceFactory(tc.rc)
+			return newSourceFactory(tc.rc, tc.knownLength)
 		}()
 		if tc.wantsPanic {
 			continue