Support Gradio queue protocol with diff streaming and call fallback

gr2gw.go

@@ -1205,6 +1205,18 @@ func extractGradioErrorMessage(dataStr string) string {
   return clean
 }
 
+func isProtocolOrInputError(errMsg string) bool {
+  lower := strings.ToLower(errMsg)
+  return strings.Contains(lower, "check gradio inputs/types") ||
+    strings.Contains(lower, "null error") ||
+    strings.Contains(lower, "typeerror") ||
+    strings.Contains(lower, "missing") ||
+    strings.Contains(lower, "required positional argument") ||
+    strings.Contains(lower, "internal server error") ||
+    strings.Contains(lower, "not found") ||
+    strings.Contains(lower, "unknown upstream gradio error")
+}
+
 type Streamer struct {
   w       http.ResponseWriter
   flusher http.Flusher
@@ -1622,6 +1634,7 @@ type SpaceDiscovery struct {
   Models                 []string            `json:"models"`
   PrimaryModel           string              `json:"primary_model"`
   TotalInputs            int                 `json:"total_inputs"`
+  RawTotalInputs         int                 `json:"raw_total_inputs,omitempty"`
   ParamMappings          []SpaceParamMapping `json:"param_mappings"`
   DefaultInputs          []interface{}       `json:"default_inputs"`
   MessageIsMultimodal    bool                `json:"message_is_multimodal"`
@@ -2270,6 +2283,7 @@ func InspectSpace(client *http.Client, rawURL, userAgent string) (*SpaceDiscover
   // 6. Correlate with config.dependencies to determine exact input count & state padding
   if bestMatchingDep != nil {
     discovery.TotalInputs = len(bestMatchingDep.Inputs)
+    discovery.RawTotalInputs = len(bestMatchingDep.Inputs)
     discovery.DefaultInputs = make([]interface{}, len(bestMatchingDep.Inputs))
     discovery.ParamMappings = nil
     discovery.MessageIndex = -1
@@ -3062,9 +3076,45 @@ type GradioOutputFrame struct {
   Content   string
   Reasoning string
   ToolCalls []ToolCall
+  IsDelta   bool
   OK        bool
 }
 
+// extractGradioDiffDelta extracts delta string from Gradio 6 streaming diff operations
+func extractGradioDiffDelta(v []interface{}) (string, bool) {
+  if len(v) == 0 {
+    return "", false
+  }
+  if len(v) >= 3 {
+    if op, ok := v[0].(string); ok && (op == "append" || op == "add") {
+      if delta, ok := v[2].(string); ok {
+        return delta, true
+      }
+    }
+  }
+  for _, item := range v {
+    if innerList, ok := item.([]interface{}); ok && len(innerList) > 0 {
+      for _, opItem := range innerList {
+        if opArr, ok := opItem.([]interface{}); ok && len(opArr) >= 3 {
+          if op, ok := opArr[0].(string); ok && (op == "append" || op == "add") {
+            if delta, ok := opArr[2].(string); ok {
+              return delta, true
+            }
+          }
+        }
+      }
+      if len(innerList) >= 3 {
+        if op, ok := innerList[0].(string); ok && (op == "append" || op == "add") {
+          if delta, ok := innerList[2].(string); ok {
+            return delta, true
+          }
+        }
+      }
+    }
+  }
+  return "", false
+}
+
 // ParseGradioStreamOutput extracts structured content, reasoning, and tool calls from Gradio output
 func ParseGradioStreamOutput(rawJSON string) (frame GradioOutputFrame) {
   defer func() {
@@ -3093,6 +3143,13 @@ func ParseGradioStreamOutput(rawJSON string) (frame GradioOutputFrame) {
       return frame
     }
 
+    if delta, ok := extractGradioDiffDelta(v); ok {
+      frame.Content = delta
+      frame.IsDelta = true
+      frame.OK = true
+      return frame
+    }
+
     // 1. Check if v[0] is an inner slice with len >= 3 (e.g. Hy3: [[content, reasoning, tool_calls, history]])
     if inner, ok := v[0].([]interface{}); ok && len(inner) >= 3 {
       s0, _ := inner[0].(string)
@@ -3344,8 +3401,20 @@ func (g *GradioGateway) executePredictCompletion(w http.ResponseWriter, r *http.
     fnIndex = 0
   }
 
+  predictData := make([]interface{}, len(gradioData))
+  copy(predictData, gradioData)
+  if disc.RawTotalInputs > len(predictData) {
+    for i := len(predictData); i < disc.RawTotalInputs; i++ {
+      var defVal interface{}
+      if i < len(disc.DefaultInputs) {
+        defVal = disc.DefaultInputs[i]
+      }
+      predictData = append(predictData, defVal)
+    }
+  }
+
   payloadMap := map[string]interface{}{
-    "data":         gradioData,
+    "data":         predictData,
     "fn_index":     fnIndex,
     "session_hash": GenerateUUID(),
   }
@@ -3453,6 +3522,417 @@ func (g *GradioGateway) executePredictCompletion(w http.ResponseWriter, r *http.
   return nil
 }
 
+// executeQueueCompletion handles completions using Gradio queue SSE protocol (/queue/join + /queue/data).
+func (g *GradioGateway) executeQueueCompletion(w http.ResponseWriter, r *http.Request, disc *SpaceDiscovery, gradioData []interface{}, req ChatCompletionRequest, completionID string, createdTime int64, modelName, effUA string) error {
+  fnIndex := disc.FnIndex
+  if fnIndex < 0 {
+    fnIndex = 0
+  }
+
+  queueData := make([]interface{}, len(gradioData))
+  copy(queueData, gradioData)
+  if disc.RawTotalInputs > len(queueData) {
+    for i := len(queueData); i < disc.RawTotalInputs; i++ {
+      var defVal interface{}
+      if i < len(disc.DefaultInputs) {
+        defVal = disc.DefaultInputs[i]
+      }
+      queueData = append(queueData, defVal)
+    }
+  }
+
+  sessionHash := GenerateUUID()
+  payloadMap := map[string]interface{}{
+    "data":         queueData,
+    "fn_index":     fnIndex,
+    "session_hash": sessionHash,
+  }
+
+  jsonPayload, err := json.Marshal(payloadMap)
+  if err != nil {
+    return fmt.Errorf("failed to marshal queue payload: %w", err)
+  }
+
+  var joinURLs []string
+  if disc.APIPrefix != "" {
+    joinURLs = append(joinURLs, fmt.Sprintf("%s%s/queue/join", disc.SpaceURL, disc.APIPrefix))
+  }
+  joinURLs = append(joinURLs, fmt.Sprintf("%s/queue/join", disc.SpaceURL))
+
+  var resp *http.Response
+  var lastErr error
+
+  for _, targetURL := range joinURLs {
+    curURL := targetURL
+    makeReq := func() (*http.Request, error) {
+      req, err := http.NewRequest("POST", curURL, bytes.NewBuffer(jsonPayload))
+      if err != nil {
+        return nil, err
+      }
+      req.Header.Set("Content-Type", "application/json")
+      req.Header.Set("User-Agent", effUA)
+      return req, nil
+    }
+    resp, lastErr = DoWithFibonacciRetry(g.client, makeReq, 3)
+    if lastErr == nil && resp != nil && resp.StatusCode == http.StatusOK {
+      break
+    }
+    if resp != nil {
+      resp.Body.Close()
+      resp = nil
+    }
+  }
+
+  if resp == nil {
+    log.Printf("Gradio /queue/join unavailable (%v), falling back to /run/predict protocol...", lastErr)
+    return g.executePredictCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+  }
+  resp.Body.Close()
+
+  // 2. Connect to Gradio SSE queue data stream
+  var dataURLs []string
+  if disc.APIPrefix != "" {
+    dataURLs = append(dataURLs, fmt.Sprintf("%s%s/queue/data?session_hash=%s", disc.SpaceURL, disc.APIPrefix, sessionHash))
+  }
+  dataURLs = append(dataURLs, fmt.Sprintf("%s/queue/data?session_hash=%s", disc.SpaceURL, sessionHash))
+
+  var streamResp *http.Response
+  for _, targetURL := range dataURLs {
+    curURL := targetURL
+    makeStreamReq := func() (*http.Request, error) {
+      req, err := http.NewRequest("GET", curURL, nil)
+      if err != nil {
+        return nil, err
+      }
+      req.Header.Set("Accept", "text/event-stream")
+      req.Header.Set("User-Agent", effUA)
+      return req, nil
+    }
+    streamResp, lastErr = DoWithFibonacciRetry(g.client, makeStreamReq, 3)
+    if lastErr == nil && streamResp != nil && streamResp.StatusCode == http.StatusOK {
+      break
+    }
+    if streamResp != nil {
+      streamResp.Body.Close()
+      streamResp = nil
+    }
+  }
+
+  if streamResp == nil {
+    log.Printf("Gradio /queue/data unavailable (%v), falling back to /run/predict protocol...", lastErr)
+    return g.executePredictCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+  }
+  defer streamResp.Body.Close()
+
+  type queueMsg struct {
+    Msg     string                 `json:"msg"`
+    EventID string                 `json:"event_id,omitempty"`
+    Success *bool                  `json:"success,omitempty"`
+    Output  map[string]interface{} `json:"output,omitempty"`
+  }
+
+  // 3. Handle Non-Streaming vs Streaming
+  if !req.Stream {
+    reader := bufio.NewReader(streamResp.Body)
+    var latestFrame GradioOutputFrame
+
+    for {
+      line, err := reader.ReadString('\n')
+      if err != nil {
+        break
+      }
+      line = strings.TrimRight(line, "\r\n")
+
+      if strings.HasPrefix(line, "data: ") {
+        dataStr := strings.TrimPrefix(line, "data: ")
+        var qMsg queueMsg
+        if err := json.Unmarshal([]byte(dataStr), &qMsg); err != nil {
+          continue
+        }
+
+        if qMsg.Msg == "close_stream" {
+          break
+        }
+
+        if qMsg.Msg == "process_generating" || qMsg.Msg == "process_completed" {
+          if qMsg.Success != nil && !*qMsg.Success {
+            errBytes, _ := json.Marshal(qMsg.Output)
+            errMsg := extractGradioErrorMessage(string(errBytes))
+            log.Printf("Upstream Gradio error: %s", errMsg)
+            return fmt.Errorf("upstream Gradio error: %s", errMsg)
+          }
+
+          if qMsg.Output != nil && qMsg.Output["data"] != nil {
+            dataBytes, _ := json.Marshal(qMsg.Output["data"])
+            frame := ParseGradioStreamOutput(string(dataBytes))
+            if frame.OK {
+              if frame.IsDelta {
+                latestFrame.Content += frame.Content
+              } else {
+                if frame.Content != "" || latestFrame.Content == "" {
+                  latestFrame.Content = frame.Content
+                }
+              }
+              if frame.Reasoning != "" || latestFrame.Reasoning == "" {
+                latestFrame.Reasoning = frame.Reasoning
+              }
+              if len(frame.ToolCalls) > 0 {
+                latestFrame.ToolCalls = frame.ToolCalls
+              }
+              latestFrame.OK = true
+            }
+          }
+          if qMsg.Msg == "process_completed" {
+            break
+          }
+        }
+      }
+    }
+
+    if !latestFrame.OK {
+      return fmt.Errorf("upstream Gradio space returned empty or unparseable response")
+    }
+
+    cleanText := latestFrame.Content
+    reasoning := latestFrame.Reasoning
+    toolCalls := latestFrame.ToolCalls
+    hasTools := len(toolCalls) > 0
+
+    if reasoning == "" {
+      cleanText, reasoning = ExtractThinking(cleanText)
+    }
+    if !hasTools {
+      toolCalls, cleanText, hasTools = DetectToolCalls(cleanText)
+    }
+
+    finishReason := "stop"
+    var finalContent interface{} = cleanText
+    if hasTools && len(toolCalls) > 0 {
+      finishReason = "tool_calls"
+      if strings.TrimSpace(cleanText) == "" {
+        finalContent = nil
+      }
+    }
+
+    WriteCompletionResponse(w, completionID, createdTime, modelName, FinalOutput{
+      Content:          finalContent,
+      ReasoningContent: reasoning,
+      ToolCalls:        toolCalls,
+      FinishReason:     finishReason,
+    })
+    disc.Protocol = "queue"
+    return nil
+  }
+
+  // 4. Streaming Mode
+  flusher, _ := w.(http.Flusher)
+  streamer := NewStreamer(w, flusher, completionID, createdTime, modelName)
+
+  thinkFilter := NewStreamThinkingFilter()
+  toolFilter := NewStreamToolCallFilter()
+
+  reader := bufio.NewReader(streamResp.Body)
+  var prevContent string
+  var prevReasoning string
+  prevToolArgs := make(map[int]string)
+  nativeReasoningSeen := false
+  nativeToolCallsSeen := false
+  var streamErr error
+
+  for {
+    line, err := reader.ReadString('\n')
+    if err != nil {
+      break
+    }
+    line = strings.TrimRight(line, "\r\n")
+
+    if strings.HasPrefix(line, "data: ") {
+      dataStr := strings.TrimPrefix(line, "data: ")
+      var qMsg queueMsg
+      if err := json.Unmarshal([]byte(dataStr), &qMsg); err != nil {
+        continue
+      }
+
+      if qMsg.Msg == "close_stream" {
+        break
+      }
+
+      if qMsg.Msg == "process_generating" || qMsg.Msg == "process_completed" {
+        if qMsg.Success != nil && !*qMsg.Success {
+          errBytes, _ := json.Marshal(qMsg.Output)
+          errMsg := extractGradioErrorMessage(string(errBytes))
+          log.Printf("Upstream Gradio error: %s", errMsg)
+          if !streamer.started {
+            return fmt.Errorf("upstream Gradio error: %s", errMsg)
+          }
+          streamer.Error(errMsg)
+          streamErr = fmt.Errorf("upstream Gradio error: %s", errMsg)
+          break
+        }
+
+        if qMsg.Output != nil && qMsg.Output["data"] != nil {
+          dataBytes, _ := json.Marshal(qMsg.Output["data"])
+          frame := ParseGradioStreamOutput(string(dataBytes))
+          if frame.OK {
+            // 1. Native reasoning handling
+            if frame.Reasoning != "" || nativeReasoningSeen {
+              nativeReasoningSeen = true
+              if len(frame.Reasoning) > len(prevReasoning) && strings.HasPrefix(frame.Reasoning, prevReasoning) {
+                delta := frame.Reasoning[len(prevReasoning):]
+                streamer.Reasoning(delta)
+                prevReasoning = frame.Reasoning
+              } else if prevReasoning == "" && frame.Reasoning != "" {
+                streamer.Reasoning(frame.Reasoning)
+                prevReasoning = frame.Reasoning
+              }
+            }
+
+            // 2. Native tool call handling
+            if len(frame.ToolCalls) > 0 || nativeToolCallsSeen {
+              nativeToolCallsSeen = true
+              for i, tc := range frame.ToolCalls {
+                prevArgs := prevToolArgs[i]
+                fullArgs := tc.Function.Arguments
+                if len(fullArgs) > len(prevArgs) && strings.HasPrefix(fullArgs, prevArgs) {
+                  deltaArgs := fullArgs[len(prevArgs):]
+                  iCopy := i
+                  streamer.ToolCallDelta(ToolCall{
+                    Index: &iCopy,
+                    ID:    tc.ID,
+                    Type:  tc.Type,
+                    Function: ToolCallFunction{
+                      Name:      tc.Function.Name,
+                      Arguments: deltaArgs,
+                    },
+                  })
+                  prevToolArgs[i] = fullArgs
+                } else if prevArgs == "" {
+                  iCopy := i
+                  streamer.ToolCallDelta(ToolCall{
+                    Index: &iCopy,
+                    ID:    tc.ID,
+                    Type:  tc.Type,
+                    Function: ToolCallFunction{
+                      Name:      tc.Function.Name,
+                      Arguments: fullArgs,
+                    },
+                  })
+                  prevToolArgs[i] = fullArgs
+                }
+              }
+            }
+
+            // 3. Content handling
+            currentText := frame.Content
+            var delta string
+            if frame.IsDelta {
+              delta = frame.Content
+              prevContent += delta
+            } else {
+              if strings.HasPrefix(currentText, prevContent) {
+                delta = currentText[len(prevContent):]
+              } else if prevContent == "" {
+                delta = currentText
+              } else {
+                delta = currentText
+              }
+              prevContent = currentText
+            }
+
+            if delta != "" {
+              if nativeReasoningSeen || nativeToolCallsSeen {
+                if nativeReasoningSeen && nativeToolCallsSeen {
+                  streamer.Content(delta)
+                } else if nativeReasoningSeen {
+                  toolFilter.Feed(delta, func(cleanChunk string) {
+                    if cleanChunk != "" {
+                      streamer.Content(cleanChunk)
+                    }
+                  }, func(tc ToolCall) {
+                    streamer.ToolCallDelta(tc)
+                  })
+                } else {
+                  thinkFilter.Feed(delta, func(contentChunk string) {
+                    if contentChunk != "" {
+                      streamer.Content(contentChunk)
+                    }
+                  }, func(reasoningChunk string) {
+                    if reasoningChunk != "" {
+                      streamer.Reasoning(reasoningChunk)
+                    }
+                  })
+                }
+              } else {
+                thinkFilter.Feed(delta, func(contentChunk string) {
+                  toolFilter.Feed(contentChunk, func(cleanChunk string) {
+                    if cleanChunk != "" {
+                      streamer.Content(cleanChunk)
+                    }
+                  }, func(tc ToolCall) {
+                    streamer.ToolCallDelta(tc)
+                  })
+                }, func(reasoningChunk string) {
+                  if reasoningChunk != "" {
+                    streamer.Reasoning(reasoningChunk)
+                  }
+                })
+              }
+            }
+          }
+        }
+        if qMsg.Msg == "process_completed" {
+          break
+        }
+      }
+    }
+  }
+
+  if streamErr != nil {
+    return streamErr
+  }
+
+  // Flush remaining tokens in filters if used
+  if !nativeReasoningSeen {
+    thinkFilter.Flush(func(contentChunk string) {
+      if !nativeToolCallsSeen {
+        toolFilter.Feed(contentChunk, func(cleanChunk string) {
+          if cleanChunk != "" {
+            streamer.Content(cleanChunk)
+          }
+        }, func(tc ToolCall) {
+          streamer.ToolCallDelta(tc)
+        })
+      } else if contentChunk != "" {
+        streamer.Content(contentChunk)
+      }
+    }, func(reasoningChunk string) {
+      if reasoningChunk != "" {
+        streamer.Reasoning(reasoningChunk)
+      }
+    })
+  }
+
+  if !nativeToolCallsSeen {
+    toolFilter.Flush(func(cleanChunk string) {
+      if cleanChunk != "" {
+        streamer.Content(cleanChunk)
+      }
+    }, func(tc ToolCall) {
+      streamer.ToolCallDelta(tc)
+    })
+  }
+
+  finishReason := "stop"
+  if nativeToolCallsSeen || toolFilter.emittedCall {
+    finishReason = "tool_calls"
+  }
+
+  streamer.Finish(finishReason)
+  streamer.Done()
+  disc.Protocol = "queue"
+  return nil
+}
+
 // ExecuteChatCompletion handles both streaming and non-streaming requests.
 func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Request, req ChatCompletionRequest) error {
   effUA := EffectiveUserAgent(r)
@@ -3488,12 +3968,18 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
   if disc.Protocol == "predict" {
     return g.executePredictCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
   }
+  if disc.Protocol == "queue" {
+    return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+  }
 
   isV2 := disc.Protocol == "call_v2"
   buildPayload := func(v2 bool) ([]byte, error) {
     if v2 {
       v2Payload := make(map[string]interface{})
       for idx, val := range gradioData {
+        if idx < len(disc.ParamMappings) && disc.ParamMappings[idx].ParamType == "state" {
+          continue
+        }
         pName := ""
         if idx < len(disc.ParamMappings) {
           if disc.ParamMappings[idx].ParamName != "" {
@@ -3602,9 +4088,9 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
           return nil
         }
       }
-      if strings.Contains(err.Error(), "404") || strings.Contains(err.Error(), "405") {
+      if strings.Contains(err.Error(), "404") || strings.Contains(err.Error(), "405") || strings.Contains(err.Error(), "500") {
-        log.Printf("Gradio /call endpoint unavailable (%v), falling back to /run/predict protocol...", err)
+        log.Printf("Gradio /call endpoint unavailable (%v), falling back to /queue/join protocol...", err)
-        return g.executePredictCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+        return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
       }
       return fmt.Errorf("upstream Gradio call error: %w", err)
     }
@@ -3613,8 +4099,8 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
 
   var joinRes GradioJoinResponse
   if err := json.NewDecoder(resp.Body).Decode(&joinRes); err != nil || joinRes.EventID == "" {
-    log.Printf("Gradio /call returned non-SSE response, falling back to /run/predict protocol...")
+    log.Printf("Gradio /call returned non-SSE response, falling back to /queue/join protocol...")
-    return g.executePredictCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+    return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
   }
 
   // 2. Connect to Gradio SSE EventStream
@@ -3652,7 +4138,8 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
         return nil
       }
     }
-    return fmt.Errorf("upstream Gradio stream error: %w", err)
+    log.Printf("Gradio /call stream connection failed (%v), falling back to /queue/join protocol...", err)
+    return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
   }
   defer streamResp.Body.Close()
 
@@ -3687,6 +4174,10 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
             }
           }
           errMsg := extractGradioErrorMessage(dataStr)
+          if isProtocolOrInputError(errMsg) {
+            log.Printf("Upstream Gradio /call stream error (%s), falling back to /queue/join protocol...", errMsg)
+            return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+          }
           log.Printf("Upstream Gradio error: %s", errMsg)
           return fmt.Errorf("upstream Gradio error: %s", errMsg)
         }
@@ -3785,10 +4276,15 @@ func (g *GradioGateway) ExecuteChatCompletion(w http.ResponseWriter, r *http.Req
           }
         }
         errMsg := extractGradioErrorMessage(dataStr)
-        log.Printf("Upstream Gradio error: %s", errMsg)
         if !streamer.started {
+          if isProtocolOrInputError(errMsg) {
+            log.Printf("Upstream Gradio /call stream error (%s), falling back to /queue/join protocol...", errMsg)
+            return g.executeQueueCompletion(w, r, disc, gradioData, req, completionID, createdTime, modelName, effUA)
+          }
+          log.Printf("Upstream Gradio error: %s", errMsg)
           return fmt.Errorf("upstream Gradio error: %s", errMsg)
         }
+        log.Printf("Upstream Gradio error: %s", errMsg)
         streamer.Error(errMsg)
         streamErr = fmt.Errorf("upstream Gradio error: %s", errMsg)
         break

gr2gw_test.go

@@ -2321,6 +2321,196 @@ func TestGradio6CallV2Protocol(t *testing.T) {
   }
 }
 
+// TestGradioQueueProtocol verifies direct queue join and queue data streaming.
+func TestGradioQueueProtocol(t *testing.T) {
+  var joinReached bool
+  var receivedFnIndex int
+
+  ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+    if r.URL.Path == "/gradio_api/queue/join" {
+      joinReached = true
+      var body struct {
+        Data        []interface{} `json:"data"`
+        FnIndex     int           `json:"fn_index"`
+        SessionHash string        `json:"session_hash"`
+      }
+      if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+        http.Error(w, err.Error(), http.StatusBadRequest)
+        return
+      }
+      receivedFnIndex = body.FnIndex
+      w.Header().Set("Content-Type", "application/json")
+      json.NewEncoder(w).Encode(map[string]interface{}{"event_id": "evt-q-1"})
+      return
+    }
+
+    if strings.HasPrefix(r.URL.Path, "/gradio_api/queue/data") {
+      w.Header().Set("Content-Type", "text/event-stream")
+      flusher, _ := w.(http.Flusher)
+      fmt.Fprintf(w, "data: {\"msg\":\"process_generating\",\"output\":{\"data\":[\"Hello\",null]},\"success\":true}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      fmt.Fprintf(w, "data: {\"msg\":\"process_generating\",\"output\":{\"data\":[[[\"append\",[],\" world!\"]]]},\"success\":true}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      fmt.Fprintf(w, "data: {\"msg\":\"process_completed\",\"output\":{\"data\":[\"Hello world!\",null]},\"success\":true}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      fmt.Fprintf(w, "data: {\"msg\":\"close_stream\"}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      return
+    }
+
+    http.NotFound(w, r)
+  }))
+  defer ts.Close()
+
+  gw := NewGradioGateway(ts.URL, "", 10*time.Second)
+  disc := &SpaceDiscovery{
+    SpaceURL:      ts.URL,
+    APIPrefix:     "/gradio_api",
+    Protocol:      "queue",
+    FnIndex:       7,
+    TotalInputs:   1,
+    RawTotalInputs: 2,
+    DefaultInputs: []interface{}{nil, nil},
+    ParamMappings: []SpaceParamMapping{
+      {InputIndex: 0, ParamType: "message"},
+      {InputIndex: 1, ParamType: "state"},
+    },
+  }
+  gw.discoveries[ts.URL] = disc
+  disc.LastDiscovered = time.Now()
+
+  req := ChatCompletionRequest{
+    Model:    "default",
+    Messages: []ChatMessage{{Role: "user", Content: "Hi"}},
+  }
+  httpReq := httptest.NewRequest("POST", "/v1/chat/completions", nil)
+  rec := httptest.NewRecorder()
+
+  err := gw.ExecuteChatCompletion(rec, httpReq, req)
+  if err != nil {
+    t.Fatalf("ExecuteChatCompletion failed: %v", err)
+  }
+  if !joinReached {
+    t.Errorf("expected /gradio_api/queue/join to be reached")
+  }
+  if receivedFnIndex != 7 {
+    t.Errorf("expected fn_index 7, got %d", receivedFnIndex)
+  }
+
+  var resp ChatCompletionResponse
+  if err := json.NewDecoder(rec.Body).Decode(&resp); err != nil {
+    t.Fatalf("failed to decode response: %v", err)
+  }
+  if len(resp.Choices) == 0 || resp.Choices[0].Message.Content != "Hello world!" {
+    t.Errorf("expected content 'Hello world!', got %v", resp.Choices)
+  }
+}
+
+// TestGradioCallFallbackToQueue verifies that when /call returns a protocol or input binding error,
+// the gateway automatically falls back to /queue/join and completes successfully.
+func TestGradioCallFallbackToQueue(t *testing.T) {
+  var callReached, queueReached bool
+
+  ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+    if r.URL.Path == "/gradio_api/call/v2/lisa_stream" {
+      callReached = true
+      w.Header().Set("Content-Type", "application/json")
+      json.NewEncoder(w).Encode(map[string]interface{}{"event_id": "call-err-1"})
+      return
+    }
+
+    if r.URL.Path == "/gradio_api/call/lisa_stream/call-err-1" {
+      w.Header().Set("Content-Type", "text/event-stream")
+      flusher, _ := w.(http.Flusher)
+      fmt.Fprintf(w, "event: error\ndata: {\"error\": null}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      return
+    }
+
+    if r.URL.Path == "/gradio_api/queue/join" {
+      queueReached = true
+      w.Header().Set("Content-Type", "application/json")
+      json.NewEncoder(w).Encode(map[string]interface{}{"event_id": "queue-succ-1"})
+      return
+    }
+
+    if strings.HasPrefix(r.URL.Path, "/gradio_api/queue/data") {
+      w.Header().Set("Content-Type", "text/event-stream")
+      flusher, _ := w.(http.Flusher)
+      fmt.Fprintf(w, "data: {\"msg\":\"process_completed\",\"output\":{\"data\":[\"Recovered via queue!\",null]},\"success\":true}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      fmt.Fprintf(w, "data: {\"msg\":\"close_stream\"}\n\n")
+      if flusher != nil {
+        flusher.Flush()
+      }
+      return
+    }
+
+    http.NotFound(w, r)
+  }))
+  defer ts.Close()
+
+  gw := NewGradioGateway(ts.URL, "", 10*time.Second)
+  disc := &SpaceDiscovery{
+    SpaceURL:      ts.URL,
+    APIPrefix:     "/gradio_api",
+    Endpoint:      "/lisa_stream",
+    CleanEndpoint: "lisa_stream",
+    Protocol:      "call_v2",
+    FnIndex:       7,
+    TotalInputs:   1,
+    RawTotalInputs: 2,
+    DefaultInputs: []interface{}{nil, nil},
+    ParamMappings: []SpaceParamMapping{
+      {InputIndex: 0, ParamName: "message", ParamType: "message"},
+    },
+  }
+  gw.discoveries[ts.URL] = disc
+  disc.LastDiscovered = time.Now()
+
+  req := ChatCompletionRequest{
+    Model:    "default",
+    Messages: []ChatMessage{{Role: "user", Content: "Test fallback"}},
+  }
+  httpReq := httptest.NewRequest("POST", "/v1/chat/completions", nil)
+  rec := httptest.NewRecorder()
+
+  err := gw.ExecuteChatCompletion(rec, httpReq, req)
+  if err != nil {
+    t.Fatalf("ExecuteChatCompletion failed: %v", err)
+  }
+  if !callReached {
+    t.Errorf("expected /call to be attempted first")
+  }
+  if !queueReached {
+    t.Errorf("expected fallback to /queue/join")
+  }
+
+  var resp ChatCompletionResponse
+  if err := json.NewDecoder(rec.Body).Decode(&resp); err != nil {
+    t.Fatalf("failed to decode response: %v", err)
+  }
+  if len(resp.Choices) == 0 || resp.Choices[0].Message.Content != "Recovered via queue!" {
+    t.Errorf("expected content 'Recovered via queue!', got %v", resp.Choices)
+  }
+  if disc.Protocol != "queue" {
+    t.Errorf("expected disc.Protocol to be switched to 'queue', got %s", disc.Protocol)
+  }
+}
+
+