fix: handle 429 response https://github.com/BeehiveInnovations/zen-mcp-server/issues/273

clink/parsers/gemini.py

@@ -23,8 +23,7 @@ class GeminiJSONParser(BaseParser):
             raise ParserError(f"Failed to decode Gemini CLI JSON output: {exc}") from exc
 
         response = payload.get("response")
-        if not isinstance(response, str) or not response.strip():
+        response_text = response.strip() if isinstance(response, str) else ""
-            raise ParserError("Gemini CLI response is missing a textual 'response' field")
 
         metadata: dict[str, Any] = {"raw": payload}
 
@@ -43,7 +42,57 @@ class GeminiJSONParser(BaseParser):
                 if isinstance(api_stats, dict):
                     metadata["latency_ms"] = api_stats.get("totalLatencyMs")
 
-        if stderr and stderr.strip():
+        if response_text:
-            metadata["stderr"] = stderr.strip()
+            if stderr and stderr.strip():
+                metadata["stderr"] = stderr.strip()
+            return ParsedCLIResponse(content=response_text, metadata=metadata)
 
-        return ParsedCLIResponse(content=response.strip(), metadata=metadata)
+        fallback_message, extra_metadata = self._build_fallback_message(payload, stderr)
+        if fallback_message:
+            metadata.update(extra_metadata)
+            if stderr and stderr.strip():
+                metadata["stderr"] = stderr.strip()
+            return ParsedCLIResponse(content=fallback_message, metadata=metadata)
+
+        raise ParserError("Gemini CLI response is missing a textual 'response' field")
+
+    def _build_fallback_message(self, payload: dict[str, Any], stderr: str) -> tuple[str | None, dict[str, Any]]:
+        """Derive a human friendly message when Gemini returns empty content."""
+
+        stderr_text = stderr.strip() if stderr else ""
+        stderr_lower = stderr_text.lower()
+        extra_metadata: dict[str, Any] = {"empty_response": True}
+
+        if "429" in stderr_lower or "rate limit" in stderr_lower:
+            extra_metadata["rate_limit_status"] = 429
+            message = (
+                "Gemini request returned no content because the API reported a 429 rate limit. "
+                "Retry after reducing the request size or waiting for quota to replenish."
+            )
+            return message, extra_metadata
+
+        stats = payload.get("stats")
+        if isinstance(stats, dict):
+            models = stats.get("models")
+            if isinstance(models, dict) and models:
+                first_model = next(iter(models.values()))
+                if isinstance(first_model, dict):
+                    api_stats = first_model.get("api")
+                    if isinstance(api_stats, dict):
+                        total_errors = api_stats.get("totalErrors")
+                        total_requests = api_stats.get("totalRequests")
+                        if isinstance(total_errors, int) and total_errors > 0:
+                            extra_metadata["api_total_errors"] = total_errors
+                            if isinstance(total_requests, int):
+                                extra_metadata["api_total_requests"] = total_requests
+                            message = (
+                                "Gemini CLI returned no textual output. The API reported "
+                                f"{total_errors} error(s); see stderr for details."
+                            )
+                            return message, extra_metadata
+
+        if stderr_text:
+            message = "Gemini CLI returned no textual output. Raw stderr was preserved for troubleshooting."
+            return message, extra_metadata
+
+        return None, extra_metadata

tests/test_clink_gemini_parser.py

@@ -0,0 +1,48 @@
+"""Tests for the Gemini CLI JSON parser."""
+
+import pytest
+
+from clink.parsers.gemini import GeminiJSONParser, ParserError
+
+
+def _build_rate_limit_stdout() -> str:
+    return (
+        "{\n"
+        '  "response": "",\n'
+        '  "stats": {\n'
+        '    "models": {\n'
+        '      "gemini-2.5-pro": {\n'
+        '        "api": {\n'
+        '          "totalRequests": 5,\n'
+        '          "totalErrors": 5,\n'
+        '          "totalLatencyMs": 13319\n'
+        "        },\n"
+        '        "tokens": {"prompt": 0, "candidates": 0, "total": 0, "cached": 0, "thoughts": 0, "tool": 0}\n'
+        "      }\n"
+        "    },\n"
+        '    "tools": {"totalCalls": 0},\n'
+        '    "files": {"totalLinesAdded": 0, "totalLinesRemoved": 0}\n'
+        "  }\n"
+        "}"
+    )
+
+
+def test_gemini_parser_handles_rate_limit_empty_response():
+    parser = GeminiJSONParser()
+    stdout = _build_rate_limit_stdout()
+    stderr = "Attempt 1 failed with status 429. Retrying with backoff... ApiError: quota exceeded"
+
+    parsed = parser.parse(stdout, stderr)
+
+    assert "429" in parsed.content
+    assert parsed.metadata.get("rate_limit_status") == 429
+    assert parsed.metadata.get("empty_response") is True
+    assert "Attempt 1 failed" in parsed.metadata.get("stderr", "")
+
+
+def test_gemini_parser_still_errors_when_no_fallback_available():
+    parser = GeminiJSONParser()
+    stdout = '{"response": "", "stats": {}}'
+
+    with pytest.raises(ParserError):
+        parser.parse(stdout, stderr="")