fix: LiteLLMA2ACardResolver

litellm/a2a_protocol/card_resolver.py

@@ -0,0 +1,97 @@
+"""
+Custom A2A Card Resolver for LiteLLM.
+
+Extends the A2A SDK's card resolver to support multiple well-known paths.
+"""
+
+from typing import TYPE_CHECKING, Any, Dict, Optional
+
+from litellm._logging import verbose_logger
+
+if TYPE_CHECKING:
+    from a2a.types import AgentCard
+
+# Runtime imports with availability check
+_A2ACardResolver: Any = None
+AGENT_CARD_WELL_KNOWN_PATH: str = "/.well-known/agent-card.json"
+PREV_AGENT_CARD_WELL_KNOWN_PATH: str = "/.well-known/agent.json"
+
+try:
+    from a2a.client import A2ACardResolver as _A2ACardResolver  # type: ignore[no-redef]
+    from a2a.utils.constants import (  # type: ignore[no-redef]
+        AGENT_CARD_WELL_KNOWN_PATH,
+        PREV_AGENT_CARD_WELL_KNOWN_PATH,
+    )
+except ImportError:
+    pass
+
+
+class LiteLLMA2ACardResolver(_A2ACardResolver):  # type: ignore[misc]
+    """
+    Custom A2A card resolver that supports multiple well-known paths.
+    
+    Extends the base A2ACardResolver to try both:
+    - /.well-known/agent-card.json (standard)
+    - /.well-known/agent.json (previous/alternative)
+    """
+    
+    async def get_agent_card(
+        self,
+        relative_card_path: Optional[str] = None,
+        http_kwargs: Optional[Dict[str, Any]] = None,
+    ) -> "AgentCard":
+        """
+        Fetch the agent card, trying multiple well-known paths.
+        
+        First tries the standard path, then falls back to the previous path.
+        
+        Args:
+            relative_card_path: Optional path to the agent card endpoint.
+                If None, tries both well-known paths.
+            http_kwargs: Optional dictionary of keyword arguments to pass to httpx.get
+            
+        Returns:
+            AgentCard from the A2A agent
+            
+        Raises:
+            A2AClientHTTPError or A2AClientJSONError if both paths fail
+        """
+        # If a specific path is provided, use the parent implementation
+        if relative_card_path is not None:
+            return await super().get_agent_card(
+                relative_card_path=relative_card_path,
+                http_kwargs=http_kwargs,
+            )
+        
+        # Try both well-known paths
+        paths = [
+            AGENT_CARD_WELL_KNOWN_PATH,
+            PREV_AGENT_CARD_WELL_KNOWN_PATH,
+        ]
+        
+        last_error = None
+        for path in paths:
+            try:
+                verbose_logger.debug(
+                    f"Attempting to fetch agent card from {self.base_url}{path}"
+                )
+                return await super().get_agent_card(
+                    relative_card_path=path,
+                    http_kwargs=http_kwargs,
+                )
+            except Exception as e:
+                verbose_logger.debug(
+                    f"Failed to fetch agent card from {self.base_url}{path}: {e}"
+                )
+                last_error = e
+                continue
+        
+        # If we get here, all paths failed - re-raise the last error
+        if last_error is not None:
+            raise last_error
+        
+        # This shouldn't happen, but just in case
+        raise Exception(
+            f"Failed to fetch agent card from {self.base_url}. "
+            f"Tried paths: {', '.join(paths)}"
+        )