fix(mcpserver): return resource not found code

src/mcp/server/mcpserver/exceptions.py

@@ -12,6 +12,10 @@ class ValidationError(MCPServerError):
 class ResourceError(MCPServerError):
     """Error in resource operations."""
 
+    def __init__(self, message: str, code: int | None = None):
+        super().__init__(message)
+        self.code = code
+
 
 class ToolError(MCPServerError):
     """Error in tool operations."""

src/mcp/server/mcpserver/server.py

@@ -341,7 +341,13 @@ async def _handle_read_resource(
         self, ctx: ServerRequestContext[LifespanResultT], params: ReadResourceRequestParams
     ) -> ReadResourceResult:
         context = Context(request_context=ctx, mcp_server=self)
-        results = await self.read_resource(params.uri, context)
+        try:
+            results = await self.read_resource(params.uri, context)
+        except ResourceError as exc:
+            if exc.code is not None:
+                message = f"Resource not found: {params.uri}" if exc.code == -32002 else str(exc)
+                raise MCPError(code=exc.code, message=message) from exc
+            raise
         contents: list[TextResourceContents | BlobResourceContents] = []
         for item in results:
             if isinstance(item.content, bytes):
@@ -448,7 +454,7 @@ async def read_resource(
         try:
             resource = await self._resource_manager.get_resource(uri, context)
         except ValueError as exc:
-            raise ResourceError(f"Unknown resource: {uri}") from exc
+            raise ResourceError(f"Resource not found: {uri}", code=-32002) from exc
 
         try:
             content = await resource.read()

tests/interaction/_requirements.py

@@ -901,12 +901,6 @@ def __post_init__(self) -> None:
     "mcpserver:resource:unknown-uri": Requirement(
         source=f"{SPEC_BASE_URL}/server/resources#error-handling",
         behavior="resources/read for a URI matching no registered resource returns JSON-RPC error -32002.",
-        divergence=Divergence(
-            note=(
-                "The spec reserves -32002 for resource-not-found; MCPServer raises ResourceError, which "
-                "the low-level server converts to error code 0."
-            ),
-        ),
     ),
     # ═══════════════════════════════════════════════════════════════════════════
     # Prompts

tests/interaction/mcpserver/test_resources.py

@@ -114,7 +114,7 @@ def user_profile(user_id: str) -> str:
 async def test_read_unknown_uri_is_error(connect: Connect) -> None:
     """Reading a URI that matches no registered resource fails with a JSON-RPC error.
 
-    The spec reserves -32002 for resource-not-found; see the divergence note on the requirement.
+    The spec reserves -32002 for resource-not-found.
     """
     mcp = MCPServer("library")
 
@@ -127,7 +127,7 @@ def app_config() -> str:
         with pytest.raises(MCPError) as exc_info:
             await client.read_resource("config://missing")
 
-    assert exc_info.value.error == snapshot(ErrorData(code=0, message="Unknown resource: config://missing"))
+    assert exc_info.value.error == snapshot(ErrorData(code=-32002, message="Resource not found: config://missing"))
 
 
 @requirement("mcpserver:resource:read-throws-surfaced")

tests/issues/test_141_resource_templates.py

@@ -55,10 +55,10 @@ def get_user_profile_missing(user_id: str) -> str:  # pragma: no cover
     assert result_list[0].mime_type == "text/plain"
 
     # Verify invalid parameters raise error
-    with pytest.raises(ResourceError, match="Unknown resource"):
+    with pytest.raises(ResourceError, match="Resource not found"):
         await mcp.read_resource("resource://users/123/posts")  # Missing post_id
 
-    with pytest.raises(ResourceError, match="Unknown resource"):
+    with pytest.raises(ResourceError, match="Resource not found"):
         await mcp.read_resource("resource://users/123/posts/456/extra")  # Extra path component
 
 

tests/server/mcpserver/test_server.py

@@ -730,7 +730,7 @@ async def test_read_unknown_resource(self):
         mcp = MCPServer()
 
         async with Client(mcp) as client:
-            with pytest.raises(MCPError, match="Unknown resource: unknown://missing"):
+            with pytest.raises(MCPError, match="Resource not found: unknown://missing"):
                 await client.read_resource("unknown://missing")
 
     async def test_read_resource_error(self):