fix(server): return -32602 for resource not found (SEP-2164)

src/mcp/server/mcpserver/exceptions.py

@@ -13,6 +13,10 @@ class ResourceError(MCPServerError):
     """Error in resource operations."""
 
 
+class ResourceNotFoundError(ResourceError):
+    """Resource does not exist."""
+
+
 class ToolError(MCPServerError):
     """Error in tool operations."""
 

src/mcp/server/mcpserver/server.py

@@ -31,7 +31,7 @@
 from mcp.server.lowlevel.server import LifespanResultT, Server
 from mcp.server.lowlevel.server import lifespan as default_lifespan
 from mcp.server.mcpserver.context import Context
-from mcp.server.mcpserver.exceptions import ResourceError
+from mcp.server.mcpserver.exceptions import ResourceError, ResourceNotFoundError
 from mcp.server.mcpserver.prompts import Prompt, PromptManager
 from mcp.server.mcpserver.resources import FunctionResource, Resource, ResourceManager
 from mcp.server.mcpserver.tools import Tool, ToolManager
@@ -44,6 +44,7 @@
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.exceptions import MCPError
 from mcp.types import (
+    INVALID_PARAMS,
     Annotations,
     BlobResourceContents,
     CallToolRequestParams,
@@ -332,7 +333,10 @@ 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 ResourceNotFoundError as err:
+            raise MCPError(code=INVALID_PARAMS, message=str(err), data={"uri": str(params.uri)})
         contents: list[TextResourceContents | BlobResourceContents] = []
         for item in results:
             if isinstance(item.content, bytes):
@@ -439,7 +443,7 @@ async def read_resource(
         try:
             resource = await self._resource_manager.get_resource(uri, context)
         except ValueError:
-            raise ResourceError(f"Unknown resource: {uri}")
+            raise ResourceNotFoundError(f"Unknown resource: {uri}")
 
         try:
             content = await resource.read()

tests/server/mcpserver/test_server.py

@@ -20,6 +20,7 @@
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.exceptions import MCPError
 from mcp.types import (
+    INVALID_PARAMS,
     AudioContent,
     BlobResourceContents,
     Completion,
@@ -692,13 +693,16 @@ def get_text():
             assert result.contents[0].text == "Hello, world!"
 
     async def test_read_unknown_resource(self):
-        """Test that reading an unknown resource raises MCPError."""
+        """Test that reading an unknown resource returns -32602 with uri in data (SEP-2164)."""
         mcp = MCPServer()
 
         async with Client(mcp) as client:
-            with pytest.raises(MCPError, match="Unknown resource: unknown://missing"):
+            with pytest.raises(MCPError, match="Unknown resource: unknown://missing") as exc_info:
                 await client.read_resource("unknown://missing")
 
+            assert exc_info.value.error.code == INVALID_PARAMS
+            assert exc_info.value.error.data == {"uri": "unknown://missing"}
+
     async def test_read_resource_error(self):
         """Test that resource read errors are properly wrapped in MCPError."""
         mcp = MCPServer()