Merge pull request #186 from modelcontextprotocol/fix/141-resource-templates

fix: standardize resource response format

Author: dsp-ant

Diff for: src/mcp/client/session.py

@@ -120,6 +120,17 @@ async def list_resources(self) -> types.ListResourcesResult:
             types.ListResourcesResult,
         )
 
+    async def list_resource_templates(self) -> types.ListResourceTemplatesResult:
+        """Send a resources/templates/list request."""
+        return await self.send_request(
+            types.ClientRequest(
+                types.ListResourceTemplatesRequest(
+                    method="resources/templates/list",
+                )
+            ),
+            types.ListResourceTemplatesResult,
+        )
+
     async def read_resource(self, uri: AnyUrl) -> types.ReadResourceResult:
         """Send a resources/read request."""
         return await self.send_request(

Diff for: tests/issues/test_141_resource_templates.py

@@ -0,0 +1,118 @@
+import pytest
+from pydantic import AnyUrl
+
+from mcp.server.fastmcp import FastMCP
+from mcp.shared.memory import (
+    create_connected_server_and_client_session as client_session,
+)
+from mcp.types import (
+    ListResourceTemplatesResult,
+    TextResourceContents,
+)
+
+
+@pytest.mark.anyio
+async def test_resource_template_edge_cases():
+    """Test server-side resource template validation"""
+    mcp = FastMCP("Demo")
+
+    # Test case 1: Template with multiple parameters
+    @mcp.resource("resource://users/{user_id}/posts/{post_id}")
+    def get_user_post(user_id: str, post_id: str) -> str:
+        return f"Post {post_id} by user {user_id}"
+
+    # Test case 2: Template with optional parameter (should fail)
+    with pytest.raises(ValueError, match="Mismatch between URI parameters"):
+
+        @mcp.resource("resource://users/{user_id}/profile")
+        def get_user_profile(user_id: str, optional_param: str | None = None) -> str:
+            return f"Profile for user {user_id}"
+
+    # Test case 3: Template with mismatched parameters
+    with pytest.raises(ValueError, match="Mismatch between URI parameters"):
+
+        @mcp.resource("resource://users/{user_id}/profile")
+        def get_user_profile_mismatch(different_param: str) -> str:
+            return f"Profile for user {different_param}"
+
+    # Test case 4: Template with extra function parameters
+    with pytest.raises(ValueError, match="Mismatch between URI parameters"):
+
+        @mcp.resource("resource://users/{user_id}/profile")
+        def get_user_profile_extra(user_id: str, extra_param: str) -> str:
+            return f"Profile for user {user_id}"
+
+    # Test case 5: Template with missing function parameters
+    with pytest.raises(ValueError, match="Mismatch between URI parameters"):
+
+        @mcp.resource("resource://users/{user_id}/profile/{section}")
+        def get_user_profile_missing(user_id: str) -> str:
+            return f"Profile for user {user_id}"
+
+    # Verify valid template works
+    result = await mcp.read_resource("resource://users/123/posts/456")
+    assert result.content == "Post 456 by user 123"
+    assert result.mime_type == "text/plain"
+
+    # Verify invalid parameters raise error
+    with pytest.raises(ValueError, match="Unknown resource"):
+        await mcp.read_resource("resource://users/123/posts")  # Missing post_id
+
+    with pytest.raises(ValueError, match="Unknown resource"):
+        await mcp.read_resource(
+            "resource://users/123/posts/456/extra"
+        )  # Extra path component
+
+
+@pytest.mark.anyio
+async def test_resource_template_client_interaction():
+    """Test client-side resource template interaction"""
+    mcp = FastMCP("Demo")
+
+    # Register some templated resources
+    @mcp.resource("resource://users/{user_id}/posts/{post_id}")
+    def get_user_post(user_id: str, post_id: str) -> str:
+        return f"Post {post_id} by user {user_id}"
+
+    @mcp.resource("resource://users/{user_id}/profile")
+    def get_user_profile(user_id: str) -> str:
+        return f"Profile for user {user_id}"
+
+    async with client_session(mcp._mcp_server) as session:
+        # Initialize the session
+        await session.initialize()
+
+        # List available resources
+        resources = await session.list_resource_templates()
+        assert isinstance(resources, ListResourceTemplatesResult)
+        assert len(resources.resourceTemplates) == 2
+
+        # Verify resource templates are listed correctly
+        templates = [r.uriTemplate for r in resources.resourceTemplates]
+        assert "resource://users/{user_id}/posts/{post_id}" in templates
+        assert "resource://users/{user_id}/profile" in templates
+
+        # Read a resource with valid parameters
+        result = await session.read_resource(AnyUrl("resource://users/123/posts/456"))
+        contents = result.contents[0]
+        assert isinstance(contents, TextResourceContents)
+        assert contents.text == "Post 456 by user 123"
+        assert contents.mimeType == "text/plain"
+
+        # Read another resource with valid parameters
+        result = await session.read_resource(AnyUrl("resource://users/789/profile"))
+        contents = result.contents[0]
+        assert isinstance(contents, TextResourceContents)
+        assert contents.text == "Profile for user 789"
+        assert contents.mimeType == "text/plain"
+
+        # Verify invalid resource URIs raise appropriate errors
+        with pytest.raises(Exception):  # Specific exception type may vary
+            await session.read_resource(
+                AnyUrl("resource://users/123/posts")
+            )  # Missing post_id
+
+        with pytest.raises(Exception):  # Specific exception type may vary
+            await session.read_resource(
+                AnyUrl("resource://users/123/invalid")
+            )  # Invalid template