fix: return resource-not-found error code

Author: sarvesh1327

src/mcp/server/mcpserver/resources/__init__.py

@@ -1,5 +1,5 @@
 from .base import Resource
-from .resource_manager import ResourceManager
+from .resource_manager import ResourceManager, UnknownResourceError
 from .templates import ResourceTemplate
 from .types import (
     BinaryResource,
@@ -20,4 +20,5 @@
     "DirectoryResource",
     "ResourceTemplate",
     "ResourceManager",
+    "UnknownResourceError",
 ]

src/mcp/server/mcpserver/resources/resource_manager.py

@@ -19,6 +19,10 @@
 logger = get_logger(__name__)
 
 
+class UnknownResourceError(ValueError):
+    """Raised when no registered resource or resource template matches a URI."""
+
+
 class ResourceManager:
     """Manages MCPServer resources."""
 
@@ -95,7 +99,7 @@ async def get_resource(self, uri: AnyUrl | str, context: Context[LifespanContext
                 except Exception as e:  # pragma: no cover
                     raise ValueError(f"Error creating resource from template: {e}")
 
-        raise ValueError(f"Unknown resource: {uri}")
+        raise UnknownResourceError(f"Unknown resource: {uri}")
 
     def list_resources(self) -> list[Resource]:
         """List all registered resources."""

src/mcp/server/mcpserver/server.py

@@ -33,7 +33,7 @@
 from mcp.server.mcpserver.context import Context
 from mcp.server.mcpserver.exceptions import ResourceError
 from mcp.server.mcpserver.prompts import Prompt, PromptManager
-from mcp.server.mcpserver.resources import FunctionResource, Resource, ResourceManager
+from mcp.server.mcpserver.resources import FunctionResource, Resource, ResourceManager, UnknownResourceError
 from mcp.server.mcpserver.tools import Tool, ToolManager
 from mcp.server.mcpserver.utilities.context_injection import find_context_parameter
 from mcp.server.mcpserver.utilities.logging import configure_logging, get_logger
@@ -44,6 +44,7 @@
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.exceptions import MCPError
 from mcp.types import (
+    RESOURCE_NOT_FOUND,
     Annotations,
     BlobResourceContents,
     CallToolRequestParams,
@@ -447,8 +448,11 @@ async def read_resource(
             context = Context(mcp_server=self)
         try:
             resource = await self._resource_manager.get_resource(uri, context)
+        except UnknownResourceError as exc:
+            raise MCPError(RESOURCE_NOT_FOUND, f"Unknown resource: {uri}") from exc
         except ValueError as exc:
-            raise ResourceError(f"Unknown resource: {uri}") from exc
+            logger.exception(f"Error getting resource {uri}")
+            raise ResourceError(f"Error reading resource {uri}") from exc
 
         try:
             content = await resource.read()

src/mcp/types/__init__.py

@@ -153,6 +153,7 @@
     METHOD_NOT_FOUND,
     PARSE_ERROR,
     REQUEST_TIMEOUT,
+    RESOURCE_NOT_FOUND,
     URL_ELICITATION_REQUIRED,
     ErrorData,
     JSONRPCError,
@@ -320,6 +321,7 @@
     "METHOD_NOT_FOUND",
     "PARSE_ERROR",
     "REQUEST_TIMEOUT",
+    "RESOURCE_NOT_FOUND",
     "URL_ELICITATION_REQUIRED",
     "ErrorData",
     "JSONRPCError",

src/mcp/types/jsonrpc.py

@@ -37,6 +37,9 @@ class JSONRPCResponse(BaseModel):
 
 
 # MCP-specific error codes in the range [-32000, -32099]
+RESOURCE_NOT_FOUND = -32002
+"""Error code indicating that a requested resource URI does not exist."""
+
 URL_ELICITATION_REQUIRED = -32042
 """Error code indicating that a URL mode elicitation is required before the request can be processed."""
 

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

@@ -6,6 +6,7 @@
 from mcp import MCPError
 from mcp.server.mcpserver import MCPServer
 from mcp.types import (
+    RESOURCE_NOT_FOUND,
     ErrorData,
     ListResourcesResult,
     ListResourceTemplatesResult,
@@ -114,7 +115,7 @@ 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 +128,9 @@ 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=RESOURCE_NOT_FOUND, message="Unknown resource: config://missing")
+    )
 
 
 @requirement("mcpserver:resource:read-throws-surfaced")
@@ -151,6 +154,24 @@ def boom() -> str:
     assert exc_info.value.error == snapshot(ErrorData(code=0, message="Error reading resource res://boom"))
 
 
+@requirement("mcpserver:resource:read-throws-surfaced")
+async def test_templated_resource_function_that_raises_is_not_reported_as_missing(connect: Connect) -> None:
+    """A matching resource template that raises is a read failure, not a missing resource."""
+    mcp = MCPServer("library")
+
+    @mcp.resource("users://{user_id}/profile")
+    def user_profile(user_id: str) -> str:
+        raise RuntimeError(f"profile unavailable for {user_id}")
+
+    async with connect(mcp) as client:
+        with pytest.raises(MCPError) as exc_info:
+            await client.read_resource("users://42/profile")
+
+    assert exc_info.value.error == snapshot(
+        ErrorData(code=0, message="Error reading resource users://42/profile")
+    )
+
+
 @requirement("mcpserver:resource:duplicate-name")
 async def test_registering_a_duplicate_resource_uri_warns_and_keeps_the_first(connect: Connect) -> None:
     """Registering a second static resource at an already-used URI keeps the first registration.