mcp: unexport incidentally exported error codes

Unexport error codes that were accidentally exported. I don't think it's
possible that they could be useful for users (see #535).

Fixes #535

Author: findleyr

mcp/client.go

@@ -283,21 +283,21 @@ func (c *Client) listRoots(_ context.Context, req *ListRootsRequest) (*ListRoots
 func (c *Client) createMessage(ctx context.Context, req *CreateMessageRequest) (*CreateMessageResult, error) {
 	if c.opts.CreateMessageHandler == nil {
 		// TODO: wrap or annotate this error? Pick a standard code?
-		return nil, jsonrpc2.NewError(CodeUnsupportedMethod, "client does not support CreateMessage")
+		return nil, jsonrpc2.NewError(codeUnsupportedMethod, "client does not support CreateMessage")
 	}
 	return c.opts.CreateMessageHandler(ctx, req)
 }
 
 func (c *Client) elicit(ctx context.Context, req *ElicitRequest) (*ElicitResult, error) {
 	if c.opts.ElicitationHandler == nil {
 		// TODO: wrap or annotate this error? Pick a standard code?
-		return nil, jsonrpc2.NewError(CodeUnsupportedMethod, "client does not support elicitation")
+		return nil, jsonrpc2.NewError(codeUnsupportedMethod, "client does not support elicitation")
 	}
 
 	// Validate that the requested schema only contains top-level properties without nesting
 	schema, err := validateElicitSchema(req.Params.RequestedSchema)
 	if err != nil {
-		return nil, jsonrpc2.NewError(CodeInvalidParams, err.Error())
+		return nil, jsonrpc2.NewError(codeInvalidParams, err.Error())
 	}
 
 	res, err := c.opts.ElicitationHandler(ctx, req)
@@ -312,11 +312,11 @@ func (c *Client) elicit(ctx context.Context, req *ElicitRequest) (*ElicitResult,
 		// this code to the server?
 		resolved, err := schema.Resolve(nil)
 		if err != nil {
-			return nil, jsonrpc2.NewError(CodeInvalidParams, fmt.Sprintf("failed to resolve requested schema: %v", err))
+			return nil, jsonrpc2.NewError(codeInvalidParams, fmt.Sprintf("failed to resolve requested schema: %v", err))
 		}
 
 		if err := resolved.Validate(res.Content); err != nil {
-			return nil, jsonrpc2.NewError(CodeInvalidParams, fmt.Sprintf("elicitation result content does not match requested schema: %v", err))
+			return nil, jsonrpc2.NewError(codeInvalidParams, fmt.Sprintf("elicitation result content does not match requested schema: %v", err))
 		}
 	}
 

mcp/mcp_test.go

@@ -322,7 +322,7 @@ func TestEndToEnd(t *testing.T) {
 		} {
 			rres, err := cs.ReadResource(ctx, &ReadResourceParams{URI: tt.uri})
 			if err != nil {
-				if code := errorCode(err); code == CodeResourceNotFound {
+				if code := errorCode(err); code == codeResourceNotFound {
 					if tt.mimeType != "" {
 						t.Errorf("%s: not found but expected it to be", tt.uri)
 					}
@@ -994,8 +994,8 @@ func TestElicitationUnsupportedMethod(t *testing.T) {
 	if err == nil {
 		t.Error("expected error when ElicitationHandler is not provided, got nil")
 	}
-	if code := errorCode(err); code != CodeUnsupportedMethod {
-		t.Errorf("got error code %d, want %d (CodeUnsupportedMethod)", code, CodeUnsupportedMethod)
+	if code := errorCode(err); code != codeUnsupportedMethod {
+		t.Errorf("got error code %d, want %d (CodeUnsupportedMethod)", code, codeUnsupportedMethod)
 	}
 	if !strings.Contains(err.Error(), "does not support elicitation") {
 		t.Errorf("error should mention unsupported elicitation, got: %v", err)
@@ -1342,8 +1342,8 @@ func TestElicitationSchemaValidation(t *testing.T) {
 				t.Errorf("expected error for invalid schema %q, got nil", tc.name)
 				return
 			}
-			if code := errorCode(err); code != CodeInvalidParams {
-				t.Errorf("got error code %d, want %d (CodeInvalidParams)", code, CodeInvalidParams)
+			if code := errorCode(err); code != codeInvalidParams {
+				t.Errorf("got error code %d, want %d (CodeInvalidParams)", code, codeInvalidParams)
 			}
 			if !strings.Contains(err.Error(), tc.expectedError) {
 				t.Errorf("error message %q does not contain expected text %q", err.Error(), tc.expectedError)
@@ -1462,8 +1462,8 @@ func TestElicitationCapabilityDeclaration(t *testing.T) {
 		if err == nil {
 			t.Error("expected UnsupportedMethod error when no capability declared")
 		}
-		if code := errorCode(err); code != CodeUnsupportedMethod {
-			t.Errorf("got error code %d, want %d (CodeUnsupportedMethod)", code, CodeUnsupportedMethod)
+		if code := errorCode(err); code != codeUnsupportedMethod {
+			t.Errorf("got error code %d, want %d (CodeUnsupportedMethod)", code, codeUnsupportedMethod)
 		}
 	})
 }

mcp/resource.go

@@ -41,7 +41,7 @@ type ResourceHandler func(context.Context, *ReadResourceRequest) (*ReadResourceR
 // not be found.
 func ResourceNotFoundError(uri string) error {
 	return &jsonrpc2.WireError{
-		Code:    CodeResourceNotFound,
+		Code:    codeResourceNotFound,
 		Message: "Resource not found",
 		Data:    json.RawMessage(fmt.Sprintf(`{"uri":%q}`, uri)),
 	}

mcp/server.go

@@ -526,7 +526,7 @@ func (s *Server) getPrompt(ctx context.Context, req *GetPromptRequest) (*GetProm
 	if !ok {
 		// Return a proper JSON-RPC error with the correct error code
 		return nil, &jsonrpc2.WireError{
-			Code:    CodeInvalidParams,
+			Code:    codeInvalidParams,
 			Message: fmt.Sprintf("unknown prompt %q", req.Params.Name),
 		}
 	}
@@ -553,7 +553,7 @@ func (s *Server) callTool(ctx context.Context, req *CallToolRequest) (*CallToolR
 	s.mu.Unlock()
 	if !ok {
 		return nil, &jsonrpc2.WireError{
-			Code:    CodeInvalidParams,
+			Code:    codeInvalidParams,
 			Message: fmt.Sprintf("unknown tool %q", req.Params.Name),
 		}
 	}

mcp/shared.go

@@ -331,13 +331,11 @@ func clientSessionMethod[P Params, R Result](f func(*ClientSession, context.Cont
 
 // Error codes
 const (
-	// TODO: should these be unexported?
-
-	CodeResourceNotFound = -32002
+	codeResourceNotFound = -32002
 	// The error code if the method exists and was called properly, but the peer does not support it.
-	CodeUnsupportedMethod = -31001
+	codeUnsupportedMethod = -31001
 	// The error code for invalid parameters
-	CodeInvalidParams = -32602
+	codeInvalidParams = -32602
 )
 
 // notifySessions calls Notify on all the sessions.

mcp/tool_test.go

@@ -66,7 +66,7 @@ func TestToolErrorHandling(t *testing.T) {
 	// Create a tool that returns a structured error
 	structuredErrorHandler := func(ctx context.Context, req *CallToolRequest, args map[string]any) (*CallToolResult, any, error) {
 		return nil, nil, &jsonrpc2.WireError{
-			Code:    CodeInvalidParams,
+			Code:    codeInvalidParams,
 			Message: "internal server error",
 		}
 	}
@@ -111,8 +111,8 @@ func TestToolErrorHandling(t *testing.T) {
 			t.Fatalf("expected WireError, got %[1]T: %[1]v", err)
 		}
 
-		if wireErr.Code != CodeInvalidParams {
-			t.Errorf("expected error code %d, got %d", CodeInvalidParams, wireErr.Code)
+		if wireErr.Code != codeInvalidParams {
+			t.Errorf("expected error code %d, got %d", codeInvalidParams, wireErr.Code)
 		}
 	})