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all: expose JSON-RPC error codes, and support URLElicitationRequired errors (#655)

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Expose the jsonrpc.Error type to allow access to underlying JSON-RPC
error codes. Also, expose common JSON-RPC error codes in the jsonrpc
package, and MCP error codes in the mcp package.

Also, implement support for the MCP URL elicitation required error
(-32042), enabling servers to request out-of-band user authorization and
clients to automatically handle these requests with retry logic.

Server-side:
- Add CodeURLElicitationRequired constant
- Add URLElicitationRequiredError() constructor.

Client-side:
- Add urlElicitationMiddleware to intercept URLElicitationRequired
  errors and retry calls.
- Update callElicitationCompleteHandler to signal waiting operations.
- Fix capability advertisement to support both form and URL modes.

Fixes #452
Fixes #623
This commit is contained in:
Robert Findley 2025-12-01 11:29:17 -05:00 • committed by GitHub
commit 2ce44d45e9
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1 changed files with 670 additions and 44 deletions
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14
mcp/server.go
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@ -146,7 +146,7 @@ func NewServer(impl *Implementation, options *ServerOptions) *Server {
tools: newFeatureSet(func(t *serverTool) string { return t.tool.Name }),
resources: newFeatureSet(func(r *serverResource) string { return r.resource.URI }),
resourceTemplates: newFeatureSet(func(t *serverResourceTemplate) string { return t.resourceTemplate.URITemplate }),
sendingMethodHandler_: defaultSendingMethodHandler[*ServerSession],
sendingMethodHandler_: defaultSendingMethodHandler,
receivingMethodHandler_: defaultReceivingMethodHandler[*ServerSession],
resourceSubscriptions: make(map[string]map[*ServerSession]bool),
}
@ -293,12 +293,12 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHan
// Call typed handler.
res, out, err := h(ctx, req, in)
// Handle server errors appropriately:
// - If the handler returns a structured error (like jsonrpc2.WireError), return it directly
// - If the handler returns a structured error (like jsonrpc.Error), return it directly
// - If the handler returns a regular error, wrap it in a CallToolResult with IsError=true
// - This allows tools to distinguish between protocol errors and tool execution errors
if err != nil {
// Check if this is already a structured JSON-RPC error
if wireErr, ok := err.(*jsonrpc2.WireError); ok {
if wireErr, ok := err.(*jsonrpc.Error); ok {
return nil, wireErr
}
// For regular errors, embed them in the tool result as per MCP spec
@ -542,8 +542,8 @@ func (s *Server) getPrompt(ctx context.Context, req *GetPromptRequest) (*GetProm
s.mu.Unlock()
if !ok {
// Return a proper JSON-RPC error with the correct error code
return nil, &jsonrpc2.WireError{
Code: codeInvalidParams,
return nil, &jsonrpc.Error{
Code: jsonrpc.CodeInvalidParams,
Message: fmt.Sprintf("unknown prompt %q", req.Params.Name),
}
}
@ -569,8 +569,8 @@ func (s *Server) callTool(ctx context.Context, req *CallToolRequest) (*CallToolR
st, ok := s.tools.get(req.Params.Name)
s.mu.Unlock()
if !ok {
return nil, &jsonrpc2.WireError{
Code: codeInvalidParams,
return nil, &jsonrpc.Error{
Code: jsonrpc.CodeInvalidParams,
Message: fmt.Sprintf("unknown tool %q", req.Params.Name),
}
}