Skip to content

feat: add custom handler support for all MCP server methods #580

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 2 commits into
base: main
Choose a base branch
from
Open

feat: add custom handler support for all MCP server methods #580

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
c7e9b30
feat: add custom handler support for all MCP server methods
lbbniu Sep 12, 2025
51ffe02
fix: message endpoint generate
lbbniu Sep 12, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
142 changes: 138 additions & 4 deletions server/server.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,19 @@ type MCPServer struct {
paginationLimit *int
sessions sync.Map
hooks *Hooks

// custom handlers for basic methods
InitializeHandler func(ctx context.Context, request mcp.InitializeRequest) (*mcp.InitializeResult, error)
PingHandler func(ctx context.Context, request mcp.PingRequest) (*mcp.EmptyResult, error)
ListResourcesHandler func(ctx context.Context, request mcp.ListResourcesRequest) (*mcp.ListResourcesResult, error)
ListResourceTemplatesHandler func(ctx context.Context, request mcp.ListResourceTemplatesRequest) (*mcp.ListResourceTemplatesResult, error)
ReadResourceHandler func(ctx context.Context, request mcp.ReadResourceRequest) (*mcp.ReadResourceResult, error)
ListPromptsHandler func(ctx context.Context, request mcp.ListPromptsRequest) (*mcp.ListPromptsResult, error)
GetPromptHandler func(ctx context.Context, request mcp.GetPromptRequest) (*mcp.GetPromptResult, error)
ListToolsHandler func(ctx context.Context, request mcp.ListToolsRequest) (*mcp.ListToolsResult, error)
CallToolHandler func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error)
SetLevelHandler func(ctx context.Context, request mcp.SetLevelRequest) (*mcp.EmptyResult, error)
NotificationHandler func(ctx context.Context, notification mcp.JSONRPCNotification)
}

// WithPaginationLimit sets the pagination limit for the server.
Expand Down Expand Up @@ -647,9 +660,21 @@ func (s *MCPServer) AddNotificationHandler(

func (s *MCPServer) handleInitialize(
ctx context.Context,
_ any,
id any,
request mcp.InitializeRequest,
) (*mcp.InitializeResult, *requestError) {
if s.InitializeHandler != nil {
result, err := s.InitializeHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

capabilities := mcp.ServerCapabilities{}

// Only add resource capabilities if they're configured
Expand Down Expand Up @@ -729,10 +754,21 @@ func (s *MCPServer) protocolVersion(clientVersion string) string {
}

func (s *MCPServer) handlePing(
_ context.Context,
_ any,
_ mcp.PingRequest,
ctx context.Context,
id any,
request mcp.PingRequest,
) (*mcp.EmptyResult, *requestError) {
if s.PingHandler != nil {
result, err := s.PingHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}
return &mcp.EmptyResult{}, nil
}

Expand All @@ -741,6 +777,18 @@ func (s *MCPServer) handleSetLevel(
id any,
request mcp.SetLevelRequest,
) (*mcp.EmptyResult, *requestError) {
if s.SetLevelHandler != nil {
result, err := s.SetLevelHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

clientSession := ClientSessionFromContext(ctx)
if clientSession == nil || !clientSession.Initialized() {
return nil, &requestError{
Expand Down Expand Up @@ -820,6 +868,18 @@ func (s *MCPServer) handleListResources(
id any,
request mcp.ListResourcesRequest,
) (*mcp.ListResourcesResult, *requestError) {
if s.ListResourcesHandler != nil {
result, err := s.ListResourcesHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

s.resourcesMu.RLock()
resources := make([]mcp.Resource, 0, len(s.resources))
for _, entry := range s.resources {
Expand Down Expand Up @@ -858,6 +918,18 @@ func (s *MCPServer) handleListResourceTemplates(
id any,
request mcp.ListResourceTemplatesRequest,
) (*mcp.ListResourceTemplatesResult, *requestError) {
if s.ListResourceTemplatesHandler != nil {
result, err := s.ListResourceTemplatesHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

s.resourcesMu.RLock()
templates := make([]mcp.ResourceTemplate, 0, len(s.resourceTemplates))
for _, entry := range s.resourceTemplates {
Expand Down Expand Up @@ -894,6 +966,18 @@ func (s *MCPServer) handleReadResource(
id any,
request mcp.ReadResourceRequest,
) (*mcp.ReadResourceResult, *requestError) {
if s.ReadResourceHandler != nil {
result, err := s.ReadResourceHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

s.resourcesMu.RLock()
// First try direct resource handlers
if entry, ok := s.resources[request.Params.URI]; ok {
Expand Down Expand Up @@ -972,6 +1056,18 @@ func (s *MCPServer) handleListPrompts(
id any,
request mcp.ListPromptsRequest,
) (*mcp.ListPromptsResult, *requestError) {
if s.ListPromptsHandler != nil {
result, err := s.ListPromptsHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

s.promptsMu.RLock()
prompts := make([]mcp.Prompt, 0, len(s.prompts))
for _, prompt := range s.prompts {
Expand Down Expand Up @@ -1010,6 +1106,18 @@ func (s *MCPServer) handleGetPrompt(
id any,
request mcp.GetPromptRequest,
) (*mcp.GetPromptResult, *requestError) {
if s.GetPromptHandler != nil {
result, err := s.GetPromptHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}

s.promptsMu.RLock()
handler, ok := s.promptHandlers[request.Params.Name]
s.promptsMu.RUnlock()
Expand Down Expand Up @@ -1039,6 +1147,17 @@ func (s *MCPServer) handleListTools(
id any,
request mcp.ListToolsRequest,
) (*mcp.ListToolsResult, *requestError) {
if s.ListToolsHandler != nil {
result, err := s.ListToolsHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}
// Get the base tools from the server
s.toolsMu.RLock()
tools := make([]mcp.Tool, 0, len(s.tools))
Expand Down Expand Up @@ -1129,6 +1248,17 @@ func (s *MCPServer) handleToolCall(
id any,
request mcp.CallToolRequest,
) (*mcp.CallToolResult, *requestError) {
if s.CallToolHandler != nil {
result, err := s.CallToolHandler(ctx, request)
if err != nil {
return nil, &requestError{
id: id,
code: mcp.INTERNAL_ERROR,
err: err,
}
}
return result, nil
}
// First check session-specific tools
var tool ServerTool
var ok bool
Expand Down Expand Up @@ -1188,6 +1318,10 @@ func (s *MCPServer) handleNotification(
ctx context.Context,
notification mcp.JSONRPCNotification,
) mcp.JSONRPCMessage {
if s.NotificationHandler != nil {
s.NotificationHandler(ctx, notification)
return nil
}
s.notificationHandlersMu.RLock()
handler, ok := s.notificationHandlers[notification.Method]
s.notificationHandlersMu.RUnlock()
Expand Down
8 changes: 6 additions & 2 deletions server/sse.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -473,8 +473,12 @@ func (s *SSEServer) GetMessageEndpointForClient(r *http.Request, sessionID strin
if s.useFullURLForMessageEndpoint && s.baseURL != "" {
endpointPath = s.baseURL + endpointPath
}

return fmt.Sprintf("%s?sessionId=%s", endpointPath, sessionID)
if strings.Contains(endpointPath, "?") {
endpointPath += "&"
} else {
endpointPath += "?"
}
return fmt.Sprintf("%ssessionId=%s", endpointPath, sessionID)
}

// handleMessage processes incoming JSON-RPC messages from clients and sends responses
Expand Down