mcp: add resource subscriptions #138
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This CL adds the ability for clients to subscribe and receive updates for resources as described in https://modelcontextprotocol.io/specification/2025-06-18/server/resources#subscriptions
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Pull Request Overview
This PR implements resource subscriptions for the MCP (Model Context Protocol), allowing clients to subscribe to and receive notifications when specific resources change. The implementation follows the MCP specification for resource subscriptions.
Key changes:
- Added server-side subscription management with handlers for subscribe/unsubscribe operations
- Implemented client-side subscription methods and notification handling
- Added comprehensive test coverage for the subscription workflow
Reviewed Changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| mcp/protocol.go | Defines subscription-related protocol structures (SubscribeParams, UnsubscribeParams, ResourceUpdatedNotificationParams) |
| mcp/server.go | Implements server-side subscription tracking, handlers, and notification routing |
| mcp/client.go | Adds client-side subscription methods and notification handler registration |
| mcp/server_test.go | Tests server capability reporting for resource subscriptions |
| mcp/mcp_test.go | End-to-end integration tests for the complete subscription workflow |
| design/design.md | Documentation updates explaining subscription usage patterns |
Co-authored-by: Copilot <[email protected]>
| @@ -224,6 +236,12 @@ func (s *Server) capabilities() *serverCapabilities { | |||
| if s.resources.len() > 0 || s.resourceTemplates.len() > 0 { | |||
| caps.Resources = &resourceCapabilities{ListChanged: true} | |||
| } | |||
| if s.opts.SubscribeHandler != nil { | |||
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Hmm.
I think that if there are no resources, it doesn't matter if there's a subscribe handler. There is no resource capability.
It's OK to provide a handler, it just doesn't do anything.
| defer s.mu.Unlock() | ||
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| uri := params.URI | ||
| if sessions, ok := s.resourceSubscriptions[uri]; ok { |
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Might as well skip the check and just call DeleteFunc.
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(If you prefer to use a slice.)
| @@ -97,6 +108,7 @@ func NewServer(impl *Implementation, opts *ServerOptions) *Server { | |||
| resourceTemplates: newFeatureSet(func(t *serverResourceTemplate) string { return t.resourceTemplate.URITemplate }), | |||
| sendingMethodHandler_: defaultSendingMethodHandler[*ServerSession], | |||
| receivingMethodHandler_: defaultReceivingMethodHandler[*ServerSession], | |||
| resourceSubscriptions: make(map[string][]*ServerSession), | |||
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I think this would be a little nicer if it was a map[string]map[string]bool. Adding and deleting would be trivial.
| @@ -614,6 +686,8 @@ var serverMethodInfos = map[string]methodInfo{ | |||
| methodListResourceTemplates: newMethodInfo(serverMethod((*Server).listResourceTemplates)), | |||
| methodReadResource: newMethodInfo(serverMethod((*Server).readResource)), | |||
| methodSetLevel: newMethodInfo(sessionMethod((*ServerSession).setLevel)), | |||
| methodSubscribe: newMethodInfo(serverMethod((*Server).subscribe)), | |||
| methodUnsubscribe: newMethodInfo(serverMethod((*Server).unsubscribe)), | |||
This CL adds the ability for clients to subscribe and receive updates for resources as described in https://modelcontextprotocol.io/specification/2025-06-18/server/resources#subscriptions
Fixes: #23