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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

Fixes: #23
This commit is contained in:
Sam Thanawalla 2025-07-23 15:23:50 -04:00 • committed by GitHub
commit bcbb31f072
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17
design/design.md
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@ -748,13 +748,26 @@ Server sessions also support the spec methods `ListResources` and `ListResourceT
#### Subscriptions
ClientSessions can manage change notifications on particular resources:
##### Client-Side Usage
Use the Subscribe and Unsubscribe methods on a ClientSession to start or stop receiving updates for a specific resource.
```go
func (*ClientSession) Subscribe(context.Context, *SubscribeParams) error
func (*ClientSession) Unsubscribe(context.Context, *UnsubscribeParams) error
```
To process incoming update notifications, you must provide a ResourceUpdatedHandler in your ClientOptions. The SDK calls this function automatically whenever the server sends a notification for a resource you're subscribed to.
```go
type ClientOptions struct {
...
ResourceUpdatedHandler func(context.Context, *ClientSession, *ResourceUpdatedNotificationParams)
}
```
##### Server-Side Implementation
The server does not implement resource subscriptions. It passes along subscription requests to the user, and supplies a method to notify clients of changes. It tracks which sessions have subscribed to which resources so the user doesn't have to.
If a server author wants to support resource subscriptions, they must provide handlers to be called when clients subscribe and unsubscribe. It is an error to provide only one of these handlers.
@ -772,7 +785,7 @@ type ServerOptions struct {
User code should call `ResourceUpdated` when a subscribed resource changes.
```go
func (*Server) ResourceUpdated(context.Context, *ResourceUpdatedNotification) error
func (*Server) ResourceUpdated(context.Context, *ResourceUpdatedNotificationParams) error
```
The server routes these notifications to the server sessions that subscribed to the resource.