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internal/mcp: add resource subscriptions

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Handle resource subscriptions by delegating to the user.

We don't need to use the word "Resource" in the handlers because
the Subscribe and Unsubscribe methods in the spec don't use that
name. If the spec adds another kind of subscription, they will pick
a new name.

The need for two handlers is dictated by backward compatibility.
We must pass the RPC params to the subscription handler, which means
we need different signatures for subscribe and unsubscribe.

Change-Id: I045abaf52dc9c3e96181331728d50cf36cc8ed91
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671895
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
This commit is contained in:
Jonathan Amsterdam 2025-05-12 08:36:32 -04:00
commit acd35cb7e5
1 changed files with 35 additions and 9 deletions
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44
design/design.md
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@ -891,20 +891,46 @@ func (*Server) RemoveResourceTemplates(names ...string)
Resource templates don't have unique identifiers, so removing a name will remove all
resource templates with that name.
Clients call `ListResources` to list the available resources, `ReadResource` to read
one of them, and `ListResourceTemplates` to list the templates:
```go
func (*ClientSession) ListResources(context.Context, *ListResourcesParams) (*ListResourcesResult, error)
func (*ClientSession) ListResourceTemplates(context.Context, *ListResourceTemplatesParams) (*ListResourceTemplatesResult, error)
func (*ClientSession) ReadResource(context.Context, *ReadResourceParams) (*ReadResourceResult, error)
```
Servers support all of the resource-related spec methods:
- `ListResources` and `ListResourceTemplates` for listings.
- `ReadResource` to get the contents of a resource.
- `Subscribe` and `Unsubscribe` to manage subscriptions on resources.
`ReadResource` checks the incoming URI against the server's list of
resources and resource templates to make sure it matches one of them,
then returns the result of calling the associated reader function.
<!-- TODO: subscriptions -->
#### Subscriptions
ClientSessions can manage change notifications on particular resources:
```go
func (*ClientSession) Subscribe(context.Context, *SubscribeParams) error
func (*ClientSession) Unsubscribe(context.Context, *UnsubscribeParams) error
```
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.
```go
type ServerOptions struct {
...
// Function called when a client session subscribes to a resource.
SubscribeHandler func(context.Context, *SubscribeParams) error
// Function called when a client session unsubscribes from a resource.
UnsubscribeHandler func(context.Context, *UnsubscribeParams) error
}
```
User code should call `ResourceUpdated` when a subscribed resource changes.
```go
func (*Server) ResourceUpdated(context.Context, *ResourceUpdatedNotification) error
```
The server routes these notifications to the server sessions that subscribed to the resource.
### ListChanged notifications