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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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GPG key ID: B5690EEEBB952194
1 changed files with 214 additions and 6 deletions
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20
mcp/client.go
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@ -60,6 +60,7 @@ type ClientOptions struct {
ToolListChangedHandler func(context.Context, *ClientSession, *ToolListChangedParams)
PromptListChangedHandler func(context.Context, *ClientSession, *PromptListChangedParams)
ResourceListChangedHandler func(context.Context, *ClientSession, *ResourceListChangedParams)
ResourceUpdatedHandler func(context.Context, *ClientSession, *ResourceUpdatedNotificationParams)
LoggingMessageHandler func(context.Context, *ClientSession, *LoggingMessageParams)
ProgressNotificationHandler func(context.Context, *ClientSession, *ProgressNotificationParams)
// If non-zero, defines an interval for regular "ping" requests.
@ -293,6 +294,7 @@ var clientMethodInfos = map[string]methodInfo{
notificationToolListChanged: newMethodInfo(clientMethod((*Client).callToolChangedHandler)),
notificationPromptListChanged: newMethodInfo(clientMethod((*Client).callPromptChangedHandler)),
notificationResourceListChanged: newMethodInfo(clientMethod((*Client).callResourceChangedHandler)),
notificationResourceUpdated: newMethodInfo(clientMethod((*Client).callResourceUpdatedHandler)),
notificationLoggingMessage: newMethodInfo(clientMethod((*Client).callLoggingHandler)),
notificationProgress: newMethodInfo(sessionMethod((*ClientSession).callProgressNotificationHandler)),
}
@ -386,6 +388,20 @@ func (cs *ClientSession) Complete(ctx context.Context, params *CompleteParams) (
return handleSend[*CompleteResult](ctx, cs, methodComplete, orZero[Params](params))
}
// Subscribe sends a "resources/subscribe" request to the server, asking for
// notifications when the specified resource changes.
func (cs *ClientSession) Subscribe(ctx context.Context, params *SubscribeParams) error {
_, err := handleSend[*emptyResult](ctx, cs, methodSubscribe, orZero[Params](params))
return err
}
// Unsubscribe sends a "resources/unsubscribe" request to the server, cancelling
// a previous subscription.
func (cs *ClientSession) Unsubscribe(ctx context.Context, params *UnsubscribeParams) error {
_, err := handleSend[*emptyResult](ctx, cs, methodUnsubscribe, orZero[Params](params))
return err
}
func (c *Client) callToolChangedHandler(ctx context.Context, s *ClientSession, params *ToolListChangedParams) (Result, error) {
return callNotificationHandler(ctx, c.opts.ToolListChangedHandler, s, params)
}
@ -398,6 +414,10 @@ func (c *Client) callResourceChangedHandler(ctx context.Context, s *ClientSessio
return callNotificationHandler(ctx, c.opts.ResourceListChangedHandler, s, params)
}
func (c *Client) callResourceUpdatedHandler(ctx context.Context, s *ClientSession, params *ResourceUpdatedNotificationParams) (Result, error) {
return callNotificationHandler(ctx, c.opts.ResourceUpdatedHandler, s, params)
}
func (c *Client) callLoggingHandler(ctx context.Context, cs *ClientSession, params *LoggingMessageParams) (Result, error) {
if h := c.opts.LoggingMessageHandler; h != nil {
h(ctx, cs, params)