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internal/mcp: implement logging

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Provide a ServerSession method that directly implements the spec
method.

Also provide a custom slog.Handler that writes a notification on each
log call. It uses a slog.JSONHandler to format the message as JSON, then
adds the additional fields of LoggingMessageParams.

I decided that the direct method should handle levels, since that is
in the spec, but that rate-limiting is an extra feature, so is only
provided in the slog handler.

Change-Id: I1190ca124e992e61fb633ac52ee3492c8e6d99c9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674498
Auto-Submit: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
This commit is contained in:
Jonathan Amsterdam 2025-05-12 08:35:02 -04:00 • committed by Gopher Robot
commit edda031578
1 changed files with 416 additions and 42 deletions
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13
mcp/client.go
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@ -53,6 +53,7 @@ type ClientOptions struct {
ToolListChangedHandler func(context.Context, *ClientSession, *ToolListChangedParams)
PromptListChangedHandler func(context.Context, *ClientSession, *PromptListChangedParams)
ResourceListChangedHandler func(context.Context, *ClientSession, *ResourceListChangedParams)
LoggingMessageHandler func(context.Context, *ClientSession, *LoggingMessageParams)
}
// bind implements the binder[*ClientSession] interface, so that Clients can
@ -208,6 +209,7 @@ var clientMethodInfos = map[string]methodInfo[ClientSession]{
notificationToolListChanged: newMethodInfo(clientMethod((*Client).callToolChangedHandler)),
notificationPromptListChanged: newMethodInfo(clientMethod((*Client).callPromptChangedHandler)),
notificationResourceListChanged: newMethodInfo(clientMethod((*Client).callResourceChangedHandler)),
notificationLoggingMessage: newMethodInfo(clientMethod((*Client).callLoggingHandler)),
}
var _ session[ClientSession] = (*ClientSession)(nil)
@ -273,6 +275,10 @@ func (c *ClientSession) CallTool(ctx context.Context, name string, args map[stri
return standardCall[CallToolResult](ctx, c.conn, methodCallTool, params)
}
func (c *ClientSession) SetLevel(ctx context.Context, params *SetLevelParams) error {
return call(ctx, c.conn, methodSetLevel, params, nil)
}
// NOTE: the following struct should consist of all fields of callToolParams except name and arguments.
// CallToolOptions contains options to [ClientSession.CallTool].
@ -302,6 +308,13 @@ func (c *Client) callResourceChangedHandler(ctx context.Context, s *ClientSessio
return callNotificationHandler(ctx, c.opts.ResourceListChangedHandler, s, params)
}
func (c *Client) callLoggingHandler(ctx context.Context, cs *ClientSession, params *LoggingMessageParams) (any, error) {
if h := c.opts.LoggingMessageHandler; h != nil {
h(ctx, cs, params)
}
return nil, nil
}
func standardCall[TRes, TParams any](ctx context.Context, conn *jsonrpc2.Connection, method string, params TParams) (*TRes, error) {
var result TRes
if err := call(ctx, conn, method, params, &result); err != nil {