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mcp: add support for logging level (SEP-2575) (#997)

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## Description

This PR adds the support for logging feature in meta.

Fixes #966
This commit is contained in:
Guglielmo Colombo 2026-06-08 15:56:38 +02:00 • committed by GitHub
commit 00d3642840
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1 changed files with 67 additions and 10 deletions
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31
mcp/server.go
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@ -1367,13 +1367,28 @@ func (ss *ServerSession) Elicit(ctx context.Context, params *ElicitParams) (*Eli
return res, nil
}
// logLevelContextKey carries the per-request log level from
// [ServerSession.handle] to [ServerSession.Log] for new-protocol
// (>= 2026-06-30) requests. The level is scoped to a single in-flight request
// — including handler goroutines that call [ServerSession.Log] concurrently —
// rather than to the session, which avoids races between concurrent requests
// and aligns with SEP-2575's per-request opt-in model. The value type is
// [LoggingLevel]; an empty string means the request opted out of log messages.
type logLevelContextKey struct{}
// Log sends a log message to the client.
// The message is not sent if the client has not called SetLevel, or if its level
// is below that of the last SetLevel.
//
// For new-protocol (>= 2026-06-30) requests, the level is taken from the
// originating request's `_meta` field (SEP-2575); an absent or empty value
// suppresses the message per spec. For old-protocol requests, the level is
// taken from the session state set via `logging/setLevel`.
func (ss *ServerSession) Log(ctx context.Context, params *LoggingMessageParams) error {
ss.mu.Lock()
logLevel := ss.state.LogLevel
ss.mu.Unlock()
logLevel, ok := ctx.Value(logLevelContextKey{}).(LoggingLevel)
if !ok {
ss.mu.Lock()
logLevel = ss.state.LogLevel
ss.mu.Unlock()
}
if logLevel == "" {
// The spec is unclear, but seems to imply that no log messages are sent until the client
// sets the level.
@ -1498,7 +1513,7 @@ func (ss *ServerSession) handle(ctx context.Context, req *jsonrpc.Request) (any,
}
switch req.Method {
case methodInitialize, methodPing, notificationInitialized:
case methodInitialize, methodPing, notificationInitialized, methodSetLevel:
if validatedMeta.usesNewProtocol {
ss.server.opts.Logger.Error("method removed in the new protocol", "method", req.Method)
return nil, &jsonrpc.Error{
@ -1533,6 +1548,10 @@ func (ss *ServerSession) handle(ctx context.Context, req *jsonrpc.Request) (any,
// server->client calls and notifications to the incoming request from which
// they originated. See [idContextKey] for details.
ctx = context.WithValue(ctx, idContextKey{}, req.ID)
// For new-protocol requests, propagate the per-request log level.
if validatedMeta.usesNewProtocol {
ctx = context.WithValue(ctx, logLevelContextKey{}, validatedMeta.logLevel)
}
return handleReceive(ctx, ss, req)
}