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mcp: improve documentation of Add*Middleware #688

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mcp: improve documentation of Add*Middleware #688

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16 changes: 11 additions & 5 deletions mcp/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1101,12 +1101,15 @@ func (ss *ServerSession) Log(ctx context.Context, params *LoggingMessageParams)
return handleNotify(ctx, notificationLoggingMessage, newServerRequest(ss, orZero[Params](params)))
}

// AddSendingMiddleware wraps the current sending method handler using the provided
// middleware. Middleware is applied from right to left, so that the first one is
// executed first.
// AddSendingMiddleware wraps the current sending method handler using
// the provided middleware.
// Middleware supplied via arguments is applied from right to left at the time it is added,
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@findleyr findleyr Dec 5, 2025

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When I first read this, I wondered "how else can middleware be applied other than as arguments" -- to me at least, it's a bit hard to parse.

How about "Arguments to AddSendingMiddleware are applied from right to left, so that the first middleware is executed first."

// so that the first one among these is executed first.
//
// For example, AddSendingMiddleware(m1, m2, m3) augments the method handler as
// m1(m2(m3(handler))).
// Then adding another set of middleware with AddSendingMiddleware(m4, m5, m6) yields
// m4(m5(m6(m1(m2(m3(handler)))))).
//
// Sending middleware is called when a request is sent. It is useful for tasks
// such as tracing, metrics, and adding progress tokens.
Expand All @@ -1117,11 +1120,14 @@ func (s *Server) AddSendingMiddleware(middleware ...Middleware) {
}

// AddReceivingMiddleware wraps the current receiving method handler using
// the provided middleware. Middleware is applied from right to left, so that the
// first one is executed first.
// the provided middleware.
// Middleware supplied via arguments is applied from right to left at the time it is added,
// so that the first one among these is executed first.
//
// For example, AddReceivingMiddleware(m1, m2, m3) augments the method handler as
// m1(m2(m3(handler))).
// Then adding another set of middleware with AddReceivingMiddleware(m4, m5, m6) yields
// m4(m5(m6(m1(m2(m3(handler)))))).
//
// Receiving middleware is called when a request is received. It is useful for tasks
// such as authentication, request logging and metrics.
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