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May 14th 2020
Last Modified

cmux: Connection Mux Build Status GoDoc

cmux is a generic Go library to multiplex connections based on their payload. Using cmux, you can serve gRPC, SSH, HTTPS, HTTP, Go RPC, and pretty much any other protocol on the same TCP listener.


Simply create your main listener, create a cmux for that listener, and then match connections:

// Create the main listener.
l, err := net.Listen("tcp", ":23456")
if err != nil {

// Create a cmux.
m := cmux.New(l)

// Match connections in order:
// First grpc, then HTTP, and otherwise Go RPC/TCP.
grpcL := m.Match(cmux.HTTP2HeaderField("content-type", "application/grpc"))
httpL := m.Match(cmux.HTTP1Fast())
trpcL := m.Match(cmux.Any()) // Any means anything that is not yet matched.

// Create your protocol servers.
grpcS := grpc.NewServer()
grpchello.RegisterGreeterServer(grpcs, &server{})

httpS := &http.Server{
	Handler: &helloHTTP1Handler{},

trpcS := rpc.NewServer()

// Use the muxed listeners for your servers.
go grpcS.Serve(grpcL)
go httpS.Serve(httpL)
go trpcS.Accept(trpcL)

// Start serving!

There are more examples on GoDoc.


Since we are only matching the very first bytes of a connection, the performance overhead on long-lived connections (i.e., RPCs and pipelined HTTP streams) is negligible.


  • TLS: net/http uses a type assertion to identify TLS connections; since cmux’s lookahead-implementing connection wraps the underlying TLS connection, this type assertion fails. This means you can serve HTTPS using cmux but http.Request.TLS will not be set in your handlers. If you are able to wrap TLS around cmux, you can work around this limitation. See for an example of this approach.

  • Different Protocols on The Same Connection: cmux matches the connection when it’s accepted. For example, one connection can be either gRPC or REST, but not both. That is, we assume that a client connection is either used for gRPC or REST.

Copyright and License

Copyright 2016 The CMux Authors. All rights reserved.

See CONTRIBUTORS for the CMux Authors. Code is released under the Apache 2 license.