Websocketaf.HandshakeSourceval upgrade_headers :
sha1:(string -> string) ->
request_method:Httpaf.Method.t ->
Httpaf.Headers.t ->
((string * string) list, string) resultval respond_with_upgrade :
?headers:Httpaf.Headers.t ->
sha1:(string -> string) ->
Httpaf.Reqd.t ->
(unit -> unit) ->
(unit, string) result