TsgcWebSocketServer › Events › OnSSLALPNSelect

OnSSLALPNSelect Event

Fires during an ALPN-enabled handshake so the application can pick which protocol to negotiate.

Syntax

property OnSSLALPNSelect: TsgcWSOnSSLALPNSelect;
// TsgcWSOnSSLALPNSelect = procedure(Sender: TObject; aProtocols: TStringList; var aProtocol: String) of object

Default Value

—

Remarks

When a client advertises Application-Layer Protocol Negotiation during the TLS handshake, OnSSLALPNSelect is raised so the server can decide which protocol to negotiate. The aProtocols parameter is a TStringList with the names advertised by the client (for example "h2", "http/1.1"); assign aProtocol to the one that the server wants to use. Returning an empty string leaves the default behaviour in place, in which case the TLS layer picks the first advertised protocol the server supports.

Example

procedure OnSSLALPNSelect(Sender: TObject; aProtocols: TStringList;
  var aProtocol: String);
begin
  if aProtocols.IndexOf('h2') >= 0 then
    aProtocol := 'h2'
  else
    aProtocol := 'http/1.1';
end;

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