Question

I’m new to Indy and I want to build a simple proxy-server with it. This is a quite big library, and I just don’t know where to start. When client connects to server, OnExucute fires up and receives client connection as parameter (AContext.Connection).

I want to do following:

[client connection] := AContext.Connection
read host/port from [client connection]
[remote connection] := connect to host/port
while both connections alive:
  if data available in [client connection]:
    read data from [client connection]
    write data to [remote connection]
  if data available in [remote connection]:
    read data from [remote connection]
    write data to [client connection]

The question is what functions should I use for that? There is IOHandler property in Connection object with tons of them. Please, help.

I’m using Indy that ships with Delphi2010.

Answer 1

Indy has its own proxy components that do what you are asking for. Look at the TIdMappedPortTCP and TIdHTTPProxyServer components as starting places.

TIdMappedPortTCP is a general-purpose proxy that just passes raw data back and forth. You can use its OnConnect event to dynamically configure the target Host/Port for that connection (such as by reading it from the client), or you can set its MappedHost and MappedPort properties statically for all connections. You can use its OnExecute and OnOutboundData events to modify data as it passes through the proxy, if needed.

TIdHTTPProxyServer is a specialized proxy only for HTTP-based proxying, where the client uses the HTTP GET, POST, HEAD, and CONNECT verbs, specifying absolute URLs to the target Host/Port, and then passes HTTP headers and data back and forth as needed (CONNECT is commonly used for proxying an SSL/TLS connection through a firewall).