Transparent HTTP proxy for ipfw's fwd rule or IPFILTER's ipnat command
transproxy - transparently proxy HTTP requests. This program is used with ipfw's fwd rules or Darren Reed's IPFILTER package, and is used to intercept HTTP requests and divert them to a HTTP proxy server (eg: squid), without requiring user intervention or configuration. It accepts connections on the redirected port, connects to the real proxy server, and transports data between the two sockets. The original HTTP request is modified to allow the HTTP proxy server to fetch the correct document. In most cases this doesn't cause any DNS activity. Unlike some other transparent proxy solutions, this does not require the HTTP proxy server to run on the machine itself. See /usr/local/sbin/tproxyrun for an example of how to add filter rules and start tproxy. Also see /usr/local/sbin/tproxywatch for an example of how to ensure that tproxy keeps running regardless of faults.
pkg install transproxy