Loggen: command line parameters for proxy protocol header

[norberttak]

This PR adds three new command-line option to the loggen to allow the users to define the
source IP, destination IP, and port parameters used in the proxy protocol header.

[kira-syslogng]

Build SUCCESS

[alltilla]

Thanks for the PR!

What was the reason behind moving the proxy header generation from socket_plugin.c to loggen.c? Was it to make it work with ssl?
If so, than I think we should use generate_proxy_header() in ssl_plugin.c instead. I think it is not an accident that we have generate_proxy_header() in loggen_helpers.c, so any plugin can use it.

[norberttak]

Thanks @alltilla for your review comment. Proxy protocol is no more than (from loggen point of view) generate a simple text message at the beginning of the connection. To generate the log lines (or read from a file) we already have a separated part which is the generate_message() function used by every plugin.
Neither socket nor SSL plugin needs to know about proxy protocol. This is a higher-level function.

In the original form of the code if somebody call the SSL plugin with the proxied option, it will silently ignore the option which is not a good solution. To put the same code to all plugin is also not what I really want to do.

[alltilla]

I see.

Just thinking out loud:
We might have plugins which does not support proxy protocol (*cough* ALTP). With the common solution they will be able to produce proxy protocol messages, which we cannot handle in syslog-ng. But after all, it might not be a problem, maybe we will have that implemented in syslog-ng some time.

Thanks for the explanation, I am convinced. :)

[kira-syslogng]

Build SUCCESS