Handlers
There are three main types of handler functions for ProFTPD: configuration
directive handlers, command handlers, and authentication handlers.
Configuration Handlers
Configuration handlers are used to process the
configuration directives encountered in the main proftpd.conf
configuration file, any Included configuration files, and any
.ftpaccess files encountered. The context in which these
functions operate is one without connected clients; much of the
"processing" entails syntax and availability checks of directive
arguments, and the setting of configuration records.
Command Handlers
The command handlers are responsible for the
processing of the client-sent FTP commands; these are the heart of the
server, providing the services requested by the connecting user.
Authentication Handlers
The last type, authentication handlers, are
not really handlers so much as they are replacement functions, to be used by
ProFTPD for the purposes of authentication in place of the system or library
provided functions. These types of functions are not as frequently used
as the other two types of functions. For the curious reader, however, the
sources for mod_ldap,
mod_auth_pam, and
mod_auth_unix
illustrate how these functions are implemented; note that the tracing of the
calling of these functions in the course of a live connection can be tricky.
Response Handlers
While not quite true handlers, per se, the
response functions are also important piece of
module handler development. These functions deal with how ProFTPD sends
its responses back to the connecting clients.
Handler Macros
There are also several pre-defined macros to help in the checking of
various handler argument conditions, such as argument number and syntax.
These macros are described here.