cvs/lpr-agent/protocol.txt

The protocol on the socket is not meant to be used by other programs,
and can be changed at any time.  It is documented for completeness
only, and to make it easy to follow the source code.

Communication is one way only, from the client to the agent.  The
first line is the command, which is one word, usually "print".  After
that follows a number of RFC 822-compliant header lines with any
additional information, followed by an empty line.  Any unknown
headers are ignored by the agent.  If the command is not "quit",
unspecified amount of data followes, which the agent processes
according to what command was given.
1	The protocol on the socket is not meant to be used by other programs,
2	and can be changed at any time. It is documented for completeness
3	only, and to make it easy to follow the source code.
4
5	Communication is one way only, from the client to the agent. The
6	first line is the command, which is one word, usually "print". After
7	that follows a number of RFC 822-compliant header lines with any
8	additional information, followed by an empty line. Any unknown
9	headers are ignored by the agent. If the command is not "quit",
10	unspecified amount of data followes, which the agent processes
11	according to what command was given.