NaCl(1) 						      General Commands Manual							   NaCl(1)

NAME

       CurveCP -- Message-handling programs

SYNOPSIS

       curvecpserver [-q (optional)]  [-Q (optional)]  [-v (optional)]	[-c n(optional)]  [sname]  [keydir]  [ip]  [port]  [ext]  [prog]

DESCRIPTION

       This manual page documents briefly the CurveCP commands.

       A  traditional UNIX-style server such as ftpd handles just one network connection, reading input from stdin and writing output to stdout. A
       "superserver" such as inetd or tcpserver listens for network connections and starts a separate server process for each connection.

       The CurveCP command-line tools have an extra level of modularity. The curvecpserver  superserver listens for network connections. For  each
       connection,  curvecpserver  starts the curvecpmessage message handler; curvecpmessage then starts a server such as ftpd.  Then ftpd sends a
       stream of data to curvecpmessage, which in turn sends messages to curvecpserver, which encrypts and authenticates the  messages	and  sends
       them  inside  network  packets. At the same time curvecpclient receives network packets, verifies and decrypts messages inside the packets,
       and passes the messages to curvecpmessage; curvecpmessage sends a stream of data to ftpd.  The same curvecpmessage tool	is  also  used	by
       curvecpclient.

       curvecpserver  and  curvecpclient  can use programs other than curvecpmessage. Those programs can directly generate messages in the CurveCP
       message format without talking to separate tools such as ftpd; or they can support a completely different protocol  that  reuses  CurveCP's
       cryptographic layer but transmits different kinds of messages.

       This page explains what programmers have to do to write curvecpmessage replacements that talk to curvecpserver and curvecpclient.

Incoming messagess
       File  descriptor  8  is a pipe. Read from this pipe a length byte n, between 1 and 68, and a 16*n-byte message. Repeat.	The pipe is set to
       non-blocking mode; be prepared for EAGAIN and EWOULDBLOCK, even in the middle of a message.

       This pipe reading must always be active. The curvecpclient and curvecpserver programs assume that every message is read immediately. If you
       can't  handle a message immediately, read it and put it onto a queue. If you don't have queue space, throw the message away; this shouldn't
       cause trouble, since you have to be able to handle missing messages in any case.

Outgoing messagess
       File descriptor 9 is a pipe. Write to this pipe a length byte n, between 1 and 68, and a 16*n-byte message. Repeat.  The  pipe  is  set	to
       non-blocking mode; be prepared for EAGAIN and EWOULDBLOCK, even in the middle of a message.

       As  a  client,  do not use length bytes above 40 until a message has arrived from the server. (The messages inside CurveCP Initiate packets
       are limited to 640 bytes.)

       The CurveCP server does not start until it has received a message from the client. Furthermore, the CurveCP server must receive	this  mes-
       sage within 60 seconds of the client starting up. (The CurveCP Initiate packet is valid for only 60 seconds after the corresponding CurveCP
       Cookie packet.)	This does not mean that the client must start sending messages immediately, but it does mean that waiting for more than  a
       second to send a message is a bad idea.

OPTIONS

       How to use curvecpserver:

       -q	    optional
		 no error messages

       -Q	    optional
		 print error messages (default)

       -v	    optional
		 print extra information

       -c n	      optional
		 allow at most n clients at once (default 100)

       sname	 server's name

       keydir	 use this public-key directory

       ip	 server's IP address

       port	 server's UDP port

       ext	 server's extension

       prog	 run this server

SEE ALSO

       curvecpmessage (1), curvecpclient (1), inetd (8), tcpserver (1).

AUTHOR

       This  manual  page was written by Sergiusz Pawlowicz debian@pawlowicz.name for the Debian system (and may be used by others). The source of
       this page is a webpage http://curvecp.org/messageapi.html .  Permission is granted to copy, distribute and/or modify  this  document  under
       public domain.

       This manual page was rewritten for the Debian distribution because the original program does not have a manual page.

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