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\chapter{FTP server}\label{cha:ftpd}
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\begin{description}
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\item[Used files:] ftpd.scm
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\item[Name of the package:] ftpd
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\end{description}
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The \ex{ftpd} structure contains a complete anonymous ftp server.
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\section{What users want to know}
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\defun{ftpd}{options}{\noreturn}
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\defunx{ftp-inetd}{options}{\noreturn}
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\begin{desc}
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\ex{Ftpd} starts the server, using \var{anonymous-home} as the
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root directory of the server.
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\section{Entry points}
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\ex{ftpd-inetd} is the version to be used from \ex{inetd}.
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\ex{Ftpd-inetd} handles the connection through the current standard
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output and input ports.
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\end{desc}
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%
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The \var{options} argument can be constructed through a number of
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procedures with names of the form \texttt{with-\ldots}. Each of these
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procedures either creates a fresh options value or adds a
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configuration parameter to an old options argument. The configuration
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parameter value is always the first argument, the (old) options value
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the optional second one. Here they are:
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\defun {ftpd} {options} {\noreturn}
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\begin{defundescx}{ftp-inetd} {anonymous-home} {\noreturn}
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\ex{ftpd} starts the server, using \semvar{anonymous-home} as the
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root directory of the server. Usage of relative paths is not
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encouraged. \semvar{port} specifies the port the server is
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listening for connections. It defaults to 21. \ex{ftpd} makes a log
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entry for each file sent or retrieved. These logs are written to
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\semvar{logfile}, if given. If \semvar{dns-lookup?} is \sharpt, the
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logfile will contain the host names instead of their IP
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addresses. If \semvar{dns-lookup?} is not specified or \sharpf, the
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IP addresses are stored.
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\defun{with-port}{port [options]}{options}
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\begin{desc}
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This specifies the port on which the server listens. Defaults to 21.
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\end{desc}
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The log format of \ex{ftpd} is the same as the one of
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\ex{wuftpd}. The fields are seperated by spaces and contain
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following informations:
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\codex{Fri Apr 19 17:08:14 2002 4 134.2.2.171 56881 /files.lst b \_ i a nop@ssword ftp 0 *}
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\begin{enumerate}
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\defun{with-anonymous-home}{string [options]}{options}
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\begin{desc}
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This specifies the home directory for anonymous logins. Defaults to
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\verb|"~ftp"|.
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\end{desc}
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\defun{with-banner}{list [options]}{options}
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\begin{desc}
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This specifies an alternative greeting banner for those members of
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the Untergrund who prefer to remain covert. The banner is
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represented as a list of strings, one for each line of output.
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\end{desc}
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\defun{with-logfile}{file-name [options]}{options}
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\begin{desc}
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If this is non-\sharpf, ex{ftpd} makes a log entry for each file
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sent or retrieved in \var{file-name}. Defaults to \sharpf.
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\end{desc}
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\defun{with-dns-lookup?}{boolean [options]}{options}
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\begin{desc}
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If \var{dns-lookup?} is \sharpt, the log file will contain the host
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names instead of their IP addresses. If \var{dns-lookup?} is \sharpf,
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the log will only contain IP addresses. Defaults to \sharpf.
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\end{desc}
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The log format of \ex{ftpd} is the same as the one of
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\ex{wuftpd}. The entries look like this:
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%
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\begin{verbatim}
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Fri Apr 19 17:08:14 2002 4 134.2.2.171 56881 /files.lst b _ i a nop@ssword ftp 0 *
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\end{verbatim}
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%
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These are the fields:
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\begin{enumerate}
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\item Current date and time. This field contains
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spaces and is 24 characters long.
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\item Transfer time in seconds.
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\item Remote host IP (wuftpd puts the name here).
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\item Remote host IP (wu-ftpd puts the name here).
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\item File size in bytes
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\item Name of file (spaces are converted to underscores)
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\item Transfer type: \underline{a}scii or \underline{b}inary (image type).
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\item Special action flags. As \ex{ftpd} does not support any special
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action, we are always `\ex{\_}' here.
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action, it always has \ex{\_} here.
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\item File was sent to user (\underline{o}utgoing) or received from user
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(\underline{i}ncoming)
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\item \underline{A}nonymous access
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\item Anonymous ftp password. We do not use anyone.
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\item Service name - always \ex{ftp}.
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\item Authentication mode (always none = `\ex{0}').
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\item Authenticated user ID (always not available = `\ex{*}')
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\item Anonymous ftp password.
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\item Service name---always \ex{ftp}.
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\item Authentication mode (always ``none'' = `\ex{0}').
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\item Authenticated user ID (always ``not available'' = `\ex{*}')
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\end{enumerate}
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As the procedure does not return, you have to do a \ex{fork} in
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order to have a ``real'' daemon: \codex{(fork (lambda () (ftpd
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"/data/ftp" 8080)))} \ex{ftpd-inetd} is the version to be used with
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a daemon like \ex{inetd}. If the server is started this way, it
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handles the connection through the current standard output and input
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ports.
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\end{defundescx}
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\subsubsection*{Examples}
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To start the server with the current home directory as root directory
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and listening on port 8080, use
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\codex{(ftpd (cwd) 8080)}
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This is how the ftp server at the computing faculty of the university
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of Tuebingen\footnote{\texttt{archive.informatik.uni-tuebingen.de}} is
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started:
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\begin{alltt}
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#!/bin/sh /scsh-0.6-alpha/bin/scsh <<EOF
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,batch on
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,config ,load modules.scm
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,open ftpd
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,open threads
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(define (archive-ftpd args)
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(with-syslog-destination
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#f
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#f
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(syslog-facility local0)
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#f
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(lambda ()
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(ftpd "/data/archive/"))))
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(dump-scsh-program archive-ftpd "archive-ftpd.image")
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;; (dump-scsh "archive-ftpd.image")
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EOF
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\end{alltt}
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Perhaps you have noticed the \ex{with-syslog-destination} command.
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\ex{ftpd} generates syslog-messages that can be controlled via this
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command. The following section gives you an overview of what is logged
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at which level. See \ex{man 3 syslog} or the
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\ex{with-syslog-destination} command in the scsh-manual for further
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details.
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\subsubsection*{Syslog messages}
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\ex{ftpd} outputs a lot of syslog-messages. A syslog-message may look like
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this:
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\codex{Jul 24 18:34:52 axl ftpd: (thread 21) anonymous user login (230)}
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The log gives you following informations (including those delivered by
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the syslog-daemon):
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\begin{enumerate}
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\item The date and time the log was made (here: Jul 24 18:34:52)
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\item The machine the log was made on (here: axl)
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\item The program, that output the log (ftpd)
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\item The thread the message concerns (here thread 21)
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Each connection is linked with a thread, that handles the commands
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of this connection. When the thread is created, there is a entry in
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the log file containing the remote address and the thread number, so
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in future logs the thread number labels the connection. As at any
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given time the thread number is unique, this is a bijection. (Note
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that the thread numbers are not unique over a period of time).
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\item The log message (here: notification about an anonymous user login)
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\item The reply code returned by ftpd, if any (here: 230)
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\end{enumerate}
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\subsubsection*{The Syslog-levels used\footnote{For further details
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on syslog levels see \ex{man 3 syslog}}}
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Following events are logged as
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The server also writes log information to the syslog facility.
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The following syslog levels occur in the output:
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\begin{description}
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\item[\ex{NOTICE} level:]
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\item[\ex{notice}]
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\begin{itemize}
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\item Messages concerning \emph{connections} (establishing connection,
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\item messages concerning \emph{connections} (establishing connection,
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connection refused, closing connection due to timeout, etc.)
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\item The execution of the \ex{STOR} command. Its success (\ie
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\item the execution of the \ex{STOR} command\\
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Its success (\ie
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somebody is putting something on your server via ftp, also known as
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\ex{PUT}) is also logged at notice-level. In fact, the log is made
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before the storing is started actually.
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\item Internal errors
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\ex{PUT}) is also logged at \ex{notice}.
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\item internal errors
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\item Unix errors
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\item Reaching of actually unreachable case branches
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\item reaching of actually unreachable case branches
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\end{itemize}
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\item[\ex{INFO} level:] Messages concerning all \emph{other commands},
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\item[\ex{info}] Messages concerning all other commands,
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including the \ex{RETR} command.
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\item[\ex{DEBUG} level:] All other messages, including debug messages.
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If you want to debug ftpd, put all the messages in one single file,
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since the debug-messages may refer to messages of other levels.
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\item[\ex{debug}] all other messages, including debug messages
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\end{description}
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Success (as long as interesting) and failure of commands are logged at
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info-level, except the success of the STOR-command, that is logged at
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notice-level (as mentioned above).
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\subsubsection*{Supported commands}
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For those of you who are intrested, the table \ref{ftpd-commands}
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shows the list of supported commands by \ex{ftpd} according to
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RFC~959:
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%{Can there be a pagebreak in a table?}
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\begin{table}
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\label{ftpd-commands}
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\begin{center}
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\begin{tabular}{|lp{10cm}|}
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\hline
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\ex{ABOR} & abort connection \\
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\ex{CDUP} & move to parent directory \\
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\ex{CWD} & move to specified directory (relative paths may be used) \\
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\ex{DELE} & delete file \\
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\ex{LIST} & list files in current directory (long format) \\
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\ex{MDTM} & deliver modification time of a regular file \\
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\ex{MKD} & make directory \\
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\ex{MODE} & change mode (only stream mode (S) is supported) \\
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\ex{NLST} & list files in current directory (short format) \\
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\ex{NOOP} & do nothing \\
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\ex{PASS} & read in passphrase (\ex{ftpd} currently does not support
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non-anonymous logins) \\
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\ex{PASV} & change to passive mode \\
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\ex{PORT} & change connection port \\
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\ex{PWD} & return name of working directory (print working directory) \\
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\ex{QUIT} & quit session \\
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\ex{RETR} & return file (GET) \\
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\ex{RMD} & remove directory \\
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\ex{RNFR} & read in the name of a file to be renamed (use \ex{RNTO} next) \\
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\ex{RNTO} & rename file mentioned before in a \ex{RNFR} command \\
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\ex{SIZE} & return size of a regular file \\
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\ex{STOR} & store file (PUT) \\
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\ex{STRU}& change structure to transfer files
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(only the file structure is supported) \\
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\ex{SYST} & return system type \\
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\ex{TYPE} & change type (supported types: A is ascii mode,
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I or L8 are 8-bit binary mode) \\
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\ex{USER} & login user (only anonymous logins allowed,
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use ``anonymous'' or ``ftp'' as user name) \\
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\hline
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\end{tabular}
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\caption{Supported RFC~959 commands by the server.}
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\end{center}
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\end{table}
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%\subsection{What programmers want to know}
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%Let me know what you want to know. As long as you are waiting for my
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%answer, have a look in the source file (I'm sorry).
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%%% Local Variables:
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%%% mode: latex
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%%% TeX-master: "man"
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