413 lines
14 KiB
TeX
413 lines
14 KiB
TeX
%&latex -*- latex -*-
|
|
|
|
\chapter{Miscellaneous routines}
|
|
|
|
\section{Integer bitwise ops}
|
|
\label{sec:bitwise}
|
|
\defun{arithmetic-shift} {i j} \integer
|
|
\defunx {bitwise-and} {i j} \integer
|
|
\defunx {bitwise-ior} {i j} \integer
|
|
\defunx {bitwise-not} {i} \integer
|
|
\defunx {bitwise-xor} {i j} \integer
|
|
\begin{desc}
|
|
These operations operate on integers representing semi-infinite
|
|
bit strings, using a 2's-complement encoding.
|
|
|
|
\ex{arithmetic-shift} shifts \var{i} by \var{j} bits.
|
|
A left shift is $j > 0$; a right shift is $j < 0$.
|
|
\end{desc}
|
|
|
|
\section{List procedures}
|
|
\dfn{nth}{list i}{object}{procedure \textbf{(obsolete)}}
|
|
\begin{desc}
|
|
Returns the $i^{\mathrm th}$ element of \var{list}.
|
|
The first element (the car) is \ex{(nth \var{list} 0)},
|
|
the second element is \ex{(nth \var{list} 1)}, and so on.
|
|
|
|
This procedure is provided as it is useful for accessing elements
|
|
from the lists returned by the field-readers (chapter~\ref{chapt:fr-awk}).
|
|
|
|
The functionality of \ex{nth} is equivalent to that of \RnRS{}'s
|
|
\ex{list-ref}. Therefore, \ex{nth} will go away in a future release.
|
|
\end{desc}
|
|
|
|
\section{Password encryption}
|
|
|
|
\defun {crypt} {key salt} {encrypted value}
|
|
|
|
Decrypts \var{key} by directly calling the \texttt{crypt} function
|
|
using \var{salt} to perturb the hashing algorithm. \var{Salt} must be
|
|
a two-character string consisting of digits, alphabetic characters,
|
|
``.'' or ``\verb+\+''. The length of \var{key} may be at most eight.
|
|
|
|
\section{Dot-Locking}
|
|
Section \ref{sec:filelocking} already points out that {\Posix}'s file
|
|
locks are almost useless in practice. To bypass this restriction other
|
|
advisory locking mechanisms, based only on standard file operations,
|
|
where invented. One of them is the so-called \emph{dot-locking} scheme
|
|
where the lock of \textit{file-name} is represented by the file
|
|
\textit{file-name}\texttt{.lock}. Care is taken that only one process
|
|
may generate the lock for a given file.
|
|
|
|
Here is scsh's interface to dot-locking:
|
|
|
|
\defun {obtain-dot-lock} {file-name [interval retry-number stale-time]} {\boolean}
|
|
|
|
\begin{desc}
|
|
Tries to obtain the lock for \var{file-name}. If the file is already
|
|
locked, the thread sleeps for \var{interval} seconds (default is 1)
|
|
before it retries. If the lock cannot be obtained after
|
|
\var{retry-number} attempts, the procedure returns \sharpf,
|
|
otherwise \sharpt. The default value of \var{retry-number} is
|
|
\sharpf{} which corresponds to an infinite number of retires.
|
|
|
|
If \var{stale-time} is non-\sharpf, it specifies the minimum age a
|
|
lock may have (in seconds) before it is considered \textit{stale}.
|
|
\ex{Obtain-dot-lock} attempts to delete stale locks. If it was
|
|
succcessful obtaining a lock after breaking it, \ex{obtain-dot-lock}
|
|
returns \ex{broken}. If \var{stale-time} is \sharpf,
|
|
\ex{obtain-dot-lock} never considers a lock stale. The default for
|
|
\var{stale-time} is 300.
|
|
|
|
Note that it is possible that \ex{obtain-dot-lock} breaks a lock
|
|
but nevertheless fails to obtain it otherwise. If it is necessary
|
|
to handle this case specially, use \ex{break-dot-lock} directly
|
|
(see below) rather than specifying a non-\sharpf{} \var{stale-time}
|
|
\end{desc}
|
|
|
|
\defun {break-dot-lock} {file-name} {undefined}
|
|
|
|
\begin{desc}
|
|
Breaks the lock for \var{file-name} if one exists. Note that
|
|
breaking a lock does \emph{not} imply a subsequent
|
|
\ex{obtain-dot-lock} will succeed, as another party may have
|
|
acquired the lock between \ex{break-dot-lock} and
|
|
\ex{obtain-dot-lock}.
|
|
\end{desc}
|
|
|
|
\defun {release-dot-lock} {file-name} {\boolean}
|
|
|
|
\begin{desc}
|
|
Releases the lock for \var{file-name}. On success,
|
|
\ex{release-dot-lock} returns \sharpt, otherwise \sharpf. Note that
|
|
this procedure can also be used to break the lock for
|
|
\var{file-name}.
|
|
\end{desc}
|
|
|
|
|
|
\defun{with-dot-lock*} {file-name thunk} {value(s) of thunk}
|
|
\dfnx{with-dot-lock} {file-name body \ldots} {value(s) of body}{syntax}
|
|
|
|
\begin{desc}
|
|
The procedure \ex{with-dot-lock*} obtains the requested lock, and
|
|
then calls \ex{(\var{thunk})}. When \var{thunk} returns, the lock is
|
|
released. A non-local exit (\eg, throwing to a saved continuation
|
|
or raising an exception) also causes the lock to be released.
|
|
|
|
After a normal return from \var{thunk}, its return values are
|
|
returned by \ex{with-dot-lock*}. The \ex{with-dot-lock} special
|
|
form is equivalent syntactic sugar.
|
|
\end{desc}
|
|
|
|
\section{Syslog facility}
|
|
\label{syslog-facility}
|
|
|
|
(Note: the functionality presented in this section is still somewhat
|
|
experimental and thus subject to interface changes.)
|
|
|
|
The procedures in this section provide access to the 4.2BSD syslog
|
|
facility present in most POSIX systems. The functionality is in a
|
|
structure called \ex{syslog}. There's an additional structure
|
|
\ex{syslog-channels} documented below. The scsh interface to
|
|
the syslog facility differs significantly from that of the Unix
|
|
library functionality in order to support multiple simultaneous
|
|
connections to the syslog facility.
|
|
|
|
Log messages carry a variety of parameters beside the text of the
|
|
message itself, namely a set of options controlling the output format
|
|
and destination, the facility identifying the class of programs the
|
|
message is coming from, an identifier specifying the conrete program,
|
|
and the level identifying the importance of the message. Moreover, a
|
|
log mask can prevent messages at certain levels to be actually sent to
|
|
the syslog daemon.
|
|
|
|
\subsection*{Log options}
|
|
|
|
A log option specifies details of the I/O behavior of the syslog
|
|
facility. A syslog option is an element of a finite type (see
|
|
the \scm~manual) constructed by the
|
|
\ex{syslog-option} macro. The syslog facility works with sets of
|
|
options which are represented as enum sets (see
|
|
the \scm~manual).
|
|
|
|
\dfn{syslog-option}{option-name}{option}{syntax}
|
|
|
|
\defun{syslog-option?}{x}{boolean}
|
|
|
|
\defun{make-syslog-options}{list}{options}
|
|
|
|
\dfn{syslog-options}{option-name \ldots}{options}{syntax}
|
|
|
|
\defun{syslog-options?}{x}{boolean}
|
|
|
|
\begin{desc}
|
|
\ex{Syslog-option} constructs a log option from the name of an
|
|
option. (The possible names are listed below.) \ex{Syslog-option?}
|
|
is a predicate for log options. Options are comparable using
|
|
\ex{eq?}. \ex{Make-syslog-options} constructs a set of options
|
|
from a list of options. \ex{Syslog-options} is a macro which
|
|
expands into an expression returning a set of options from names.
|
|
\ex{Syslog-options?} is a predicate for sets of options.
|
|
\end{desc}
|
|
%
|
|
Here is a list of possible names of syslog options:
|
|
|
|
\begin{description}
|
|
\item[\ex{console}]
|
|
If syslog cannot pass the message to syslogd it will attempt to
|
|
write the message to the console.
|
|
|
|
\item[\ex{delay}]
|
|
Delay opening the connection to syslogd immediately until the first
|
|
message is logged.
|
|
|
|
\item[\ex{no-delay}]
|
|
Open the connection to syslogd immediately. Normally
|
|
the open is delayed until the first message is logged.
|
|
Useful for programs that need to manage the order in which
|
|
file descriptors are allocated.
|
|
|
|
\noindent\textbf{NOTA BENE:}
|
|
The \ex{delay} and \ex{no-delay} options are included for
|
|
completeness, but do not have the expected effect in the present
|
|
Scheme interface: Because the Scheme interface has to multiplex
|
|
multiple simultaneous connections to the syslog facility over a
|
|
single one, open and close operations on that facility happen at
|
|
unpredictable times.
|
|
|
|
\item[\ex{log-pid}]
|
|
Log the process id with each message: useful for identifying
|
|
instantiations of daemons.
|
|
\end{description}
|
|
|
|
\subsection*{Log facilities}
|
|
|
|
A log facility identifies the originator of a log message from a
|
|
finite set known to the system. Each originator is identified by a
|
|
name:
|
|
|
|
\dfn{syslog-facility}{facility-name}{facility}{syntax}
|
|
\defun{syslog-facility?}{x}{boolean}
|
|
|
|
\begin{desc}
|
|
\ex{Syslog-facility} is macro that expands into an expression
|
|
returning a facility for a given name. \ex{Syslog-facility?} is a
|
|
predicate for facilities. Facilities are comparable via \ex{eq?}.
|
|
\end{desc}
|
|
%
|
|
Here is a list of possible names of syslog facilities:
|
|
|
|
\begin{description}
|
|
\item[\ex{authorization}]
|
|
The authorization system: login, su, getty, etc.
|
|
|
|
\item[\ex{cron}]
|
|
The cron daemon.
|
|
|
|
\item[\ex{daemon}]
|
|
System daemons, such as routed, that are not provided for explicitly
|
|
by other facilities.
|
|
|
|
\item[\ex{kernel}]
|
|
Messages generated by the kernel.
|
|
|
|
\item[\ex{lpr}]
|
|
The line printer spooling system: lpr, lpc, lpd, etc.
|
|
|
|
\item[\ex{mail}]
|
|
The mail system.
|
|
|
|
\item[\ex{news}]
|
|
The network news system.
|
|
|
|
\item[\ex{user}]
|
|
Messages generated by random user processes.
|
|
|
|
\item[\ex{uucp}]
|
|
The uucp system.
|
|
|
|
\item[\ex{local0} \ex{local1} \ex{local2} \ex{local3} \ex{local4} \ex{local5} \ex{local6} \ex{local7}]
|
|
Reserved for local use.
|
|
\end{description}
|
|
|
|
\subsection*{Log levels}
|
|
|
|
A log level identifies the importance of a message from a fixed set
|
|
of possible levels.
|
|
|
|
\dfn{syslog-level}{level-name}{level}{syntax}
|
|
\defun{syslog-level?}{x}{boolean}
|
|
%
|
|
\begin{desc}
|
|
\ex{Syslog-level} is macro that expands into an expression returning
|
|
a facility for a given name. \ex{Syslog-level?} is a predicate for
|
|
facilities. Levels are comparable via \ex{eq?}.
|
|
\end{desc}
|
|
%
|
|
Here is a list of possible names of syslog levels:
|
|
|
|
\begin{description}
|
|
\item[\ex{emergency}]
|
|
A panic condition. This is normally broadcast to all users.
|
|
|
|
\item[\ex{alert}]
|
|
A condition that should be corrected immediately, such as a
|
|
corrupted system database.
|
|
|
|
\item[\ex{critical}]
|
|
Critical conditions, e.g., hard device errors.
|
|
|
|
\item[\ex{error}]
|
|
Errors.
|
|
|
|
\item[\ex{warning}]
|
|
Warning messages.
|
|
|
|
\item[\ex{notice}]
|
|
Conditions that are not error conditions, but should possibly be
|
|
handled specially.
|
|
|
|
\item[\ex{info}]
|
|
Informational messages.
|
|
|
|
\item[\ex{debug}]
|
|
Messages that contain information normally of use only when
|
|
debugging a program.
|
|
\end{description}
|
|
|
|
\subsection*{Log masks}
|
|
|
|
A log masks can mask out log messages at a set of levels. A log
|
|
mask is an enum set of log levels.
|
|
|
|
\defun{make-syslog-mask}{list}{mask}
|
|
\dfn{syslog-mask}{level-name \ldots}{mask}{syntax}
|
|
\defvar{syslog-mask-all}{mask}
|
|
\defun{syslog-mask-upto}{level}{mask}
|
|
\defun{syslog-mask?}{x}{boolean}
|
|
|
|
\begin{desc}
|
|
\ex{Make-syslog-mask} constructs a mask from a list of levels.
|
|
\ex{Syslog-mask} is a macro which constructs a mask from names of
|
|
levels. \ex{Syslog-mask-all} is a predefined log mask containing
|
|
all levels. \ex{Syslog-mask-upto} returns a mask consisting of all
|
|
levels up to and including a certain level, starting with
|
|
\ex{emergency}.
|
|
\end{desc}
|
|
|
|
\subsection*{Logging}
|
|
|
|
Scheme~48 dynamically maintains implicit connections to the syslog
|
|
facility specifying a current identifier, current options, a current
|
|
facility and a current log mask. This implicit connection is held in
|
|
a thread fluid (see
|
|
Section~\ref{sec:ps_interac}). Hence, every thread
|
|
maintains it own implicit connection to syslog. Note that the
|
|
connection is not implicitly preserved across a \ex{spawn}, but it
|
|
is preserved across a \ex{fork-thread}:
|
|
|
|
|
|
\defun{with-syslog-destination}{string options facility mask thunk}{value}
|
|
\defun{set-syslog-destination!}{string options facility mask}{undefined}
|
|
%
|
|
\begin{desc}
|
|
\ex{With-syslog-destination} dynamically binds parameters of the
|
|
implicit connection to the syslog facility and runs \var{thunk}
|
|
within those parameter bindings, returning what \var{thunk}
|
|
returns. Each of the parameters may be \ex{\#f} in which case the
|
|
previous values will be used. \ex{Set-syslog-destination!} sets the
|
|
parameters of the implicit connection of the current thread.
|
|
\end{desc}
|
|
|
|
\defun{syslog}{level message}{undefined}
|
|
\defun{syslog}{level message [string options syslog-facility]}{undefined}
|
|
%
|
|
\begin{desc}
|
|
\ex{Syslog} actually logs a message. Each of the parameters of the
|
|
implicit connection (except for the log mask) can be explicitly
|
|
specified as well for the current call to \ex{syslog}, overriding
|
|
the parameters of the channel. The parameters revert to their
|
|
original values after the call.
|
|
\end{desc}
|
|
|
|
\subsection*{Syslog channels}
|
|
%
|
|
The \ex{syslog-channels} structure allows direct manipulation of
|
|
syslog channels, the objects that represent connections to the syslog
|
|
facility. Note that it is
|
|
not necessary to explicitly open a syslog channel to do logging.
|
|
|
|
\defun{open-syslog-channel}{string options facility mask}{channel}
|
|
\defun{close-syslog-channel}{channel}{undefined}
|
|
\defun{syslog}{level message channel}{undefined}
|
|
%
|
|
\begin{desc}
|
|
\ex{Open-syslog-channel} and \ex{close-syslog-channel} create and
|
|
destroy a connection to the syslog facility, respectively. The
|
|
specified form of calling \ex{syslog} logs to the specified channel.
|
|
\end{desc}
|
|
|
|
|
|
\section{MD5 interface}
|
|
\label{sec:md5}
|
|
|
|
Scsh provides a direct interface to the MD5 functions to compute the
|
|
``fingerprint'' or ``message digest'' of a file or string. It uses the
|
|
C library written by Colin Plum.
|
|
|
|
\defun{md5-digest-for-string}{string}{md5-digest}
|
|
\begin{desc}
|
|
Calculates the MD5 digest for the given string.
|
|
\end{desc}
|
|
\defun{md5-digest-for-port}{port [buffer-size]}{md5-digest}
|
|
\begin{desc}
|
|
Reads the contents of the port and calculates the MD5 digest for it.
|
|
The optional argument \var{buffer-size} determines the size of the
|
|
port's input buffer in bytes. It defaults to 1024 bytes.
|
|
\end{desc}
|
|
|
|
\defun{md5-digest?}{thing}{boolean}
|
|
\begin{desc}
|
|
The type predicate for MD5 digests: \ex{md5-digest?} returns true if
|
|
and only if \var{thing} is a MD5 digest.
|
|
\end{desc}
|
|
\defun{md5-digest->number}{md5-digest}{number}
|
|
\begin{desc}
|
|
Returns the number corresponding to the MD5 digest.
|
|
\end{desc}
|
|
\defun{number->md5-digest}{number}{md5-digest}
|
|
\begin{desc}
|
|
Creates a MD5 digest from a number.
|
|
\end{desc}
|
|
|
|
\defun{make-md5-context}{}{md5-context}
|
|
\defunx{md5-context?}{thing}{boolean}
|
|
\defunx{update-md5-context!}{md5-context string}\undefined
|
|
\defunx{md5-context->md5-digest}{md5-context}{md5-digest}
|
|
\begin{desc}
|
|
These procedures provide a low-level interface to the library. A
|
|
\var{md5-context} stores the state of a MD5 computation, it is
|
|
created by \ex{make-md5-context}, its type predicate is
|
|
\ex{md5-context?}. The procedure \ex{update-md5-context!} extends
|
|
the \var{md5-context} by the given string. Finally,
|
|
\ex{md5-context->md5-digest} returns the \var{md5-digest} for the
|
|
\var{md5-context}. With these procedures it is possible to
|
|
incrementally add strings to a \var{md5-context} before computing
|
|
the digest.
|
|
\end{desc}
|
|
|
|
%%% Local Variables:
|
|
%%% mode: latex
|
|
%%% TeX-master: "man"
|
|
%%% End:
|