POSIX System Calls and Networking
*********************************

POSIX Interface Conventions
===========================

These interfaces provide access to operating system facilities. They provide a simple wrapping around the underlying C interfaces to make usage from Scheme more convenient.  They are also used to implement the Guile port of The Scheme shell (scsh).

Generally there is a single procedure for each corresponding Unix facility.  There are some exceptions, such as procedures implemented for speed and convenience in Scheme with no primitive Unix equivalent, e.g., copy-file.

The interfaces are intended as far as possible to be portable across different versions of Unix.  In some cases procedures which can't be implemented on particular systems may become no-ops, or perform limited actions.  In other cases they may throw errors.

General naming conventions are as follows:

  * The Scheme name is often identical to the name of the underlying Unix facility.

  * Underscores in Unix procedure names are converted to hyphens.

  * Procedures which destructively modify Scheme data have exclaimation marks appended, e.g., recv!.

  * Predicates (returning only #t or #f) have question marks appended, e.g., access?.

  * Some names are changed to avoid conflict with dissimilar interfaces defined by scsh, e.g., primitive-fork.

  * Unix preprocessor names such as EPERM or R_OK are converted to Scheme variables of the same name (underscores are not replaced with hyphens).

Unexpected conditions are generally handled by raising exceptions. There are a few procedures which return a special value if they don't succeed, e.g., getenv returns #f if it the requested string is not found in the environment.  These cases are noted in the documentation.

For ways to deal with exceptions, Exceptions.

Errors which the C-library would report by returning a NULL pointer or through some other means are reported by raising a system-error exception. The value of the Unix errno variable is available in the data passed by the exception.

Here's an ad-hoc (This may be changed in the future; be prepared to rewrite this sort of code.) way to extract the errno value from an exception:

     (catch
      'system-error
      (lambda ()
        (mkdir "/this-ought-to-fail-if-I'm-not-root"))
      (lambda stuff
        (let ((errno (car (list-ref stuff 4))))
          (cond
           ((= errno EACCES)
            (display "You're not allowed to do that."))
           ((= errno EEXIST)
            (display "Already exists."))
           (#t
            (display (strerror errno))))
          (newline))))

The important thing to note is that the errno value can be extracted with (car (list-ref stuff 4)).

Ports and File Descriptors
==========================

Conventions generally follow those of scsh, The Scheme shell (scsh).

File ports are implemented using low-level operating system I/O facilities, with optional buffering to improve efficiency see File Ports

Note that some procedures (e.g., recv!) will accept ports as arguments, but will actually operate directly on the file descriptor underlying the port.  Any port buffering is ignored, including the buffer which implements peek-char and unread-char.

The force-output and drain-input procedures can be used to clear the buffers.

Each open file port has an associated operating system file descriptor. File descriptors are generally not useful in Scheme programs; however they may be needed when interfacing with foreign code and the Unix environment.

A file descriptor can be extracted from a port and a new port can be created from a file descriptor.  However a file descriptor is just an integer and the garbage collector doesn't recognise it as a reference to the port.  If all other references to the port were dropped, then it's likely that the garbage collector would free the port, with the side-effect of closing the file descriptor prematurely.

To assist the programmer in avoiding this problem, each port has an associated "revealed count" which can be used to keep track of how many times the underlying file descriptor has been stored in other places. If a port's revealed count is greater than zero, the file descriptor will not be closed when the port is gabage collected.  A programmer can therefore ensure that the revealed count will be greater than zero if the file descriptor is needed elsewhere.

For the simple case where a file descriptor is "imported" once to become a port, it does not matter if the file descriptor is closed when the port is garbage collected.  There is no need to maintain a revealed count.  Likewise when "exporting" a file descriptor to the external environment, setting the revealed count is not required provided the port is kept open (i.e., is pointed to by a live Scheme binding) while the file descriptor is in use.

To correspond with traditional Unix behaviour, the three file descriptors (0, 1 and 2) are automatically imported when a program starts up and assigned to the initial values of the current input, output and error ports.  The revealed count for each is initially set to one, so that dropping references to one of these ports will not result in its garbage collection: it could be retrieved with fdopen or fdes->ports.

 -- primitive: port-revealed port
     Return the revealed count for PORT.

 -- primitive: set-port-revealed! port rcount
     Sets the revealed count for a port to a given value. The return value is unspecified.

 -- primitive: fileno port
     Return the integer file descriptor underlying PORT.  Does not change its revealed count.

 -- procedure: port->fdes port
     Returns the integer file descriptor underlying PORT.  As a side effect the revealed count of PORT is incremented.

 -- primitive: fdopen fdes modes
     Return a new port based on the file descriptor FDES. Modes are given by the string MODES.  The revealed count of the port is initialized to zero.  The modes string is the same as that accepted by open-file.

 -- primitive: fdes->ports fd
     Return a list of existing ports which have FDES as an underlying file descriptor, without changing their revealed counts.

 -- procedure: fdes->inport fdes
     Returns an existing input port which has FDES as its underlying file descriptor, if one exists, and increments its revealed count. Otherwise, returns a new input port with a revealed count of 1.

 -- procedure: fdes->outport fdes
     Returns an existing output port which has FDES as its underlying file descriptor, if one exists, and increments its revealed count. Otherwise, returns a new output port with a revealed count of 1.

 -- primitive: primitive-move->fdes port fd
     Moves the underlying file descriptor for PORT to the integer value FDES without changing the revealed count of PORT. Any other ports already using this descriptor will be automatically shifted to new descriptors and their revealed counts reset to zero. The return value is #f if the file descriptor already had the required value or #t if it was moved.

 -- procedure: move->fdes port fdes
     Moves the underlying file descriptor for PORT to the integer value FDES and sets its revealed count to one.  Any other ports already using this descriptor will be automatically shifted to new descriptors and their revealed counts reset to zero. The return value is unspecified.

 -- procedure: release-port-handle port
     Decrements the revealed count for a port.

 -- primitive: fsync object
     Copies any unwritten data for the specified output file descriptor to disk. If PORT/FD is a port, its buffer is flushed before the underlying file descriptor is fsync'd. The return value is unspecified.

 -- primitive: open path flags [mode]
     Open the file named by PATH for reading and/or writing. FLAGS is an integer specifying how the file should be opened. MODE is an integer specifying the permission bits of the file, if it needs to be created, before the umask is applied.  The default is 666 (Unix itself has no default).

     FLAGS can be constructed by combining variables using logior. Basic flags are:

      -- Variable: O_RDONLY
          Open the file read-only.

      -- Variable: O_WRONLY
          Open the file write-only.

      -- Variable: O_RDWR
          Open the file read/write.

      -- Variable: O_APPEND
          Append to the file instead of truncating.

      -- Variable: O_CREAT
          Create the file if it does not already exist.

     See the Unix documentation of the open system call for additional flags.

 -- primitive: open-fdes path flags [mode]
     Similar to open but return a file descriptor instead of a port.

 -- primitive: close fd_or_port
     Similar to close-port (see close-port), but also works on file descriptors.  A side effect of closing a file descriptor is that any ports using that file descriptor are moved to a different file descriptor and have their revealed counts set to zero.

 -- primitive: close-fdes fd
     A simple wrapper for the close system call. Close file descriptor FD, which must be an integer. Unlike close (see close), the file descriptor will be closed even if a port is using it. The return value is unspecified.

 -- primitive: unread-char char [port]
     Place CHAR in PORT so that it will be read by the next read operation.  If called multiple times, the unread characters will be read again in last-in first-out order.  If PORT is not supplied, the current input port is used.

 -- primitive: unread-string str port
     Place the string STR in PORT so that its characters will be read in subsequent read operations.  If called multiple times, the unread characters will be read again in last-in first-out order.  If PORT is not supplied, the current-input-port is used.

 -- primitive: pipe
     Return a newly created pipe: a pair of ports which are linked together on the local machine.  The car is the input port and the cdr is the output port.  Data written (and flushed) to the output port can be read from the input port. Pipes are commonly used for communication with a newly forked child process.  The need to flush the output port can be avoided by making it unbuffered using setvbuf. Writes occur atomically provided the size of the data in bytes is not greater than the value of PIPE_BUF.  Note that the output port is likely to block if too much data (typically equal to PIPE_BUF) has been written but not yet read from the input port.

The next group of procedures perform a dup2 system call, if NEWFD (an integer) is supplied, otherwise a dup.  The file descriptor to be duplicated can be supplied as an integer or contained in a port.  The type of value returned varies depending on which procedure is used.

All procedures also have the side effect when performing dup2 that any ports using NEWFD are moved to a different file descriptor and have their revealed counts set to zero.

 -- primitive: dup->fdes fd_or_port [fd]
     Return a new integer file descriptor referring to the open file designated by FD_OR_PORT, which must be either an open file port or a file descriptor.

 -- procedure: dup->inport port/fd [newfd]
     Returns a new input port using the new file descriptor.

 -- procedure: dup->outport port/fd [newfd]
     Returns a new output port using the new file descriptor.

 -- procedure: dup port/fd [newfd]
     Returns a new port if PORT/FD is a port, with the same mode as the supplied port, otherwise returns an integer file descriptor.

 -- procedure: dup->port port/fd mode [newfd]
     Returns a new port using the new file descriptor.  MODE supplies a mode string for the port (see open-file).

 -- procedure: duplicate-port port modes
     Returns a new port which is opened on a duplicate of the file descriptor underlying PORT, with mode string MODES as for open-file.  The two ports will share a file position and file status flags.

     Unexpected behaviour can result if both ports are subsequently used and the original and/or duplicate ports are buffered. The mode string can include 0 to obtain an unbuffered duplicate port.

     This procedure is equivalent to (dup->port PORT MODES).

 -- primitive: redirect-port old new
     This procedure takes two ports and duplicates the underlying file descriptor from OLD-PORT into NEW-PORT.  The current file descriptor in NEW-PORT will be closed. After the redirection the two ports will share a file position and file status flags.

     The return value is unspecified.

     Unexpected behaviour can result if both ports are subsequently used and the original and/or duplicate ports are buffered.

     This procedure does not have any side effects on other ports or revealed counts.

 -- primitive: dup2 oldfd newfd
     A simple wrapper for the dup2 system call. Copies the file descriptor OLDFD to descriptor number NEWFD, replacing the previous meaning of NEWFD.  Both OLDFD and NEWFD must be integers. Unlike for dup->fdes or primitive-move->fdes, no attempt is made to move away ports which are using NEWFD. The return value is unspecified.

 -- primitive: port-mode port
     Return the port modes associated with the open port PORT. These will not necessarily be identical to the modes used when the port was opened, since modes such as "append" which are used only during port creation are not retained.

 -- primitive: close-all-ports-except . ports
     [DEPRECATED] Close all open file ports used by the interpreter except for those supplied as arguments.  This procedure was intended to be used before an exec call to close file descriptors which are not needed in the new process.  However it has the undesirable side-effect of flushing buffes, so it's deprecated. Use port-for-each instead.

 -- primitive: port-for-each proc
     Apply PROC to each port in the Guile port table in turn.  The return value is unspecified.  More specifically, PROC is applied exactly once to every port that exists in the system at the time PORT-FOR-EACH is invoked. Changes to the port table while PORT-FOR-EACH is running have no effect as far as PORT-FOR-EACH is concerned.

 -- primitive: setvbuf port mode [size]
     Set the buffering mode for PORT.  MODE can be:

     _IONBF
          non-buffered

     _IOLBF
          line buffered

     _IOFBF
          block buffered, using a newly allocated buffer of SIZE bytes. If SIZE is omitted, a default size will be used.

 -- primitive: fcntl object cmd [value]
     Apply COMMAND to the specified file descriptor or the underlying file descriptor of the specified port.  VALUE is an optional integer argument.

     Values for COMMAND are:

     F_DUPFD
          Duplicate a file descriptor

     F_GETFD
          Get flags associated with the file descriptor.

     F_SETFD
          Set flags associated with the file descriptor to VALUE.

     F_GETFL
          Get flags associated with the open file.

     F_SETFL
          Set flags associated with the open file to VALUE

     F_GETOWN
          Get the process ID of a socket's owner, for SIGIO signals.

     F_SETOWN
          Set the process that owns a socket to VALUE, for SIGIO signals.

     FD_CLOEXEC
          The value used to indicate the "close on exec" flag with F_GETFL or F_SETFL.

 -- primitive: flock file operation
     Apply or remove an advisory lock on an open file. OPERATION specifies the action to be done:

     LOCK_SH
          Shared lock.  More than one process may hold a shared lock for a given file at a given time.

     LOCK_EX
          Exclusive lock.  Only one process may hold an exclusive lock for a given file at a given time.

     LOCK_UN
          Unlock the file.

     LOCK_NB
          Don't block when locking.  May be specified by bitwise OR'ing it to one of the other operations.

     The return value is not specified. FILE may be an open file descriptor or an open file descriptior port.

 -- primitive: select reads writes excepts [secs [usecs]]
     This procedure has a variety of uses: waiting for the ability to provide input, accept output, or the existance of exceptional conditions on a collection of ports or file descriptors, or waiting for a timeout to occur. It also returns if interrupted by a signal.

     READS, WRITES and EXCEPTS can be lists or vectors, with each member a port or a file descriptor. The value returned is a list of three corresponding lists or vectors containing only the members which meet the specified requirement.  The ability of port buffers to provide input or accept output is taken into account. Ordering of the input lists or vectors is not preserved.

     The optional arguments SECS and USECS specify the timeout.  Either SECS can be specified alone, as either an integer or a real number, or both SECS and USECS can be specified as integers, in which case USECS is an additional timeout expressed in microseconds.  If SECS is omitted or is #f then select will wait for as long as it takes for one of the other conditions to be satisfied.

     The scsh version of select differs as follows: Only vectors are accepted for the first three arguments. The USECS argument is not supported. Multiple values are returned instead of a list. Duplicates in the input vectors appear only once in output. An additional select! interface is provided.

File System
===========

These procedures allow querying and setting file system attributes (such as owner, permissions, sizes and types of files); deleting, copying, renaming and linking files; creating and removing directories and querying their contents; syncing the file system and creating special files.

 -- primitive: access? path how
     Return #t if PATH corresponds to an existing file and the current process has the type of access specified by HOW, otherwise #f.  HOW should be specified using the values of the variables listed below.  Multiple values can be combined using a bitwise or, in which case #t will only be returned if all accesses are granted. Permissions are checked using the real id of the current process, not the effective id, although it's the effective id which determines whether the access would actually be granted.
      -- Variable: R_OK
          test for read permission.

      -- Variable: W_OK
          test for write permission.

      -- Variable: X_OK
          test for execute permission.

      -- Variable: F_OK
          test for existence of the file.

 -- primitive: stat object
     Return an object containing various information about the file determined by OBJ.  OBJ can be a string containing a file name or a port or integer file descriptor which is open on a file (in which case fstat is used as the underlying system call). The object returned by stat can be passed as a single parameter to the following procedures, all of which return integers:

     stat:dev
          The device containing the file.

     stat:ino
          The file serial number, which distinguishes this file from all other files on the same device.

     stat:mode
          The mode of the file.  This includes file type information and the file permission bits.  See stat:type and stat:perms below.

     stat:nlink
          The number of hard links to the file.

     stat:uid
          The user ID of the file's owner.

     stat:gid
          The group ID of the file.

     stat:rdev
          Device ID; this entry is defined only for character or block special files.

     stat:size
          The size of a regular file in bytes.

     stat:atime
          The last access time for the file.

     stat:mtime
          The last modification time for the file.

     stat:ctime
          The last modification time for the attributes of the file.

     stat:blksize
          The optimal block size for reading or writing the file, in bytes.

     stat:blocks
          The amount of disk space that the file occupies measured in units of 512 byte blocks.

     In addition, the following procedures return the information from stat:mode in a more convenient form:

     stat:type
          A symbol representing the type of file.  Possible values are regular, directory, symlink, block-special, char-special, fifo, socket and unknown

     stat:perms
          An integer representing the access permission bits.

 -- primitive: lstat str
     Similar to stat, but does not follow symbolic links, i.e., it will return information about a symbolic link itself, not the file it points to.  PATH must be a string.

 -- primitive: readlink path
     Return the value of the symbolic link named by PATH (a string), i.e., the file that the link points to.

 -- primitive: chown object owner group
     Change the ownership and group of the file referred to by OBJECT to the integer values OWNER and GROUP.  OBJECT can be a string containing a file name or, if the platform supports fchown, a port or integer file descriptor which is open on the file.  The return value is unspecified.

     If OBJECT is a symbolic link, either the ownership of the link or the ownership of the referenced file will be changed depending on the operating system (lchown is unsupported at present).  If OWNER or GROUP is specified as -1, then that ID is not changed.

 -- primitive: chmod object mode
     Changes the permissions of the file referred to by OBJ. OBJ can be a string containing a file name or a port or integer file descriptor which is open on a file (in which case fchmod is used as the underlying system call). MODE specifies the new permissions as a decimal number, e.g., (chmod "foo" #o755). The return value is unspecified.

 -- primitive: utime pathname [actime [modtime]]
     utime sets the access and modification times for the file named by PATH.  If ACTIME or MODTIME is not supplied, then the current time is used.  ACTIME and MODTIME must be integer time values as returned by the current-time procedure.

          (utime "foo" (- (current-time) 3600))

     will set the access time to one hour in the past and the modification time to the current time.

 -- primitive: delete-file str
     Deletes (or "unlinks") the file specified by PATH.

 -- primitive: copy-file oldfile newfile
     Copy the file specified by PATH-FROM to PATH-TO. The return value is unspecified.

 -- primitive: rename-file oldname newname
     Renames the file specified by OLDNAME to NEWNAME. The return value is unspecified.

 -- primitive: link oldpath newpath
     Creates a new name NEWPATH in the file system for the file named by OLDPATH.  If OLDPATH is a symbolic link, the link may or may not be followed depending on the system.

 -- primitive: symlink oldpath newpath
     Create a symbolic link named PATH-TO with the value (i.e., pointing to) PATH-FROM.  The return value is unspecified.

 -- primitive: mkdir path [mode]
     Create a new directory named by PATH.  If MODE is omitted then the permissions of the directory file are set using the current umask.  Otherwise they are set to the decimal value specified with MODE.  The return value is unspecified.

 -- primitive: rmdir path
     Remove the existing directory named by PATH.  The directory must be empty for this to succeed.  The return value is unspecified.

 -- primitive: opendir dirname
     Open the directory specified by PATH and return a directory stream.

 -- primitive: directory-stream? obj
     Return a boolean indicating whether OBJECT is a directory stream as returned by opendir.

 -- primitive: readdir port
     Return (as a string) the next directory entry from the directory stream STREAM.  If there is no remaining entry to be read then the end of file object is returned.

 -- primitive: rewinddir port
     Reset the directory port STREAM so that the next call to readdir will return the first directory entry.

 -- primitive: closedir port
     Close the directory stream STREAM. The return value is unspecified.

 -- primitive: sync
     Flush the operating system disk buffers. The return value is unspecified.

 -- primitive: mknod path type perms dev
     Creates a new special file, such as a file corresponding to a device. PATH specifies the name of the file.  TYPE should be one of the following symbols: regular, directory, symlink, block-special, char-special, fifo, or socket.  PERMS (an integer) specifies the file permissions. DEV (an integer) specifies which device the special file refers to.  Its exact interpretation depends on the kind of special file being created.

     E.g.,

          (mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))

     The return value is unspecified.

 -- primitive: tmpnam
     Return a name in the file system that does not match any existing file.  However there is no guarantee that another process will not create the file after tmpnam is called. Care should be taken if opening the file, e.g., use the O_EXCL open flag or use mkstemp! instead.

 -- primitive: mkstemp! tmpl
     Create a new unique file in the file system and returns a new buffered port open for reading and writing to the file. TMPL is a string specifying where the file should be created: it must end with XXXXXX and will be changed in place to return the name of the temporary file.

 -- primitive: dirname filename
     Return the directory name component of the file name FILENAME. If FILENAME does not contain a directory component, . is returned.

 -- primitive: basename filename [suffix]
     Return the base name of the file name FILENAME. The base name is the file name without any directory components. If SUFFIX is privided, and is equal to the end of BASENAME, it is removed also.

User Information
================

The facilities in this section provide an interface to the user and group database. They should be used with care since they are not reentrant.

The following functions accept an object representing user information and return a selected component:

passwd:name
     The name of the userid.

passwd:passwd
     The encrypted passwd.

passwd:uid
     The user id number.

passwd:gid
     The group id number.

passwd:gecos
     The full name.

passwd:dir
     The home directory.

passwd:shell
     The login shell.

 -- procedure: getpwuid uid
     Look up an integer userid in the user database.

 -- procedure: getpwnam name
     Look up a user name string in the user database.

 -- procedure: setpwent
     Initializes a stream used by getpwent to read from the user database. The next use of getpwent will return the first entry.  The return value is unspecified.

 -- procedure: getpwent
     Return the next entry in the user database, using the stream set by setpwent.

 -- procedure: endpwent
     Closes the stream used by getpwent.  The return value is unspecified.

 -- primitive: setpw [arg]
     If called with a true argument, initialize or reset the password data stream.  Otherwise, close the stream.  The setpwent and endpwent procedures are implemented on top of this.

 -- primitive: getpw [user]
     Look up an entry in the user database.  OBJ can be an integer, a string, or omitted, giving the behaviour of getpwuid, getpwnam or getpwent respectively.

The following functions accept an object representing group information and return a selected component:

group:name
     The group name.

group:passwd
     The encrypted group password.

group:gid
     The group id number.

group:mem
     A list of userids which have this group as a supplimentary group.

 -- procedure: getgrgid gid
     Look up an integer groupid in the group database.

 -- procedure: getgrnam name
     Look up a group name in the group database.

 -- procedure: setgrent
     Initializes a stream used by getgrent to read from the group database. The next use of getgrent will return the first entry. The return value is unspecified.

 -- procedure: getgrent
     Return the next entry in the group database, using the stream set by setgrent.

 -- procedure: endgrent
     Closes the stream used by getgrent. The return value is unspecified.

 -- primitive: setgr [arg]
     If called with a true argument, initialize or reset the group data stream.  Otherwise, close the stream.  The setgrent and endgrent procedures are implemented on top of this.

 -- primitive: getgr [name]
     Look up an entry in the group database.  OBJ can be an integer, a string, or omitted, giving the behaviour of getgrgid, getgrnam or getgrent respectively.

In addition to the accessor procedures for the user database, the following shortcut procedures are also available.

 -- primitive: cuserid
     Return a string containing a user name associated with the effective user id of the process.  Return #f if this information cannot be obtained.

 -- primitive: getlogin
     Return a string containing the name of the user logged in on the controlling terminal of the process, or #f if this information cannot be obtained.

Time
====

 -- primitive: current-time
     Return the number of seconds since 1970-01-01 00:00:00 UTC, excluding leap seconds.

 -- primitive: gettimeofday
     Return a pair containing the number of seconds and microseconds since 1970-01-01 00:00:00 UTC, excluding leap seconds.  Note: whether true microsecond resolution is available depends on the operating system.

The following procedures either accept an object representing a broken down time and return a selected component, or accept an object representing a broken down time and a value and set the component to the value. The numbers in parentheses give the usual range.

tm:sec, set-tm:sec
     Seconds (0-59).

tm:min, set-tm:min
     Minutes (0-59).

tm:hour, set-tm:hour
     Hours (0-23).

tm:mday, set-tm:mday
     Day of the month (1-31).

tm:mon, set-tm:mon
     Month (0-11).

tm:year, set-tm:year
     Year (70-), the year minus 1900.

tm:wday, set-tm:wday
     Day of the week (0-6) with Sunday represented as 0.

tm:yday, set-tm:yday
     Day of the year (0-364, 365 in leap years).

tm:isdst, set-tm:isdst
     Daylight saving indicator (0 for "no", greater than 0 for "yes", less than 0 for "unknown").

tm:gmtoff, set-tm:gmtoff
     Time zone offset in seconds west of UTC (-46800 to 43200).

tm:zone, set-tm:zone
     Time zone label (a string), not necessarily unique.

 -- primitive: localtime time [zone]
     Return an object representing the broken down components of TIME, an integer like the one returned by current-time.  The time zone for the calculation is optionally specified by ZONE (a string), otherwise the TZ environment variable or the system default is used.

 -- primitive: gmtime time
     Return an object representing the broken down components of TIME, an integer like the one returned by current-time.  The values are calculated for UTC.

 -- primitive: mktime sbd_time [zone]
     BD-TIME is an object representing broken down time and zone is an optional time zone specifier (otherwise the TZ environment variable or the system default is used).

     Returns a pair: the car is a corresponding integer time value like that returned by current-time; the cdr is a broken down time object, similar to as BD-TIME but with normalized values.

 -- primitive: tzset
     Initialize the timezone from the TZ environment variable or the system default.  It's not usually necessary to call this procedure since it's done automatically by other procedures that depend on the timezone.

 -- primitive: strftime format stime
     Formats a time specification TIME using TEMPLATE.  TIME is an object with time components in the form returned by localtime or gmtime.  TEMPLATE is a string which can include formatting specifications introduced by a % character.  The formatting of month and day names is dependent on the current locale.  The value returned is the formatted string. See Formatting Date and Time (The GNU C Library Reference Manual).)

 -- primitive: strptime format string
     Performs the reverse action to strftime, parsing STRING according to the specification supplied in TEMPLATE.  The interpretation of month and day names is dependent on the current locale.  The value returned is a pair. The car has an object with time components in the form returned by localtime or gmtime, but the time zone components are not usefully set. The cdr reports the number of characters from STRING which were used for the conversion.

 -- Variable: internal-time-units-per-second
     The value of this variable is the number of time units per second reported by the following procedures.

 -- primitive: times
     Return an object with information about real and processor time.  The following procedures accept such an object as an argument and return a selected component:

     tms:clock
          The current real time, expressed as time units relative to an arbitrary base.

     tms:utime
          The CPU time units used by the calling process.

     tms:stime
          The CPU time units used by the system on behalf of the calling process.

     tms:cutime
          The CPU time units used by terminated child processes of the calling process, whose status has been collected (e.g., using waitpid).

     tms:cstime
          Similarly, the CPU times units used by the system on behalf of terminated child processes.

 -- primitive: get-internal-real-time
     Return the number of time units since the interpreter was started.

 -- primitive: get-internal-run-time
     Return the number of time units of processor time used by the interpreter.  Both system and user time are included but subprocesses are not.

Runtime Environment
===================

 -- primitive: program-arguments
 -- procedure: command-line
     Return the list of command line arguments passed to Guile, as a list of strings.  The list includes the invoked program name, which is usually "guile", but excludes switches and parameters for command line options like -e and -l.

 -- primitive: getenv nam
     Looks up the string NAME in the current environment.  The return value is #f unless a string of the form NAME=VALUE is found, in which case the string VALUE is returned.

 -- procedure: setenv name value
     Modifies the environment of the current process, which is also the default environment inherited by child processes.

     If VALUE is #f, then NAME is removed from the environment.  Otherwise, the string NAME=VALUE is added to the environment, replacing any existing string with name matching NAME.

     The return value is unspecified.

 -- primitive: environ [env]
     If ENV is omitted, return the current environment (in the Unix sense) as a list of strings.  Otherwise set the current environment, which is also the default environment for child processes, to the supplied list of strings.  Each member of ENV should be of the form NAME=VALUE and values of NAME should not be duplicated.  If ENV is supplied then the return value is unspecified.

 -- primitive: putenv str
     Modifies the environment of the current process, which is also the default environment inherited by child processes.

     If STRING is of the form NAME=VALUE then it will be written directly into the environment, replacing any existing environment string with name matching NAME.  If STRING does not contain an equal sign, then any existing string with name matching STRING will be removed.

     The return value is unspecified.

Processes
=========

 -- primitive: chdir str
     Change the current working directory to PATH. The return value is unspecified.

 -- primitive: getcwd
     Return the name of the current working directory.

 -- primitive: umask [mode]
     If MODE is omitted, retuns a decimal number representing the current file creation mask.  Otherwise the file creation mask is set to MODE and the previous value is returned.

     E.g., (umask #o022) sets the mask to octal 22, decimal 18.

 -- primitive: chroot path
     Change the root directory to that specified in PATH. This directory will be used for path names beginning with /.  The root directory is inherited by all children of the current process.  Only the superuser may change the root directory.

 -- primitive: getpid
     Return an integer representing the current process ID.

 -- primitive: getgroups
     Return a vector of integers representing the current supplimentary group IDs.

 -- primitive: getppid
     Return an integer representing the process ID of the parent process.

 -- primitive: getuid
     Return an integer representing the current real user ID.

 -- primitive: getgid
     Return an integer representing the current real group ID.

 -- primitive: geteuid
     Return an integer representing the current effective user ID. If the system does not support effective IDs, then the real ID is returned.  (feature? 'EIDs) reports whether the system supports effective IDs.

 -- primitive: getegid
     Return an integer representing the current effective group ID. If the system does not support effective IDs, then the real ID is returned.  (feature? 'EIDs) reports whether the system supports effective IDs.

 -- primitive: setuid id
     Sets both the real and effective user IDs to the integer ID, provided the process has appropriate privileges. The return value is unspecified.

 -- primitive: setgid id
     Sets both the real and effective group IDs to the integer ID, provided the process has appropriate privileges. The return value is unspecified.

 -- primitive: seteuid id
     Sets the effective user ID to the integer ID, provided the process has appropriate privileges.  If effective IDs are not supported, the real ID is set instead -- (feature? 'EIDs) reports whether the system supports effective IDs. The return value is unspecified.

 -- primitive: setegid id
     Sets the effective group ID to the integer ID, provided the process has appropriate privileges.  If effective IDs are not supported, the real ID is set instead -- (feature? 'EIDs) reports whether the system supports effective IDs. The return value is unspecified.

 -- primitive: getpgrp
     Return an integer representing the current process group ID. This is the POSIX definition, not BSD.

 -- primitive: setpgid pid pgid
     Move the process PID into the process group PGID.  PID or PGID must be integers: they can be zero to indicate the ID of the current process. Fails on systems that do not support job control. The return value is unspecified.

 -- primitive: setsid
     Creates a new session.  The current process becomes the session leader and is put in a new process group.  The process will be detached from its controlling terminal if it has one. The return value is an integer representing the new process group ID.

 -- primitive: waitpid pid [options]
     This procedure collects status information from a child process which has terminated or (optionally) stopped.  Normally it will suspend the calling process until this can be done.  If more than one child process is eligible then one will be chosen by the operating system.

     The value of PID determines the behaviour:

     PID greater than 0
          Request status information from the specified child process.

     PID equal to -1 or WAIT_ANY
          Request status information for any child process.

     PID equal to 0 or WAIT_MYPGRP
          Request status information for any child process in the current process group.

     PID less than -1
          Request status information for any child process whose process group ID is -PID.

     The OPTIONS argument, if supplied, should be the bitwise OR of the values of zero or more of the following variables:

      -- Variable: WNOHANG
          Return immediately even if there are no child processes to be collected.

      -- Variable: WUNTRACED
          Report status information for stopped processes as well as terminated processes.

     The return value is a pair containing:

      1. The process ID of the child process, or 0 if WNOHANG was specified and no process was collected.

      2. The integer status value.

The following three functions can be used to decode the process status code returned by waitpid.

 -- primitive: status:exit-val status
     Return the exit status value, as would be set if a process ended normally through a call to exit or _exit, if any, otherwise #f.

 -- primitive: status:term-sig status
     Return the signal number which terminated the process, if any, otherwise #f.

 -- primitive: status:stop-sig status
     Return the signal number which stopped the process, if any, otherwise #f.

 -- primitive: system [cmd]
     Execute CMD using the operating system's "command processor".  Under Unix this is usually the default shell sh.  The value returned is CMD's exit status as returned by waitpid, which can be interpreted using the functions above. If system is called without arguments, return a boolean indicating whether the command processor is available.

 -- primitive: primitive-exit [status]
     Terminate the current process without unwinding the Scheme stack. This is would typically be useful after a fork.  The exit status is STATUS if supplied, otherwise zero.

 -- primitive: execl filename . args
     Executes the file named by PATH as a new process image. The remaining arguments are supplied to the process; from a C program they are accessable as the argv argument to main. Conventionally the first ARG is the same as PATH. All arguments must be strings.

     If ARG is missing, PATH is executed with a null argument list, which may have system-dependent side-effects.

     This procedure is currently implemented using the execv system call, but we call it execl because of its Scheme calling interface.

 -- primitive: execlp filename . args
     Similar to execl, however if FILENAME does not contain a slash then the file to execute will be located by searching the directories listed in the PATH environment variable.

     This procedure is currently implemented using the execvp system call, but we call it execlp because of its Scheme calling interface.

 -- primitive: execle filename env . args
     Similar to execl, but the environment of the new process is specified by ENV, which must be a list of strings as returned by the environ procedure.

     This procedure is currently implemented using the execve system call, but we call it execle because of its Scheme calling interface.

 -- primitive: primitive-fork
     Creates a new "child" process by duplicating the current "parent" process. In the child the return value is 0.  In the parent the return value is the integer process ID of the child.

     This procedure has been renamed from fork to avoid a naming conflict with the scsh fork.

 -- primitive: nice incr
     Increment the priority of the current process by INCR.  A higher priority value means that the process runs less often. The return value is unspecified.

 -- primitive: setpriority which who prio
     Set the scheduling priority of the process, process group or user, as indicated by WHICH and WHO. WHICH is one of the variables PRIO_PROCESS, PRIO_PGRP or PRIO_USER, and WHO is interpreted relative to WHICH (a process identifier for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user identifier for PRIO_USER.  A zero value of WHO denotes the current process, process group, or user. PRIO is a value in the range -20 and 20, the default priority is 0; lower priorities cause more favorable scheduling.  Sets the priority of all of the specified processes.  Only the super-user may lower priorities. The return value is not specified.

 -- primitive: getpriority which who
     Return the scheduling priority of the process, process group or user, as indicated by WHICH and WHO. WHICH is one of the variables PRIO_PROCESS, PRIO_PGRP or PRIO_USER, and WHO is interpreted relative to WHICH (a process identifier for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user identifier for PRIO_USER.  A zero value of WHO denotes the current process, process group, or user.  Return the highest priority (lowest numerical value) of any of the specified processes.

Signals
=======

Procedures to raise, handle and wait for signals.

 -- primitive: kill pid sig
     Sends a signal to the specified process or group of processes.

     PID specifies the processes to which the signal is sent:

     PID greater than 0
          The process whose identifier is PID.

     PID equal to 0
          All processes in the current process group.

     PID less than -1
          The process group whose identifier is -PID

     PID equal to -1
          If the process is privileged, all processes except for some special system processes.  Otherwise, all processes with the current effective user ID.

     SIG should be specified using a variable corresponding to the Unix symbolic name, e.g.,

      -- Variable: SIGHUP
          Hang-up signal.

      -- Variable: SIGINT
          Interrupt signal.

 -- primitive: raise sig
     Sends a specified signal SIG to the current process, where SIG is as described for the kill procedure.

 -- primitive: sigaction signum [handler [flags]]
     Install or report the signal handler for a specified signal.

     SIGNUM is the signal number, which can be specified using the value of variables such as SIGINT.

     If ACTION is omitted, sigaction returns a pair: the CAR is the current signal hander, which will be either an integer with the value SIG_DFL (default action) or SIG_IGN (ignore), or the Scheme procedure which handles the signal, or #f if a non-Scheme procedure handles the signal.  The CDR contains the current sigaction flags for the handler.

     If ACTION is provided, it is installed as the new handler for SIGNUM.  ACTION can be a Scheme procedure taking one argument, or the value of SIG_DFL (default action) or SIG_IGN (ignore), or #f to restore whatever signal handler was installed before sigaction was first used.  Flags can optionally be specified for the new handler (SA_RESTART will always be added if it's available and the system is using restartable system calls.)  The return value is a pair with information about the old handler as described above.

     This interface does not provide access to the "signal blocking" facility.  Maybe this is not needed, since the thread support may provide solutions to the problem of consistent access to data structures.

 -- primitive: restore-signals
     Return all signal handlers to the values they had before any call to sigaction was made.  The return value is unspecified.

 -- primitive: alarm i
     Set a timer to raise a SIGALRM signal after the specified number of seconds (an integer).  It's advisable to install a signal handler for SIGALRM beforehand, since the default action is to terminate the process.

     The return value indicates the time remaining for the previous alarm, if any.  The new value replaces the previous alarm.  If there was no previous alarm, the return value is zero.

 -- primitive: pause
     Pause the current process (thread?) until a signal arrives whose action is to either terminate the current process or invoke a handler procedure.  The return value is unspecified.

 -- primitive: sleep i
     Wait for the given number of seconds (an integer) or until a signal arrives.  The return value is zero if the time elapses or the number of seconds remaining otherwise.

 -- primitive: usleep i
     Sleep for I microseconds.  usleep is not available on all platforms.

Terminals and Ptys
==================

 -- primitive: isatty? port
     Return #t if PORT is using a serial non--file device, otherwise #f.

 -- primitive: ttyname port
     Return a string with the name of the serial terminal device underlying PORT.

 -- primitive: ctermid
     Return a string containing the file name of the controlling terminal for the current process.

 -- primitive: tcgetpgrp port
     Return the process group ID of the foreground process group associated with the terminal open on the file descriptor underlying PORT. If there is no foreground process group, the return value is a number greater than 1 that does not match the process group ID of any existing process group.  This can happen if all of the processes in the job that was formerly the foreground job have terminated, and no other job has yet been moved into the foreground.

 -- primitive: tcsetpgrp port pgid
     Set the foreground process group ID for the terminal used by the file descriptor underlying PORT to the integer PGID. The calling process must be a member of the same session as PGID and must have the same controlling terminal.  The return value is unspecified.

Pipes
=====

The following procedures provide an interface to the popen and pclose system routines.  The code is in a separate "popen" module:

     (use-modules (ice-9 popen))

 -- procedure: open-pipe command modes
     Executes the shell command COMMAND (a string) in a subprocess. A pipe to the process is created and returned.  MODES specifies whether an input or output pipe to the process is created: it should be the value of OPEN_READ or OPEN_WRITE.

 -- procedure: open-input-pipe command
     Equivalent to open-pipe with mode OPEN_READ.

 -- procedure: open-output-pipe command
     Equivalent to open-pipe with mode OPEN_WRITE.

 -- procedure: close-pipe port
     Closes the pipe created by open-pipe, then waits for the process to terminate and returns its status value, see waitpid, for information on how to interpret this value.

     close-port (see close-port) can also be used to close a pipe, but doesn't return the status.

Networking
==========

Network Databases and Address Conversion
----------------------------------------

This section describes procedures which convert internet addresses and query various network databases.  Care should be taken when using the database routines since they are not reentrant.

Address Conversion
..................

 -- primitive: inet-aton address
     Converts a string containing an Internet host address in the traditional dotted decimal notation into an integer.

          (inet-aton "127.0.0.1") => 2130706433

 -- primitive: inet-ntoa inetid
     Converts an integer Internet host address into a string with the traditional dotted decimal representation.

          (inet-ntoa 2130706433) => "127.0.0.1"

 -- primitive: inet-netof address
     Return the network number part of the given integer Internet address.

          (inet-netof 2130706433) => 127

 -- primitive: inet-lnaof address
     Return the local-address-with-network part of the given Internet address.

          (inet-lnaof 2130706433) => 1

 -- primitive: inet-makeaddr net lna
     Makes an Internet host address by combining the network number NET with the local-address-within-network number LNA.

          (inet-makeaddr 127 1) => 2130706433

The Host Database
.................

A host object is a structure that represents what is known about a network host, and is the usual way of representing a system's network identity inside software.

The following functions accept a host object and return a selected component:

 -- procedure: hostent:name host
     The "official" hostname for HOST.

 -- procedure: hostent:aliases host
     A list of aliases for HOST.

 -- procedure: hostent:addrtype host
     The host address type.  For hosts with Internet addresses, this will return AF_INET.

 -- procedure: hostent:length host
     The length of each address for HOST, in bytes.

 -- procedure: hostent:addr-list host
     The list of network addresses associated with HOST.

The following procedures are used to search the host database:

 -- primitive: gethost [host]
 -- procedure: gethostbyname hostname
 -- procedure: gethostbyaddr address
     Look up a host by name or address, returning a host object.  The gethost procedure will accept either a string name or an integer address; if given no arguments, it behaves like gethostent (see below).  If a name or address is supplied but the address can not be found, an error will be thrown to one of the keys: host-not-found, try-again, no-recovery or no-data, corresponding to the equivalent h_error values. Unusual conditions may result in errors thrown to the system-error or misc_error keys.

The following procedures may be used to step through the host database from beginning to end.

 -- procedure: sethostent [stayopen]
     Initialize an internal stream from which host objects may be read.  This procedure must be called before any calls to gethostent, and may also be called afterward to reset the host entry stream.  If STAYOPEN is supplied and is not #f, the database is not closed by subsequent gethostbyname or gethostbyaddr calls, possibly giving an efficiency gain.

 -- procedure: gethostent
     Return the next host object from the host database, or #f if there are no more hosts to be found (or an error has been encountered). This procedure may not be used before sethostent has been called.

 -- procedure: endhostent
     Close the stream used by gethostent.  The return value is unspecified.

 -- primitive: sethost [stayopen]
     If STAYOPEN is omitted, this is equivalent to endhostent. Otherwise it is equivalent to sethostent stayopen.

The Network Database
....................

The following functions accept an object representing a network and return a selected component:

 -- procedure: netent:name net
     The "official" network name.

 -- procedure: netent:aliases net
     A list of aliases for the network.

 -- procedure: netent:addrtype net
     The type of the network number.  Currently, this returns only AF_INET.

 -- procedure: netent:net net
     The network number.

The following procedures are used to search the network database:

 -- primitive: getnet [net]
 -- procedure: getnetbyname net-name
 -- procedure: getnetbyaddr net-number
     Look up a network by name or net number in the network database.  The NET-NAME argument must be a string, and the NET-NUMBER argument must be an integer.  getnet will accept either type of argument, behaving like getnetent (see below) if no arguments are given.

The following procedures may be used to step through the network database from beginning to end.

 -- procedure: setnetent [stayopen]
     Initialize an internal stream from which network objects may be read.  This procedure must be called before any calls to getnetent, and may also be called afterward to reset the net entry stream.  If STAYOPEN is supplied and is not #f, the database is not closed by subsequent getnetbyname or getnetbyaddr calls, possibly giving an efficiency gain.

 -- procedure: getnetent
     Return the next entry from the network database.

 -- procedure: endnetent
     Close the stream used by getnetent.  The return value is unspecified.

 -- primitive: setnet [stayopen]
     If STAYOPEN is omitted, this is equivalent to endnetent. Otherwise it is equivalent to setnetent stayopen.

The Protocol Database
.....................

The following functions accept an object representing a protocol and return a selected component:

 -- procedure: protoent:name protocol
     The "official" protocol name.

 -- procedure: protoent:aliases protocol
     A list of aliases for the protocol.

 -- procedure: protoent:proto protocol
     The protocol number.

The following procedures are used to search the protocol database:

 -- primitive: getproto [protocol]
 -- procedure: getprotobyname name
 -- procedure: getprotobynumber number
     Look up a network protocol by name or by number.  getprotobyname takes a string argument, and getprotobynumber takes an integer argument.  getproto will accept either type, behaving like getprotoent (see below) if no arguments are supplied.

The following procedures may be used to step through the protocol database from beginning to end.

 -- procedure: setprotoent [stayopen]
     Initialize an internal stream from which protocol objects may be read.  This procedure must be called before any calls to getprotoent, and may also be called afterward to reset the protocol entry stream.  If STAYOPEN is supplied and is not #f, the database is not closed by subsequent getprotobyname or getprotobynumber calls, possibly giving an efficiency gain.

 -- procedure: getprotoent
     Return the next entry from the protocol database.

 -- procedure: endprotoent
     Close the stream used by getprotoent.  The return value is unspecified.

 -- primitive: setproto [stayopen]
     If STAYOPEN is omitted, this is equivalent to endprotoent. Otherwise it is equivalent to setprotoent stayopen.

The Service Database
....................

The following functions accept an object representing a service and return a selected component:

 -- procedure: servent:name serv
     The "official" name of the network service.

 -- procedure: servent:aliases serv
     A list of aliases for the network service.

 -- procedure: servent:port serv
     The Internet port used by the service.

 -- procedure: servent:proto serv
     The protocol used by the service.  A service may be listed many times in the database under different protocol names.

The following procedures are used to search the service database:

 -- primitive: getserv [name [protocol]]
 -- procedure: getservbyname name protocol
 -- procedure: getservbyport port protocol
     Look up a network service by name or by service number, and return a network service object.  The PROTOCOL argument specifies the name of the desired protocol; if the protocol found in the network service database does not match this name, a system error is signalled.

     The getserv procedure will take either a service name or number as its first argument; if given no arguments, it behaves like getservent (see below).

The following procedures may be used to step through the service database from beginning to end.

 -- procedure: setservent [stayopen]
     Initialize an internal stream from which service objects may be read.  This procedure must be called before any calls to getservent, and may also be called afterward to reset the service entry stream.  If STAYOPEN is supplied and is not #f, the database is not closed by subsequent getservbyname or getservbyport calls, possibly giving an efficiency gain.

 -- procedure: getservent
     Return the next entry from the services database.

 -- procedure: endservent
     Close the stream used by getservent.  The return value is unspecified.

 -- primitive: setserv [stayopen]
     If STAYOPEN is omitted, this is equivalent to endservent. Otherwise it is equivalent to setservent stayopen.

Network Sockets and Communication
---------------------------------

Socket ports can be created using socket and socketpair. The ports are initially unbuffered, to makes reading and writing to the same port more reliable. A buffer can be added to the port using setvbuf, see Ports and File Descriptors.

The convention used for "host" vs "network" addresses is that addresses are always held in host order at the Scheme level.  The procedures in this section automatically convert between host and network order when required.  The arguments and return values are thus in host order.

 -- primitive: socket family style proto
     Return a new socket port of the type specified by FAMILY, STYLE and PROTOCOL.  All three parameters are integers.  Typical values for FAMILY are the values of AF_UNIX and AF_INET.  Typical values for STYLE are the values of SOCK_STREAM, SOCK_DGRAM and SOCK_RAW. PROTOCOL can be obtained from a protocol name using getprotobyname.  A value of zero specifies the default protocol, which is usually right. A single socket port cannot by used for communication until it has been connected to another socket.

 -- primitive: socketpair family style proto
     Return a pair of connected (but unnamed) socket ports of the type specified by FAMILY, STYLE and PROTOCOL. Many systems support only socket pairs of the AF_UNIX family.  Zero is likely to be the only meaningful value for PROTOCOL.

 -- primitive: getsockopt sock level optname
     Return the value of a particular socket option for the socket port SOCKET.  LEVEL is an integer code for type of option being requested, e.g., SOL_SOCKET for socket-level options.  OPTNAME is an integer code for the option required and should be specified using one of the symbols SO_DEBUG, SO_REUSEADDR etc. The returned value is typically an integer but SO_LINGER returns a pair of integers.

 -- primitive: setsockopt sock level optname value
     Sets the value of a particular socket option for the socket port SOCKET.  LEVEL is an integer code for type of option being set, e.g., SOL_SOCKET for socket-level options. OPTNAME is an integer code for the option to set and should be specified using one of the symbols SO_DEBUG, SO_REUSEADDR etc. VALUE is the value to which the option should be set.  For most options this must be an integer, but for SO_LINGER it must be a pair.

     The return value is unspecified.

 -- primitive: shutdown sock how
     Sockets can be closed simply by using close-port. The shutdown procedure allows reception or tranmission on a connection to be shut down individually, according to the parameter HOW:

     0
          Stop receiving data for this socket.  If further data arrives,  reject it.

     1
          Stop trying to transmit data from this socket.  Discard any data waiting to be sent.  Stop looking for acknowledgement of data already sent; don't retransmit it if it is lost.

     2
          Stop both reception and transmission.

     The return value is unspecified.

 -- primitive: connect sock fam address . args
     Initiates a connection from SOCKET to the address specified by ADDRESS and possibly ARG ....  The format required for ADDRESS and ARG ... depends on the family of the socket.

     For a socket of family AF_UNIX, only address is specified and must be a string with the filename where the socket is to be created.

     For a socket of family AF_INET, address must be an integer Internet host address and ARG ... must be a single integer port number.

     The return value is unspecified.

 -- primitive: bind sock fam address . args
     Assigns an address to the socket port SOCKET. Generally this only needs to be done for server sockets, so they know where to look for incoming connections.  A socket without an address will be assigned one automatically when it starts communicating.

     The format of ADDRESS and ARG ... depends on the family of the socket.

     For a socket of family AF_UNIX, only ADDRESS is specified and must be a string with the filename where the socket is to be created.

     For a socket of family AF_INET, ADDRESS must be an integer Internet host address and ARG ... must be a single integer port number.

     The values of the following variables can also be used for ADDRESS:

      -- Variable: INADDR_ANY
          Allow connections from any address.

      -- Variable: INADDR_LOOPBACK
          The address of the local host using the loopback device.

      -- Variable: INADDR_BROADCAST
          The broadcast address on the local network.

      -- Variable: INADDR_NONE
          No address.

     The return value is unspecified.

 -- primitive: listen sock backlog
     This procedure enables SOCKET to accept connection requests.  BACKLOG is an integer specifying the maximum length of the queue for pending connections. If the queue fills, new clients will fail to connect until the server calls accept to accept a connection from the queue.

     The return value is unspecified.

 -- primitive: accept sock
     Accepts a connection on a bound, listening socket SOCKET.  If there are no pending connections in the queue, it waits until one is available unless the non-blocking option has been set on the socket.

     The return value is a pair in which the CAR is a new socket port for the connection and the CDR is an object with address information about the client which initiated the connection.

     If the address is not available then the CDR will be an empty vector.

     SOCKET does not become part of the connection and will continue to accept new requests.

The following functions take a socket address object, as returned by accept and other procedures, and return a selected component.

sockaddr:fam
     The socket family, typically equal to the value of AF_UNIX or AF_INET.

sockaddr:path
     If the socket family is AF_UNIX, returns the path of the filename the socket is based on.

sockaddr:addr
     If the socket family is AF_INET, returns the Internet host address.

sockaddr:port
     If the socket family is AF_INET, returns the Internet port number.

 -- primitive: getsockname sock
     Return the address of SOCKET, in the same form as the object returned by accept.  On many systems the address of a socket in the AF_FILE namespace cannot be read.

 -- primitive: getpeername sock
     Return the address of the socket that the socket SOCKET is connected to, in the same form as the object returned by accept.  On many systems the address of a socket in the AF_FILE namespace cannot be read.

 -- primitive: recv! sock buf [flags]
     Receives data from the socket port SOCKET.  SOCKET must already be bound to the address from which data is to be received. BUF is a string into which the data will be written.  The size of BUF limits the amount of data which can be received: in the case of packet protocols, if a packet larger than this limit is encountered then some data will be irrevocably lost.

     The optional FLAGS argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

     The value returned is the number of bytes read from the socket.

     Note that the data is read directly from the socket file descriptor: any unread buffered port data is ignored.

 -- primitive: send sock message [flags]
     Transmits the string MESSAGE on the socket port SOCKET. SOCKET must already be bound to a destination address.  The value returned is the number of bytes transmitted -- it's possible for this to be less than the length of MESSAGE if the socket is set to be non-blocking.  The optional FLAGS argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

     Note that the data is written directly to the socket file descriptor: any unflushed buffered port data is ignored.

 -- primitive: recvfrom! sock str [flags [start [end]]]
     Return data from the socket port SOCKET and also information about where the data was received from. SOCKET must already be bound to the address from which data is to be received.  str, is a string into which the data will be written.  The size of STR limits the amount of data which can be received: in the case of packet protocols, if a packet larger than this limit is encountered then some data will be irrevocably lost. The optional FLAGS argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc. The value returned is a pair: the car is the number of bytes read from the socket and the cdr an address object in the same form as returned by accept. The START and END arguments specify a substring of STR to which the data should be written. Note that the data is read directly from the socket file descriptor: any unread buffered port data is ignored.

 -- primitive: sendto sock message fam address . args_and_flags
     Transmits the string MESSAGE on the socket port SOCKET.  The destination address is specified using the FAMILY, ADDRESS and ARG arguments, in a similar way to the connect procedure.  The value returned is the number of bytes transmitted -- it's possible for this to be less than the length of MESSAGE if the socket is set to be non-blocking.  The optional FLAGS argument is a value or bitwise OR of MSG_OOB, MSG_PEEK, MSG_DONTROUTE etc.

     Note that the data is written directly to the socket file descriptor: any unflushed buffered port data is ignored.

The following functions can be used to convert short and long integers between "host" and "network" order.  Although the procedures above do this automatically for addresses, the conversion will still need to be done when sending or receiving encoded integer data from the network.

 -- primitive: htons in
     Return a new integer from VALUE by converting from host to network order. VALUE must be within the range of a C unsigned short integer.

 -- primitive: ntohs in
     Return a new integer from VALUE by converting from network to host order.  VALUE must be within the range of a C unsigned short integer.

 -- primitive: htonl in
     Return a new integer from VALUE by converting from host to network order. VALUE must be within the range of a C unsigned long integer.

 -- primitive: ntohl in
     Return a new integer from VALUE by converting from network to host order. VALUE must be within the range of a C unsigned long integer.

These procedures are inconvenient to use at present, but consider:

     (define write-network-long
       (lambda (value port)
         (let ((v (make-uniform-vector 1 1 0)))
           (uniform-vector-set! v 0 (htonl value))
           (uniform-vector-write v port))))

     (define read-network-long
       (lambda (port)
         (let ((v (make-uniform-vector 1 1 0)))
           (uniform-vector-read! v port)
           (ntohl (uniform-vector-ref v 0)))))

System Identification
=====================

This section lists the various procedures Guile provides for accessing information about the system it runs on.

 -- primitive: uname
     Return an object with some information about the computer system the program is running on.

The following procedures accept an object as returned by uname and return a selected component.

utsname:sysname
     The name of the operating system.

utsname:nodename
     The network name of the computer.

utsname:release
     The current release level of the operating system implementation.

utsname:version
     The current version level within the release of the operating system.

utsname:machine
     A description of the hardware.

 -- primitive: gethostname
     Return the host name of the current processor.

 -- primitive: sethostname name
     Set the host name of the current processor to NAME. May only be used by the superuser.  The return value is not specified.

 -- primitive: software-type
     Return a symbol describing the current platform's operating system. This may be one of AIX, VMS, UNIX, COHERENT, WINDOWS, MS-DOS, OS/2, THINKC, AMIGA, ATARIST, MACH, or ACORN.

     Note that most varieties of Unix are considered to be simply "UNIX". That is because when a program depends on features that are not present on every operating system, it is usually better to test for the presence or absence of that specific feature.  The return value of software-type should only be used for this purpose when there is no other easy or unambiguous way of detecting such features.

Locales
=======

 -- primitive: setlocale category [locale]
     If LOCALE is omitted, return the current value of the specified locale category as a system-dependent string. CATEGORY should be specified using the values LC_COLLATE, LC_ALL etc. Otherwise the specified locale category is set to the string LOCALE and the new value is returned as a system-dependent string.  If LOCALE is an empty string, the locale will be set using envirionment variables.

Encryption
==========

Please note that the procedures in this section are not suited for strong encryption, they are only interfaces to the well--known and common system library functions of the same name.  They are just as good (or bad) as the underlying functions, so you should refer to your system documentation before using them.

 -- primitive: crypt key salt
     Encrypt KEY using SALT as the salt value to the crypt(3) library call

getpass is no encryption procedure at all, but it is often used in compination with crypt, that is why it appears in this section.

 -- primitive: getpass prompt
     Display PROMPT to the standard error output and read a password from /dev/tty.  If this file is not accessible, it reads from standard input.  The password may be up to 127 characters in length.  Additional characters and the terminating newline character are discarded.  While reading the password, echoing and the generation of signals by special characters is disabled.