[fwd] / fwd.h

/* -*-c-*-
 *
 * Main header file for port forwarder
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the `fwd' port forwarder.
 *
 * `fwd' is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * `fwd' is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with `fwd'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#ifndef FW_H
#define FW_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

/* --- Configuration --- */

#include "config.h"
#define _GNU_SOURCE

/* --- ANSI C --- */

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* --- Unix --- */

#include <fcntl.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/wait.h>

#include <sys/socket.h>
#include <sys/un.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <pwd.h>
#include <grp.h>

#include <syslog.h>

/* --- mLib --- */

#include <mLib/alloc.h>
#include <mLib/bres.h>
#include <mLib/conn.h>
#include <mLib/darray.h>
#include <mLib/dstr.h>
#include <mLib/env.h>
#include <mLib/fdflags.h>
#include <mLib/fdpass.h>
#include <mLib/ident.h>
#include <mLib/mdup.h>
#include <mLib/mdwopt.h>
#include <mLib/quis.h>
#include <mLib/report.h>
#include <mLib/sel.h>
#include <mLib/selbuf.h>
#include <mLib/sig.h>
#include <mLib/str.h>
#include <mLib/sub.h>
#include <mLib/sym.h>
#include <mLib/tv.h>

/*----- Other subtleties --------------------------------------------------*/

#if defined(HAVE_DECL_ENVIRON) && !HAVE_DECL_ENVIRON
  extern char **environ;
#endif

/*----- Resource limit names ----------------------------------------------*/

#if defined(RLIMIT_OFILE) && !defined(RLIMIT_NOFILE)
#  define RLIMIT_NOFILE RLIMIT_OFILE
#endif

/*
   ;;; The resource-limit name table is very boring to type and less fun to
   ;;; maintain.  To make life less awful, put the names in this list and
   ;;; evaluate the code to get Emacs to regenerate it.

   (let ((limits '(as core cpu data fsize locks memlock msgqueue
                   nice nofile nproc rss rtprio sigpending stack
                   vmem)))
     (save-excursion
       (goto-char
        (point-min))
       (search-forward (concat "***" "BEGIN rlimitlist" "***"))
       (beginning-of-line 2)
       (delete-region (point)
                      (progn
                        (search-forward "***END***")
                        (beginning-of-line)
                        (point)))
       (let ((avail (make-marker))
             (list (make-marker)))
         (set-marker avail (point))
         (insert "#define RLIMITS(_)")
         (set-marker list (point))
         (dolist (limit (sort (copy-list limits) #'string<))
           (let* ((name (symbol-name limit))
                  (constant (concat "RLIMIT_" (upcase name)))
                  (have (concat "HAVE_" constant "_P")))
             (goto-char avail)
             (insert-before-markers (format (concat "#ifdef %s\n"
                                                    "#  define %s t\n"
                                                    "#else\n"
                                                    "#  define %s nil\n"
                                                    "#endif\n")
                                            constant have have))
             (goto-char list)
             (insert-before-markers
              (format " \\\n  MAYBE_ITEM(_, %s, (%s, %s))"
                      have name constant))))
         (goto-char list)
         (insert "\n"))))
*/

/***BEGIN rlimitlist***/
#ifdef RLIMIT_AS
#  define HAVE_RLIMIT_AS_P t
#else
#  define HAVE_RLIMIT_AS_P nil
#endif
#ifdef RLIMIT_CORE
#  define HAVE_RLIMIT_CORE_P t
#else
#  define HAVE_RLIMIT_CORE_P nil
#endif
#ifdef RLIMIT_CPU
#  define HAVE_RLIMIT_CPU_P t
#else
#  define HAVE_RLIMIT_CPU_P nil
#endif
#ifdef RLIMIT_DATA
#  define HAVE_RLIMIT_DATA_P t
#else
#  define HAVE_RLIMIT_DATA_P nil
#endif
#ifdef RLIMIT_FSIZE
#  define HAVE_RLIMIT_FSIZE_P t
#else
#  define HAVE_RLIMIT_FSIZE_P nil
#endif
#ifdef RLIMIT_LOCKS
#  define HAVE_RLIMIT_LOCKS_P t
#else
#  define HAVE_RLIMIT_LOCKS_P nil
#endif
#ifdef RLIMIT_MEMLOCK
#  define HAVE_RLIMIT_MEMLOCK_P t
#else
#  define HAVE_RLIMIT_MEMLOCK_P nil
#endif
#ifdef RLIMIT_MSGQUEUE
#  define HAVE_RLIMIT_MSGQUEUE_P t
#else
#  define HAVE_RLIMIT_MSGQUEUE_P nil
#endif
#ifdef RLIMIT_NICE
#  define HAVE_RLIMIT_NICE_P t
#else
#  define HAVE_RLIMIT_NICE_P nil
#endif
#ifdef RLIMIT_NOFILE
#  define HAVE_RLIMIT_NOFILE_P t
#else
#  define HAVE_RLIMIT_NOFILE_P nil
#endif
#ifdef RLIMIT_NPROC
#  define HAVE_RLIMIT_NPROC_P t
#else
#  define HAVE_RLIMIT_NPROC_P nil
#endif
#ifdef RLIMIT_RSS
#  define HAVE_RLIMIT_RSS_P t
#else
#  define HAVE_RLIMIT_RSS_P nil
#endif
#ifdef RLIMIT_RTPRIO
#  define HAVE_RLIMIT_RTPRIO_P t
#else
#  define HAVE_RLIMIT_RTPRIO_P nil
#endif
#ifdef RLIMIT_SIGPENDING
#  define HAVE_RLIMIT_SIGPENDING_P t
#else
#  define HAVE_RLIMIT_SIGPENDING_P nil
#endif
#ifdef RLIMIT_STACK
#  define HAVE_RLIMIT_STACK_P t
#else
#  define HAVE_RLIMIT_STACK_P nil
#endif
#ifdef RLIMIT_VMEM
#  define HAVE_RLIMIT_VMEM_P t
#else
#  define HAVE_RLIMIT_VMEM_P nil
#endif
#define RLIMITS(_) \
  MAYBE_ITEM(_, HAVE_RLIMIT_AS_P, (as, RLIMIT_AS)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_CORE_P, (core, RLIMIT_CORE)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_CPU_P, (cpu, RLIMIT_CPU)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_DATA_P, (data, RLIMIT_DATA)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_FSIZE_P, (fsize, RLIMIT_FSIZE)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_LOCKS_P, (locks, RLIMIT_LOCKS)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_MEMLOCK_P, (memlock, RLIMIT_MEMLOCK)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_MSGQUEUE_P, (msgqueue, RLIMIT_MSGQUEUE)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_NICE_P, (nice, RLIMIT_NICE)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_NOFILE_P, (nofile, RLIMIT_NOFILE)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_NPROC_P, (nproc, RLIMIT_NPROC)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_RSS_P, (rss, RLIMIT_RSS)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_RTPRIO_P, (rtprio, RLIMIT_RTPRIO)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_SIGPENDING_P, (sigpending, RLIMIT_SIGPENDING)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_STACK_P, (stack, RLIMIT_STACK)) \
  MAYBE_ITEM(_, HAVE_RLIMIT_VMEM_P, (vmem, RLIMIT_VMEM))
/***END***/

/* --- The unpleasant conditional-output machinery --- */

#define MAYBE_ITEM(_, emitp, args) GLUE(MAYBE_ITEM_, emitp)(_, args)
#define MAYBE_ITEM_t(_, args) _ args
#define MAYBE_ITEM_nil(_, args)

/*----- Main program ------------------------------------------------------*/

/* --- The global select state --- */

extern sel_state *sel;

/* --- Help text --- */

extern const char grammar_text[];
extern const char option_text[];

/* --- @fw_log@ --- *
 *
 * Arguments:   @time_t t@ = when the connection occurred or (@-1@)
 *              @const char *fmt@ = format string to fill in
 *              @...@ = other arguments
 *
 * Returns:     ---
 *
 * Use:         Logs a connection.
 */

extern void fw_log(time_t /*t*/, const char */*fmt*/, ...);

/* --- @fw_inc@, @fw_dec@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Increments or decrements the active thing count.  `fwd' won't
 *              quit while there are active things.
 */

extern void fw_inc(void);
extern void fw_dec(void);

/*----- Channel management ------------------------------------------------*/

/* --- Magic numbers --- */

#define CHAN_BUFSZ 4096

/* --- Channel structure --- */

typedef struct chan {
  unsigned base, len;                   /* Base and length of data */
  unsigned f;                           /* Various interesting flags */
  void (*func)(void */*p*/);            /* Function to call on closure */
  int err;                              /* What's wrong with the channel */
  void *p;                              /* Argument to pass function */
  sel_file r, w;                        /* Reader and writer selectors */
  char buf[CHAN_BUFSZ];                 /* The actual data buffer */
} chan;

#define CHANF_CLOSE 1u                  /* Close channel when buffer empty */
#define CHANF_READY 2u                  /* The channel destination exists */

/* --- @chan_close@ --- *
 *
 * Arguments:   @chan *c@ = pointer to channel
 *
 * Returns:     ---
 *
 * Use:         Closes down a channel prematurely.
 */

extern void chan_close(chan */*c*/);

/* --- @chan_dest@ --- *
 *
 * Arguments:   @chan *c@ = pointer to channel
 *              @int fd@ = destination file descriptor for channel
 *
 * Returns:     ---
 *
 * Use:         Sets the channel's destination so it knows where to put
 *              data.
 */

extern void chan_dest(chan */*c*/, int /*fd*/);

/* --- @chan_open@ --- *
 *
 * Arguments:   @chan *c@ = pointer to channel to open
 *              @int from, to@ = source and destination file descriptors
 *              @void (*func)(void *p)@ = function to call on closure
 *              @void *p@ = argument to pass to function
 *
 * Returns:     ---
 *
 * Use:         Opens a channel.  Data is copied from the source to the
 *              destination.  The @to@ argument may be @-1@ if the file
 *              descriptor isn't known yet.
 */

extern void chan_open(chan */*c*/, int /*from*/, int /*to*/,
                      void (*/*func*/)(void */*p*/), void */*p*/);

/*----- Character scanners ------------------------------------------------*/

/* --- A low-level scanner source --- */

typedef struct scansrc {
  struct scansrc *next;                 /* Next one in the list */
  struct scansrc_ops *ops;              /* Pointer to operations table */
  char *src;                            /* Name of this source */
  int line;                             /* Current line number */
  dstr pushback;                        /* Pushback characters */
  char *tok;                            /* Token pushback */
  unsigned t;                           /* Token type pushback */
} scansrc;

/* --- Scanner source operations --- */

typedef struct scansrc_ops {
  int (*scan)(scansrc */*ss*/);         /* Read another character */
  void (*destroy)(scansrc */*ss*/);     /* Destroy an unwanted source */
} scansrc_ops;

/* --- A character scanner --- */

typedef struct scanner {
  scansrc *head, **tail;                /* Scanner list head and tail */
  int t;                                /* Token type */
  dstr d;                               /* Current token value */
  const char *wbegin, *wcont;           /* Parsing exception strings */
} scanner;

/* --- @scan_file@ --- *
 *
 * Arguments:   @FILE *fp@ = pointer to file descriptor
 *              @const char *name@ = pointer to source file name
 *              @unsigned f@ = flags
 *
 * Returns:     A scanner source.
 *
 * Use:         Creates a new scanner source for reading from a file.
 */

#define SCF_NOCLOSE 1u                  /* Don't close @fp@ when finished */

extern scansrc *scan_file(FILE */*fp*/, const char */*name*/,
                          unsigned /*f*/);

/* --- @scan_argv@ --- *
 *
 * Arguments:   @char **av@ = pointer to argument array (null terminated)
 *
 * Returns:     A scanner source.
 *
 * Use:         Creates a new scanner source for reading from an @argv@
 *              array.
 */

extern scansrc *scan_argv(char **/*av*/);

/* --- @scan@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to main scanner context
 *
 * Returns:     Character read, or end-of-file.
 *
 * Use:         Scans a character from a source of characters.
 */

extern int scan(scanner */*sc*/);

/* --- @unscan@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to main scanner context
 *              @int ch@ = character to unscan
 *
 * Returns:     ---
 *
 * Use:         Scans a character from a source of characters.
 */

extern void unscan(scanner */*sc*/, int /*ch*/);

/* --- @scan_push@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to main scanner context
 *              @scansrc *ss@ = souorce to push
 *
 * Returns:     ---
 *
 * Use:         Pushes a scanner source onto the front of the queue.
 */

extern void scan_push(scanner */*sc*/, scansrc */*ss*/);

/* --- @scan_add@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to main scanner context
 *              @scansrc *ss@ = souorce to push
 *
 * Returns:     ---
 *
 * Use:         Adds a scanner source onto the end of the queue.
 */

extern void scan_add(scanner */*sc*/, scansrc */*ss*/);

/* --- @scan_create@ --- *
 *
 * Arguments:   @scanner *sc@ = scanner context to initialize
 *
 * Returns:     ---
 *
 * Use:         Initializes a scanner block ready for use.
 */

extern void scan_create(scanner */*sc*/);

/* --- @scan_destroy@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner context
 *
 * Returns:     ---
 *
 * Use:         Destroys a scanner and all the sources attached to it.
 */

extern void scan_destroy(scanner */*sc*/);

/*----- Configuration parsing ---------------------------------------------*/

/* --- Magical constants --- */

#define CTOK_EOF (-1)
#define CTOK_WORD 256

/* --- @conf_undelim@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner definition
 *              @const char *d, *dd@ = pointer to characters to escape
 *
 * Returns:     ---
 *
 * Use:         Modifies the tokenizer.  Characters in the first list will
 *              always be considered to begin a word.  Characters in the
 *              second list will always be allowed to continue a word.
 */

extern void conf_undelim(scanner */*sc*/,
                         const char */*d*/, const char */*dd*/);

/* --- @token@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner definition
 *
 * Returns:     Type of token scanned.
 *
 * Use:         Reads the next token from the character scanner.
 */

extern int token(scanner */*sc*/);

/* --- @error@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner definition
 *              @const char *msg@ = message skeleton string
 *              @...@ = extra arguments for the skeleton
 *
 * Returns:     Doesn't
 *
 * Use:         Reports an error at the current scanner location.
 */

extern void error(scanner */*sc*/, const char */*msg*/, ...);

/* --- @pushback@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner definition
 *
 * Returns:     ---
 *
 * Use:         Pushes the current token back.  This is normally a precursor
 *              to pushing a new scanner source.
 */

extern void pushback(scanner */*sc*/);

/* --- @conf_enum@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to a scanner object
 *              @const char *list@ = comma-separated things to allow
 *              @unsigned @f = flags for the search
 *              @const char *err@ = error message if not found
 *
 * Returns:     Index into list, zero-based, or @-1@.
 *
 * Use:         Checks whether the current token is a string which matches
 *              one of the comma-separated items given.  The return value is
 *              the index (zero-based) of the matched string in the list.
 *
 *              The flags control the behaviour if no exact match is found.
 *              If @ENUM_ABBREV@ is set, and the current token is a left
 *              substring of exactly one of the possibilities, then that one
 *              is chosen.  If @ENUM_NONE@ is set, the value @-1@ is
 *              returned; otherwise an error is reported and the program is
 *              terminated.
 */

#define ENUM_ABBREV 1u
#define ENUM_NONE 2u

extern int conf_enum(scanner */*sc*/, const char */*list*/,
                     unsigned /*flags*/, const char */*err*/);

/* --- @conf_prefix@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to a scanner object
 *              @const char *p@ = pointer to prefix string to check
 *
 * Returns:     Nonzero if the prefix matches.
 *
 * Use:         If the current token is a word matching the given prefix
 *              string, then it and an optional `.' character are removed and
 *              a nonzero result is returned.  Otherwise the current token is
 *              left as it is, and zero is returned.
 *
 *              Typical options parsing code would remove an expected prefix,
 *              scan an option anyway (since qualifying prefixes are
 *              optional) and if a match is found, claim the option.  If no
 *              match is found, and a prefix was stripped, then an error
 *              should be reported.
 */

extern int conf_prefix(scanner */*sc*/, const char */*p*/);

/* --- @CONF_BEGIN@, @CONF_END@ --- *
 *
 * Arguments:   @sc@ = scanner to read from
 *              @prefix@ = prefix to scan for
 *              @desc@ = description of what we're parsing
 *
 * Use:         Bracket an options parsing routine.  The current token is
 *              checked to see whether it matches the prefix.  If so, it is
 *              removed and the following token examined.  If that's a `.'
 *              then it's removed.  If it's a `{' then the enclosed
 *              option-parsing code is executed in a loop until a matching
 *              '}' is found.  If the options parser doesn't accept an
 *              option, the behaviour is dependent on whether a prefix was
 *              seen: if so, an error is reported; otherwse a zero return is
 *              made.
 */

#define CS_PLAIN 0
#define CS_PREFIX 1
#define CS_BRACE 2
#define CS_UNKNOWN 3

#define CONF_BEGIN(sc, prefix, desc) do {                               \
  scanner *_conf_sc = (sc);                                             \
  const char *_conf_desc = (desc);                                      \
  int _conf_state = CS_PLAIN;                                           \
                                                                        \
  /* --- Read the initial prefix --- */                                 \
                                                                        \
  if (_conf_sc->t == CTOK_WORD &&                                       \
      strcmp(_conf_sc->d.buf, (prefix)) == 0) {                         \
    token(_conf_sc);                                                    \
    _conf_state = CS_PREFIX;                                            \
    if (_conf_sc->t == '.')                                             \
      token(_conf_sc);                                                  \
    else if (_conf_sc->t == '{') {                                      \
      token(_conf_sc);                                                  \
      _conf_state = CS_BRACE;                                           \
    }                                                                   \
  }                                                                     \
                                                                        \
  /* --- Ensure the next token is a word --- */                         \
                                                                        \
  if (_conf_sc->t != CTOK_WORD)                                         \
    error(_conf_sc, "parse error, expected option keyword");            \
  do {

#define CONF_END                                                        \
                                                                        \
    /* --- Reject an option --- *                                       \
     *                                                                  \
     * We could get here as a result of an explicit @CONF_REJECT@ or    \
     * because the option wasn't accepted.                              \
     */                                                                 \
                                                                        \
    goto _conf_reject;                                                  \
  _conf_reject:                                                         \
    if (_conf_state == CS_PLAIN)                                        \
      _conf_state = CS_UNKNOWN;                                         \
    else {                                                              \
      error(_conf_sc, "unknown %s option `%s'",                         \
            _conf_desc, _conf_sc->d.buf);                               \
    }                                                                   \
                                                                        \
    /* --- Accept an option --- *                                       \
     *                                                                  \
     * It's safe to drop through from above.  Either an error will have \
     * been reported, or the state is not @CS_BRACE@.                   \
     */                                                                 \
                                                                        \
  _conf_accept:                                                         \
    if (_conf_state == CS_BRACE && _conf_sc->t == ';')                  \
      token(_conf_sc);                                                  \
  } while (_conf_state == CS_BRACE && _conf_sc->t == CTOK_WORD);        \
                                                                        \
  /* --- Check for a closing brace --- */                               \
                                                                        \
  if (_conf_state == CS_BRACE) {                                        \
    if (_conf_sc->t == '}')                                             \
      token(_conf_sc);                                                  \
    else                                                                \
      error(_conf_sc, "parse error, expected `}'");                     \
  }                                                                     \
                                                                        \
  /* --- Return an appropriate value --- */                             \
                                                                        \
  return (_conf_state != CS_UNKNOWN);                                   \
} while (0)

/* --- @CONF_ACCEPT@, @CONF_REJECT@ --- *
 *
 * Arguments:   ---
 *
 * Use:         Within an options parser (between @CONF_BEGIN@ and
 *              @CONF_END@), accept or reject an option.
 */

#define CONF_ACCEPT goto _conf_accept
#define CONF_REJECT goto _conf_reject

/* --- @CONF_QUAL@ --- *
 *
 * Arguments:   ---
 *
 * Use:         Evaluates to a nonzero value if the current option is
 *              qualified.  This can be used to decide whether abbreviations
 *              for options should be accepted.
 */

#define CONF_QUAL (_conf_state != CS_PLAIN)

/* --- @conf_name@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner
 *              @char delim@ = delimiter character to look for
 *              @dstr *d@ = pointer to dynamic string for output
 *
 * Returns:     ---
 *
 * Use:         Reads in a compound name consisting of words separated by
 *              delimiters.  Leading and trailing delimiters are permitted,
 *              although they'll probably cause confusion if used.  The name
 *              may be enclosed in square brackets if that helps at all.
 *
 *              Examples of compound names are filenames (delimited by `/')
 *              and IP addresses (delimited by `.').
 */

extern void conf_name(scanner */*sc*/, char /*delim*/, dstr */*d*/);

/* --- @conf_fname@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner
 *              @dstr *d@ = pointer to dynamic string for output
 *
 * Returns:     ---
 *
 * Use:         Reads a file name from the input and stores it in @d@.
 */

extern void conf_fname(scanner */*sc*/, dstr */*d*/);

/*----- Reference-counted file descriptors --------------------------------*/

typedef struct reffd {
  int fd;
  unsigned ref;
  void (*proc)(void */*p*/);
  void *p;
} reffd;

/* --- @reffd_init@ --- *
 *
 * Arguments:   @int fd@ = file descriptor
 *
 * Returns:     Reference-counted file descriptor object.
 *
 * Use:         Creates a refcounted file descriptor.
 */

extern reffd *reffd_init(int /*fd*/);

/* --- @reffd_handler@ --- *
 *
 * Arguments:   @reffd *r@ = pointer to reference counted filehandle
 *              @void (*proc)(void *p)@ = procedure to call
 *              @void *p@
 *
 * Returns:     ---
 *
 * Use:         Sets the reference counted file descriptor to call @proc@
 *              when it is no longer required.
 */

extern void reffd_handler(reffd */*r*/, void (*/*proc*/)(void */*p*/),
                          void */*p*/);

/* --- @reffd_inc@ --- *
 *
 * Arguments:   @reffd *r@ = pointer to reference counted filehandle
 *
 * Returns:     ---
 *
 * Use:         Increments the reference count for a file descriptor.
 */

#define REFFD_INC(r) do { (r)->ref++; } while (0)

extern void reffd_inc(reffd */*r*/);

/* --- @reffd_dec@ --- *
 *
 * Arguments:   @reffd *r@ = pointer to reference counted filehandle
 *
 * Returns:     ---
 *
 * Use:         Decrements the reference count for a file descriptor.
 */

#define REFFD_DEC(r) do {                                               \
  reffd *_r = (r);                                                      \
  _r->ref--;                                                            \
  if (_r->ref == 0) {                                                   \
    close(_r->fd);                                                      \
    if (_r->proc)                                                       \
      _r->proc(_r->p);                                                  \
    DESTROY(_r);                                                        \
  }                                                                     \
} while (0)

extern void reffd_dec(reffd */*r*/);

/*----- Sources, targets and endpoints ------------------------------------*/

/* --- Basic endpoint structure --- */

typedef struct endpt {
  struct endpt_ops *ops;                /* Pointer to operations table */
  struct endpt *other;                  /* Pointer to sibling endpoint */
  unsigned f;                           /* Various flags */
  struct tango *t;                      /* Private data structure */
  reffd *in, *out;                      /* File descriptors */
} endpt;

/* --- Endpoint flags --- */

#define EPF_PENDING 1u                  /* Endpoint creation in progress */
#define EPF_FILE 2u                     /* Endpoint smells like a file */

/* --- Endpoint operations table --- */

typedef struct endpt_ops {

  /* --- @attach@ --- *
   *
   * Arguments: @endpt *e@ = pointer to endpoint to be attached
   *            @reffd *in, *out@ = input and output file descriptors
   *
   * Returns:   ---
   *
   * Use:       Instructs a non-file endpoint to attach itself to a pair of
   *            files.
   */

  void (*attach)(endpt */*e*/, reffd */*in*/, reffd */*out*/);

  /* --- @file@ --- *
   *
   * Arguments: @endpt *e@ = pointer to endpoint in question
   *            @endpt *f@ = pointer to a file endpoint
   *
   * Returns:   ---
   *
   * Use:       Informs a non-file endpoint of a file endpoint which will
   *            want to be closed when it's finished with.  At that time, the
   *            endpoint should arrange to have both itself and its partner
   *            closed.  If no file is registered, the endpoint manager will
   *            close both endpoints itself.
   */

  void (*file)(endpt */*e*/, endpt */*f*/);

  /* --- @wclose@ --- *
   *
   * Arguments: @endpt *e@ = endpoint to be partially closed
   *
   * Returns:   ---
   *
   * Use:       Announces that the endpoint will not be written to any more.
   */

  void (*wclose)(endpt */*e*/);

  /* --- @close@ --- *
   *
   * Arguments: @endpt *e@ = endpoint to be closed
   *
   * Returns:   ---
   *
   * Use:       Completely closes an endpoint.  The endpoint's data may be
   *            freed, although some endpoints may wish to delay freeing for
   *            some reason.
   */

  void (*close)(endpt */*e*/);

} endpt_ops;

/* --- A basic target object --- */

typedef struct target {
  struct target_ops *ops;
  char *desc;
} target;

/* --- Forwarding target operations --- */

typedef struct target_ops {
  const char *name;                     /* Name of this target */

  /* --- @option@ --- *
   *
   * Arguments: @target *t@ = pointer to target object, or zero if global
   *            @scanner *sc@ = scanner to read from
   *
   * Returns:   Nonzero to claim the option.
   *
   * Use:       Handles an option string from the configuration file.
   */

  int (*option)(target */*t*/, scanner */*sc*/);

  /* --- @read@ --- *
   *
   * Arguments: @scanner *sc@ = pointer to scanner to read from
   *
   * Returns:   Pointer to a target object to claim, null to reject.
   *
   * Use:       Parses a target description from the configuration file.
   *            Only the socket target is allowed to omit the prefix on a
   *            target specification.
   */

  target *(*read)(scanner */*sc*/);

  /* --- @confirm@ --- *
   *
   * Arguments: @target *t@ = pointer to target
   *
   * Returns:   ---
   *
   * Use:       Confirms configuration of a target.
   */

  void (*confirm)(target */*t*/);

  /* --- @create@ --- *
   *
   * Arguments: @target *t@ = pointer to target
   *            @const char *desc@ = description of connection
   *
   * Returns:   Pointer to a created endpoint.
   *
   * Use:       Generates a target endpoint for communication.
   */

  endpt *(*create)(target */*t*/, const char */*desc*/);

  /* --- @destroy@ --- *
   *
   * Arguments: @target *t@ = pointer to target
   *
   * Returns:   ---
   *
   * Use:       Destroys a target.
   */

  void (*destroy)(target */*t*/);

} target_ops;

/* --- A basic source object --- */

typedef struct source {
  struct source *next, *prev;
  struct source_ops *ops;
  char *desc;
} source;

/* --- Forwarding source operations --- */

typedef struct source_ops {
  const char *name;                     /* Name of this source */

  /* --- @option@ --- *
   *
   * Arguments: @scanner *sc@ = scanner to read from
   *            @source *s@ = pointer to source object, or zero if global
   *
   * Returns:   Nonzero to claim the option.
   *
   * Use:       Handles an option string from the configuration file.
   */

  int (*option)(source */*s*/, scanner */*sc*/);

  /* --- @read@ --- *
   *
   * Arguments: @scanner *sc@ = pointer to scanner to read from
   *
   * Returns:   Pointer to a source object to claim, null to reject.
   *
   * Use:       Parses a source description from the configuration file.
   *            Only the socket source is allowed to omit the prefix on a
   *            source specification.
   */

  source *(*read)(scanner */*sc*/);

  /* --- @attach@ --- *
   *
   * Arguments: @source *s@ = pointer to source
   *            @scanner *sc@ = scanner (for error reporting)
   *            @target *t@ = pointer to target to attach
   *
   * Returns:   ---
   *
   * Use:       Attaches a target to a source.
   */

  void (*attach)(source */*s*/, scanner */*sc*/, target */*t*/);

  /* --- @destroy@ --- *
   *
   * Arguments: @source *s@ = pointer to source
   *
   * Returns:   ---
   *
   * Use:       Destroys a source.  Used when closing the system down, for
   *            example as a result of a signal.
   */

  void (*destroy)(source */*s*/);

} source_ops;

/* --- @endpt_kill@ --- *
 *
 * Arguments:   @endpt *a@ = an endpoint
 *
 * Returns:     ---
 *
 * Use:         Kills an endpoint.  If the endpoint is joined to another, the
 *              other endpoint is also killed, as is the connection between
 *              them (and that's the tricky bit).
 */

extern void endpt_kill(endpt */*a*/);

/* --- @endpt_killall@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Destroys all current endpoint connections.  Used when
 *              shutting down.
 */

extern void endpt_killall(void);

/* --- @endpt_join@ --- *
 *
 * Arguments:   @endpt *a@ = pointer to first endpoint
 *              @endpt *b@ = pointer to second endpoint
 *              @const char *desc@ = description of connection
 *
 * Returns:     ---
 *
 * Use:         Joins two endpoints together.  It's OK to join endpoints
 *              which are already joined; in fact, the the right thing to do
 *              when your endpoint decides that it's not pending any more is
 *              to join it to its partner again.
 *
 *              If the endpoints are already connected then the description
 *              string is ignored.  The endpoint manager takes a copy of
 *              the string, so you don't need to keep it around.
 */

extern void endpt_join(endpt */*a*/, endpt */*b*/, const char */*desc*/);

/* --- @source_add@ --- *
 *
 * Arguments:   @source *s@ = pointer to a source
 *
 * Returns:     ---
 *
 * Use:         Adds a source to the master list.  Only do this for passive
 *              sources (e.g., listening sockets), not active sources (e.g.,
 *              executable programs).
 */

extern void source_add(source */*s*/);

/* --- @source_remove@ --- *
 *
 * Arguments:   @source *s@ = pointer to a source
 *
 * Returns:     ---
 *
 * Use:         Removes a source from the master list.
 */

extern void source_remove(source */*s*/);

/* --- @source_killall@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Frees all sources.
 */

extern void source_killall(void);

/*----- The exec source and target ----------------------------------------*/

extern source_ops xsource_ops;
extern target_ops xtarget_ops;

/* --- @exec_init@ --- *
 *
 * Arguments:   ---
 *
 * Returns:     ---
 *
 * Use:         Initializes the executable problem source and target.
 */

extern void exec_init(void);

/*----- The file source and target ----------------------------------------*/

extern source_ops fsource_ops;
extern target_ops ftarget_ops;

/*----- The socket source and target --------------------------------------*/

extern source_ops ssource_ops;
extern target_ops starget_ops;

/* --- @starget_connected@ --- *
 *
 * Arguments:   @int fd@ = file descriptor now ready for use
 *              @void *p@ = pointer to an endpoint structure
 *
 * Returns:     ---
 *
 * Use:         Handles successful connection of the target endpoint.
 */

extern void starget_connected(int /*fd*/, void */*p*/);

/*----- Handling of file attributes ---------------------------------------*/

/* --- File attribute options structure --- */

typedef struct fattr {
  unsigned mode;
  uid_t uid;
  gid_t gid;
} fattr;

/* --- Shared global options --- */

extern fattr fattr_global;

/* --- @fattr_init@ --- *
 *
 * Arguments:   @fattr *f@ = pointer to file attributes
 *
 * Returns:     ---
 *
 * Use:         Initializes a set of file attributes to default values.
 */

extern void fattr_init(fattr */*f*/);

/* --- @fattr_option@ --- *
 *
 * Arguments:   @scanner *sc@ = pointer to scanner to read
 *              @fattr *f@ = pointer to file attributes to set
 *
 * Returns:     Whether the option was clamed.
 *
 * Use:         Reads file attributes from a scanner.
 */

extern int fattr_option(scanner */*sc*/, fattr */*f*/);

/* --- @fattr_apply@ --- *
 *
 * Arguments:   @const char *file@ = pointer to filename
 *              @fattr *f@ = pointer to attribute set
 *
 * Returns:     @-1@ if it failed.
 *
 * Use:         Applies file attributes to a file.  For best results, try to
 *              create the file with the right permissions and so on.  This
 *              call will fix everything up, but there are potential races
 *              which might catch you out if you're not careful.
 */

extern int fattr_apply(const char */*file*/, fattr */*f*/);

/*----- Making privileged connections -------------------------------------*/

/* --- @privconn_split@ --- *
 *
 * Arguments:   @sel_state *s@ = select state
 *
 * Returns:     ---
 *
 * Use:         Splits off the privileged binding code into a separate
 *              process.
 */

extern void privconn_split(sel_state */*s*/);

/* --- @privconn_adddest@ --- *
 *
 * Arguments:   @struct in_addr peer@ = address to connect to
 *              @unsigned port@ = port to connect to
 *
 * Returns:     Index for this destination address, or @-1@ if not
 *              available.
 *
 * Use:         Adds a valid destination for a privileged connection.
 */

extern int privconn_adddest(struct in_addr /*peer*/, unsigned /*port*/);

/* --- @privconn_connect@ --- *
 *
 * Arguments:   @conn *c@ = connection structure to fill in
 *              @sel_state *s@ = pointer to select state to attach to
 *              @int i@ = address index to connect to
 *              @struct in_addr bind@ = address to bind to
 *              @void (*func)(int, void *)@ = function to call on connect
 *              @void *p@ = argument for the function
 *
 * Returns:     Zero on success, @-1@ on failure.
 *
 * Use:         Sets up a privileged connection job.
 */

extern int privconn_connect(conn */*c*/, sel_state */*s*/,
                            int /*i*/, struct in_addr /*bind*/,
                            void (*/*func*/)(int, void *), void */*p*/);

/*----- Identifying remote clients ----------------------------------------*/

typedef struct id_req {
  struct sockaddr_in lsin;              /* Local address of connection */
  struct sockaddr_in rsin;              /* Remote address of connection */
  const char *desc;                     /* Description of connection */
  const char *act;                      /* Action taken by server */
  reffd *r;                             /* Pointer to file descriptor */
} id_req;

/* --- @identify@ --- *
 *
 * Arguments:   @const id_req *q@ = pointer to request block
 *
 * Returns:     ---
 *
 * Use:         Starts a background ident lookup and reverse-resolve job
 *              which will, eventually, report a message to the system log.
 */

extern void identify(const id_req */*q*/);

/*----- Host-based access control -----------------------------------------*/

/* --- An access control entry --- */

typedef struct acl_entry {
  struct acl_entry *next;               /* Next entry in the list */
  const struct acl_ops *ops;            /* Operations for the ACL entry */
  unsigned act;                         /* What to do with matching hosts */
} acl_entry;

#define ACL_DENY 0                      /* Deny access to matching conns */
#define ACL_ALLOW 1                     /* Allow access to matching conns */
#define ACL_PERM 1u                     /* Bit mask for permission bit */

/* --- Host-based access control --- */

typedef struct acl_host {
  acl_entry a;                          /* Base structure */
  struct in_addr addr, mask;            /* Address and netmask */
} acl_host;

/* --- ACL methods --- */

typedef struct acl_ops {
  int (*check)(void */*a*/, struct in_addr /*addr*/, unsigned /*port*/);
  void (*dump)(void */*a*/, FILE */*fp*/);
  void (*free)(void */*a*/);
} acl_ops;

/* --- @acl_check@ --- *
 *
 * Arguments:   @acl_entry *a@ = pointer to ACL to check against
 *              @struct in_addr addr@ = address to check
 *              @unsigned port@ = port number to check
 *              @int *act@ = verdict (should initially be @ACT_ALLOW@)
 *
 * Returns:     Zero if undecided, nonzero if a rule matched.
 *
 * Use:         Checks an address against an ACL.
 */

extern int acl_check(acl_entry */*a*/,
                     struct in_addr /*addr*/, unsigned /*port*/,
                     int */*act*/);

/* --- @acl_dump@ --- *
 *
 * Arguments:   @acl_entry *a@ = pointer to ACL to dump
 *              @FILE *fp@ = pointer to stream to dump on
 *
 * Returns:     ---
 *
 * Use:         Dumps an access control list to an output stream.
 */

extern void acl_dump(acl_entry */*a*/, FILE */*fp*/);

/* --- @acl_free@ --- *
 *
 * Arguments:   @acl_entry *a@ = pointer to a list of ACLs
 *
 * Returns:     ---
 *
 * Use:         Frees all of the memory used by an ACL.
 */

extern void acl_free(acl_entry */*a*/);

/* --- @acl_addhost@ --- *
 *
 * Arguments:   @acl_entry ***a@ = address of pointer to list tail
 *              @unsigned act@ = what to do with matching addresses
 *              @struct in_addr addr, mask@ = address and mask to match
 *
 * Returns:     ---
 *
 * Use:         Adds a host-authentication entry to the end of an access
 *              control list.
 */

extern void acl_addhost(acl_entry ***/*a*/, unsigned /*act*/,
                        struct in_addr /*addr*/, struct in_addr /*mask*/);

/* --- @acl_addpriv@ --- *
 *
 * Arguments:   @acl_entry ***a@ = address of pointer to list tail
 *              @unsigned act@ = what to do with matching addresses
 *
 * Returns:     ---
 *
 * Use:         Adds a privileged-port check to the end of an access control
 *              list.
 */

extern void acl_addpriv(acl_entry ***/*a*/, unsigned /*act*/);

/*----- Network addresses -------------------------------------------------*/

/* --- A generic socket address --- *
 *
 * Not all systems understand @sa_len@ fields.  (In particular, Linux
 * doesn't.)  Some fairly ugly hacking is then performed on particular
 * address types.
 */

typedef struct addr {
  struct addr_ops *ops;
  size_t sz;
} addr;

#define ADDRSZ(sz) (sizeof(addr) + (sz))

/* --- Address configuration --- *
 *
 * An address family will want to extend this.
 */

typedef struct addr_opts {
  unsigned f;
} addr_opts;

#define ADDRF_NOLOG 1u

/* --- Address types --- *
 *
 * For things like Internet addresses, source and destinations look
 * different.
 */

enum {
  ADDR_SRC,
  ADDR_DEST,
  ADDR_GLOBAL
};

/* --- Description of an address type handler --- */

typedef struct addr_ops {
  const char *name;                     /* Protocol's internal name */

  /* --- @read@ --- *
   *
   * Arguments: @scanner *sc@ = pointer to scanner to read from
   *            @unsigned type@ = type of address to be read
   *
   * Returns:   A filled-in socket address.
   *
   * Use:       Parses a textual representation of a socket address.
   */

  addr *(*read)(scanner */*sc*/, unsigned /*type*/);

  /* --- @destroy@ --- *
   *
   * Arguments: @addr *a@ = pointer to an address block
   *
   * Returns:   ---
   *
   * Use:       Disposes of an address block in some suitable fashion.
   */

  void (*destroy)(addr */*a*/);

  /* --- @print@ --- *
   *
   * Arguments: @addr *a@ = pointer to socket address to read
   *            @unsigned type@ = type of address to be written
   *            @dstr *d@ = string on which to write the description
   *
   * Returns:   ---
   *
   * Use:       Writes a textual representation of a socket address to
   *            a string.
   */

  void (*print)(addr */*a*/, unsigned /*type*/, dstr */*d*/);

  /* --- @initsrcopts@ --- *
   *
   * Arguments: ---
   *
   * Returns:   A pointer to a protocol-specific data block for a listener
   *
   * Use:       Creates a data block for a listener.  This is attached to the
   *            listener data structure.  Options can then be requested, and
   *            are added to the block when necessary.
   */

  addr_opts *(*initsrcopts)(void);

  /* --- @option@ --- *
   *
   * Arguments: @scanner *sc@ = pointer to a scanner to read from
   *            @unsigned type@ = kind of option this is
   *            @addr_opts *ao@ = data block to modify (from @init@), or null
   *
   * Returns:   Nonzero to claim the option.
   *
   * Use:       Parses a source option, either global or listener-specific.
   */

  int (*option)(scanner */*sc*/, addr_opts */*ao*/, unsigned /*type*/);

  /* --- @confirm@ --- *
   *
   * Arguments: @addr *a@ = pointer to an address structure
   *            @unsigned type@ = kind of address this is
   *            @addr_opts *ao@ = address options
   *
   * Returns:   ---
   *
   * Use:       Called during initialization when an address is fully
   *            configured.
   */

  void (*confirm)(addr */*a*/, unsigned /*type*/, addr_opts */*ao*/);

  /* --- @freesrcopts@ --- *
   *
   * Arguments: @addr_opts *ao@ = data block to remove
   *
   * Returns:   ---
   *
   * Use:       Throws away all the configuration data for an address type.
   */

  void (*freesrcopts)(addr_opts */*ao*/);

  /* --- @bind@ --- *
   *
   * Arguments: @addr *a@ = the address to bind to
   *            @addr_opts *ao@ = the address options
   *
   * Returns:   File descriptor of bound socket if OK, or @-1@ on error.
   *
   * Use:       Binds a listening socket.  The tedious stuff with @listen@
   *            isn't necessary.
   */

  int (*bind)(addr */*a*/, addr_opts */*ao*/);

  /* --- @unbind@ --- *
   *
   * Arguments: @addr *a@ = pointer to an address
   *
   * Returns:   ---
   *
   * Use:       Unbinds an address.  This is used when tidying up.  The main
   *            purpose is to let the Unix-domain handler remove its socket
   *            node from the filesystem.
   */

  void (*unbind)(addr */*a*/);

  /* --- @accept@ --- *
   *
   * Arguments: @int fd@ = listening file descriptor
   *            @addr_opts *ao@ = data block to get configuration from
   *            @const char *desc@ = description of the listener
   *
   * Returns:   Pointer to a reference counted file descriptor.
   *
   * Use:       Accepts, verifies and logs an incoming connection.
   */

  reffd *(*accept)(int /*fd*/, addr_opts */*ao*/, const char */*desc*/);

  /* --- @inittargopts@ --- *
   *
   * Arguments: ---
   *
   * Returns:   A pointer to a protocol-specific data block for a connecter
   *
   * Use:       Creates a data block for a target.  This is attached to the
   *            target data structure.  Options can then be requested, and
   *            are added to the block when necessary.
   */

  addr_opts *(*inittargopts)(void);

  /* --- @freetargopts@ --- *
   *
   * Arguments: @addr_opts *ao@ = data block to remove
   *
   * Returns:   ---
   *
   * Use:       Throws away all the configuration data for an address type.
   */

  void (*freetargopts)(addr_opts */*ao*/);

  /* --- @connect@ --- *
   *
   * Arguments: @addr *a@ = destination address
   *            @addr_opts *ao@ = target address options
   *            @conn *c@ = connection structure
   *            @endpt *e@ = endpoint structure
   *
   * Returns:   Zero if OK, @-1@ on some error.
   *
   * Use:       Requests that a connection be made, or at least set in
   *            motion.  An address may do one of these things:
   *
   *              * Return @-1@.
   *
   *              * Call @starget_connected@ with @-1@ or a connected file
   *                descriptor and the pointer @e@.
   *
   *              * Call @conn_init@ or @conn_fd@, giving @starget_connected@
   *                and @e@ as the function to call.
   */

  int (*connect)(addr */*a*/, addr_opts */*ao*/, conn */*c*/, endpt */*e*/);

} addr_ops;

/* --- Address types --- */

extern addr_ops un_ops;
extern addr_ops inet_ops;

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif