auto_clnt.c

[詳解]

/*++
/* NAME
/*  auto_clnt 3
/* SUMMARY
/*  client endpoint maintenance
/* SYNOPSIS
/*  #include <auto_clnt.h>
/*
/*  AUTO_CLNT *auto_clnt_create(service, timeout, max_idle, max_ttl)
/*  const char *service;
/*  int timeout;
/*  int max_idle;
/*  int max_ttl;
/*
/*  VSTREAM *auto_clnt_access(auto_clnt)
/*  AUTO_CLNT *auto_clnt;
/*
/*  void    auto_clnt_recover(auto_clnt)
/*  AUTO_CLNT *auto_clnt;
/*
/*  const char *auto_clnt_name(auto_clnt)
/*  AUTO_CLNT *auto_clnt;
/*
/*  void    auto_clnt_free(auto_clnt)
/*  AUTO_CLNT *auto_clnt;
/* DESCRIPTION
/*  This module maintains IPC client endpoints that automatically
/*  disconnect after a being idle for a configurable amount of time,
/*  that disconnect after a configurable time to live,
/*  and that transparently handle most server-initiated disconnects.
/*
/*  This module tries each operation only a limited number of
/*  times and then reports an error.  This is unlike the
/*  clnt_stream(3) module which will retry forever, so that
/*  the application never experiences an error.
/*
/*  auto_clnt_create() instantiates a client endpoint.
/*
/*  auto_clnt_access() returns an open stream to the service specified
/*  to auto_clnt_create(). The stream instance may change between calls.
/*  The result is a null pointer in case of failure.
/*
/*  auto_clnt_recover() recovers from a server-initiated disconnect
/*  that happened in the middle of an I/O operation.
/*
/*  auto_clnt_name() returns the name of the specified client endpoint.
/*
/*  auto_clnt_free() destroys of the specified client endpoint.
/*
/*  Arguments:
/* .IP service
/*  The service argument specifies "transport:servername" where
/*  transport is currently limited to one of the following:
/* .RS
/* .IP inet
/*  servername has the form "inet:host:port".
/* .IP local
/*  servername has the form "local:private/servicename" or
/*  "local:public/servicename". This is the preferred way to
/*  specify Postfix daemons that are configured as "unix" in
/*  master.cf.
/* .IP unix
/*  servername has the form "unix:private/servicename" or
/*  "unix:public/servicename". This does not work on Solaris,
/*  where Postfix uses STREAMS instead of UNIX-domain sockets.
/* .RE
/* .IP timeout
/*  The time limit for sending, receiving, or for connecting
/*  to a server. Specify a value <=0 to disable the time limit.
/* .IP max_idle
/*  Idle time after which the client disconnects. Specify 0 to
/*  disable the limit.
/* .IP max_ttl
/*  Upper bound on the time that a connection is allowed to persist.
/*  Specify 0 to disable the limit.
/* .IP open_action
/*  Application call-back routine that opens a stream or returns a
/*  null pointer upon failure. In case of success, the call-back routine
/*  is expected to set the stream pathname to the server endpoint name.
/* .IP context
/*  Application context that is passed to the open_action routine.
/* DIAGNOSTICS
/*  Warnings: communication failure. Fatal error: out of memory.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <string.h>

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <vstream.h>
#include <events.h>
#include <iostuff.h>
#include <connect.h>
#include <split_at.h>
#include <auto_clnt.h>

/* Application-specific. */

 /*
  * AUTO_CLNT is an opaque structure. None of the access methods can easily
  * be implemented as a macro, and access is not performance critical anyway.
  */
struct AUTO_CLNT {
    VSTREAM *vstream;           /* buffered I/O */
    char   *endpoint;           /* host:port or pathname */
    int     timeout;            /* I/O time limit */
    int     max_idle;           /* time before client disconnect */
    int     max_ttl;            /* time before client disconnect */
    int     (*connect) (const char *, int, int);    /* unix, local, inet */
};

static void auto_clnt_close(AUTO_CLNT *);

/* auto_clnt_event - server-initiated disconnect or client-side max_idle */

static void auto_clnt_event(int unused_event, void *context)
{
    AUTO_CLNT *auto_clnt = (AUTO_CLNT *) context;

    /*
     * Sanity check. This routine causes the stream to be closed, so it
     * cannot be called when the stream is already closed.
     */
    if (auto_clnt->vstream == 0)
    msg_panic("auto_clnt_event: stream is closed");

    auto_clnt_close(auto_clnt);
}

/* auto_clnt_ttl_event - client-side expiration */

static void auto_clnt_ttl_event(int event, void *context)
{

    /*
     * XXX This function is needed only because event_request_timer() cannot
     * distinguish between requests that specify the same call-back routine
     * and call-back context. The fix is obvious: specify a request ID along
     * with the call-back routine, but there is too much code that would have
     * to be changed.
     * 
     * XXX Should we be concerned that an overly aggressive optimizer will
     * eliminate this function and replace calls to auto_clnt_ttl_event() by
     * direct calls to auto_clnt_event()? It should not, because there exists
     * code that takes the address of both functions.
     */
    auto_clnt_event(event, context);
}

/* auto_clnt_open - connect to service */

static void auto_clnt_open(AUTO_CLNT *auto_clnt)
{
    const char *myname = "auto_clnt_open";
    int     fd;

    /*
     * Sanity check.
     */
    if (auto_clnt->vstream)
    msg_panic("auto_clnt_open: stream is open");

    /*
     * Schedule a read event so that we can clean up when the remote side
     * disconnects, and schedule a timer event so that we can cleanup an idle
     * connection. Note that both events are handled by the same routine.
     * 
     * Finally, schedule an event to force disconnection even when the
     * connection is not idle. This is to prevent one client from clinging on
     * to a server forever.
     */
    fd = auto_clnt->connect(auto_clnt->endpoint, BLOCKING, auto_clnt->timeout);
    if (fd < 0) {
    msg_warn("connect to %s: %m", auto_clnt->endpoint);
    } else {
    if (msg_verbose)
        msg_info("%s: connected to %s", myname, auto_clnt->endpoint);
    auto_clnt->vstream = vstream_fdopen(fd, O_RDWR);
    vstream_control(auto_clnt->vstream,
            CA_VSTREAM_CTL_PATH(auto_clnt->endpoint),
            CA_VSTREAM_CTL_TIMEOUT(auto_clnt->timeout),
            CA_VSTREAM_CTL_END);
    }

    if (auto_clnt->vstream != 0) {
    close_on_exec(vstream_fileno(auto_clnt->vstream), CLOSE_ON_EXEC);
    event_enable_read(vstream_fileno(auto_clnt->vstream), auto_clnt_event,
              (void *) auto_clnt);
    if (auto_clnt->max_idle > 0)
        event_request_timer(auto_clnt_event, (void *) auto_clnt,
                auto_clnt->max_idle);
    if (auto_clnt->max_ttl > 0)
        event_request_timer(auto_clnt_ttl_event, (void *) auto_clnt,
                auto_clnt->max_ttl);
    }
}

/* auto_clnt_close - disconnect from service */

static void auto_clnt_close(AUTO_CLNT *auto_clnt)
{
    const char *myname = "auto_clnt_close";

    /*
     * Sanity check.
     */
    if (auto_clnt->vstream == 0)
    msg_panic("%s: stream is closed", myname);

    /*
     * Be sure to disable read and timer events.
     */
    if (msg_verbose)
    msg_info("%s: disconnect %s stream",
         myname, VSTREAM_PATH(auto_clnt->vstream));
    event_disable_readwrite(vstream_fileno(auto_clnt->vstream));
    event_cancel_timer(auto_clnt_event, (void *) auto_clnt);
    event_cancel_timer(auto_clnt_ttl_event, (void *) auto_clnt);
    (void) vstream_fclose(auto_clnt->vstream);
    auto_clnt->vstream = 0;
}

/* auto_clnt_recover - recover from server-initiated disconnect */

void    auto_clnt_recover(AUTO_CLNT *auto_clnt)
{

    /*
     * Clean up. Don't re-connect until the caller needs it.
     */
    if (auto_clnt->vstream)
    auto_clnt_close(auto_clnt);
}

/* auto_clnt_access - access a client stream */

VSTREAM *auto_clnt_access(AUTO_CLNT *auto_clnt)
{

    /*
     * Open a stream or restart the idle timer.
     * 
     * Important! Do not restart the TTL timer!
     */
    if (auto_clnt->vstream == 0) {
    auto_clnt_open(auto_clnt);
    } else {
    if (auto_clnt->max_idle > 0)
        event_request_timer(auto_clnt_event, (void *) auto_clnt,
                auto_clnt->max_idle);
    }
    return (auto_clnt->vstream);
}

/* auto_clnt_create - create client stream object */

AUTO_CLNT *auto_clnt_create(const char *service, int timeout,
                        int max_idle, int max_ttl)
{
    const char *myname = "auto_clnt_create";
    char   *transport = mystrdup(service);
    char   *endpoint;
    AUTO_CLNT *auto_clnt;

    /*
     * Don't open the stream until the caller needs it.
     */
    if ((endpoint = split_at(transport, ':')) == 0
    || *endpoint == 0 || *transport == 0)
    msg_fatal("need service transport:endpoint instead of \"%s\"", service);
    if (msg_verbose)
    msg_info("%s: transport=%s endpoint=%s", myname, transport, endpoint);
    auto_clnt = (AUTO_CLNT *) mymalloc(sizeof(*auto_clnt));
    auto_clnt->vstream = 0;
    auto_clnt->endpoint = mystrdup(endpoint);
    auto_clnt->timeout = timeout;
    auto_clnt->max_idle = max_idle;
    auto_clnt->max_ttl = max_ttl;
    if (strcmp(transport, "inet") == 0) {
    auto_clnt->connect = inet_connect;
    } else if (strcmp(transport, "local") == 0) {
    auto_clnt->connect = LOCAL_CONNECT;
    } else if (strcmp(transport, "unix") == 0) {
    auto_clnt->connect = unix_connect;
    } else {
    msg_fatal("invalid transport name: %s in service: %s",
          transport, service);
    }
    myfree(transport);
    return (auto_clnt);
}

/* auto_clnt_name - return client stream name */

const char *auto_clnt_name(AUTO_CLNT *auto_clnt)
{
    return (auto_clnt->endpoint);
}

/* auto_clnt_free - destroy client stream instance */

void    auto_clnt_free(AUTO_CLNT *auto_clnt)
{
    if (auto_clnt->vstream)
    auto_clnt_close(auto_clnt);
    myfree(auto_clnt->endpoint);
    myfree((void *) auto_clnt);
}