/*	$NetBSD: auto_clnt.c,v 1.4 2022/10/08 16:12:50 christos Exp $	*/

/*++
/* NAME
/*	auto_clnt 3
/* SUMMARY
/*	client endpoint maintenance
/* SYNOPSIS
/*	#include <auto_clnt.h>
/*
/*	typedef void (*AUTO_CLNT_HANDSHAKE_FN)(VSTREAM *);
/*
/*	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;
/*
/*	void	auto_clnt_control(auto_clnt, name, value, ... AUTO_CLNT_CTL_END)
/*	AUTO_CLNT *auto_clnt;
/*	int	name;
/* 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.
/*
/*	auto_clnt_control() allows the user to fine tune the behavior of
/*      the specified client. The arguments are a list of (name, value)
/*      terminated with AUTO_CLNT_CTL_END.
/*      The following lists the names and the types of the corresponding
/*      value arguments.
/* .IP "AUTO_CLNT_CTL_HANDSHAKE(VSTREAM *)"
/*      A pointer to function that will be called at the start of a
/*      new connection, and that returns 0 in case of success.
/* .PP
/*	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.
/* .IP handshake
/*	A null pointer, or a pointer to function that will be called
/*	at the start of a new connection and that returns 0 in case
/*	of success.
/* 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
/*
/*	Wietse Venema
/*	Google, Inc.
/*	111 8th Avenue
/*	New York, NY 10011, 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 */
    AUTO_CLNT_HANDSHAKE_FN handshake;	/* new connection only */
    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)
{
    AUTO_CLNT_HANDSHAKE_FN handshake;

    /*
     * 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);
	handshake = (auto_clnt->vstream ? auto_clnt->handshake : 0);
    } else {
	if (auto_clnt->max_idle > 0)
	    event_request_timer(auto_clnt_event, (void *) auto_clnt,
				auto_clnt->max_idle);
	handshake = 0;
    }
    if (handshake != 0 && handshake(auto_clnt->vstream) != 0)
	return (0);
    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;
    auto_clnt->handshake = 0;
    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);
}

/* auto_clnt_control - fine control */

void    auto_clnt_control(AUTO_CLNT *client, int name,...)
{
    const char *myname = "auto_clnt_control";
    va_list ap;

    for (va_start(ap, name); name != AUTO_CLNT_CTL_END; name = va_arg(ap, int)) {
	switch (name) {
	case AUTO_CLNT_CTL_HANDSHAKE:
	    client->handshake = va_arg(ap, AUTO_CLNT_HANDSHAKE_FN);
	    break;
	default:
	    msg_panic("%s: bad name %d", myname, name);
	}
    }
    va_end(ap);
}