/*++
/* NAME
/*	msg_output 3
/* SUMMARY
/*	diagnostics output management
/* SYNOPSIS
/*	#include <msg_output.h>
/*
/*	typedef void (*MSG_OUTPUT_FN)(int level, char *text)
/*
/*	void	msg_output(output_fn)
/*	MSG_OUTPUT_FN output_fn;
/*
/*	void	msg_printf(level, format, ...)
/*	int	level;
/*	const char *format;
/*
/*	void	msg_vprintf(level, format, ap)
/*	int	level;
/*	const char *format;
/*	va_list ap;
/* DESCRIPTION
/*	This module implements low-level output management for the
/*	msg(3) diagnostics interface.
/*
/*	msg_output() registers an output handler for the diagnostics
/*	interface. An application can register multiple output handlers.
/*	Output handlers are called in the specified order.
/*	An output handler takes as arguments a severity level (MSG_INFO,
/*	MSG_WARN, MSG_ERROR, MSG_FATAL, MSG_PANIC, monotonically increasing
/*	integer values ranging from 0 to MSG_LAST) and pre-formatted,
/*	sanitized, text in the form of a null-terminated string.
/*
/*	msg_printf() and msg_vprintf() format their arguments, sanitize the
/*	result, and call the output handlers registered with msg_output().
/*
/*	msg_text() copies a pre-formatted text, sanitizes the result, and
/*	calls the output handlers registered with msg_output().
/* REENTRANCY
/* .ad
/* .fi
/*	The above output routines are protected against ordinary
/*	recursive calls and against re-entry by signal
/*	handlers, with the following limitations:
/* .IP \(bu
/*	The signal handlers must never return. In other words, the
/*	signal handlers must do one or more of the following: call
/*	_exit(), kill the process with a signal, and permanently
/*	block the process.
/* .IP \(bu
/*	The signal handlers must call the above output routines not
/*	until after msg_output() completes initialization, and not
/*	until after the first formatted output to a VSTRING or
/*	VSTREAM.
/* .IP \(bu
/*	Each msg_output() call-back function, and each Postfix or
/*	system function called by that call-back function, either
/*	must protect itself against recursive calls and re-entry
/*	by a terminating signal handler, or it must be called
/*	exclusively by functions in the msg_output(3) module.
/* .PP
/*	When re-entrancy is detected, the requested output operation
/*	is skipped. This prevents memory corruption of VSTREAM_ERR
/*	data structures, and prevents deadlock on Linux releases
/*	that use mutexes within system library routines such as
/*	syslog(). This protection exists under the condition that
/*	these specific resources are accessed exclusively via
/*	msg_output() call-back functions.
/* 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 <stdarg.h>
#include <errno.h>

/* Utility library. */

#include <mymalloc.h>
#include <vstring.h>
#include <vstream.h>
#include <msg_vstream.h>
#include <stringops.h>
#include <msg_output.h>

 /*
  * Global scope, to discourage the compiler from doing smart things.
  */
volatile int msg_vprintf_level;

 /*
  * Private state. Allow one nested call, so that one logging error can be
  * reported to stderr before bailing out.
  */
#define MSG_OUT_NESTING_LIMIT	2
static MSG_OUTPUT_FN *msg_output_fn = 0;
static int msg_output_fn_count = 0;
static VSTRING *msg_buffers[MSG_OUT_NESTING_LIMIT];

/* msg_output - specify output handler */

void    msg_output(MSG_OUTPUT_FN output_fn)
{
    int     i;

    /*
     * Allocate all resources during initialization. This may result in a
     * recursive call due to memory allocation error.
     */
    if (msg_buffers[MSG_OUT_NESTING_LIMIT - 1] == 0) {
	for (i = 0; i < MSG_OUT_NESTING_LIMIT; i++)
	    msg_buffers[i] = vstring_alloc(100);
    }

    /*
     * We're not doing this often, so avoid complexity and allocate memory
     * for an exact fit.
     */
    if (msg_output_fn_count == 0)
	msg_output_fn = (MSG_OUTPUT_FN *) mymalloc(sizeof(*msg_output_fn));
    else
	msg_output_fn = (MSG_OUTPUT_FN *) myrealloc((void *) msg_output_fn,
			(msg_output_fn_count + 1) * sizeof(*msg_output_fn));
    msg_output_fn[msg_output_fn_count++] = output_fn;
}

/* msg_printf - format text and log it */

void    msg_printf(int level, const char *format,...)
{
    va_list ap;

    va_start(ap, format);
    msg_vprintf(level, format, ap);
    va_end(ap);
}

/* msg_vprintf - format text and log it */

void    msg_vprintf(int level, const char *format, va_list ap)
{
    int     saved_errno = errno;
    VSTRING *vp;
    int     i;

    if (msg_vprintf_level < MSG_OUT_NESTING_LIMIT) {
	msg_vprintf_level += 1;
	/* On-the-fly initialization for test programs and startup errors. */
	if (msg_output_fn_count == 0)
	    msg_vstream_init("unknown", VSTREAM_ERR);
	vp = msg_buffers[msg_vprintf_level - 1];
	/* OK if terminating signal handler hijacks control before next stmt. */
	vstring_vsprintf(vp, format, ap);
	printable(vstring_str(vp), '?');
	for (i = 0; i < msg_output_fn_count; i++)
	    msg_output_fn[i] (level, vstring_str(vp));
	msg_vprintf_level -= 1;
    }
    errno = saved_errno;
}