#!/bin/bash

# Compile server manager for systemtap
#
# Copyright (C) 2008 Red Hat Inc.
#
# This file is part of systemtap, and is free software.  You can
# redistribute it and/or modify it under the terms of the GNU General
# Public License (GPL); either version 2, or (at your option) any
# later version.

# This script publishes its presence on the network and then listens for
# incoming connections. When a connection is detected, the stap-server script
# is run to handle the request.

# Catch ctrl-c and other termination signals
trap 'terminate' SIGTERM SIGINT

#-----------------------------------------------------------------------------
# Helper functions.
#-----------------------------------------------------------------------------
# function: initialization PORT
function initialization {
    # Default settings.
    tmpdir_prefix_serverd=stap.serverd
    avahi_type=_stap._tcp
    port=$1
    test "X$port" = "X" && port=65000
    port2=$(($port + 1))
    if netstat -atn | awk '{print $4}' | cut -f2 -d: | egrep -q "^($port|$port2)\$"; then
        # Whoops, the port is busy; try another one.
        initialization $((1024+($port + $RANDOM)%64000))
    fi
}

# function: advertise_presence
#
# Advertise the availability of the server on the network.
function advertise_presence {
    # Build up a string representing our server's properties.
    # TODO: this needs fleshing out.
    local sysinfo=`uname -rvm`
    local txt="sysinfo=$sysinfo"

    # Call avahi-publish-service to advertise our presence.
    avahi-publish-service "Systemtap Compile Server on `uname -n`" \
	$avahi_type $port "$txt" > /dev/null 2>&1 &

    echo "Systemtap Compile Server on `uname -n` listening on port $port"
}

# function: listen
#
# Listen for and handle requests to the server.
function listen {
    # Work in a temporary directory
    tmpdir=`mktemp -dt $tmpdir_prefix_serverd.XXXXXX` || \
	fatal "ERROR: cannot create temporary directory " $tmpdir
    cd $tmpdir

    # Create a fifo for communicating with the server
    local fifo_name=$tmpdir_prefix_serverd.fifo
    mknod $fifo_name p || \
	fatal "ERROR: cannot create temporary fifo " $tmpdir/$fifo_name

    # Loop forever accepting requests
    first=1
    set -o pipefail # We want the status of 'nc' not 'stap-server'.
    while true
    do
	# Run this in the background and wait for it. This way any signals
	# received (i.e. SIGTERM) will be processed. Make sure we don't
	# advertise our presence until we're actually listening.
	for ((attempt=0; $attempt < 5; ++attempt))
	do
	    nc -l $port < $fifo_name | stap-server $((port + 1)) > $fifo_name 2>&1 &
	    if test $first = 1; then
		advertise_presence
		first=0
	    fi
	    wait %nc
	    rc=$?
            if test $rc = 127 -o $rc = 0; then
		break; # success
            fi
	    sleep 1
	done
	if test $attempt = 5; then
	    fatal "ERROR: cannot listen on port $port. rc==$rc"
	fi
    done
    set +o pipefail # restore
}

# function: fatal [ MESSAGE ]
#
# Fatal error
# Prints its arguments to stderr and exits
function fatal {
    echo "$@" >&2
    terminate
    exit 1
}

# function: terminate
#
# Terminate gracefully.
function terminate {
    echo "$0: Exiting"

    # Kill the running 'avahi-publish-service' job
    kill -s SIGTERM %avahi-publish-service 2> /dev/null
    wait %avahi-publish-service 2> /dev/null

    # Kill any running 'nc -l' job.
    kill -s SIGTERM "%nc -l" 2> /dev/null
    wait "%nc - l" 2> /dev/null

    # Clean up
    cd `dirname $tmpdir`
    rm -fr $tmpdir

    exit
}

#-----------------------------------------------------------------------------
# Beginning of main line execution.
#-----------------------------------------------------------------------------
initialization "$@"
listen