#!/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.
    avahi_type=_stap._tcp
    port=$1
    test "X$port" = "X" && port=65000
    export 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 {
    # Loop forever accepting requests
    while true
    do
	for ((attempt=0; $attempt < 5; ++attempt))
	do
            nc -ld $port 2>/dev/null | process_request &
	    wait '%nc -l'
	    rc=$?
	    if test $rc = 0 -o $rc = 127; then
		break; # port was read ok
            fi
	done
	if test $attempt = 5; then
	    fatal "ERROR: cannot listen on port $port. rc==$rc"
	fi
    done
}

# function: process_request
#
# Process an incoming request on stdin
function process_request {
    read
    case $REPLY in
	request:)
	    stap-server $port2 >/dev/null 2>&1 &
	    wait '%stap-server'
	    rc=$?
	    test $rc = 127 && rc=0
	    ;;
	*)
	    rc=1
    esac

    exit $rc
}

# 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' >/dev/null 2>&1

    # Kill any running 'stap-server' job.
    kill -s SIGTERM "%stap-server" 2> /dev/null
    wait "%stap-server"  >/dev/null 2>&1

    # Kill any running 'nc -l' job.
    kill -s SIGTERM "%?nc -l" 2> /dev/null
    wait "%?nc - l"  >/dev/null 2>&1

    exit
}

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