#!/bin/bash

# Find compile servers 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 uses avahi to find systemtap compile servers on the local
# network. Information about each server found is printed to stdout.

#-----------------------------------------------------------------------------
# Helper functions.
#-----------------------------------------------------------------------------
# function: configuration
function configuration {
    avahi_service_tag=_stap._tcp
}

# function: initialization
function initialization {
    rc=1 # not found yet
    if test "X$1" = "X--all"; then
	find_all=1
    else
	find_all=0
    fi
}

# function: find_and_connect_to_server
#
# Find and establish connection with a compatibale stap server.
function find_servers {
    # Find a server
    avahi-browse $avahi_service_tag --terminate -r 2>/dev/null | match_server
    rc=$?
}

# function: match_server
#
# Find a suitable server using the avahi-browse output provided on stdin.
function match_server {
    local server_ip
    local server_name
    local server_sysinfo
    local server_port
    local rc=1 # not found yet

    # Loop over the avahi service descriptors.
    while read
    do
	# Examine the next service descriptor
	# Is it a stap server?
	(echo $REPLY | grep -q "^=.*_stap") || continue
	
	# Get the details of the service
	local service_tag equal data
	while read service_tag equal service_data
	do
	    case $service_tag in
		'=' )
		    break ;;
		hostname )
		    server_name=`expr "$service_data" : '\[\([^]]*\)\]'`
		    ;;
		address )
		    # Sometimes (seems random), avahi-resolve-host-name resolves a local server to its
		    # hardware address rather its ip address. Keep trying until we get
		    # an ip address.
		    server_ip=`expr "$service_data" : '\[\([^]]*\)\]'`
		    local attempt
		    for ((attempt=0; $attempt < 5; ++attempt))
		    do
			server_ip=`expr "$server_ip" : '^\([0-9]*\.[0-9]*\.[0-9]*\.[0-9]*\)$'`
			if test "X$server_ip" != "X"; then
			    break
			fi
		        # Resolve the server.domain to an ip address.
			server_ip=`avahi-resolve-host-name $hostname`
			server_ip=`expr "$server_ip" : '.*	\(.*\)$'`
		    done
		    ;;
		port )
		    server_port=`expr "$service_data" : '\[\([^]]*\)\]'`
		    ;;
		txt )
		    server_sysinfo=`expr "$service_data" : '\[.*\"\(sysinfo=[^]]*\)\"\]'`
		    ;;
		* )
		    break ;;
	    esac
	done

	# It is a stap server, but is it compatible?
	if test $find_all = 0 -a "$server_sysinfo" != "`client_sysinfo`"; then
	    continue
	fi

	# It's compatible, or we're finding all servers. Print a summary line
	echo $server_name $server_ip $server_port "'$server_sysinfo'"
	rc=0
    done

    exit $rc
}

# function client_sysinfo
#
# Generate the client's sysinfo and echo it to stdout
function client_sysinfo {
    if test "X$sysinfo_client" = "X"; then
	# Add some info from uname
	sysinfo_client="`uname -rvm`"
    fi
    echo sysinfo=$sysinfo_client
}

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

exit $rc