// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Read system port mappings from /etc/services

package net

import (
	"once";
	"os";
)

var services map[string] map[string] int
var servicesError os.Error

func readServices() {
	services = make(map[string] map[string] int);
	var file *file;
	file, servicesError = open("/etc/services");
	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
		// "http 80/tcp www www-http # World Wide Web HTTP"
		if i := byteIndex(line, '#'); i >= 0 {
			line = line[0:i];
		}
		f := getFields(line);
		if len(f) < 2 {
			continue;
		}
		portnet := f[1];	// "tcp/80"
		port, j, ok := dtoi(portnet, 0);
		if !ok || port <= 0 || j >= len(portnet) || portnet[j] != '/' {
			continue
		}
		netw := portnet[j+1:len(portnet)];	// "tcp"
		m, ok1 := services[netw];
		if !ok1 {
			m = make(map[string] int);
			services[netw] = m;
		}
		for i := 0; i < len(f); i++ {
			if i != 1 {	// f[1] was port/net
				m[f[i]] = port;
			}
		}
	}
	file.close();
}

// LookupPort looks up the port for the given network and service.
func LookupPort(network, service string) (port int, err os.Error) {
	once.Do(readServices);

	switch network {
	case "tcp4", "tcp6":
		network = "tcp";
	case "udp4", "udp6":
		network = "udp";
	}

	if m, ok := services[network]; ok {
		if port, ok = m[service]; ok {
			return;
		}
	}
	return 0, &AddrError{"unknown port", network + "/" + service};
}