// 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 (
	"os"
	"sync"
)

var services map[string]map[string]int
var servicesError os.Error
var onceReadServices sync.Once

func readServices() {
	services = make(map[string]map[string]int)
	var file *file
	if file, servicesError = open("/etc/services"); servicesError != nil {
		return
	}
	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:] // "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) {
	onceReadServices.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}
}