Source file src/pkg/net/port.go

// 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
    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:] // "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}
}