github.com/code-reading/golang@v0.0.0-20220303082512-ba5bc0e589a3/go/src/net/port_unix.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build aix || darwin || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris
     6  // +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris
     7  
     8  // Read system port mappings from /etc/services
     9  
    10  package net
    11  
    12  import (
    13  	"internal/bytealg"
    14  	"sync"
    15  )
    16  
    17  var onceReadServices sync.Once
    18  
    19  func readServices() {
    20  	file, err := open("/etc/services")
    21  	if err != nil {
    22  		return
    23  	}
    24  	defer file.close()
    25  
    26  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    27  		// "http 80/tcp www www-http # World Wide Web HTTP"
    28  		if i := bytealg.IndexByteString(line, '#'); i >= 0 {
    29  			line = line[:i]
    30  		}
    31  		f := getFields(line)
    32  		if len(f) < 2 {
    33  			continue
    34  		}
    35  		portnet := f[1] // "80/tcp"
    36  		port, j, ok := dtoi(portnet)
    37  		if !ok || port <= 0 || j >= len(portnet) || portnet[j] != '/' {
    38  			continue
    39  		}
    40  		netw := portnet[j+1:] // "tcp"
    41  		m, ok1 := services[netw]
    42  		if !ok1 {
    43  			m = make(map[string]int)
    44  			services[netw] = m
    45  		}
    46  		for i := 0; i < len(f); i++ {
    47  			if i != 1 { // f[1] was port/net
    48  				m[f[i]] = port
    49  			}
    50  		}
    51  	}
    52  }
    53  
    54  // goLookupPort is the native Go implementation of LookupPort.
    55  func goLookupPort(network, service string) (port int, err error) {
    56  	onceReadServices.Do(readServices)
    57  	return lookupPortMap(network, service)
    58  }