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

     1  // Copyright 2010 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 || plan9
     6  // +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris plan9
     7  
     8  // Unix environment variables.
     9  
    10  package syscall
    11  
    12  import (
    13  	"runtime"
    14  	"sync"
    15  )
    16  
    17  var (
    18  	// envOnce guards initialization by copyenv, which populates env.
    19  	envOnce sync.Once
    20  
    21  	// envLock guards env and envs.
    22  	envLock sync.RWMutex
    23  
    24  	// env maps from an environment variable to its first occurrence in envs.
    25  	env map[string]int
    26  
    27  	// envs is provided by the runtime. elements are expected to
    28  	// be of the form "key=value". An empty string means deleted
    29  	// (or a duplicate to be ignored).
    30  	envs []string = runtime_envs()
    31  )
    32  
    33  func runtime_envs() []string // in package runtime
    34  
    35  // setenv_c and unsetenv_c are provided by the runtime but are no-ops
    36  // if cgo isn't loaded.
    37  func setenv_c(k, v string)
    38  func unsetenv_c(k string)
    39  
    40  func copyenv() {
    41  	env = make(map[string]int)
    42  	for i, s := range envs {
    43  		for j := 0; j < len(s); j++ {
    44  			if s[j] == '=' {
    45  				key := s[:j]
    46  				if _, ok := env[key]; !ok {
    47  					env[key] = i // first mention of key
    48  				} else {
    49  					// Clear duplicate keys. This permits Unsetenv to
    50  					// safely delete only the first item without
    51  					// worrying about unshadowing a later one,
    52  					// which might be a security problem.
    53  					envs[i] = ""
    54  				}
    55  				break
    56  			}
    57  		}
    58  	}
    59  }
    60  
    61  func Unsetenv(key string) error {
    62  	envOnce.Do(copyenv)
    63  
    64  	envLock.Lock()
    65  	defer envLock.Unlock()
    66  
    67  	if i, ok := env[key]; ok {
    68  		envs[i] = ""
    69  		delete(env, key)
    70  	}
    71  	unsetenv_c(key)
    72  	return nil
    73  }
    74  
    75  func Getenv(key string) (value string, found bool) {
    76  	envOnce.Do(copyenv)
    77  	if len(key) == 0 {
    78  		return "", false
    79  	}
    80  
    81  	envLock.RLock()
    82  	defer envLock.RUnlock()
    83  
    84  	i, ok := env[key]
    85  	if !ok {
    86  		return "", false
    87  	}
    88  	s := envs[i]
    89  	for i := 0; i < len(s); i++ {
    90  		if s[i] == '=' {
    91  			return s[i+1:], true
    92  		}
    93  	}
    94  	return "", false
    95  }
    96  
    97  func Setenv(key, value string) error {
    98  	envOnce.Do(copyenv)
    99  	if len(key) == 0 {
   100  		return EINVAL
   101  	}
   102  	for i := 0; i < len(key); i++ {
   103  		if key[i] == '=' || key[i] == 0 {
   104  			return EINVAL
   105  		}
   106  	}
   107  	// On Plan 9, null is used as a separator, eg in $path.
   108  	if runtime.GOOS != "plan9" {
   109  		for i := 0; i < len(value); i++ {
   110  			if value[i] == 0 {
   111  				return EINVAL
   112  			}
   113  		}
   114  	}
   115  
   116  	envLock.Lock()
   117  	defer envLock.Unlock()
   118  
   119  	i, ok := env[key]
   120  	kv := key + "=" + value
   121  	if ok {
   122  		envs[i] = kv
   123  	} else {
   124  		i = len(envs)
   125  		envs = append(envs, kv)
   126  	}
   127  	env[key] = i
   128  	setenv_c(key, value)
   129  	return nil
   130  }
   131  
   132  func Clearenv() {
   133  	envOnce.Do(copyenv) // prevent copyenv in Getenv/Setenv
   134  
   135  	envLock.Lock()
   136  	defer envLock.Unlock()
   137  
   138  	for k := range env {
   139  		unsetenv_c(k)
   140  	}
   141  	env = make(map[string]int)
   142  	envs = []string{}
   143  }
   144  
   145  func Environ() []string {
   146  	envOnce.Do(copyenv)
   147  	envLock.RLock()
   148  	defer envLock.RUnlock()
   149  	a := make([]string, 0, len(envs))
   150  	for _, env := range envs {
   151  		if env != "" {
   152  			a = append(a, env)
   153  		}
   154  	}
   155  	return a
   156  }