env_posix.go

     1  // Copyright 2012 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  package runtime
     6  
     7  import "unsafe"
     8  
     9  func gogetenv(key string) string {
    10  	env := environ()
    11  	if env == nil {
    12  		throw("getenv before env init")
    13  	}
    14  	for _, s := range env {
    15  		if len(s) > len(key) && s[len(key)] == '=' && envKeyEqual(s[:len(key)], key) {
    16  			return s[len(key)+1:]
    17  		}
    18  	}
    19  	return ""
    20  }
    21  
    22  // envKeyEqual reports whether a == b, with ASCII-only case insensitivity
    23  // on Windows. The two strings must have the same length.
    24  func envKeyEqual(a, b string) bool {
    25  	if GOOS == "windows" { // case insensitive
    26  		for i := 0; i < len(a); i++ {
    27  			ca, cb := a[i], b[i]
    28  			if ca == cb || lowerASCII(ca) == lowerASCII(cb) {
    29  				continue
    30  			}
    31  			return false
    32  		}
    33  		return true
    34  	}
    35  	return a == b
    36  }
    37  
    38  func lowerASCII(c byte) byte {
    39  	if 'A' <= c && c <= 'Z' {
    40  		return c + ('a' - 'A')
    41  	}
    42  	return c
    43  }
    44  
    45  // _cgo_setenv should be an internal detail,
    46  // but widely used packages access it using linkname.
    47  // Notable members of the hall of shame include:
    48  //   - github.com/ebitengine/purego
    49  //
    50  // Do not remove or change the type signature.
    51  // See go.dev/issue/67401.
    52  //
    53  //go:linkname _cgo_setenv
    54  var _cgo_setenv unsafe.Pointer // pointer to C function
    55  
    56  // _cgo_unsetenv should be an internal detail,
    57  // but widely used packages access it using linkname.
    58  // Notable members of the hall of shame include:
    59  //   - github.com/ebitengine/purego
    60  //
    61  // Do not remove or change the type signature.
    62  // See go.dev/issue/67401.
    63  //
    64  //go:linkname _cgo_unsetenv
    65  var _cgo_unsetenv unsafe.Pointer // pointer to C function
    66  
    67  // Update the C environment if cgo is loaded.
    68  func setenv_c(k string, v string) {
    69  	if _cgo_setenv == nil {
    70  		return
    71  	}
    72  	arg := [2]unsafe.Pointer{cstring(k), cstring(v)}
    73  	asmcgocall(_cgo_setenv, unsafe.Pointer(&arg))
    74  }
    75  
    76  // Update the C environment if cgo is loaded.
    77  func unsetenv_c(k string) {
    78  	if _cgo_unsetenv == nil {
    79  		return
    80  	}
    81  	arg := [1]unsafe.Pointer{cstring(k)}
    82  	asmcgocall(_cgo_unsetenv, unsafe.Pointer(&arg))
    83  }
    84  
    85  func cstring(s string) unsafe.Pointer {
    86  	p := make([]byte, len(s)+1)
    87  	copy(p, s)
    88  	return unsafe.Pointer(&p[0])
    89  }
    90
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