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
5package runtime
6
7import "unsafe"
8
9func 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.
24func 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
38func 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
54var _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
65var _cgo_unsetenv unsafe.Pointer // pointer to C function
66
67// Update the C environment if cgo is loaded.
68func 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.
77func 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
85func cstring(s string) unsafe.Pointer {
86	p := make([]byte, len(s)+1)
87	copy(p, s)
88	return unsafe.Pointer(&p[0])
89}
90