}

// AcquireNet acquires a semaphore token for a network operation.
func AcquireNet() (release func(), err error) {
	hasToken := false
	if n, ok := NetLimit(); ok {
		if n == 0 {
			return nil, fmt.Errorf("network disabled by %v=%v", NetLimitGodebug.Name(), NetLimitGodebug.Value())
		}
		netLimitSem <- struct{}{}
		hasToken = true
	}

	checker := new(netTokenChecker)
	runtime.SetFinalizer(checker, (*netTokenChecker).panicUnreleased)

	{"BAR, FOO, BAZ", "foo", true},
	{"foobar", "foo", false},
	{"barfoo ", "foo", false},
}

func TestHasToken(t *testing.T) {
	for _, tt := range hasTokenTests {
		if hasToken(tt.header, tt.token) != tt.want {
			t.Errorf("hasToken(%q, %q) = %v; want %v", tt.header, tt.token, !tt.want, tt.want)
		}
	}
}

func TestNilHeaderClone(t *testing.T) {
	t1 := Header(nil)
	t2 := t1.Clone()
	if t2 != nil {

// returned without modifications.
func CanonicalHeaderKey(s string) string { return textproto.CanonicalMIMEHeaderKey(s) }

// hasToken reports whether token appears with v, ASCII
// case-insensitive, with space or comma boundaries.
// token must be all lowercase.
// v may contain mixed cased.
func hasToken(v, token string) bool {
	if len(token) > len(v) || token == "" {
		return false
	}
	if v == token {
		return true
	}