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tailscale/util/syspolicy/handler.go

59 lines
1.6 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package syspolicy
import (
"errors"
"sync/atomic"
)
var (
handlerUsed atomic.Bool
handler Handler = defaultHandler{}
)
// Handler reads system policies from OS-specific storage.
type Handler interface {
// ReadString reads the policy settings value string given the key.
ReadString(key string) (string, error)
// ReadUInt64 reads the policy settings uint64 value given the key.
ReadUInt64(key string) (uint64, error)
// ReadBool reads the policy setting's boolean value, given the key.
ReadBoolean(key string) (bool, error)
}
// ErrNoSuchKey is returned when the specified key does not have a value set.
var ErrNoSuchKey = errors.New("no such key")
// defaultHandler is the catch all syspolicy type for anything that isn't windows or apple.
type defaultHandler struct{}
func (defaultHandler) ReadString(_ string) (string, error) {
return "", ErrNoSuchKey
}
func (defaultHandler) ReadUInt64(_ string) (uint64, error) {
return 0, ErrNoSuchKey
}
func (defaultHandler) ReadBoolean(_ string) (bool, error) {
return false, ErrNoSuchKey
}
// markHandlerInUse is called before handler methods are called.
func markHandlerInUse() {
handlerUsed.Store(true)
}
// RegisterHandler initializes the policy handler and ensures registration will happen once.
func RegisterHandler(h Handler) {
// Technically this assignment is not concurrency safe, but in the
// event that there was any risk of a data race, we will panic due to
// the CompareAndSwap failing.
handler = h
if !handlerUsed.CompareAndSwap(false, true) {
panic("handler was already used before registration")
}
}