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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package syspolicy
import (
"errors"
"sync"
)
// CachingHandler is a handler that reads policies from an underlying handler the first time each key is requested
// and permanently caches the result unless there is an error. If there is an ErrNoSuchKey error, that result is cached,
// otherwise the actual error is returned and the next read for that key will retry using the handler.
type CachingHandler struct {
mu sync.Mutex
strings map[string]string
uint64s map[string]uint64
bools map[string]bool
notFound map[string]bool
handler Handler
}
// NewCachingHandler creates a CachingHandler given a handler.
func NewCachingHandler(handler Handler) *CachingHandler {
return &CachingHandler{
handler: handler,
strings: make(map[string]string),
uint64s: make(map[string]uint64),
bools: make(map[string]bool),
notFound: make(map[string]bool),
}
}
// ReadString reads the policy settings value string given the key.
// ReadString first reads from the handler's cache before resorting to using the handler.
func (ch *CachingHandler) ReadString(key string) (string, error) {
ch.mu.Lock()
defer ch.mu.Unlock()
if val, ok := ch.strings[key]; ok {
return val, nil
}
if notFound := ch.notFound[key]; notFound {
return "", ErrNoSuchKey
}
val, err := ch.handler.ReadString(key)
if errors.Is(err, ErrNoSuchKey) {
ch.notFound[key] = true
return "", err
} else if err != nil {
return "", err
}
ch.strings[key] = val
return val, nil
}
// ReadUInt64 reads the policy settings uint64 value given the key.
// ReadUInt64 first reads from the handler's cache before resorting to using the handler.
func (ch *CachingHandler) ReadUInt64(key string) (uint64, error) {
ch.mu.Lock()
defer ch.mu.Unlock()
if val, ok := ch.uint64s[key]; ok {
return val, nil
}
if notFound := ch.notFound[key]; notFound {
return 0, ErrNoSuchKey
}
val, err := ch.handler.ReadUInt64(key)
if errors.Is(err, ErrNoSuchKey) {
ch.notFound[key] = true
return 0, err
} else if err != nil {
return 0, err
}
ch.uint64s[key] = val
return val, nil
}
// ReadBoolean reads the policy settings boolean value given the key.
// ReadBoolean first reads from the handler's cache before resorting to using the handler.
func (ch *CachingHandler) ReadBoolean(key string) (bool, error) {
ch.mu.Lock()
defer ch.mu.Unlock()
if val, ok := ch.bools[key]; ok {
return val, nil
}
if notFound := ch.notFound[key]; notFound {
return false, ErrNoSuchKey
}
val, err := ch.handler.ReadBoolean(key)
if errors.Is(err, ErrNoSuchKey) {
ch.notFound[key] = true
return false, err
} else if err != nil {
return false, err
}
ch.bools[key] = val
return val, nil
}
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