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b8a2aedccd
Fixes tailscale/corp#15850 Co-authored-by: Adrian Dewhurst <adrian@tailscale.com> Signed-off-by: Claire Wang <claire@tailscale.com>
99 lines
2.7 KiB
Go
99 lines
2.7 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package syspolicy
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import (
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"errors"
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"sync"
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)
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// CachingHandler is a handler that reads policies from an underlying handler the first time each key is requested
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// and permanently caches the result unless there is an error. If there is an ErrNoSuchKey error, that result is cached,
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// otherwise the actual error is returned and the next read for that key will retry using the handler.
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type CachingHandler struct {
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mu sync.Mutex
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strings map[string]string
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uint64s map[string]uint64
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bools map[string]bool
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notFound map[string]bool
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handler Handler
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}
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// NewCachingHandler creates a CachingHandler given a handler.
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func NewCachingHandler(handler Handler) *CachingHandler {
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return &CachingHandler{
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handler: handler,
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strings: make(map[string]string),
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uint64s: make(map[string]uint64),
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bools: make(map[string]bool),
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notFound: make(map[string]bool),
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}
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}
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// ReadString reads the policy settings value string given the key.
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// ReadString first reads from the handler's cache before resorting to using the handler.
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func (ch *CachingHandler) ReadString(key string) (string, error) {
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ch.mu.Lock()
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defer ch.mu.Unlock()
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if val, ok := ch.strings[key]; ok {
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return val, nil
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}
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if notFound := ch.notFound[key]; notFound {
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return "", ErrNoSuchKey
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}
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val, err := ch.handler.ReadString(key)
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if errors.Is(err, ErrNoSuchKey) {
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ch.notFound[key] = true
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return "", err
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} else if err != nil {
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return "", err
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}
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ch.strings[key] = val
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return val, nil
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}
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// ReadUInt64 reads the policy settings uint64 value given the key.
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// ReadUInt64 first reads from the handler's cache before resorting to using the handler.
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func (ch *CachingHandler) ReadUInt64(key string) (uint64, error) {
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ch.mu.Lock()
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defer ch.mu.Unlock()
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if val, ok := ch.uint64s[key]; ok {
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return val, nil
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}
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if notFound := ch.notFound[key]; notFound {
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return 0, ErrNoSuchKey
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}
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val, err := ch.handler.ReadUInt64(key)
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if errors.Is(err, ErrNoSuchKey) {
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ch.notFound[key] = true
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return 0, err
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} else if err != nil {
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return 0, err
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}
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ch.uint64s[key] = val
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return val, nil
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}
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// ReadBoolean reads the policy settings boolean value given the key.
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// ReadBoolean first reads from the handler's cache before resorting to using the handler.
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func (ch *CachingHandler) ReadBoolean(key string) (bool, error) {
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ch.mu.Lock()
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defer ch.mu.Unlock()
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if val, ok := ch.bools[key]; ok {
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return val, nil
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}
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if notFound := ch.notFound[key]; notFound {
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return false, ErrNoSuchKey
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}
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val, err := ch.handler.ReadBoolean(key)
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if errors.Is(err, ErrNoSuchKey) {
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ch.notFound[key] = true
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return false, err
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} else if err != nil {
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return false, err
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}
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ch.bools[key] = val
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return val, nil
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}
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