godns/cache.go

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package main
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import (
"crypto/md5"
"encoding/json"
"fmt"
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"github.com/hoisie/redis"
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"github.com/miekg/dns"
"time"
)
type KeyNotFound struct {
key string
}
func (e KeyNotFound) Error() string {
return e.key + " " + "not found"
}
type KeyExpired struct {
Key string
}
func (e KeyExpired) Error() string {
return e.Key + " " + "expired"
}
type CacheIsFull struct {
}
func (e CacheIsFull) Error() string {
return "Cache is Full"
}
type SerializerError struct {
}
func (e SerializerError) Error() string {
return "Serializer error"
}
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type Mesg struct {
Msg *dns.Msg
Expire time.Time
}
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type Cache interface {
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Get(key string) (Msg *dns.Msg, err error)
Set(key string, Msg *dns.Msg) error
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Exists(key string) bool
Remove(key string)
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Length() int
}
type MemoryCache struct {
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Backend map[string]Mesg
Expire time.Duration
Maxcount int
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}
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func (c *MemoryCache) Get(key string) (*dns.Msg, error) {
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mesg, ok := c.Backend[key]
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if !ok {
return nil, KeyNotFound{key}
}
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if mesg.Expire.Before(time.Now()) {
c.Remove(key)
return nil, KeyExpired{key}
}
return mesg.Msg, nil
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}
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func (c *MemoryCache) Set(key string, msg *dns.Msg) error {
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if c.Full() && !c.Exists(key) {
return CacheIsFull{}
}
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expire := time.Now().Add(c.Expire)
mesg := Mesg{msg, expire}
c.Backend[key] = mesg
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return nil
}
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func (c *MemoryCache) Remove(key string) {
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delete(c.Backend, key)
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}
func (c *MemoryCache) Exists(key string) bool {
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_, ok := c.Backend[key]
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return ok
}
func (c *MemoryCache) Length() int {
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return len(c.Backend)
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}
func (c *MemoryCache) Full() bool {
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// if Maxcount is zero. the cache will never be full.
if c.Maxcount == 0 {
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return false
}
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return c.Length() >= c.Maxcount
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}
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/*
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TODO: Redis cache Backend
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*/
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type RedisCache struct {
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Backend *redis.Client
Serializer JsonSerializer
Expire time.Duration
Maxcount int
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}
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func (c *RedisCache) Get() {
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}
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func (c *RedisCache) Set() {
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}
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func (c *RedisCache) Remove() {
}
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func KeyGen(q Question) string {
h := md5.New()
h.Write([]byte(q.String()))
x := h.Sum(nil)
key := fmt.Sprintf("%x", x)
return key
}
type JsonSerializer struct {
}
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func (*JsonSerializer) Dumps(mesg *dns.Msg) (encoded []byte, err error) {
encoded, err = json.Marshal(mesg)
return
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}
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func (*JsonSerializer) Loads(data []byte, mesg **dns.Msg) error {
err := json.Unmarshal(data, mesg)
return err
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}