A simple, go-based DNS resolver/caching server
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package main
import (
"github.com/miekg/dns"
"sync"
"time"
)
type MemoryCache struct {
Cache
Backend map[string]Mesg
Expire time.Duration
Maxcount int
mu sync.RWMutex
}
func (c *MemoryCache) Get(key string) (*dns.Msg, error) {
c.mu.RLock()
mesg, ok := c.Backend[key]
c.mu.RUnlock()
if !ok {
return nil, KeyNotFound{key}
}
if mesg.Expire.Before(time.Now()) {
c.Remove(key)
return nil, KeyExpired{key}
}
return mesg.Msg, nil
}
func (c *MemoryCache) Set(key string, msg *dns.Msg) error {
if c.Full() && !c.Exists(key) {
return CacheIsFull{}
}
expire := time.Now().Add(c.Expire)
mesg := Mesg{msg, expire}
c.mu.Lock()
c.Backend[key] = mesg
c.mu.Unlock()
return nil
}
func (c *MemoryCache) Remove(key string) error {
c.mu.Lock()
delete(c.Backend, key)
c.mu.Unlock()
return nil
}
func (c *MemoryCache) Exists(key string) bool {
c.mu.RLock()
_, ok := c.Backend[key]
c.mu.RUnlock()
return ok
}
func (c *MemoryCache) Length() int {
c.mu.RLock()
defer c.mu.RUnlock()
return len(c.Backend)
}
func (c *MemoryCache) Full() bool {
// if Maxcount is zero. the cache will never be full.
if c.Maxcount == 0 {
return false
}
return c.Length() >= c.Maxcount
}