mirror of
https://github.com/miekg/dns.git
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118 lines
2.5 KiB
Go
118 lines
2.5 KiB
Go
package main
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// Keep a local cache of DNS packets. Match incoming
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// qname,qclass,qtype and return the saved packet.
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// On a cache miss consult the nameserver
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import (
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"dns"
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"sync"
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"time"
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)
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// Keep everything in the cache for 60 seconds
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const (
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CACHETTL = 1
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_CLASS = 2 << 16
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INSERT = iota
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DELETE
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)
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var cache Cache
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type item struct {
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epoch int64
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msg []byte
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}
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// Number in the second map denotes the class + type.
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func intval(c, t uint16) int {
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return int(c)*_CLASS + int(t)
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}
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// Mutex entry in the cache, if non-nill take the lock
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// Ala Zone in zone.go, but slightly different
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type Cache struct {
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data map[string]map[int]*item
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rw *sync.RWMutex
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}
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func NewCache() Cache {
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c := new(Cache)
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c.data = make(map[string]map[int]*item)
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c.rw = new(sync.RWMutex)
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return *c
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}
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// Add an entry to the cache. The old entry (if any) gets overwritten
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func (c Cache) add(q *dns.Msg) {
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c.rw.Lock()
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defer c.rw.Unlock()
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qname := q.Question[0].Name
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i := intval(q.Question[0].Qclass, q.Question[0].Qtype)
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if c.data[qname] == nil {
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im := make(map[int]*item)
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c.data[qname] = im
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}
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buf, _ := q.Pack()
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im := c.data[qname]
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im[i] = &item{time.Seconds(), buf}
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}
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// Lookup an entry in the cache. Returns nil
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// when nothing found.
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func (c Cache) lookup(q *dns.Msg) []byte {
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// Use the question section for looking up
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c.rw.RLock()
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defer c.rw.RUnlock()
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i := intval(q.Question[0].Qclass, q.Question[0].Qtype)
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if im, ok := c.data[q.Question[0].Name]; ok {
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// we have the name
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if d, ok := im[i]; ok {
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// We even have the entry, check cache time
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if time.Seconds()-d.epoch > CACHETTL {
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// Too olds means we get a new one
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return nil
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}
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e := make([]byte, len(d.msg))
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copy(e, d.msg)
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return e
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}
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}
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return nil
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}
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func checkcache(m *dns.Msg) (o []byte) {
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// Check if we have the packet in Cache
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// if so, return it. Otherwise ask the
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// server, return that answer and put it
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// in the cache.
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o = cache.lookup(m)
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if o != nil {
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// octet 1 and 2 contain the Id, set the one for the current pkt
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dns.RawSetId(o, 0, m.MsgHdr.Id)
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return
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}
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println("Cache miss")
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var p *dns.Msg
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for _, c := range qr {
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p, _ = c.Client.Exchange(m, c.Addr)
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}
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cache.add(p)
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o, _ = p.Pack()
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return
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}
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// Return the configration
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func NewFunkenSturm() *FunkenSturm {
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f := new(FunkenSturm)
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f.Funk = make([]*Funk, 1)
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f.Setup = func() bool { cache = NewCache(); return true }
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f.Funk[0] = new(Funk)
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f.Funk[0].Match = func(m *dns.Msg) (*dns.Msg, bool) { return m, true }
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f.Funk[0].Action = checkcache
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return f
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}
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