410 lines
8.6 KiB
Go
410 lines
8.6 KiB
Go
package dns
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import (
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"context"
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"math"
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"net"
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"sync"
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"time"
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"go.unistack.org/micro/v4/meter"
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"go.unistack.org/micro/v4/semconv"
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)
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// DialFunc is a [net.Resolver.Dial] function.
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type DialFunc func(ctx context.Context, network, address string) (net.Conn, error)
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// NewNetResolver creates a caching [net.Resolver] that uses parent to resolve names.
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func NewNetResolver(opts ...Option) *net.Resolver {
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options := Options{Resolver: &net.Resolver{}}
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for _, o := range opts {
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o(&options)
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}
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if options.Meter == nil {
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options.Meter = meter.DefaultMeter
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opts = append(opts, Meter(options.Meter))
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}
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return &net.Resolver{
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PreferGo: true,
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StrictErrors: options.Resolver.StrictErrors,
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Dial: NewNetDialer(options.Resolver.Dial, append(opts, Resolver(options.Resolver))...),
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}
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}
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// NewNetDialer adds caching to a [net.Resolver.Dial] function.
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func NewNetDialer(parent DialFunc, opts ...Option) DialFunc {
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cache := cache{dial: parent, opts: Options{}}
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for _, o := range opts {
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o(&cache.opts)
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}
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if cache.opts.MaxCacheEntries == 0 {
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cache.opts.MaxCacheEntries = DefaultMaxCacheEntries
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}
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return func(_ context.Context, network, address string) (net.Conn, error) {
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conn := &dnsConn{}
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conn.roundTrip = cachingRoundTrip(&cache, network, address)
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return conn, nil
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}
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}
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const DefaultMaxCacheEntries = 300
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// A Option customizes the resolver cache.
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type Option func(*Options)
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type Options struct {
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Resolver *net.Resolver
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MaxCacheEntries int
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MaxCacheTTL time.Duration
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MinCacheTTL time.Duration
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NegativeCache bool
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PreferIPV4 bool
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PreferIPV6 bool
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Timeout time.Duration
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Meter meter.Meter
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}
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// MaxCacheEntries sets the maximum number of entries to cache.
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// If zero, [DefaultMaxCacheEntries] is used; negative means no limit.
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func MaxCacheEntries(n int) Option {
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return func(o *Options) {
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o.MaxCacheEntries = n
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}
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}
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// MaxCacheTTL sets the maximum time-to-live for entries in the cache.
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func MaxCacheTTL(td time.Duration) Option {
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return func(o *Options) {
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o.MaxCacheTTL = td
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}
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}
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// MinCacheTTL sets the minimum time-to-live for entries in the cache.
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func MinCacheTTL(td time.Duration) Option {
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return func(o *Options) {
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o.MinCacheTTL = td
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}
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}
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// NegativeCache sets whether to cache negative responses.
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func NegativeCache(b bool) Option {
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return func(o *Options) {
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o.NegativeCache = b
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}
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}
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// Meter sets meter.Meter
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func Meter(m meter.Meter) Option {
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return func(o *Options) {
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o.Meter = m
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}
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}
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// Timeout sets upstream *net.Resolver timeout
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func Timeout(td time.Duration) Option {
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return func(o *Options) {
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o.Timeout = td
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}
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}
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// Resolver sets upstream *net.Resolver.
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func Resolver(r *net.Resolver) Option {
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return func(o *Options) {
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o.Resolver = r
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}
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}
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// PreferIPV4 resolve ipv4 records.
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func PreferIPV4(b bool) Option {
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return func(o *Options) {
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o.PreferIPV4 = b
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}
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}
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// PreferIPV6 resolve ipv4 records.
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func PreferIPV6(b bool) Option {
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return func(o *Options) {
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o.PreferIPV6 = b
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}
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}
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type cache struct {
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entries map[string]cacheEntry
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dial DialFunc
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opts Options
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mu sync.RWMutex
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}
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type cacheEntry struct {
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deadline time.Time
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value string
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}
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func (c *cache) put(req string, res string) {
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// ignore uncacheable/unparseable answers
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if invalid(req, res) {
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return
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}
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// ignore errors (if requested)
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if nameError(res) && !c.opts.NegativeCache {
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return
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}
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// ignore uncacheable/unparseable answers
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ttl := getTTL(res)
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if ttl <= 0 {
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return
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}
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// adjust TTL
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if ttl < c.opts.MinCacheTTL {
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ttl = c.opts.MinCacheTTL
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}
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// maxTTL overrides minTTL
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if ttl > c.opts.MaxCacheTTL && c.opts.MaxCacheTTL != 0 {
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ttl = c.opts.MaxCacheTTL
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}
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c.mu.Lock()
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if c.entries == nil {
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c.entries = make(map[string]cacheEntry)
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}
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// do some cache evition
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var tested, evicted int
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for k, e := range c.entries {
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if time.Until(e.deadline) <= 0 {
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c.opts.Meter.Counter(semconv.CacheItemsTotal, "type", "dns").Dec()
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c.opts.Meter.Counter(semconv.CacheRequestTotal, "type", "dns", "method", "evict").Inc()
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// delete expired entry
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delete(c.entries, k)
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evicted++
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}
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tested++
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if tested < 8 {
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continue
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}
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if evicted == 0 && c.opts.MaxCacheEntries > 0 && len(c.entries) >= c.opts.MaxCacheEntries {
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c.opts.Meter.Counter(semconv.CacheItemsTotal, "type", "dns").Dec()
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c.opts.Meter.Counter(semconv.CacheRequestTotal, "type", "dns", "method", "evict").Inc()
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// delete at least one entry
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delete(c.entries, k)
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}
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break
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}
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// remove message IDs
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c.entries[req[2:]] = cacheEntry{
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deadline: time.Now().Add(ttl),
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value: res[2:],
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}
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c.opts.Meter.Counter(semconv.CacheItemsTotal, "type", "dns").Inc()
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c.mu.Unlock()
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}
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func (c *cache) get(req string) (res string) {
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// ignore invalid messages
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if len(req) < 12 {
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return ""
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}
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if req[2] >= 0x7f {
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return ""
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}
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c.mu.RLock()
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defer c.mu.RUnlock()
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if c.entries == nil {
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return ""
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}
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// remove message ID
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entry, ok := c.entries[req[2:]]
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if ok && time.Until(entry.deadline) > 0 {
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// prepend correct ID
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return req[:2] + entry.value
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}
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return ""
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}
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func invalid(req string, res string) bool {
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if len(req) < 12 || len(res) < 12 { // header size
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return true
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}
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if req[0] != res[0] || req[1] != res[1] { // IDs match
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return true
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}
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if req[2] >= 0x7f || res[2] < 0x7f { // query, response
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return true
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}
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if req[2]&0x7a != 0 || res[2]&0x7a != 0 { // standard query, not truncated
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return true
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}
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if res[3]&0xf != 0 && res[3]&0xf != 3 { // no error, or name error
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return true
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}
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return false
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}
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func nameError(res string) bool {
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return res[3]&0xf == 3
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}
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func getTTL(msg string) time.Duration {
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ttl := math.MaxInt32
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qdcount := getUint16(msg[4:])
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ancount := getUint16(msg[6:])
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nscount := getUint16(msg[8:])
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arcount := getUint16(msg[10:])
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rdcount := ancount + nscount + arcount
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msg = msg[12:] // skip header
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// skip questions
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for i := 0; i < qdcount; i++ {
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name := getNameLen(msg)
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if name < 0 || name+4 > len(msg) {
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return -1
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}
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msg = msg[name+4:]
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}
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// parse records
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for i := 0; i < rdcount; i++ {
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name := getNameLen(msg)
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if name < 0 || name+10 > len(msg) {
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return -1
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}
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rtyp := getUint16(msg[name+0:])
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rttl := getUint32(msg[name+4:])
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rlen := getUint16(msg[name+8:])
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if name+10+rlen > len(msg) {
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return -1
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}
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// skip EDNS OPT since it doesn't have a TTL
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if rtyp != 41 && rttl < ttl {
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ttl = rttl
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}
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msg = msg[name+10+rlen:]
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}
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return time.Duration(ttl) * time.Second
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}
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func getNameLen(msg string) int {
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i := 0
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for i < len(msg) {
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if msg[i] == 0 {
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// end of name
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i++
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break
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}
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if msg[i] >= 0xc0 {
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// compressed name
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i += 2
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break
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}
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if msg[i] >= 0x40 {
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// reserved
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return -1
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}
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i += int(msg[i] + 1)
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}
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return i
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}
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func getUint16(s string) int {
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return int(s[1]) | int(s[0])<<8
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}
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func getUint32(s string) int {
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return int(s[3]) | int(s[2])<<8 | int(s[1])<<16 | int(s[0])<<24
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}
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func cachingRoundTrip(cache *cache, network, address string) roundTripper {
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return func(ctx context.Context, req string) (res string, err error) {
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cache.opts.Meter.Counter(semconv.CacheRequestInflight, "type", "dns").Inc()
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defer cache.opts.Meter.Counter(semconv.CacheRequestInflight, "type", "dns").Dec()
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// check cache
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if res = cache.get(req); res != "" {
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return res, nil
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}
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cache.opts.Meter.Counter(semconv.CacheRequestTotal, "type", "dns", "method", "get", "status", "miss").Inc()
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ts := time.Now()
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defer func() {
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cache.opts.Meter.Summary(semconv.CacheRequestLatencyMicroseconds, "type", "dns", "method", "get").UpdateDuration(ts)
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cache.opts.Meter.Histogram(semconv.CacheRequestDurationSeconds, "type", "dns", "method", "get").UpdateDuration(ts)
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}()
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switch {
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case cache.opts.PreferIPV4 && cache.opts.PreferIPV6:
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network = "udp"
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case cache.opts.PreferIPV4:
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network = "udp4"
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case cache.opts.PreferIPV6:
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network = "udp6"
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default:
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network = "udp"
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}
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if cache.opts.Timeout > 0 {
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var cancel func()
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ctx, cancel = context.WithTimeout(ctx, cache.opts.Timeout)
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defer cancel()
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}
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// dial connection
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var conn net.Conn
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if cache.dial != nil {
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conn, err = cache.dial(ctx, network, address)
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} else {
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var d net.Dialer
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conn, err = d.DialContext(ctx, network, address)
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}
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if err != nil {
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return "", err
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}
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ctx, cancel := context.WithCancel(ctx)
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go func() {
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<-ctx.Done()
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conn.Close()
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}()
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defer cancel()
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if t, ok := ctx.Deadline(); ok {
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err = conn.SetDeadline(t)
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if err != nil {
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return "", err
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}
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}
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// send request
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err = writeMessage(conn, req)
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if err != nil {
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return "", err
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}
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// read response
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res, err = readMessage(conn)
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if err != nil {
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return "", err
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}
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// cache response
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cache.put(req, res)
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return res, nil
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}
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}
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