Documentation
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Overview ¶
Package dnscache contains a minimal DNS cache that makes a bunch of assumptions that are only valid for us. Not recommended for general use.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrCacheMiss = errors.New("cache miss")
ErrCacheMiss is a sentinel error returned by MessageCache.ReplyFromCache when the request can not be satisfied from cache.
Functions ¶
This section is empty.
Types ¶
type DialContextFunc ¶
func Dialer ¶
func Dialer(fwd DialContextFunc, dnsCache *Resolver) DialContextFunc
Dialer returns a wrapped DialContext func that uses the provided dnsCache.
func TLSDialer ¶
func TLSDialer(fwd DialContextFunc, dnsCache *Resolver, tlsConfigBase *tls.Config) DialContextFunc
TLSDialer is like Dialer but returns a func suitable for using with net/http.Transport.DialTLSContext. It returns a *tls.Conn type on success. On TLS cert validation failure, it can invoke a backup DNS resolution strategy.
type MessageCache ¶
type MessageCache struct {
// Clock is a clock, for testing.
// If nil, time.Now is used.
Clock func() time.Time
// contains filtered or unexported fields
}
MessageCache is a cache that works at the DNS message layer, with its cache keyed on a DNS wire-level question, and capable of replying to DNS messages.
Its zero value is ready for use with a default cache size. Use SetMaxCacheSize to specify the cache size.
It's safe for concurrent use.
func (*MessageCache) AddCacheEntry ¶
func (c *MessageCache) AddCacheEntry(qPacket, res []byte) error
AddCacheEntry adds a cache entry to the cache. It returns an error if the entry could not be cached.
func (*MessageCache) ReplyFromCache ¶
func (c *MessageCache) ReplyFromCache(w io.Writer, dnsQueryMessage []byte) error
ReplyFromCache writes a DNS reply to w for the provided DNS query message, which must begin with the two ID bytes of a DNS message.
If there's a cache miss, the message is invalid or unexpected, ErrCacheMiss is returned. On cache hit, either nil or an error from a w.Write call is returned.
func (*MessageCache) SetMaxCacheSize ¶
func (c *MessageCache) SetMaxCacheSize(n int)
SetMaxCacheSize sets the maximum number of DNS cache entries that can be stored.
type Resolver ¶
type Resolver struct {
// Forward is the resolver to use to populate the cache.
// If nil, net.DefaultResolver is used.
Forward *net.Resolver
// LookupIPFallback optionally provides a backup DNS mechanism
// to use if Forward returns an error or no results.
LookupIPFallback func(ctx context.Context, host string) ([]netip.Addr, error)
// TTL is how long to keep entries cached
//
// If zero, a default (currently 10 minutes) is used.
TTL time.Duration
// UseLastGood controls whether a cached entry older than TTL is used
// if a refresh fails.
UseLastGood bool
// SingleHostStaticResult, if non-nil, is the static result of IPs that is returned
// by Resolver.LookupIP for any hostname. When non-nil, SingleHost must also be
// set with the expected name.
SingleHostStaticResult []netip.Addr
// SingleHost is the hostname that SingleHostStaticResult is for.
// It is required when SingleHostStaticResult is present.
SingleHost string
// contains filtered or unexported fields
}
Resolver is a minimal DNS caching resolver.
The TTL is always fixed for now. It's not intended for general use. Cache entries are never cleaned up so it's intended that this is only used with a fixed set of hostnames.
func (*Resolver) LookupIP ¶
func (r *Resolver) LookupIP(ctx context.Context, host string) (ip, v6 netip.Addr, allIPs []netip.Addr, err error)
LookupIP returns the host's primary IP address (either IPv4 or IPv6, but preferring IPv4) and optionally its IPv6 address, if there is both IPv4 and IPv6.
If err is nil, ip will be non-nil. The v6 address may be nil even with a nil error.
Source Files