dnsr

README

dnsr

Iterative DNS resolver for Go.

The Resolve method on dnsr.Resolver queries DNS for given name and type (A, NS, CNAME, etc.). The resolver caches responses for queries, and liberally (aggressively?) returns DNS records for a given name, not waiting for slow or broken name servers.

This code leans heavily on Miek Gieben’s excellent DNS library, and is currently in production use at Domainr.

Install

go get github.com/nxgtw/domainr-dnsr

Usage

package main

import (
  "fmt"
  "github.com/domainr/dnsr"
  "github.com/nxgtw/domainr-dnsr"
)

func main() {
  r := dnsr.New(10000)
  for _, rr := range r.Resolve("google.com", "TXT") {
    fmt.Println(rr.String())
  }
}

Or construct with dnsr.NewExpiring() to expire cache entries based on TTL.

Documentation

Development

Run go generate in Go 1.4+ to refresh the root zone hint file. Pull requests welcome.

Copyright

© 2014–2015 nb.io, LLC

Documentation

Index

• Constants
• Variables
• type RR
  • func (rr *RR) String() string
• type RRs
• type Resolver
  • func New(capacity int) *Resolver
  • func NewExpiring(capacity int) *Resolver
  • func NewExpiringWithTimeout(capacity int, timeout time.Duration) *Resolver
  • func NewWithTimeout(capacity int, timeout time.Duration) *Resolver
  • func (r *Resolver) Resolve(qname, qtype string) RRs
  • func (r *Resolver) ResolveCtx(ctx context.Context, qname, qtype string) (RRs, error)
  • func (r *Resolver) ResolveErr(qname, qtype string) (RRs, error)

Constants

const MinCacheCapacity = 1000

const NameCollision = "127.0.53.53"

ICANN specifies that DNS servers should return the special value 127.0.53.53 for A record queries of TLDs that have recently entered the root zone, that have a high likelyhood of colliding with private DNS names. The record returned is a notice to network administrators to adjust their DNS configuration. https://www.icann.org/resources/pages/name-collision-2013-12-06-en#127.0.53.53

Variables

var (
	Timeout             = 5000 * time.Millisecond
	TypicalResponseTime = 500 * time.Millisecond
	MaxRecursion        = 10
	MaxNameservers      = 4
	MaxIPs              = 2
	MaxRetryCount       = 5
)

DNS Resolution configuration.

var (
	NXDOMAIN = fmt.Errorf("NXDOMAIN")

	ErrMaxRecursion = fmt.Errorf("maximum recursion depth reached: %d", MaxRecursion)
	ErrMaxIPs       = fmt.Errorf("maximum name server IPs queried: %d", MaxIPs)
	ErrNoARecords   = fmt.Errorf("no A records found for name server")
	ErrNoResponse   = fmt.Errorf("no responses received")
	ErrTimeout      = fmt.Errorf("timeout expired") // TODO: Timeouter interface? e.g. func (e) Timeout() bool { return true }
)

Resolver errors.

var DebugLogger io.Writer

DebugLogger will receive writes of DNS resolution traces if not nil.

Types

type RR

type RR struct {
	Name   string
	Type   string
	Value  string
	TTL    time.Duration
	Expiry time.Time
}

RR represents a DNS resource record.

func (*RR) String

func (rr *RR) String() string

String returns a string representation of an RR in zone-file format.

type RRs

type RRs []RR

RRs represents a slice of DNS resource records.

type Resolver

type Resolver struct {
	// contains filtered or unexported fields
}

Resolver implements a primitive, non-recursive, caching DNS resolver.

func New

func New(capacity int) *Resolver

New initializes a Resolver with the specified cache size.

func NewExpiring

func NewExpiring(capacity int) *Resolver

NewExpiring initializes an expiring Resolver with the specified cache size.

func NewExpiringWithTimeout

func NewExpiringWithTimeout(capacity int, timeout time.Duration) *Resolver

NewExpiringWithTimeout initializes an expiring Resolved with the specified cache size and resolution timeout.

func NewWithTimeout

func NewWithTimeout(capacity int, timeout time.Duration) *Resolver

NewWithTimeout initializes a Resolver with the specified cache size and resolution timeout.

func (*Resolver) Resolve

func (r *Resolver) Resolve(qname, qtype string) RRs

Resolve calls ResolveErr to find DNS records of type qtype for the domain qname. For nonexistent domains (NXDOMAIN), it will return an empty, non-nil slice.

func (*Resolver) ResolveCtx

func (r *Resolver) ResolveCtx(ctx context.Context, qname, qtype string) (RRs, error)

ResolveCtx finds DNS records of type qtype for the domain qname using the supplied context. Requests may time out earlier if timeout is shorter than a deadline set in ctx. For nonexistent domains, it will return an NXDOMAIN error. Specify an empty string in qtype to receive any DNS records found (currently A, AAAA, NS, CNAME, SOA, and TXT).

func (*Resolver) ResolveErr

func (r *Resolver) ResolveErr(qname, qtype string) (RRs, error)

ResolveErr finds DNS records of type qtype for the domain qname. For nonexistent domains, it will return an NXDOMAIN error. Specify an empty string in qtype to receive any DNS records found (currently A, AAAA, NS, CNAME, SOA, and TXT).