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package dns
// A concurrent client implementation.
import (
"io"
"net"
"time"
)
// hijacked connections...?
type reply struct {
client *Client
addr string
req *Msg
conn net.Conn
tsigRequestMAC string
tsigTimersOnly bool
tsigStatus error
rtt time.Duration
t time.Time
}
// A nil Client is usable.
type Client struct {
Net string // if "tcp" a TCP query will be initiated, otherwise an UDP one (default is "", is UDP)
Attempts int // number of attempts, if not set defaults to 1
Retry bool // retry with TCP
ReadTimeout time.Duration // the net.Conn.SetReadTimeout value for new connections (ns), defauls to 2 * 1e9
WriteTimeout time.Duration // the net.Conn.SetWriteTimeout value for new connections (ns), defauls to 2 * 1e9
TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>
}
func (w *reply) RemoteAddr() net.Addr {
if w.conn == nil {
return nil
} else {
return w.conn.RemoteAddr()
}
return nil
}
// Do performs an asynchronous query. The msg *Msg is the question to ask, the
// string addr is the address of the nameserver, the parameter data is used
// in the callback function. The call backback function is called with the
// original query, the answer returned from the nameserver an optional error and
// data.
func (c *Client) Do(msg *Msg, addr string, data interface{}, callback func(*Msg, *Msg, error, interface{})) {
go func() {
r, err := c.Exchange(msg, addr)
callback(msg, r, err, data)
}()
}
// DoRtt is equivalent to Do, except that is calls ExchangeRtt.
func (c *Client) DoRtt(msg *Msg, addr string, data interface{}, callback func(*Msg, *Msg, time.Duration, error, interface{})) {
go func() {
r, rtt, err := c.ExchangeRtt(msg, addr)
callback(msg, r, rtt, err, data)
}()
}
// exchangeBuffer performs a synchronous query. It sends the buffer m to the
// address contained in a.
func (c *Client) exchangeBuffer(inbuf []byte, a string, outbuf []byte) (n int, w *reply, err error) {
w = new(reply)
w.client = c
w.addr = a
if err = w.dial(); err != nil {
return 0, w, err
}
defer w.close()
w.t = time.Now()
if n, err = w.writeClient(inbuf); err != nil {
return 0, w, err
}
if n, err = w.readClient(outbuf); err != nil {
return n, w, err
}
w.rtt = time.Since(w.t)
return n, w, nil
}
// Exchange performs an synchronous query. It sends the message m to the address
// contained in a and waits for an reply. Basic use pattern with a *Client:
//
// c := new(dns.Client)
// in, err := c.Exchange(message, "127.0.0.1:53")
//
// See Client.ExchangeRtt(...) to get the round trip time.
func (c *Client) Exchange(m *Msg, a string) (r *Msg, err error) {
r, _, err = c.ExchangeRtt(m, a)
return
}
// ExchangeRtt performs an synchronous query. It sends the message m to the address
// contained in a and waits for an reply. Basic use pattern with a *Client:
//
// c := new(dns.Client)
// in, rtt, err := c.ExchangeRtt(message, "127.0.0.1:53")
//
func (c *Client) ExchangeRtt(m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
var n int
var w *reply
out, ok := m.Pack()
if !ok {
return nil, 0, ErrPack
}
var in []byte
switch c.Net {
case "tcp", "tcp4", "tcp6":
in = make([]byte, MaxMsgSize)
case "", "udp", "udp4", "udp6":
size := udpMsgSize
for _, r := range m.Extra {
if r.Header().Rrtype == TypeOPT {
size = int(r.(*RR_OPT).UDPSize())
}
}
in = make([]byte, size)
}
if n, w, err = c.exchangeBuffer(out, a, in); err != nil {
if w.conn != nil {
return nil, 0, err
}
return nil, 0, err
}
r = new(Msg)
r.Size = n
if ok := r.Unpack(in[:n]); !ok {
return nil, w.rtt, ErrUnpack
}
return r, w.rtt, nil
}
// dial connects to the address addr for the network set in c.Net
func (w *reply) dial() (err error) {
var conn net.Conn
if w.client.Net == "" {
conn, err = net.Dial("udp", w.addr)
} else {
conn, err = net.Dial(w.client.Net, w.addr)
}
if err != nil {
return
}
w.conn = conn
return nil
}
func (w *reply) receive() (*Msg, error) {
var p []byte
m := new(Msg)
switch w.client.Net {
case "tcp", "tcp4", "tcp6":
p = make([]byte, MaxMsgSize)
case "", "udp", "udp4", "udp6":
p = make([]byte, DefaultMsgSize)
}
n, err := w.readClient(p)
if err != nil || n == 0 {
return nil, err
}
p = p[:n]
if ok := m.Unpack(p); !ok {
return nil, ErrUnpack
}
w.rtt = time.Since(w.t)
m.Size = n
if m.IsTsig() {
secret := m.Extra[len(m.Extra)-1].(*RR_TSIG).Hdr.Name
if _, ok := w.client.TsigSecret[secret]; !ok {
w.tsigStatus = ErrSecret
return m, nil
}
// Need to work on the original message p, as that was used to calculate the tsig.
w.tsigStatus = TsigVerify(p, w.client.TsigSecret[secret], w.tsigRequestMAC, w.tsigTimersOnly)
}
return m, nil
}
func (w *reply) readClient(p []byte) (n int, err error) {
if w.conn == nil {
return 0, ErrConnEmpty
}
if len(p) < 1 {
return 0, io.ErrShortBuffer
}
attempts := w.client.Attempts
if attempts == 0 {
attempts = 1
}
switch w.client.Net {
case "tcp", "tcp4", "tcp6":
setTimeouts(w)
for a := 0; a < attempts; a++ {
n, err = w.conn.(*net.TCPConn).Read(p[0:2])
if err != nil || n != 2 {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
l, _ := unpackUint16(p[0:2], 0)
if l == 0 {
return 0, ErrShortRead
}
if int(l) > len(p) {
return int(l), io.ErrShortBuffer
}
n, err = w.conn.(*net.TCPConn).Read(p[:l])
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
i := n
for i < int(l) {
j, err := w.conn.(*net.TCPConn).Read(p[i:int(l)])
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
// We are half way in our read...
continue
}
return i, err
}
i += j
}
n = i
}
case "", "udp", "udp4", "udp6":
for a := 0; a < attempts; a++ {
setTimeouts(w)
n, _, err = w.conn.(*net.UDPConn).ReadFromUDP(p)
if err == nil {
return n, err
}
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
}
}
return
}
// send sends a dns msg to the address specified in w.
// If the message m contains a TSIG record the transaction
// signature is calculated.
func (w *reply) send(m *Msg) (err error) {
var out []byte
if m.IsTsig() {
mac := ""
name := m.Extra[len(m.Extra)-1].(*RR_TSIG).Hdr.Name
if _, ok := w.client.TsigSecret[name]; !ok {
return ErrSecret
}
out, mac, err = TsigGenerate(m, w.client.TsigSecret[name], w.tsigRequestMAC, w.tsigTimersOnly)
if err != nil {
return err
}
w.tsigRequestMAC = mac
} else {
ok := false
out, ok = m.Pack()
if !ok {
return ErrPack
}
}
w.t = time.Now()
if _, err = w.writeClient(out); err != nil {
return err
}
return nil
}
func (w *reply) writeClient(p []byte) (n int, err error) {
attempts := w.client.Attempts
if attempts == 0 {
attempts = 1
}
if err = w.dial(); err != nil {
return 0, err
}
switch w.client.Net {
case "tcp", "tcp4", "tcp6":
if len(p) < 2 {
return 0, io.ErrShortBuffer
}
for a := 0; a < attempts; a++ {
setTimeouts(w)
a, b := packUint16(uint16(len(p)))
n, err = w.conn.Write([]byte{a, b})
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
if n != 2 {
return n, io.ErrShortWrite
}
n, err = w.conn.Write(p)
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
i := n
if i < len(p) {
j, err := w.conn.Write(p[i:len(p)])
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
// We are half way in our write...
continue
}
return i, err
}
i += j
}
n = i
}
case "", "udp", "udp4", "udp6":
for a := 0; a < attempts; a++ {
setTimeouts(w)
n, err = w.conn.(*net.UDPConn).Write(p)
if err == nil {
return
}
if err != nil {
if e, ok := err.(net.Error); ok && e.Timeout() {
continue
}
return n, err
}
}
}
return
}
func setTimeouts(w *reply) {
if w.client.ReadTimeout == 0 {
w.conn.SetReadDeadline(time.Now().Add(2 * 1e9))
} else {
w.conn.SetReadDeadline(time.Now().Add(w.client.ReadTimeout))
}
if w.client.WriteTimeout == 0 {
w.conn.SetWriteDeadline(time.Now().Add(2 * 1e9))
} else {
w.conn.SetWriteDeadline(time.Now().Add(w.client.WriteTimeout))
}
}
func (w *reply) close() (err error) { return w.conn.Close() }
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