distribution/vendor/github.com/miekg/dns/client.go

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package dns
// A client implementation.
import (
"bytes"
"crypto/tls"
"encoding/binary"
"io"
"net"
"time"
)
const dnsTimeout time.Duration = 2 * time.Second
const tcpIdleTimeout time.Duration = 8 * time.Second
// A Conn represents a connection to a DNS server.
type Conn struct {
net.Conn // a net.Conn holding the connection
UDPSize uint16 // minimum receive buffer for UDP messages
TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>, zonename must be fully qualified
rtt time.Duration
t time.Time
tsigRequestMAC string
}
// A Client defines parameters for a DNS client.
type Client struct {
Net string // if "tcp" or "tcp-tls" (DNS over TLS) a TCP query will be initiated, otherwise an UDP one (default is "" for UDP)
UDPSize uint16 // minimum receive buffer for UDP messages
TLSConfig *tls.Config // TLS connection configuration
Timeout time.Duration // a cumulative timeout for dial, write and read, defaults to 0 (disabled) - overrides DialTimeout, ReadTimeout and WriteTimeout when non-zero
DialTimeout time.Duration // net.DialTimeout, defaults to 2 seconds - overridden by Timeout when that value is non-zero
ReadTimeout time.Duration // net.Conn.SetReadTimeout value for connections, defaults to 2 seconds - overridden by Timeout when that value is non-zero
WriteTimeout time.Duration // net.Conn.SetWriteTimeout value for connections, defaults to 2 seconds - overridden by Timeout when that value is non-zero
TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>, zonename must be fully qualified
SingleInflight bool // if true suppress multiple outstanding queries for the same Qname, Qtype and Qclass
group singleflight
}
// Exchange performs a synchronous UDP query. It sends the message m to the address
// contained in a and waits for a reply. Exchange does not retry a failed query, nor
// will it fall back to TCP in case of truncation.
// See client.Exchange for more information on setting larger buffer sizes.
func Exchange(m *Msg, a string) (r *Msg, err error) {
var co *Conn
co, err = DialTimeout("udp", a, dnsTimeout)
if err != nil {
return nil, err
}
defer co.Close()
opt := m.IsEdns0()
// If EDNS0 is used use that for size.
if opt != nil && opt.UDPSize() >= MinMsgSize {
co.UDPSize = opt.UDPSize()
}
co.SetWriteDeadline(time.Now().Add(dnsTimeout))
if err = co.WriteMsg(m); err != nil {
return nil, err
}
co.SetReadDeadline(time.Now().Add(dnsTimeout))
r, err = co.ReadMsg()
if err == nil && r.Id != m.Id {
err = ErrId
}
return r, err
}
// ExchangeConn performs a synchronous query. It sends the message m via the connection
// c and waits for a reply. The connection c is not closed by ExchangeConn.
// This function is going away, but can easily be mimicked:
//
// co := &dns.Conn{Conn: c} // c is your net.Conn
// co.WriteMsg(m)
// in, _ := co.ReadMsg()
// co.Close()
//
func ExchangeConn(c net.Conn, m *Msg) (r *Msg, err error) {
println("dns: this function is deprecated")
co := new(Conn)
co.Conn = c
if err = co.WriteMsg(m); err != nil {
return nil, err
}
r, err = co.ReadMsg()
if err == nil && r.Id != m.Id {
err = ErrId
}
return r, err
}
// Exchange performs a synchronous query. It sends the message m to the address
// contained in a and waits for a reply. Basic use pattern with a *dns.Client:
//
// c := new(dns.Client)
// in, rtt, err := c.Exchange(message, "127.0.0.1:53")
//
// Exchange does not retry a failed query, nor will it fall back to TCP in
// case of truncation.
// It is up to the caller to create a message that allows for larger responses to be
// returned. Specifically this means adding an EDNS0 OPT RR that will advertise a larger
// buffer, see SetEdns0. Messsages without an OPT RR will fallback to the historic limit
// of 512 bytes.
func (c *Client) Exchange(m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
if !c.SingleInflight {
return c.exchange(m, a)
}
// This adds a bunch of garbage, TODO(miek).
t := "nop"
if t1, ok := TypeToString[m.Question[0].Qtype]; ok {
t = t1
}
cl := "nop"
if cl1, ok := ClassToString[m.Question[0].Qclass]; ok {
cl = cl1
}
r, rtt, err, shared := c.group.Do(m.Question[0].Name+t+cl, func() (*Msg, time.Duration, error) {
return c.exchange(m, a)
})
if err != nil {
return r, rtt, err
}
if shared {
return r.Copy(), rtt, nil
}
return r, rtt, nil
}
func (c *Client) dialTimeout() time.Duration {
if c.Timeout != 0 {
return c.Timeout
}
if c.DialTimeout != 0 {
return c.DialTimeout
}
return dnsTimeout
}
func (c *Client) readTimeout() time.Duration {
if c.ReadTimeout != 0 {
return c.ReadTimeout
}
return dnsTimeout
}
func (c *Client) writeTimeout() time.Duration {
if c.WriteTimeout != 0 {
return c.WriteTimeout
}
return dnsTimeout
}
func (c *Client) exchange(m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
var co *Conn
network := "udp"
tls := false
switch c.Net {
case "tcp-tls":
network = "tcp"
tls = true
case "tcp4-tls":
network = "tcp4"
tls = true
case "tcp6-tls":
network = "tcp6"
tls = true
default:
if c.Net != "" {
network = c.Net
}
}
var deadline time.Time
if c.Timeout != 0 {
deadline = time.Now().Add(c.Timeout)
}
if tls {
co, err = DialTimeoutWithTLS(network, a, c.TLSConfig, c.dialTimeout())
} else {
co, err = DialTimeout(network, a, c.dialTimeout())
}
if err != nil {
return nil, 0, err
}
defer co.Close()
opt := m.IsEdns0()
// If EDNS0 is used use that for size.
if opt != nil && opt.UDPSize() >= MinMsgSize {
co.UDPSize = opt.UDPSize()
}
// Otherwise use the client's configured UDP size.
if opt == nil && c.UDPSize >= MinMsgSize {
co.UDPSize = c.UDPSize
}
co.TsigSecret = c.TsigSecret
co.SetWriteDeadline(deadlineOrTimeout(deadline, c.writeTimeout()))
if err = co.WriteMsg(m); err != nil {
return nil, 0, err
}
co.SetReadDeadline(deadlineOrTimeout(deadline, c.readTimeout()))
r, err = co.ReadMsg()
if err == nil && r.Id != m.Id {
err = ErrId
}
return r, co.rtt, err
}
// ReadMsg reads a message from the connection co.
// If the received message contains a TSIG record the transaction
// signature is verified.
func (co *Conn) ReadMsg() (*Msg, error) {
p, err := co.ReadMsgHeader(nil)
if err != nil {
return nil, err
}
m := new(Msg)
if err := m.Unpack(p); err != nil {
// If ErrTruncated was returned, we still want to allow the user to use
// the message, but naively they can just check err if they don't want
// to use a truncated message
if err == ErrTruncated {
return m, err
}
return nil, err
}
if t := m.IsTsig(); t != nil {
if _, ok := co.TsigSecret[t.Hdr.Name]; !ok {
return m, ErrSecret
}
// Need to work on the original message p, as that was used to calculate the tsig.
err = TsigVerify(p, co.TsigSecret[t.Hdr.Name], co.tsigRequestMAC, false)
}
return m, err
}
// ReadMsgHeader reads a DNS message, parses and populates hdr (when hdr is not nil).
// Returns message as a byte slice to be parsed with Msg.Unpack later on.
// Note that error handling on the message body is not possible as only the header is parsed.
func (co *Conn) ReadMsgHeader(hdr *Header) ([]byte, error) {
var (
p []byte
n int
err error
)
switch t := co.Conn.(type) {
case *net.TCPConn, *tls.Conn:
r := t.(io.Reader)
// First two bytes specify the length of the entire message.
l, err := tcpMsgLen(r)
if err != nil {
return nil, err
}
p = make([]byte, l)
n, err = tcpRead(r, p)
co.rtt = time.Since(co.t)
default:
if co.UDPSize > MinMsgSize {
p = make([]byte, co.UDPSize)
} else {
p = make([]byte, MinMsgSize)
}
n, err = co.Read(p)
co.rtt = time.Since(co.t)
}
if err != nil {
return nil, err
} else if n < headerSize {
return nil, ErrShortRead
}
p = p[:n]
if hdr != nil {
dh, _, err := unpackMsgHdr(p, 0)
if err != nil {
return nil, err
}
*hdr = dh
}
return p, err
}
// tcpMsgLen is a helper func to read first two bytes of stream as uint16 packet length.
func tcpMsgLen(t io.Reader) (int, error) {
p := []byte{0, 0}
n, err := t.Read(p)
if err != nil {
return 0, err
}
if n != 2 {
return 0, ErrShortRead
}
l := binary.BigEndian.Uint16(p)
if l == 0 {
return 0, ErrShortRead
}
return int(l), nil
}
// tcpRead calls TCPConn.Read enough times to fill allocated buffer.
func tcpRead(t io.Reader, p []byte) (int, error) {
n, err := t.Read(p)
if err != nil {
return n, err
}
for n < len(p) {
j, err := t.Read(p[n:])
if err != nil {
return n, err
}
n += j
}
return n, err
}
// Read implements the net.Conn read method.
func (co *Conn) Read(p []byte) (n int, err error) {
if co.Conn == nil {
return 0, ErrConnEmpty
}
if len(p) < 2 {
return 0, io.ErrShortBuffer
}
switch t := co.Conn.(type) {
case *net.TCPConn, *tls.Conn:
r := t.(io.Reader)
l, err := tcpMsgLen(r)
if err != nil {
return 0, err
}
if l > len(p) {
return int(l), io.ErrShortBuffer
}
return tcpRead(r, p[:l])
}
// UDP connection
n, err = co.Conn.Read(p)
if err != nil {
return n, err
}
return n, err
}
// WriteMsg sends a message through the connection co.
// If the message m contains a TSIG record the transaction
// signature is calculated.
func (co *Conn) WriteMsg(m *Msg) (err error) {
var out []byte
if t := m.IsTsig(); t != nil {
mac := ""
if _, ok := co.TsigSecret[t.Hdr.Name]; !ok {
return ErrSecret
}
out, mac, err = TsigGenerate(m, co.TsigSecret[t.Hdr.Name], co.tsigRequestMAC, false)
// Set for the next read, although only used in zone transfers
co.tsigRequestMAC = mac
} else {
out, err = m.Pack()
}
if err != nil {
return err
}
co.t = time.Now()
if _, err = co.Write(out); err != nil {
return err
}
return nil
}
// Write implements the net.Conn Write method.
func (co *Conn) Write(p []byte) (n int, err error) {
switch t := co.Conn.(type) {
case *net.TCPConn, *tls.Conn:
w := t.(io.Writer)
lp := len(p)
if lp < 2 {
return 0, io.ErrShortBuffer
}
if lp > MaxMsgSize {
return 0, &Error{err: "message too large"}
}
l := make([]byte, 2, lp+2)
binary.BigEndian.PutUint16(l, uint16(lp))
p = append(l, p...)
n, err := io.Copy(w, bytes.NewReader(p))
return int(n), err
}
n, err = co.Conn.(*net.UDPConn).Write(p)
return n, err
}
// Dial connects to the address on the named network.
func Dial(network, address string) (conn *Conn, err error) {
conn = new(Conn)
conn.Conn, err = net.Dial(network, address)
if err != nil {
return nil, err
}
return conn, nil
}
// DialTimeout acts like Dial but takes a timeout.
func DialTimeout(network, address string, timeout time.Duration) (conn *Conn, err error) {
conn = new(Conn)
conn.Conn, err = net.DialTimeout(network, address, timeout)
if err != nil {
return nil, err
}
return conn, nil
}
// DialWithTLS connects to the address on the named network with TLS.
func DialWithTLS(network, address string, tlsConfig *tls.Config) (conn *Conn, err error) {
conn = new(Conn)
conn.Conn, err = tls.Dial(network, address, tlsConfig)
if err != nil {
return nil, err
}
return conn, nil
}
// DialTimeoutWithTLS acts like DialWithTLS but takes a timeout.
func DialTimeoutWithTLS(network, address string, tlsConfig *tls.Config, timeout time.Duration) (conn *Conn, err error) {
var dialer net.Dialer
dialer.Timeout = timeout
conn = new(Conn)
conn.Conn, err = tls.DialWithDialer(&dialer, network, address, tlsConfig)
if err != nil {
return nil, err
}
return conn, nil
}
func deadlineOrTimeout(deadline time.Time, timeout time.Duration) time.Time {
if deadline.IsZero() {
return time.Now().Add(timeout)
}
return deadline
}