468 lines
12 KiB
Go
468 lines
12 KiB
Go
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. Messages 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 r != nil && shared {
|
|
r = r.Copy()
|
|
}
|
|
if err != nil {
|
|
return r, rtt, err
|
|
}
|
|
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
|
|
}
|
|
|
|
// As seen with my local router/switch, retursn 1 byte on the above read,
|
|
// resulting a a ShortRead. Just write it out (instead of loop) and read the
|
|
// other byte.
|
|
if n == 1 {
|
|
n1, err := t.Read(p[1:])
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
n += n1
|
|
}
|
|
|
|
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.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
|
|
}
|