416 lines
12 KiB
Go
416 lines
12 KiB
Go
package dns
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// A client implementation.
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import (
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"context"
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"crypto/tls"
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"encoding/binary"
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"fmt"
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"io"
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"net"
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"strings"
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"time"
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)
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const (
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dnsTimeout time.Duration = 2 * time.Second
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tcpIdleTimeout time.Duration = 8 * time.Second
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)
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// A Conn represents a connection to a DNS server.
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type Conn struct {
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net.Conn // a net.Conn holding the connection
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UDPSize uint16 // minimum receive buffer for UDP messages
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TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>, zonename must be in canonical form (lowercase, fqdn, see RFC 4034 Section 6.2)
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tsigRequestMAC string
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}
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// A Client defines parameters for a DNS client.
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type Client struct {
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Net string // if "tcp" or "tcp-tls" (DNS over TLS) a TCP query will be initiated, otherwise an UDP one (default is "" for UDP)
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UDPSize uint16 // minimum receive buffer for UDP messages
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TLSConfig *tls.Config // TLS connection configuration
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Dialer *net.Dialer // a net.Dialer used to set local address, timeouts and more
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// Timeout is a cumulative timeout for dial, write and read, defaults to 0 (disabled) - overrides DialTimeout, ReadTimeout,
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// WriteTimeout when non-zero. Can be overridden with net.Dialer.Timeout (see Client.ExchangeWithDialer and
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// Client.Dialer) or context.Context.Deadline (see the deprecated ExchangeContext)
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Timeout time.Duration
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DialTimeout time.Duration // net.DialTimeout, defaults to 2 seconds, or net.Dialer.Timeout if expiring earlier - overridden by Timeout when that value is non-zero
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ReadTimeout time.Duration // net.Conn.SetReadTimeout value for connections, defaults to 2 seconds - overridden by Timeout when that value is non-zero
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WriteTimeout time.Duration // net.Conn.SetWriteTimeout value for connections, defaults to 2 seconds - overridden by Timeout when that value is non-zero
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TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>, zonename must be in canonical form (lowercase, fqdn, see RFC 4034 Section 6.2)
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SingleInflight bool // if true suppress multiple outstanding queries for the same Qname, Qtype and Qclass
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group singleflight
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}
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// Exchange performs a synchronous UDP query. It sends the message m to the address
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// contained in a and waits for a reply. Exchange does not retry a failed query, nor
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// will it fall back to TCP in case of truncation.
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// See client.Exchange for more information on setting larger buffer sizes.
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func Exchange(m *Msg, a string) (r *Msg, err error) {
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client := Client{Net: "udp"}
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r, _, err = client.Exchange(m, a)
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return r, err
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}
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func (c *Client) dialTimeout() time.Duration {
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if c.Timeout != 0 {
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return c.Timeout
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}
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if c.DialTimeout != 0 {
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return c.DialTimeout
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}
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return dnsTimeout
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}
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func (c *Client) readTimeout() time.Duration {
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if c.ReadTimeout != 0 {
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return c.ReadTimeout
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}
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return dnsTimeout
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}
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func (c *Client) writeTimeout() time.Duration {
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if c.WriteTimeout != 0 {
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return c.WriteTimeout
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}
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return dnsTimeout
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}
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// Dial connects to the address on the named network.
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func (c *Client) Dial(address string) (conn *Conn, err error) {
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// create a new dialer with the appropriate timeout
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var d net.Dialer
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if c.Dialer == nil {
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d = net.Dialer{Timeout: c.getTimeoutForRequest(c.dialTimeout())}
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} else {
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d = *c.Dialer
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}
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network := c.Net
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if network == "" {
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network = "udp"
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}
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useTLS := strings.HasPrefix(network, "tcp") && strings.HasSuffix(network, "-tls")
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conn = new(Conn)
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if useTLS {
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network = strings.TrimSuffix(network, "-tls")
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conn.Conn, err = tls.DialWithDialer(&d, network, address, c.TLSConfig)
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} else {
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conn.Conn, err = d.Dial(network, address)
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}
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if err != nil {
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return nil, err
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}
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return conn, nil
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}
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// Exchange performs a synchronous query. It sends the message m to the address
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// contained in a and waits for a reply. Basic use pattern with a *dns.Client:
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//
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// c := new(dns.Client)
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// in, rtt, err := c.Exchange(message, "127.0.0.1:53")
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//
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// Exchange does not retry a failed query, nor will it fall back to TCP in
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// case of truncation.
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// It is up to the caller to create a message that allows for larger responses to be
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// returned. Specifically this means adding an EDNS0 OPT RR that will advertise a larger
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// buffer, see SetEdns0. Messages without an OPT RR will fallback to the historic limit
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// of 512 bytes
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// To specify a local address or a timeout, the caller has to set the `Client.Dialer`
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// attribute appropriately
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func (c *Client) Exchange(m *Msg, address string) (r *Msg, rtt time.Duration, err error) {
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if !c.SingleInflight {
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return c.exchange(m, address)
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}
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q := m.Question[0]
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key := fmt.Sprintf("%s:%d:%d", q.Name, q.Qtype, q.Qclass)
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r, rtt, err, shared := c.group.Do(key, func() (*Msg, time.Duration, error) {
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return c.exchange(m, address)
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})
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if r != nil && shared {
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r = r.Copy()
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}
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return r, rtt, err
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}
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func (c *Client) exchange(m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
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var co *Conn
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co, err = c.Dial(a)
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if err != nil {
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return nil, 0, err
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}
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defer co.Close()
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opt := m.IsEdns0()
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// If EDNS0 is used use that for size.
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if opt != nil && opt.UDPSize() >= MinMsgSize {
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co.UDPSize = opt.UDPSize()
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}
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// Otherwise use the client's configured UDP size.
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if opt == nil && c.UDPSize >= MinMsgSize {
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co.UDPSize = c.UDPSize
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}
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co.TsigSecret = c.TsigSecret
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t := time.Now()
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// write with the appropriate write timeout
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co.SetWriteDeadline(t.Add(c.getTimeoutForRequest(c.writeTimeout())))
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if err = co.WriteMsg(m); err != nil {
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return nil, 0, err
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}
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co.SetReadDeadline(time.Now().Add(c.getTimeoutForRequest(c.readTimeout())))
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r, err = co.ReadMsg()
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if err == nil && r.Id != m.Id {
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err = ErrId
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}
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rtt = time.Since(t)
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return r, rtt, err
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}
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// ReadMsg reads a message from the connection co.
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// If the received message contains a TSIG record the transaction signature
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// is verified. This method always tries to return the message, however if an
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// error is returned there are no guarantees that the returned message is a
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// valid representation of the packet read.
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func (co *Conn) ReadMsg() (*Msg, error) {
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p, err := co.ReadMsgHeader(nil)
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if err != nil {
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return nil, err
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}
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m := new(Msg)
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if err := m.Unpack(p); err != nil {
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// If an error was returned, we still want to allow the user to use
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// the message, but naively they can just check err if they don't want
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// to use an erroneous message
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return m, err
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}
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if t := m.IsTsig(); t != nil {
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if _, ok := co.TsigSecret[t.Hdr.Name]; !ok {
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return m, ErrSecret
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}
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// Need to work on the original message p, as that was used to calculate the tsig.
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err = TsigVerify(p, co.TsigSecret[t.Hdr.Name], co.tsigRequestMAC, false)
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}
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return m, err
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}
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// ReadMsgHeader reads a DNS message, parses and populates hdr (when hdr is not nil).
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// Returns message as a byte slice to be parsed with Msg.Unpack later on.
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// Note that error handling on the message body is not possible as only the header is parsed.
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func (co *Conn) ReadMsgHeader(hdr *Header) ([]byte, error) {
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var (
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p []byte
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n int
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err error
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)
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if _, ok := co.Conn.(net.PacketConn); ok {
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if co.UDPSize > MinMsgSize {
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p = make([]byte, co.UDPSize)
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} else {
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p = make([]byte, MinMsgSize)
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}
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n, err = co.Read(p)
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} else {
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var length uint16
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if err := binary.Read(co.Conn, binary.BigEndian, &length); err != nil {
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return nil, err
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}
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p = make([]byte, length)
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n, err = io.ReadFull(co.Conn, p)
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}
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if err != nil {
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return nil, err
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} else if n < headerSize {
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return nil, ErrShortRead
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}
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p = p[:n]
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if hdr != nil {
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dh, _, err := unpackMsgHdr(p, 0)
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if err != nil {
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return nil, err
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}
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*hdr = dh
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}
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return p, err
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}
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// Read implements the net.Conn read method.
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func (co *Conn) Read(p []byte) (n int, err error) {
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if co.Conn == nil {
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return 0, ErrConnEmpty
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}
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if _, ok := co.Conn.(net.PacketConn); ok {
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// UDP connection
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return co.Conn.Read(p)
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}
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var length uint16
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if err := binary.Read(co.Conn, binary.BigEndian, &length); err != nil {
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return 0, err
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}
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if int(length) > len(p) {
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return 0, io.ErrShortBuffer
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}
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return io.ReadFull(co.Conn, p[:length])
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}
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// WriteMsg sends a message through the connection co.
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// If the message m contains a TSIG record the transaction
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// signature is calculated.
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func (co *Conn) WriteMsg(m *Msg) (err error) {
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var out []byte
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if t := m.IsTsig(); t != nil {
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mac := ""
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if _, ok := co.TsigSecret[t.Hdr.Name]; !ok {
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return ErrSecret
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}
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out, mac, err = TsigGenerate(m, co.TsigSecret[t.Hdr.Name], co.tsigRequestMAC, false)
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// Set for the next read, although only used in zone transfers
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co.tsigRequestMAC = mac
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} else {
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out, err = m.Pack()
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}
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if err != nil {
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return err
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}
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_, err = co.Write(out)
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return err
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}
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// Write implements the net.Conn Write method.
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func (co *Conn) Write(p []byte) (int, error) {
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if len(p) > MaxMsgSize {
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return 0, &Error{err: "message too large"}
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}
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if _, ok := co.Conn.(net.PacketConn); ok {
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return co.Conn.Write(p)
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}
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l := make([]byte, 2)
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binary.BigEndian.PutUint16(l, uint16(len(p)))
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n, err := (&net.Buffers{l, p}).WriteTo(co.Conn)
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return int(n), err
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}
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// Return the appropriate timeout for a specific request
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func (c *Client) getTimeoutForRequest(timeout time.Duration) time.Duration {
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var requestTimeout time.Duration
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if c.Timeout != 0 {
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requestTimeout = c.Timeout
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} else {
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requestTimeout = timeout
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}
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// net.Dialer.Timeout has priority if smaller than the timeouts computed so
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// far
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if c.Dialer != nil && c.Dialer.Timeout != 0 {
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if c.Dialer.Timeout < requestTimeout {
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requestTimeout = c.Dialer.Timeout
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}
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}
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return requestTimeout
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}
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// Dial connects to the address on the named network.
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func Dial(network, address string) (conn *Conn, err error) {
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conn = new(Conn)
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conn.Conn, err = net.Dial(network, address)
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if err != nil {
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return nil, err
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}
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return conn, nil
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}
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// ExchangeContext performs a synchronous UDP query, like Exchange. It
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// additionally obeys deadlines from the passed Context.
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func ExchangeContext(ctx context.Context, m *Msg, a string) (r *Msg, err error) {
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client := Client{Net: "udp"}
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r, _, err = client.ExchangeContext(ctx, m, a)
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// ignorint rtt to leave the original ExchangeContext API unchanged, but
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// this function will go away
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return r, err
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}
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// ExchangeConn performs a synchronous query. It sends the message m via the connection
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// c and waits for a reply. The connection c is not closed by ExchangeConn.
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// Deprecated: This function is going away, but can easily be mimicked:
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//
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// co := &dns.Conn{Conn: c} // c is your net.Conn
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// co.WriteMsg(m)
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// in, _ := co.ReadMsg()
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// co.Close()
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//
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func ExchangeConn(c net.Conn, m *Msg) (r *Msg, err error) {
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println("dns: ExchangeConn: this function is deprecated")
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co := new(Conn)
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co.Conn = c
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if err = co.WriteMsg(m); err != nil {
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return nil, err
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}
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r, err = co.ReadMsg()
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if err == nil && r.Id != m.Id {
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err = ErrId
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}
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return r, err
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}
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// DialTimeout acts like Dial but takes a timeout.
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func DialTimeout(network, address string, timeout time.Duration) (conn *Conn, err error) {
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client := Client{Net: network, Dialer: &net.Dialer{Timeout: timeout}}
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return client.Dial(address)
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}
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// DialWithTLS connects to the address on the named network with TLS.
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func DialWithTLS(network, address string, tlsConfig *tls.Config) (conn *Conn, err error) {
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if !strings.HasSuffix(network, "-tls") {
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network += "-tls"
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}
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client := Client{Net: network, TLSConfig: tlsConfig}
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return client.Dial(address)
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}
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// DialTimeoutWithTLS acts like DialWithTLS but takes a timeout.
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func DialTimeoutWithTLS(network, address string, tlsConfig *tls.Config, timeout time.Duration) (conn *Conn, err error) {
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if !strings.HasSuffix(network, "-tls") {
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network += "-tls"
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}
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client := Client{Net: network, Dialer: &net.Dialer{Timeout: timeout}, TLSConfig: tlsConfig}
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return client.Dial(address)
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}
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// ExchangeContext acts like Exchange, but honors the deadline on the provided
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// context, if present. If there is both a context deadline and a configured
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// timeout on the client, the earliest of the two takes effect.
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func (c *Client) ExchangeContext(ctx context.Context, m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
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var timeout time.Duration
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if deadline, ok := ctx.Deadline(); !ok {
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timeout = 0
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} else {
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timeout = time.Until(deadline)
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}
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// not passing the context to the underlying calls, as the API does not support
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// context. For timeouts you should set up Client.Dialer and call Client.Exchange.
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// TODO(tmthrgd,miekg): this is a race condition.
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c.Dialer = &net.Dialer{Timeout: timeout}
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return c.Exchange(m, a)
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}
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