| package dns |
| |
| // A client implementation. |
| |
| import ( |
| "bytes" |
| "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" a TCP query will be initiated, otherwise an UDP one (default is "" for UDP) |
| UDPSize uint16 // minimum receive buffer for UDP messages |
| DialTimeout time.Duration // net.DialTimeout, defaults to 2 seconds |
| ReadTimeout time.Duration // net.Conn.SetReadTimeout value for connections, defaults to 2 seconds |
| WriteTimeout time.Duration // net.Conn.SetWriteTimeout value for connections, defaults to 2 seconds |
| 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 an reply. Exchange does not retry a failed query, nor |
| // will it fall back to TCP in case of truncation. |
| // If you need to send a DNS message on an already existing connection, you can use the |
| // following: |
| // |
| // co := &dns.Conn{Conn: c} // c is your net.Conn |
| // co.WriteMsg(m) |
| // in, err := co.ReadMsg() |
| // co.Close() |
| // |
| 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 an synchronous query. It sends the message m to the address |
| // contained in a and waits for an 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. |
| 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.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 |
| if c.Net == "" { |
| co, err = DialTimeout("udp", a, c.dialTimeout()) |
| } else { |
| co, err = DialTimeout(c.Net, 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(time.Now().Add(c.writeTimeout())) |
| if err = co.WriteMsg(m); err != nil { |
| return nil, 0, err |
| } |
| |
| co.SetReadDeadline(time.Now().Add(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 |
| ) |
| |
| if t, ok := co.Conn.(*net.TCPConn); ok { |
| // First two bytes specify the length of the entire message. |
| l, err := tcpMsgLen(t) |
| if err != nil { |
| return nil, err |
| } |
| p = make([]byte, l) |
| n, err = tcpRead(t, p) |
| } else { |
| if co.UDPSize > MinMsgSize { |
| p = make([]byte, co.UDPSize) |
| } else { |
| p = make([]byte, MinMsgSize) |
| } |
| n, err = co.Read(p) |
| } |
| |
| if err != nil { |
| return nil, err |
| } else if n < headerSize { |
| return nil, ErrShortRead |
| } |
| |
| p = p[:n] |
| if hdr != nil { |
| if _, err = UnpackStruct(hdr, p, 0); err != nil { |
| return nil, err |
| } |
| } |
| return p, err |
| } |
| |
| // tcpMsgLen is a helper func to read first two bytes of stream as uint16 packet length. |
| func tcpMsgLen(t *net.TCPConn) (int, error) { |
| p := []byte{0, 0} |
| n, err := t.Read(p) |
| if err != nil { |
| return 0, err |
| } |
| if n != 2 { |
| return 0, ErrShortRead |
| } |
| l, _ := unpackUint16(p, 0) |
| if l == 0 { |
| return 0, ErrShortRead |
| } |
| return int(l), nil |
| } |
| |
| // tcpRead calls TCPConn.Read enough times to fill allocated buffer. |
| func tcpRead(t *net.TCPConn, 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 |
| } |
| if t, ok := co.Conn.(*net.TCPConn); ok { |
| l, err := tcpMsgLen(t) |
| if err != nil { |
| return 0, err |
| } |
| if l > len(p) { |
| return int(l), io.ErrShortBuffer |
| } |
| return tcpRead(t, p[:l]) |
| } |
| // UDP connection |
| n, err = co.Conn.Read(p) |
| if err != nil { |
| return n, err |
| } |
| |
| co.rtt = time.Since(co.t) |
| return n, err |
| } |
| |
| // WriteMsg sends a message throught 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, allthough 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) { |
| if t, ok := co.Conn.(*net.TCPConn); ok { |
| 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) |
| l[0], l[1] = packUint16(uint16(lp)) |
| p = append(l, p...) |
| n, err := io.Copy(t, 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 |
| } |