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285 lines
7.4 KiB
285 lines
7.4 KiB
// SIP Transport Layer. Responsible for serializing messages to/from
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// your network.
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package sip
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import (
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"bytes"
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"errors"
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"flag"
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"log"
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"net"
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"strconv"
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"strings"
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"time"
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)
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var (
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tracing = flag.Bool("tracing", true, "Enable SIP message tracing")
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timestampTagging = flag.Bool("timestampTagging", false, "Add microsecond timestamps to Via tags")
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)
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// Transport sends and receives SIP messages over UDP with stateless routing.
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type Transport struct {
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// Channel to which received SIP messages and errors are published.
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C chan *Msg
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E chan error
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// Underlying UDP socket.
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Sock *net.UDPConn
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// When you send an outbound request (not a response) you have to set the via
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// tag: ``msg.Via = tp.Via.Copy().Branch().SetNext(msg.Via)``. The details of
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// the branch parameter... are tricky.
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Via *Via
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// Returns a linked list of all canonical names and/or IP addresses that may
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// be used to contact *this specific* transport.
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Contact *Addr
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// Reusable memory for serialization
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buf []byte
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}
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// Creates a new stateless network mechanism for transmitting and receiving SIP
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// signalling messages.
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//
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// contact is a SIP address, e.g. "<sip:1.2.3.4>", that tells how to bind
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// sockets. If contact.Uri.Port is 0, it'll be mutated with a randomly selected
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// port. This value is also used for contact headers which tell other
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// user-agents where to send responses and hence should only contain an IP or
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// canonical address.
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func NewTransport(contact *Addr) (tp *Transport, err error) {
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saddr := net.JoinHostPort(contact.Uri.Host, portstr(contact.Uri.Port))
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sock, err := net.ListenPacket("udp", saddr)
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if err != nil {
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return nil, err
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}
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addr := sock.LocalAddr().(*net.UDPAddr)
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contact.Uri.Port = uint16(addr.Port)
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contact = contact.Copy()
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contact.Uri.Port = uint16(addr.Port)
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contact.Uri.Params["transport"] = addr.Network()
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tp = &Transport{
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C: make(chan *Msg, 32),
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E: make(chan error, 1),
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Sock: sock.(*net.UDPConn),
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Contact: contact,
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Via: &Via{
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Host: contact.Uri.Host,
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Port: contact.Uri.Port,
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},
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}
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tp.launchConsumer()
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return
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}
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// Sends a SIP message.
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func (tp *Transport) Send(msg *Msg) error {
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msg, saddr, err := tp.route(msg)
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if err != nil {
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return err
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}
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addr, err := net.ResolveUDPAddr("udp", saddr)
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if err != nil {
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return err
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}
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if msg.MaxForwards > 0 {
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msg.MaxForwards--
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}
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ts := time.Now()
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addTimestamp(msg, ts)
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var b bytes.Buffer
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msg.Append(&b)
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if *tracing {
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trace("send", b.String(), addr, ts)
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}
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_, err = tp.Sock.WriteTo(b.Bytes(), addr)
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if err != nil {
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return err
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}
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return nil
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}
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func (tp *Transport) launchConsumer() {
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go func() {
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for {
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msg, err := tp.recv()
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if err != nil {
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log.Println("shutting down", err)
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tp.E <- err
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return
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}
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tp.C <- msg
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}
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}()
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}
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// Receives a SIP message. The received address is injected into the first Via
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// header as the "received" param. The Error field of msg should be checked. If
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// msg.Status is Status8xxNetworkError, it means the underlying socket died. If
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// you set a deadline, you should check: util.IsTimeout(msg.Error).
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//
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// Warning: Must only be called by one goroutine.
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func (tp *Transport) recv() (msg *Msg, err error) {
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if tp.buf == nil {
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tp.buf = make([]byte, 2048)
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}
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amt, addr, err := tp.Sock.ReadFromUDP(tp.buf)
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if err != nil {
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return nil, err
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}
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ts := time.Now()
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packet := string(tp.buf[0:amt])
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if *tracing {
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trace("recv", packet, addr, ts)
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}
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// Validation: http://tools.ietf.org/html/rfc3261#section-16.3
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msg, err = ParseMsg(packet)
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if err != nil {
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return nil, err
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}
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addReceived(msg, addr)
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addTimestamp(msg, ts)
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err = tp.sanityCheck(msg)
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if err != nil {
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return nil, err
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}
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tp.preprocess(msg)
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return
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}
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// Checks if message is acceptable, otherwise sets msg.Error and returns false.
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func (tp *Transport) sanityCheck(msg *Msg) error {
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if msg.MaxForwards <= 0 {
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go tp.Send(NewResponse(msg, 483))
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return errors.New("Froot loop detected")
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}
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if msg.IsResponse {
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if msg.Status >= 700 {
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go tp.Send(NewResponse(msg, 400))
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return errors.New("Crazy status number")
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}
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} else {
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if msg.CSeqMethod == "" || msg.CSeqMethod != msg.Method {
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go tp.Send(NewResponse(msg, 400))
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return errors.New("Bad CSeq")
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}
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}
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return nil
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}
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// Perform some ingress message mangling.
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func (tp *Transport) preprocess(msg *Msg) {
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if tp.Contact.CompareHostPort(msg.Route) {
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log.Printf("Removing our route header: %s", msg.Route)
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msg.Route = msg.Route.Next
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}
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if msg.Request != nil && msg.Request.Params.Has("lr") && msg.Route != nil && tp.Contact.Uri.CompareHostPort(msg.Request) {
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// RFC3261 16.4 Route Information Preprocessing
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// RFC3261 16.12.1.2: Traversing a Strict-Routing Proxy
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var oldReq, newReq *URI
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if msg.Route.Next == nil {
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oldReq, newReq = msg.Request, msg.Route.Uri
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msg.Request = msg.Route.Uri
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msg.Route = nil
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} else {
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seclast := msg.Route
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for ; seclast.Next.Next != nil; seclast = seclast.Next {
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}
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oldReq, newReq = msg.Request, seclast.Next.Uri
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msg.Request = seclast.Next.Uri
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seclast.Next = nil
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msg.Route.Last()
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}
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log.Printf("Fixing request URI after strict router traversal: %s -> %s", oldReq, newReq)
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}
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}
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func (tp *Transport) route(old *Msg) (msg *Msg, dest string, err error) {
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var host string
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var port uint16
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msg = new(Msg)
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*msg = *old // Start off with a shallow copy.
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if msg.Contact == nil {
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msg.Contact = tp.Contact
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}
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if msg.IsResponse {
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if msg.Via.CompareHostPort(tp.Via) {
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// In proxy scenarios, we have to remove our own Via.
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msg.Via = msg.Via.Next
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}
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if msg.Via == nil {
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return nil, "", errors.New("Message missing Via header")
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}
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if received, ok := msg.Via.Params["received"]; ok {
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return msg, received, nil
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} else {
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host, port = msg.Via.Host, msg.Via.Port
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}
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} else {
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if msg.Request == nil {
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return nil, "", errors.New("Missing request URI")
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}
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if !msg.Via.CompareHostPort(tp.Via) {
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return nil, "", errors.New("Set our Via should come first when sending messages")
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}
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if msg.Route.CompareHostPort(tp.Contact) {
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// In proxy scenarios, we have to remove our own Route.
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msg.Route = msg.Route.Next
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}
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if msg.Route != nil {
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if msg.Method == "REGISTER" {
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return nil, "", errors.New("Don't loose route register requests")
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}
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if msg.Route.Uri.Params.Has("lr") {
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// RFC3261 16.12.1.1 Basic SIP Trapezoid
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host, port = msg.Route.Uri.Host, msg.Route.Uri.GetPort()
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} else {
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// RFC3261 16.12.1.2: Traversing a Strict-Routing Proxy
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msg.Route = old.Route.Copy()
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msg.Route.Last().Next = &Addr{Uri: msg.Request}
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msg.Request = msg.Route.Uri
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msg.Route = msg.Route.Next
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host, port = msg.Request.Host, msg.Request.GetPort()
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}
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} else {
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host, port = msg.Request.Host, msg.Request.GetPort()
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}
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}
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dest = net.JoinHostPort(host, portstr(port))
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return
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}
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func addReceived(msg *Msg, addr *net.UDPAddr) {
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if msg.Via.Host != addr.IP.String() || int(msg.Via.Port) != addr.Port {
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msg.Via.Params["received"] = addr.String()
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}
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}
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func addTimestamp(msg *Msg, ts time.Time) {
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if *timestampTagging {
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msg.Via.Params["µsi"] = strconv.FormatInt(ts.UnixNano()/int64(time.Microsecond), 10)
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}
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}
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func trace(dir, pkt string, addr *net.UDPAddr, t time.Time) {
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size := len(pkt)
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bar := strings.Repeat("-", 72)
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suffix := "\n"
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if pkt[len(pkt)-1] == '\n' {
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suffix = ""
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}
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log.Printf(
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"%s %d bytes to %s/%s at %s\n"+
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"%s\n"+
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"%s%s"+
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"%s\n",
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dir, size, addr.Network(), addr.String(),
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t.Format(time.RFC3339Nano),
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bar,
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pkt, suffix,
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bar)
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}
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