/// <summary>
/// Customises the Contact header for an INVITE request or response based on the destination
/// it is being sent to.
/// </summary>
/// <param name="dstEP">The destination end point for the send.</param>
/// <param name="inviteHeader">The original header from the INVITE request or response.</param>
/// <returns>If an adjustment was made then a new SIP header instance is returned. If not, null is returned.</returns>
private SIPHeader CustomiseInviteContactHeader(SIPEndPoint dstEP, SIPHeader inviteHeader)
{
var dstAddress = dstEP.GetIPEndPoint().Address;
// Don't customise if the destination is a private IP address (which means it's staying
// on the same subnet or virtual subnet).
if (!_isPrivateSubnet(dstAddress) && inviteHeader.Contact != null && inviteHeader.Contact.Count == 1)
{
// The priority is use the public IP address fields if they are available (saves DNS lookups) and
// falls back to the hostname if they are not. The exception is if the Contact URI is using a secure
// SIP scheme "sips" in which case the priority is to use any available hostname first.
// Port of 0 is set when user agents set Contact Host to "0.0.0.0:0" which is the method to
// get the transport layer to set it at send time.
bool isDefaultPort = inviteHeader.Contact[0].ContactURI.IsDefaultPort() || inviteHeader.Contact[0].ContactURI.HostPort == "0";
if (inviteHeader.Contact[0].ContactURI.Scheme == SIPSchemesEnum.sips &&
!string.IsNullOrWhiteSpace(_publicContactHostname))
{
var copy = inviteHeader.Copy();
copy.Contact[0].ContactURI.Host = _publicContactHostname;
return(copy);
}
else if (_publicContactIPv4 != null &&
(dstAddress.AddressFamily == AddressFamily.InterNetwork || dstAddress.IsIPv4MappedToIPv6))
{
var copy = inviteHeader.Copy();
copy.Contact[0].ContactURI.Host = isDefaultPort ? _publicContactIPv4.ToString() : $"{_publicContactIPv4}:{inviteHeader.Contact[0].ContactURI.HostPort}";
return(copy);
}
else if (dstAddress.AddressFamily == AddressFamily.InterNetworkV6 && _publicContactIPv6 != null)
{
var copy = inviteHeader.Copy();
copy.Contact[0].ContactURI.Host = isDefaultPort ? $"[{_publicContactIPv6}]" : $"[{_publicContactIPv6}]:{inviteHeader.Contact[0].ContactURI.HostPort}";
return(copy);
}
else if (!string.IsNullOrWhiteSpace(_publicContactHostname))
{
var copy = inviteHeader.Copy();
copy.Contact[0].ContactURI.Host = _publicContactHostname;
return(copy);
}
}
return(null);
}
