[SR-Users] uac module From header rewriting problems

[Timo Teras]

Hi,

I fixed some uac From rewriting issues in commit e1d1c774c9ac0b4d,
however even with the latest versions I'm still seeing corruption in
From headers when they are rewritten for the whole dialogue
(from_restore_mode=auto, the default).

I spent some time analyzing the problem and the problem seems to be
connected with the fact that only the bitwise difference of the
original and modified URI are stored (XOR).  The only purpose for this
appears to be the idea to save only the difference in the rr params
instead of two full URIs.

However, it appears that in many cases (especially call transfer) the
From header will be altered during dialogue. This is explicitly allowed
in RFC 3261 § 20.20:
   The From header field indicates the initiator of the request.  This
   may be different from the initiator of the dialog.

I've seen this in practise with few commercial SIP stacks. Sometimes
the changes are minor, or even trivial - but with the difference
encoding having even one character changed (e.g. case), being deleted or
added will result in the whole header being corrupted.

I'm now wondering if we should just store both URIs in the rr params.
While taking little more space, it should fix us sending garbage to the
wire (which usually results in dropped call as the remote will reject
the garbage messages).

Any better ideas?

Cheers,
  Timo