How to intercept CANCEL and change fu&tu

[CzyerChen]

Hello, I am green hand here.
In my case, with topology_hiding and fU&tU rewrite, I have to mask initial fU & tU when proxying sip messages. All succeed, but CANCEL message inited locally by server, I can not change fu & tu, If I do it manually, tm can not match. Any suggestions?

thing I have:

CANCEL sip:[email protected]:5060 SIP/2.0                                                                                 
Via: SIP/2.0/UDP proxy.domain:5060;branch=z9hG4bK932b.33154787.0                                                                              
From: <sip:[email protected]>;tag=877556c1e3e94f9da53100d72eefa195                                                                        
Call-ID: TArYzB5EQMMZ3w1Yi5JAwtle2Bne0QGXmovMTc-                                                                                    
To: <sip:[email protected]>                                                                                                      
CSeq: 26759 CANCEL                                                                                                                             
Max-Forwards: 70                                                                                                                               
Reason: SIP;cause=487;text="ORIGINATOR_CANCEL"                                                                                                 
User-Agent: OpenSIPS (3.5.2 (x86_64/linux))                                                                                                    
Content-Length: 0  

thing I want:

CANCEL sip:[email protected]:5060 SIP/2.0                                                                                 
Via: SIP/2.0/UDP proxy.domain:5060;branch=z9hG4bK932b.33154787.0                                                                              
From: <sip:[email protected]>;tag=877556c1e3e94f9da53100d72eefa195                                                                        
Call-ID: TArYzB5EQMMZ3w1Yi5JAwtle2Bne0QGXmovMTc-                                                                                    
To: <sip:[email protected]>                                                                                                      
CSeq: 26759 CANCEL                                                                                                                             
Max-Forwards: 70                                                                                                                               
Reason: SIP;cause=487;text="ORIGINATOR_CANCEL"                                                                                                 
User-Agent: OpenSIPS (3.5.2 (x86_64/linux))                                                                                                    
Content-Length: 0