BIND 10 #221: Refactoring auth server and merge the axfr and notify logic into it

[BIND 10 Development]

#221: Refactoring auth server and merge the axfr and notify logic into it
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 Reporter:  hanfeng      |        Owner:  jinmei                                        
     Type:  enhancement  |       Status:  reviewing                                     
 Priority:  major        |    Milestone:  05. 3rd Incremental Release: Serious Secondary
Component:  b10-auth     |   Resolution:                                                
 Keywords:               |    Sensitive:  0                                             
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Changes (by hanfeng):

  * owner:  hanfeng => jinmei


Comment:

 processNotify
           o at least according to the doc Element::createFromString()
 could return NULL. If that's the case it should be handled accordingly.
 (see Trac #250)
           after checking the code I found it will raise exception when
 meet error

           o shouldn't it handle the case where "rcode" indicates an error?
           the parseAnswer function is quite strange, it raise exception,
 then I don't understand the rcode value is used for what:(
           o when the error happens, return SERVFAIL, rather than ignoring
 it.
           according to RFC 1996, the master only care three things, one is
 no reply received, and the master will send notify later, the second is
 with NOTIMP, it's same with master received NOERROR reply, master willn't
 send the notify to the slave again. So if error happens, we just ignore
 it, when wait for next try


 For asio_link wrap,
 1 if we wrap the asio lib, all the other part in BIND10 using asio should
 through the asio wrapper, maybe this should be put into another ticket.

 2 For class ServerSet, it's functionality can be replace by using auto_ptr
 which from STD, and also can make sure if exception occured, the memory
 will be freed during the construction call.

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Ticket URL: <https://bind10.isc.org/ticket/221#comment:14>
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