use LocalAddr for UDP associate bind address

[ge9]

In UDP associate, the IP address used for connection from the client should be notified to client (at least, https://github.com/3proxy/3proxy is implemented in this way).
This also fixes IPv6 address ([::]) replied for IPv4 UDP associate request (in bytes, [5, 3, 0, 1, 0, 0, 0, 0, 0, 0]). Sorry this is wrong.

[ge9]

Oh sorry I found there is another pull request of much the same purpose (#63) but I think my implementation is more appropriate because clients on other hosts require external IP address to use UDP associate bind address.

[codecov]

Codecov Report

Attention: Patch coverage is 32.39437% with 48 lines in your changes missing coverage. Please review.

Project coverage is 62.55%. Comparing base (ebe069a) to head (8cfd2f7).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
handle.go	37.09%	33 Missing and 6 partials ⚠️
option.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
- Coverage   66.66%   62.55%   -4.11%     
==========================================
  Files          14       14              
  Lines         726      836     +110     
==========================================
+ Hits          484      523      +39     
- Misses        184      253      +69     
- Partials       58       60       +2     

Flag	Coverage Δ
unittests	62.55% <32.39%> (-4.11%)	⬇️

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[ge9]

@thinkgos Hi, can you merge this pull request? I still think this is better than #63 .

[ge9]

(Sorry I mistakenly generated merge commit so I discarded that and did rebase instead. The code is unchanged.)

[thinkgos]

@ge9 sorry, I am busy recently! I have a idea, custom bind address that user can define, but the package give a default implement. so the fregie #63 implemt can easy define itself.

[ge9]

But then it will be difficult to make go-socks5 listen to the wildcard address (0.0.0.0:XXXXX)?

[thinkgos]

But then it will be difficult to make go-socks5 listen to the wildcard address (0.0.0.0:XXXXX)?

listenUDP need *net.UDPAddr, we can define a custom function like ResolveUdpAddr , define some parameter, return the *net.UDPAddr and error, this is same as this PR .

here:

  ResolveUdpAddr(bindIp net.IP, request *Request) (*net.UDPAddr, error)

@ge9 impl:

  ResolveUdpAddr(bindIp net.IP, request *Request) (*net.UDPAddr, error) {
     return  &net.UDPAddr{IP: request.LocalAddr.(*net.TCPAddr).IP, Port: 0}, nil
 }

@fregie impl:

  ResolveUdpAddr(bindIp net.IP, request *Request) (*net.UDPAddr, error) {
    if bindIp == nil {
      return nil, errors.New("not support")
   }
     return net.ResolveUDPAddr("udp", bindIp.String()+":0")
  }

any other impl:

  ResolveUdpAddr(bindIp net.IP, request *Request) (*net.UDPAddr, error) {
     panic("implment me")
  }

---

maybe we can direct get *net.UDPConn?

   ListenUdp(bindIp net.IP, request *Request) (*net.UDPConn, error) 

[ge9]

Ah, I see, that's great! Thank you for your idea.

[thinkgos]

@ge9 ResolveUdpAddr(not get real address) may be not a well name. when you implement it, think about it . thank you!

[thinkgos]

@ge9 the code change so much, not resolve #63 #65.

[ge9]

Oh, sorry, I've forgot to create a branch...

[spvkgn]

Maybe this is good to merge?