[usocket-devel] socket-connect and hostnames resolved to multiple addresses

[Chun Tian (binghe)]

Hi, Alexey

Good question.  I think your problem can be divided into two sub-problems: 1) how to get multiple addresses (when possible) behind a single hostname, 2) how to do SOCKET-CONNECT with the logic (try all one by one until connection is succeed).


For the first sub-problem, I'm afraid that not all CL platform provided such a interface, but for those supported platforms (at least CMUCL, SBCL and LispWorks), you can use a internal USOCKET function called USOCKET::GET-HOSTS-BY-NAME, i.e.

* (usocket::get-hosts-by-name "www.google.com")

(#(72 14 203 104) #(72 14 203 99))

Once you got multiple addresses, you can feed them to SOCKET-CONNECT and do whatever you want.

I think I can patch USOCKET to make USOCKET::GET-HOSTS-BY-NAME return multiple addresses on all platforms, but this is not easy, will need time.


And for the second sub-problem. I think maybe you can try to use some CL condition programming technologies to achieve your goal: some kind of mixup of RESTART-CASE and HANDLER-BIND.  However, current USOCKET didn't do condition work well: when SOCKET-CONNECT failed to connect, there's no uniform condition class signaled.  I'm working on that, but if you can investigate on this and show me a working example for just any of your favorite CL platforms, I'd like to accept it as a new feature (once other related work was done)

Regards,

Chun Tian (binghe)


在 2011-3-16，22:13， Alexey Martynov 写道：

> I have following problem: remote hostname resolves to multiple
> addresses and I want to try all one by one until connection is
> succeeded. But:
> 1. current policy when multiple addresses given for hostname - try random one.
> 2. no API for resolving addresses.
> 
> I can try to propose patch for this problem but in which direction I
> should go: provide resolving API or involve sequential trying of
> addresses?
> 
> -- 
> Alexey Martynov
> 
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