Re: How to determine if there is an internet connection available?
Re: How to determine if there is an internet connection available?
- Subject: Re: How to determine if there is an internet connection available?
- From: Jean-Daniel Dupas <email@hidden>
- Date: Sat, 12 Nov 2011 11:23:12 +0100
Le 12 nov. 2011 à 04:41, Conrad Shultz a écrit :
> On 11/11/11 6:39 PM, Vojtěch Meluzín wrote:
>> Hi,
>>
>> I'm using BSD sockets for some internet access, it works fine. But if there
>> is no connection available, it waits for say 30 seconds completely stopping
>> the application. Is there a way to determine if there is actually an
>> internet connection, so that I can check before using sockets?
>
> (This has been extensively discussed in the past in the context of iOS
> network availability. Search the archives for more info.)
>
> The only reliable way to verify connectivity is to attempt a connection.
> Checking for physical connectivity might speed up failure detection
> (assuming you don't care about connections on the loopback interface),
> but there are a host (no pun intended) of reasons that you still might
> not be able to connect.
>
> However, there are other options.
>
> For one, since you are using BSD sockets (and I have to ask: are you
> sure that a higher level API wouldn't accomplish what you need?), you
> can use setsockopt() to control various timeouts. One of the Darwin or
> networking lists might be of more assistance at this level of the
> application.
>
> More worrying is your statement that the wait "completely [stops] the
> application." Are you saying that you are blocking the main thread
> while waiting on I/O? This is almost always a bad idea in a
> user-interactive application. The BSD sockets API is thread-safe (when
> accessed from a single thread), so you could spawn a separate network
> thread. I believe there is also a non-blocking mode within the sockets
> system, but people on the Darwin list would be more helpful here.
>
> If you are able to use higher level APIs, life becomes somewhat easier.
> One level up, using CFNetwork, Apple has detailed documentation about
> how to handle this issue
> (http://developer.apple.com/library/mac/#documentation/Networking/Conceptual/CFNetwork/CFStreamTasks/CFStreamTasks.html#//apple_ref/doc/uid/TP30001132-CH6-SW19).
>
And if you find that CFStream does not fit your need (to high level for your purpose), you can just wrap you BSD socket into a CFSocketRef, and schedule it on the current run loop.
-- Jean-Daniel
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