Excellent post! I have only one small detail to add; it might actually turn out to be important, though I can't guarantee it. That detail is: DNS is almost always implemented using UDP for transport, not TCP, so there is none of TCP's measures to try to provide guaranteed delivery. Instead, the DNS client (a.k.a. the 'resolver') will retry a few times, then quit. How many times is up to the implementer.
So though it may be difficult (since the Exception is random), I would consider it worth the bother to run Wireshark captures while doing the DNS search, and see what shows up when the OP get UnknownHostException. Now here is why my one point may be so relevant: the resolver is linked into the Linux application, so it can be different even for two different applications running on the same phone (though this is unlikely, especially if all are Android Java apps). Then there are configuration parameters passed to the resolver function calls. It is not a separate daemon as are most application level networking clients. So this could explain why the OP gets the failures only with this one application and not with other hosts or other applications on the same phone. So is the OP's application pure Android Java, or did he use the NDK? What about other applications running on the same phone? If all Android Java applications fail randomly just like the OP's own application, while some NDK applications work, then the problem is most likely with the phone's implementation of the resolver for Android Java (less likely the WiFi itself). But again, to really be sure what is going on, LogCat is not enough: we need the Wireshark captures, preferebly on with tehe failure adn one without, so that we can see how your phone implemented and configured the resolver: not everyone uses BIND. There are other variations possible. To distinguish between them, the Wireshark captures are the way to go. Finally, whose DNS server is the OP using? Google's is pretty good, response time is excellent. And it is quite capable of handling either IPv6 or IPv4. If he sets up a local DNS server, not only can he have total control, it makes it a lot easier to GET those Wireshark captures. Unfortunately, we can't run Wireshark on even a rooted Android phone. If you can't do the local server, and can't run Wireshark on the WiFi AP, then it may even be worth the effort to fake it, running a simple Java program inside your LAN that does not do the whole DNS, but spits back a canned DNS response. I have done this before with success. On Jan 12, 11:00 pm, Bob Kerns <[email protected]> wrote: > UnknownHostException means your device was unable to get a positive > response to the DNS query trying to look up the hostname. > > It doesn't distinguish between "We couldn't talk to the DNS server", > "we have no network connection right now", "we have never even HEARD > of net work, what's that?", or "we carefully and thoroughly discussed > it with the DNS server, which in turn discussed it with the relevant > authoritative DNS servers, and can conclusively state, that the host > named does not exist at this time". > > What you CAN say, is it never got to the point of actually trying to > talk to that host, because it didn't get enough information to do so. > That is, it is not saying "we've heard of that host, but it doesn't > seem to be there". > > The most likely cause is a temporary failure in your wifi connection, > just as it was trying the DNS lookup. But the DNS server itself could > be to blame, or if it's a DNS server on your site, the connection > upstream, or an upstream DNS server could be to blame. > > I use my local wifi server as a DNS server. It's been giving me > problems like this lately, even on wired connections. Plus, it is not > compatible with IPv6, so I'm going to need to upgrade it soon. I could > configure it to advertise OpenDNS servers instead (which is what it > itself is using), but have slightly longer lookups and no cached data > if the cable connection hiccups. If it's the cable connection that's > at fault, then I'll have these problems anyway. It won't be easy to > track down. > > On Jan 12, 8:44 pm, Ankur Avlani <[email protected]> wrote: > > > Unfortunately, the server is not local. > > > On Wed, Jan 12, 2011 at 4:15 PM, Dan <[email protected]> wrote: > > > Hello All, > > > > I have had this error both on emulator and a Motorola Droid while > > > using a WIFI connection. I have surrounded the http request with WIFI > > > state checks and before and after WIFI is reported state 3 > > > (WIFI_STATE_ENABLED) and a connection speed of 54 . I have also > > > confirmed, using an adb shell with the emulator, that the emulator > > > cannot ping the website in question giving a domain resolution error. > > > To compare notes with Ankur, is the server on your LAN and the IP used > > > internal? mine is. > > > > I have also tried AndroidHttpClient which does work on the same url. > > > > -Dan > > > > On Jan 12, 12:23 pm, Ankur Avlani <[email protected]> wrote: > > > > True, I agree with what you say. Its just that I feel, other apps > > > > should > > > > also break or give error. > > > > > Anywayz, Thanks a lot for your inputs. > > > > > regards, > > > > Ankur. > > > > > On Wed, Jan 12, 2011 at 12:17 PM, Brill Pappin <[email protected]> wrote: > > > > > Well i suppose thats possible if your messing with the network stack, > > > > > but it's pretty low level for Java/Android. > > > > > I guess its also possible that the Android version you have has a > > > > > crappy stack or driver... or you have rooted it and have been messing > > > > > around under the covers so to speak. > > > > > > There is nothing in Android really that would allow you to mess it up > > > > > that badly AFAIK, so I doubt it's your application causing the problem > > > > > if your not specifically getting under the covers. > > > > > > However, the meaning of the exception is clear: > > > > > >http://download.oracle.com/javase/1.4.2/docs/api/java/net/UnknownHost. > > > .. > > > > > and your app doesn't really control the process of translating a > > > > > domain to an ip. > > > > > > - Brill Pappin > > > > > > On Jan 12, 2:54 pm, Ankur Avlani <[email protected]> wrote: > > > > > > Somehow I have this feeling it is related to my app only. Other > > > > > > apps > > > on > > > > > the > > > > > > phone, I don't see any such issue. Even when browsing on my phone, > > > > > > I > > > > > don't > > > > > > see any error. > > > > > > > On Wed, Jan 12, 2011 at 11:41 AM, Kumar Bibek <[email protected]> > > > > > wrote: > > > > > > > By Wi-Fi, I meant, you phone's Wi-Fi could be turning on and off. > > > There > > > > > is > > > > > > > no other reason I can think of. It happens for me as well, > > > sometimes. > > > > > > > > Kumar Bibek > > > > > > >http://techdroid.kbeanie.com > > > > > > >http://www.kbeanie.com > > > > > > > > On Thu, Jan 13, 2011 at 1:10 AM, Ankur Avlani < > > > [email protected] > > > > > >wrote: > > > > > > > >> I am sorry, that somehow doesn't convince me. I am connected to > > > the > > > > > same > > > > > > >> wifi on my laptop and i never see any web page load error on my > > > > > laptop. > > > > > > > >> On Wed, Jan 12, 2011 at 11:38 AM, Kumar Bibek < > > > [email protected] > > > > > >wrote: > > > > > > > >>> Yup, then it's a problem with your Wi-Fi. > > > > > > > >>> Kumar Bibek > > > > > > >>>http://techdroid.kbeanie.com > > > > > > >>>http://www.kbeanie.com > > > > > > > >>> On Thu, Jan 13, 2011 at 1:07 AM, Ankur Avlani < > > > [email protected] > > > > > >wrote: > > > > > > > >>>> I am connected to network, I am on Wifi. If i try again it > > > works. > > > > > Its > > > > > > >>>> just random. > > > > > > > >>>> On Wed, Jan 12, 2011 at 11:34 AM, Kumar Bibek < > > > [email protected] > > > > > >wrote: > > > > > > > >>>>> This error/exception comes because of no network connectivity. > > > > > > > >>>>> Kumar Bibek > > > > > > >>>>>http://techdroid.kbeanie.com > > > > > > >>>>>http://www.kbeanie.com > > > > > > > >>>>> On Thu, Jan 13, 2011 at 1:02 AM, Ankur Avlani < > > > > > [email protected]>wrote: > > > > > > > >>>>>> Hi All, > > > > > > > >>>>>> I am developing an application on Android. I have seen that > > > at > > > > > times > > > > > > >>>>>> when I try to connect using HttpURLConnection, for getting an > > > > > Image or > > > > > > >>>>>> anydata, I get the following error: > > > > > > > >>>>>> 01-12 11:24:05.073: WARN/System.err(16780): > > > > > > >>>>>> java.net.UnknownHostException: Host is unresolved: > > >www.XXX.com:80. > > > > > > > >>>>>> Note: I get this error on my Motorolla Droid and not in > > > emulator. > > > > > > > >>>>>> Any ideas? > > > > > > > >>>>>> Thanks, > > > > > > >>>>>> Ankur > > > > > > > >>>>>> -- > > > > > > >>>>>> You received this message because you are subscribed to the > > > Google > > > > > > >>>>>> Groups "Android Developers" group. > > > > > > >>>>>> To post to this group, send email to > > > > > > >>>>>> [email protected] > > > > > > >>>>>> To unsubscribe from this group, send email to > > > > > > >>>>>> [email protected]<android-developers%2Bunsubs > > > > > > >>>>>> [email protected]><android-developers%2Bunsubs > > > [email protected]><android-developers%2Bunsubs > > > > > [email protected]> > > > > > > >>>>>> For more options, visit this group at > > > > > > >>>>>>http://groups.google.com/group/android-developers?hl=en > > > > > > > >>>>> -- > > > > > > >>>>> You received this message because you are subscribed to the > > > Google > > > > > > >>>>> Groups "Android Developers" group. > > > > > > >>>>> To post to this group, send email to > > > > > > >>>>> [email protected] > > > > > > >>>>> To unsubscribe from this group, send email to > > > > > > >>>>> [email protected]<android-developers%2Bunsubs > > > > > > >>>>> [email protected]><android-developers%2Bunsubs > > > [email protected]><android-developers%2Bunsubs > > > > > [email protected]> > > > > > > >>>>> For more options, visit this group at > > > > > > >>>>>http://groups.google.com/group/android-developers?hl=en > > > > > > > >>>> -- > > > > > > >>>> You received this message because you are subscribed to the > > > Google > > > > > > >>>> Groups "Android Developers" group. > > > > > > >>>> To post to this group, send email to > > > > > > >>>> [email protected] > > > > > > >>>> To unsubscribe from this group, send email to > > > > > > >>>> [email protected]<android-developers%2Bunsubs > > > > > > >>>> [email protected]><android-developers%2Bunsubs > > > [email protected]><android-developers%2Bunsubs > > > > > [email protected]> > > > > > > >>>> For more options, visit this group at > > > > > > >>>>http://groups.google.com/group/android-developers?hl=en > > > > > > > >>> -- > > > > > > >>> You received this message because you are subscribed to the > > > Google > > > > > > >>> Groups "Android Developers" group. > > > > > > >>> To post to this group, send email to > > > > > [email protected] > > > > > > >>> To unsubscribe from this group, send email to > > > > > > >>> [email protected]<android-developers%2Bunsubs > > > > > > >>> [email protected]><android-developers%2Bunsubs > > > [email protected]><android-developers%2Bunsubs > > > > > [email protected]> > > > > > > >>> For more options, visit this group at > > > > > > >>>http://groups.google.com/group/android-developers?hl=en > > > > > > > >> -- > > > > > > >> You received this message because you are subscribed to the > > > > > > >> Google > > > > > > >> Groups "Android Developers" group. > > > > > > >> To post to this group, send email to > > > > > [email protected] > > > > > > >> To unsubscribe from this group, send email to > > > > > > >> [email protected]<android-developers%2Bunsubs > > > > > > >> [email protected]><android-developers%2Bunsubs > > > [email protected]><android-developers%2Bunsubs > > > > > [email protected]> > > > > > > >> For more options, visit this group at > > > > > > >>http://groups.google.com/group/android-developers?hl=en > > > > > > > > -- > > > > > > > You received this message because you are subscribed to the Google > > > > > > > Groups "Android Developers" group. > > > > > > > To post to this group, send email to > > > > > [email protected] > > > > > > > To unsubscribe from this group, send email to > > > > > > > [email protected]<android-developers%2Bunsubs > > > > > > > [email protected]><android-developers%2Bunsubs > > ... > > read more » -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
