Hi all,
I have come across with the following bug on Mono v1.1.7 run under
Linux: when I use asyncronous DNS resolution and domain name is not
found, then I get normal exception, however after that a new exception
is thrown from inside of core library and it falls into global unhandled
exceptions handler -- its as if this known exception is not suppressed
in the callback, which it is. I have attached C# sample that I used to
reproduce this error. Here are text outputs from different OSes:
Under Linux:
------------------------------------------------------------------------------------------------
About to start resolving fv7ov41hycwpjyec3p.cywater.com
AsyncDNSResolved() exception: System.Net.Sockets.SocketException: No
such host is known
in <0x0009f> System.Net.Dns:GetHostByName (System.String hostName)
in <0x00066> System.Net.Dns:Resolve (System.String hostName)
in (wrapper delegate-invoke)
System.MulticastDelegate:invoke_IPHostEntry_string (string)
BUG -- UNHANDLED EXCEPTION: System.Net.Sockets.SocketException: No such
host is known
in <0x0009f> System.Net.Dns:GetHostByName (System.String hostName)
in <0x00066> System.Net.Dns:Resolve (System.String hostName)
in (wrapper delegate-invoke)
System.MulticastDelegate:invoke_IPHostEntry_string (string)
------------------------------------------------------------------------------------------------
Note that second exception is exactly the same as the first -- it is
caught by unhandled exceptions handler.
here is what I get under windows using both Mono and native .NET 1.1:
----------------------------------------------------------------------------
About to start resolving fv7ov41hycwpjyec3p.cywater.com
AsyncDNSResolved() exception: System.Net.Sockets.SocketException: The
requested
name is valid and was found in the database, but it does not have the
correct as
sociated data being resolved for
Server stack trace:
at System.Net.Dns.GetHostByName(String hostName)
at System.Net.Dns.Resolve(String hostName)
at
System.Runtime.Remoting.Messaging.StackBuilderSink.PrivateProcessMessage(MethodBase
mb, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInC
ontext, Object[]& outArgs) at
System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMe
ssage msg, IMessageSink replySink)
Exception rethrown at [0]:
at System.Runtime.Remoting.Proxies.RealProxy.EndInvokeHelper(Message
reqMsg,Boolean bProxyCase)
at System.Runtime.Remoting.Proxies.RemotingProxy.Invoke(Object
NotUsed, MessageData& msgData)
at System.Net.ResolveDelegate.EndInvoke(IAsyncResult result)
at System.Net.Dns.EndResolve(IAsyncResult asyncResult)
at Majestic12.MonoDnsBug.AsyncDNSResolved(IAsyncResult oAR) in
h:\alex\projects\tests\monodnsbug\monodnsbug.cs:line 59
----------------------------------------------------------------------------
As you can see there is no additional exception that has to be caught by
the UNHANDLED exception handler.
I think this is because exception handled by the asyncronoous call back
routine is rethrown again by the library.
Any comments would be appreciated.
Alex
using System;
using System.Net;
namespace Majestic12
{
/// <summary>
/// Mono Dns Resolve bug test: an unhandled exception is triggered
/// when DNS name could not be resolved (using async DNS resolutions)
/// </summary>
class MonoDnsBug
{
public void GlobalExceptionHandler(object sender,
UnhandledExceptionEventArgs args)
{
Exception oEx=(Exception) args.ExceptionObject;
Console.WriteLine("BUG -- UNHANDLED EXCEPTION:
"+oEx.ToString());
}
[STAThread]
static void Main(string[] args)
{
MonoDnsBug oM=new MonoDnsBug();
oM.Start();
Console.ReadLine();
}
public void Start()
{
AppDomain oCurDomain = AppDomain.CurrentDomain;
oCurDomain.UnhandledException+=new
UnhandledExceptionEventHandler(GlobalExceptionHandler);
// this domain name is non-existant
ResolveDNS("fv7ov41hycwpjyec3p.cywater.com");
}
private void ResolveDNS(string sDomainName)
{
try
{
Console.WriteLine("About to start resolving
{0}",sDomainName);
Dns.BeginResolve(sDomainName,new
AsyncCallback(AsyncDNSResolved),null);
}
catch(Exception oEx)
{
Console.WriteLine("ResolveDNS() exception:
"+oEx.ToString());
}
}
// callback we get from DNS resolver
private void AsyncDNSResolved(IAsyncResult oAR)
{
try
{
IPHostEntry oIP=Dns.EndResolve(oAR);
Console.WriteLine("Domain name was successfully
resolved!");
}
catch(Exception oEx)
{
Console.WriteLine("AsyncDNSResolved()
exception: "+oEx.ToString());
}
}
}
}
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