Tatham Oddie

In my previous post I discussed  some issues I discovered with SSL client certificates.

For this application, I’m dealing with PayPal. Rather annoylingly, if your client certificate doesn’t check out, they don’t even bother sending an error – they just drop the TCP connection mid-SSL-handshake. Depending on how fast the connection loss is realised, .NET can return a few different errors; none of which are actually much use when it comes to debugging.

Luckily, System.Net (as with most other areas of the framework) has wonderful tracing capabilities. Particularly with a complex process like an SSL handshake, these capabilities become critical to debugging.

Better yet – they’re incredibly easy to use. Just add a block like this to the end of your app.config!

<system.diagnostics>
  <trace autoflush="true"/>
  <sources>
    <source name="System.Net" maxdatasize="1024">
      <listeners>
        <add name="TraceFile"/>
      </listeners>
    </source>
    <source name="System.Net.Sockets" maxdatasize="1024">
      <listeners>
        <add name="TraceFile"/>
      </listeners>
    </source>
  </sources>
  <sharedListeners>
    <add name="TraceFile" type="System.Diagnostics.TextWriterTraceListener"
      initializeData="trace.log"/>
  </sharedListeners>
  <switches>
    <add name="System.Net" value="Verbose" />
    <add name="System.Net.Sockets" value="Verbose" />
  </switches>
</system.diagnostics>

Now, run your app again and take a look at the wonderful lines being added to your bin\Debug\trace.log file.