Wednesday, 30 September 2015

Automated ATO scam phone calls

Yesterday and today I received some unusual calls on my mobile phone. They were both using computerised voices and claimed to be related to some legal action related to the “ATO” (presumably the Australian Tax Office). Yesterday’s call was supposedly from an “Agent John Smith”. Pretty sure the computer voice said “A-Toe”, rather than “A-T-O” too.

The calling numbers (and also the number they suggested I call them back on in the message) were:

  • 0261004343
  • 0261003101

The second number called twice as I didn’t hear or pick up the first time.

No surprises, it’s a scam - https://www.scamwatch.gov.au/news/telephone-calls-alleging-fake-arrest-warrants-used-to-scam-money

Interesting that they are calling my mobile – usually I get the “hello sir, your computer is sending us errors, would you like us to fix it” scams just on the home phone.

Sunday, 20 September 2015

Casting and foreach – swings and roundabouts

I had a good discussion the other day about a code warning that one of the new Roslyn Code Analyzers had flagged.

SonarLint comes from SonarSource, and has a whole bunch of analyzers, including this one: S3217 - "Explicit" conversions of "foreach" loops should not be used.

It is a useful warning, highlighting how the foreach instruction will cast each item for you if the collection of items is not generic. If you only use generic collections, you’ll probably never hit this – but if you ever have to deal with some of the older classes (such as the original ADO.NET types) then this may come up.

This got me curious. What does the IL (intermediate language) look like for a foreach.

The following C# code will trigger this warning:

    var table = new DataTable();

    DataRowCollection rows = table.Rows;

    foreach (var row in rows)
    {

    }

We get this IL:

  IL_0000:  nop
  IL_0001:  newobj     instance void [System.Data]System.Data.DataTable::.ctor()
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  callvirt   instance class [System.Data]System.Data.DataRowCollection [System.Data]System.Data.DataTable::get_Rows()
  IL_000d:  stloc.1
  IL_000e:  nop
  IL_000f:  ldloc.1
  IL_0010:  callvirt   instance class [mscorlib]System.Collections.IEnumerator [System.Data]System.Data.InternalDataCollectionBase::GetEnumerator()
  IL_0015:  stloc.2
  .try
  {
    IL_0016:  br.s       IL_0026
    IL_0018:  ldloc.2
    IL_0019:  callvirt   instance object [mscorlib]System.Collections.IEnumerator::get_Current()
    IL_001e:  castclass  [System.Data]System.Data.DataRow
    IL_0023:  stloc.3
    IL_0024:  nop
    IL_0025:  nop
    IL_0026:  ldloc.2
    IL_0027:  callvirt   instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
    IL_002c:  brtrue.s   IL_0018
    IL_002e:  leave.s    IL_0045
  }  // end .try
  finally
  {
    IL_0030:  ldloc.2
    IL_0031:  isinst     [mscorlib]System.IDisposable
    IL_0036:  stloc.s    V_4
    IL_0038:  ldloc.s    V_4
    IL_003a:  brfalse.s  IL_0044
    IL_003c:  ldloc.s    V_4
    IL_003e:  callvirt   instance void [mscorlib]System.IDisposable::Dispose()
    IL_0043:  nop
    IL_0044:  endfinally
  }  // end handler

I’m no IL guru, but it you can get the basic idea – and sure enough you can see line IL_001e, there’s a castclass operation that’s run for each item in the foreach loop.

So in this case, you can’t just explicitly cast a DataRowCollection to an IList<DataRow>. The LINQ Cast<> extension method can be used though.

This code no longer triggers the warning:

    foreach (DataRow row in rows.Cast<DataRow>())
    {

    }

And here is the corresponding IL:

  IL_0045:  nop
  IL_0046:  ldloc.1
  IL_0047:  call       class [mscorlib]System.Collections.Generic.IEnumerable`1 [System.Core]System.Linq.Enumerable::Cast(class [mscorlib]System.Collections.IEnumerable)
  IL_004c:  callvirt   instance class [mscorlib]System.Collections.Generic.IEnumerator`1 class [mscorlib]System.Collections.Generic.IEnumerable`1::GetEnumerator()
  IL_0051:  stloc.s    V_5
  .try
  {
    IL_0053:  br.s       IL_0060
    IL_0055:  ldloc.s    V_5
    IL_0057:  callvirt   instance !0 class [mscorlib]System.Collections.Generic.IEnumerator`1::get_Current()
    IL_005c:  stloc.s    V_6
    IL_005e:  nop
    IL_005f:  nop
    IL_0060:  ldloc.s    V_5
    IL_0062:  callvirt   instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
    IL_0067:  brtrue.s   IL_0055
    IL_0069:  leave.s    IL_0078
  }  // end .try
  finally
  {
    IL_006b:  ldloc.s    V_5
    IL_006d:  brfalse.s  IL_0077
    IL_006f:  ldloc.s    V_5
    IL_0071:  callvirt   instance void [mscorlib]System.IDisposable::Dispose()
    IL_0076:  nop
    IL_0077:  endfinally
  }  // end handler

You can see there’s no more castcall operation, but instead notice line IL_0047. Now instead the code is calling the Cast extension method on the entire enumerable.

You might be wondering, does it make any different to performance? In this case not that I could detect. I loaded up a DataTable with 1,000,000 rows and compared execution times between the two approaches, and there wasn’t any significant difference between them.

This makes sense if you think about it – the cast needs to happen – either up front before the loop, or inside the loop. There’s no avoiding it.

So I’d say this is one warning that you shouldn’t necessarily just blindly follow. Having said that, if you’re iterating over the object more than once, then you probably will see a performance boost if you do the cast up front.

Friday, 11 September 2015

User group audio and video

I’ve been pondering how to improve the ability of ADNUG (Adelaide .NET User Group) to do a decent job at:

  • Skype/Google Hangout video conferences – so that the remote presenter can see and hear attendees
  • Record audio of our group for a member with a vision impairment which means that they can’t physically attend meetings.

I’m not sure if there’s necessarily a huge overlap between those two requirements, but they both involve audio so they’re kind of related.

Microsoft LifeCam StudioFor the recent Google Hangout we had with Scott Hanselman, I purchased a Microsoft LifeCam Studio webcam. I mounted this on a tripod and used a couple of USB extension cables. Scott reported that the video quality was a bit poor with some flickering. I suspect the use of the extension cables might have reduced the quality of the signal too much – combined with the fact that I was only on Wifi instead of using the network cable (that I only noticed when the meeting was almost over!). The tripod mount is definitely a plus though.

Scott recommended the Logitech Webcam 930e, which has the advantage of being wider-angle (90° vs the LifeCam’s  75°). I’ll see how I go with the Microsoft camera, otherwise trading up might be an option.

Sound-wise was also not ideal. I didn’t have any complaints with previous hangouts earlier in the year with Jon Galloway and Sayed Hashimi, but maybe Scott was possibly more interactive and wanted to hear questions raised from and converse with the crowd. As it was, I had to repeat the questions for him (as I was standing near my laptop). So a microphone that can pick up the whole room would be great.

It seems the kind of microphone I’d need to pick up is a a conference or ‘boundary’ type. Most of these are ‘omni-directional’, meaning they pick up sound in all directions and from a wide area – contract that with a normal vocal mic, which works best right in front of your mouth.

For a USB solution, these models from MXL seem to be well regarded:

MXL AC404 USB Conference Microphone

MXL Mics AC-424 USB Boundary Microphone (MXL AC-424)

For an XLR connector (XLR is the 3-pin connector commonly used with professional audio equipment), then maybe something like this:

Samson CM11B Omnidirectional Boundary Microphone

The meeting we had this week at Marcellinas had over 40 people in attendance. It turns out Marcellinas function room has their own PA system, so I was glad to make use of that so that everyone could hear better. Having said that, they just have a hand-held microphone with no mic-stand – so that can get tricky if you’re speaking and trying to type at the same time.

Having a mic and loud speaker was a big help to the people in the room, but I didn’t have time beforehand to see if I could hook into their amplifier to record the audio.  Instead to make the audio recording of the meeting, I just used the Windows 10 Voice Recorder app on my laptop (using my laptop’s inbuilt microphone), and just left that running for the duration of the talks.

A lapel microphone would be ideal, and wireless even better (so you’re free to walk around). 

Audio2000 AWM-6032UL UHF Dual Channel Wireless Microphone System with One Handheld & One Lapel (Lavalier) Mic. This kit with a wireless hand-held and lapel would be pretty nice – wire up the main presenter with the lapel, which leaves the hand-held for the MC.

I get the impression that if you got the XLR-type microphones, you really need some kind of mixer/pre-amp that you’d then feed into the laptop (or other recording device).

Something like one of these:

So who knows if we ever get any of this. Given the costs, most of it’s probably just a pipe-dream. Having said that I’d appreciate any thoughts/suggestions/feedback on the options above or other ways that we might take some ‘baby-steps’ to improve things just a little bit.