Bad image format “Invalid access to memory location”

Wow, two bad image format posts in one day. So, the previous post talked about debugging 64bit vs 32 bit assemblies. But after that was solved I ran into another issue. This time with the message:

Unhandled Exception: System.BadImageFormatException: Could not load file or assembly 'Interop.dll' or one of its dependencies. Invalid access to memory location. (Exception from HRESULT: 0x800703E6)
   at Program.Program.Run(Args args, Boolean fastStart)
   at Program.Program.Main(String[] args) in C:\Projects\Program.cs:line 36

Gah, what gives?

It seems that I had an interop DLL that was linking against pthreads. In debug mode, the dll worked fine on a 32 bit machine, but in release mode I’d get the error. The only difference I found was that in debug the dll was being explicity linked against pthreads lib file. Since pthread was also being built as a dynamic library, it’s lib file contains information about functions and their address, but no actual code … Read more

Determining 64bit or 32 bit .NET assemblies

I work on a 64 bit machine but frequently deploy to 32 bit machines. The code I work on though has native hooks so I always need to deploy assembly entry points at 32 bit. This means I am usually paranoid about the build configuration. However, sometimes things slip up and a 64 bit dll gets sent out or an entrypoint is built with ANY CPU set. Usually this is caught on our continuous build server with some cryptic reason for a unit test that should be working is actually failing.

When this happens, what you’ll get is a message like this:

Unhandled Exception: System.BadImageFormatException: Could not load file or assembly 'Some.dll' or one of its dependencies. An attempt was made to load a program with
 an incorrect format.
   at Test.Program.Run(Args args, Boolean fastStart)
   at Test.ProgramMain(String[] args) in Program.cs:line 36

The first thing I do here is to try and … Read more

Streaming video to ios device with custom httphandler in asp.net

I ran into an interesting tidbit just now while trying to dynamically stream a video file using a custom http handler. The idea here is to bypass the static handler for a file so that I can perform authentication/preprocessing/etc when a user requests a video resource and I don’t have to expose a static folder with potentially sensitive resources.

I had everything working fine on my desktop browser, but when I went to test on my iPhone I got the dreaded play button with a circle crossed out

noVideo

I hate that thing.

Anyways, streaming a file from the static handler worked fine though, so what was the difference? This is where I pulled out charles and checked the response headers.

From the static handler I’d get this:

HTTP/1.1 200 OK
Content-Type	video/mp4
Last-Modified	Wed, 15 May 2013 20:59:30 GMT
Accept-Ranges	bytes
ETag	"9077fe17af51ce1:0"
Server	Microsoft-IIS/7.5
X-Powered-By	ASP.NET
Date	Wed, 15 … Read more
Users by connections in SignalR

SignalR gives you events when users connect, disconnect, and reconnect, however the only identifying piece of information you have at this point is their connection ID. Unfortunately it’s not very practical to identify all your connected users strictly off their connectionIDs – usually you have some other identifier in your application (userID, email, etc).

If you are using ASP.NET MVC3, you can access this information from the hub context via Context.User, but if you aren’t using mvc3 (like a .net to .net client) a good workflow is to have your client identify themselves on connect. They can call a known Register method on the hub and give you the identifying information of who they are.

At this point you have your unique identifier along with their connectionID, but you have to manage all their disconnections, reconnections, and multiple connections of the same client yourself. This post will go through … Read more

Tech Talk: Path finding algorithms

Today’s tech talk was about path finding algorithms. The topic was picked because of a recent linked shared to reddit that visualized different algorithms. The neat thing about the link is that you can really see how different algorithms and heuristics modify the route.

In general, path finding algorithms are based off a breadth first search. At each iteration while walking through the graph you check the nearest neighbors you update what was the calculated weight of the path to get to that neighbor. If it was cheaper to get to the neighbor via your own node (than whoever visited it previously) you update the neighbors weight to reflect that. This is pretty much dijsktras algorithm. Disjkstra gives you the shortest path cost, but not necessarily the shortest path. To find the shortest path you mark each node with who its cheapest parent is (i.e. the node you need to … Read more

Building better regular expressions

Every software developer has at one point in time heard the adage

If you have a problem and you think you can solve it with [threads|pointers|regex|etc], now you have two problems

For me, I’ve always told it with regex (and I think that’s the official way to do it). It’s not that threads and pointers aren’t hard, but more that with proper stylistic choices and with experience, they can be easily manageable and simple to debug. Regex though, have a tendency to spiral out of control. What starts with something simple always bloats into an enormously difficult to read haze of PERLgasms.

For example, I frequently wonder why in the 21st century why we still deal with a syntax like this:

(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]
)+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:
\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(
?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ 
\t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0
31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\
](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[

Even the most seasoned engineers couldn’t tell me what … Read more

The largest mass problem

I was recently asked to write some code to find the largest contiguous group of synonymous elements in a two dimensional array. The idea is that you want to find the largest “land mass” in a problem where you have a game board that looks something like

L L L W
W L L W
L W W W
W L L W

Where L stands for land, and W stands for water. In this example, the largest land mass would be of size 5. But there are also 2 other land masses, one of size one, and another of size two. Elements can be contiguous only if their direct adjacent neighbor is the same type, so diagonals don’t count.

In general, you can think of the largest mass problem as almost exactly the same as the flood fill problem in image graphics. Except with flood fill, you are given … Read more

Capturing union values with fparsec

I just started playing with fparsec which is a parser combinatorics library that lets you create chainable parsers to parse DSL’s. After having built my own parser, lexer, and interpreter, playing with other libraries is really fun, I like seeing how others have done it. Unlike my mutable parser written in C#, with FParsec the idea is that it will encapsulate the underlying stream state and result into a parser object. Since F# is mostly immutable, this is how the underlying modified stream state gets captured and passed as a new stream to the next parser. I actually like this kind of workflow since you don’t need to create a grammar which is parsed and creates code for you (which is what ANTLR does). There’s something very appealing to have it be dynamic.

As a quick example, I was following the tutorial on the fparsec site and wanted to understand … Read more

Tech Talk: AngularJS

Today’s tech talk was a continuation on front-end discussions we’re having. Last week we talked about typescript (I forgot to write it up) and this week we discussed the basics of angular. Angular is a front-end MVC framework written by google that, at first glance, looks completely different from previous javascript/html development. The basic gist is to strongly decouple logic into encapsulated modules. But that’s not all there is, there’s a lot to it. Angular has a templating engine, dependency injection, double bindings between views and controllers, event dispatching, etc.

Since it’s hopeless to cover all of angular in one blog post I’ll just mention a few of the good questions that came up during our discussion

  • Can a child component dispatch to a parent component? Let’s say something happened in an innner component and you need a parent compoinent to also register that?

    Sure, angular provides a function

    • … Read more

Debugging Serialization Exception: The constructor to deserialize an object was not found.

Today I was debugging an exception that was occuring when remoting a data object between two .NET processes. I kept getting 

System.Runtime.Serialization.SerializationException: The constructor to deserialize an object of type 'com.TheSilentGroup.Fluorine.ASObject' was not found.

The issue I had was that there was a .NET object that looked like this

public class ItemDto{
  public object Item { get;set; }
}

Which was used as a covariant store for any item (because everything is an object). This was needed because the code I was working in leveraged reflection to pull out certain fields at runtime depending on whatever this object type really was.

But, at some point the ItemDto object was sent to an ActionScript frontend. Later, the same object came back to .NET and the property Item was now a ASObject type due to Fluorine‘s serialization process. Next, this object had to be serialized to another .NET process, and … Read more