Posts tagged '.NET'
Sunday, 14 March 2010
0 comments .NET Over the past year or so we've been wrestling with an intermittent error from classic ASP when trying to instantiate .NET components with Server.CreateObject. Everything works fine 90% of the time, and now and then we'll start seeing this error:
Server object error 'ASP 0177 : 8000ffff'
Server.CreateObject Failed
<FileName>.asp, line <LineNumber>
8000ffff
Once this error starts happening, it generally persists until we move the application to another application pool or restart IIS. Recycling the app pool does not fix the problem.
Unfortunately, the error message and number are fairly generic, so it's been pretty tricky to track down. There are lots of people with very similar issues posting all over the web that have solved them in various ways. None of the solutions we found have ever worked for us. Most of them were people seeing the error all the time (eg. permissions errors), but we found very few people seeing our behaviour where the code would just randomly stop working.
After many, many months of searching, we found some reports of similar behaviour being caused by installing an Internet Explorer 7 patch. Many people were rolling the patch back with some success. Rolling back patches doesn't seem like the best thing in the world, so we've always avoided the complications that go with it.
The Solution
Eventually, we found the solution. It's in this Microsoft knowledgebase article KB945701. The problem appears to be a failure to read some IE-related values from the registry. The hotfix on the page above (which is included in the latest service pack, so you probably do not need the hotfix) adds the ability to ignore these errors by setting a registry key:
- Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\MAIN\
FeatureControl\FEATURE_IGNORE_ZONES_INITIALIZATION_FAILURE_KB945701
Note If the FEATURE_IGNORE_ZONES_INITIALIZATION_FAILURE_KB945701 subkey does not exist, you must manually create it. - Right-click FEATURE_IGNORE_ZONES_INITIALIZATION_FAILURE_KB945701, point to New, and then click DWORD Value.
- Type w3wp.exe to name the new registry entry, and then press ENTER.
- Right-click w3wp.exe, and then click Modify.
- In the Value data box, type 1, and then click OK.
After setting this registry key, a simple app pool restart will apply the change. No longer will your .NET COM components randomly stop working with no real solution except shuffling application pools!
Yesterday I finally got around to do something I've been planning on doing for a number of weeks. I uploaded Google Wave Notifier to Google Code. From today, Google Wave Notifier is Open Source!
In hindsight, I should have done this much sooner. The app is now very stable and contains all the features that I planned to implement (and more!). I'm still getting lots of feature requests, and I really wish I could implement them all. However, in reality, I just don't have time. By sharing the code with the world, all of these features need not go unimplemented!
I still intend to work through bugs and some feature requests myself, though it's unlikely to be at the rate of previous releases. With help from the community, hopefully we'll still see regular releases and new functionality.
For more info, or to download the source, please visit the Google Wave Notifier page on Google Code.
You probably haven't noticed, but this blog serves up different ads depending on where you're visiting from. Or at least, it'll serve Amazon UK ads if you're near the UK, and Amazon US ads otherwise. Serving up US ads to UK visitors (and vice versa) is pretty pointless, and I've always tried to avoid showing any ads unless they're relevant and at least targeted to the right country.
There are a number of ways to determine where your visitors are coming from, so I spent some time yesterday trying to find the most reliable way (and preferably one that didn't involve having a huge IP database sat alongside my site!). After much hacking and testing, I found what I believe to be the best way. Google.
Google has a JavaScript loader API, which allows developers to load JavaScript libraries from Google with various benefits. That's not really what we're interested in though, it has something more exciting:
google.loader.ClientLocation
It appears that you do not need an API key to use the JavaScript loader, you can simply reference it at http://www.google.com/jsapi. If you look at the JavaScript served up (which is incredibly fast), you'll see something like this:
google.loader.ClientLocation = { "latitude":50.123, "longitude":-2.876, "address": { "city":"Liverpool", "region":"Merseyside", "country":"United Kingdom", "country_code":"GB" } };
Not only do you get the country, but you get the county, city and even lat/lon pair. For me, the location given was within 2-3 miles of where I live, so if you wanted, you could really localise your ads!
On this site, the country is just sent to a script that will serve up some ads based on keywords I've tagged against a post. You might wish to be a bit more exciting and show your users places or people nearby. This could be especially useful for mobile applications/sites, though be sure to read any associated terms and conditions before using it!
Over the past few weeks I've been playing with Google App Engine. I find the best way to learn a new language/framework/platform is to just jump in and write something in/on it. So that's what I'm doing. I've decided to write my blog in Python for Google App Engine.
As I may have blogged about in the past, I wrote a blog engine in Microsoft ASP.NET MVC not so long ago with the aim of moving away from Blogger. It was around 90% complete when I abandoned it for a variety of reasons (one being Azure pricing).
It's entirely possible the Google App Engine blog engine will also be abandoned, but since the hosting is free it at least stands a good chance of seeing the light of day! It'll also make an interesting comparison to the ASP.NET MVC version.
I started writing code a few nights ago, and currently the blog stands at 159 non-blank lines. I'm actually quite impressed with how little code I've had to write to get up and running. Currently there's no back-end, but the displaying of posts, comments, tags and archives are all working. Here's a quick screenshot to prove it exists! :)
Over the coming weeks I'll blog about how I've built it (including code), the pitfalls and the the experience of moving from .NET and C# to Python and App Engine!
Related Reading
As a .NET developer, I was quite excited to hear about Windows Azure. It sounded like a less painful version of Amazon's EC2, supporting .NET (less painful in terms of server management!). When I saw the pricing, it didn't look too bad either. That was, until I realised that their "compute hour" referred to an hour of your app running, not an hour of actual CPU time. Wow. This changes things. To keep a single web role running, you're looking at $0.12/hour = $2.88/day = $20.16/week = $86.40/month.
Anyone that's bought hosting for a small site/app recently will know that this is not particularly cheap!
So, recently I've been playing around with Google App Engine. It has this massive problem called Python (and an even bigger one called Java ;o)), but it's such a nice framework/engine to work with that I've somehow overlooked this and started coding with it. There's so much to like about it. Everything is so simple to deploy, and it scales "out of the box". Want Cron jobs? No worries, specify them in a file in your app, and when you deploy, App Engine will pick them up and schedule them. Want to queue up work to process later so that your pages return faster? Task queues do just that. What's more, you get a ridiculous free quota every day. It may be Python, but this sounds tempting, no?
So, I thought it'd be interesting to compare the costs of App Engine vs Azure. I understand this isn't really a like-for-like comparison, but both can achieve the same sort of things, and while all programmers will have a preferred language/framework (I'm no exception), many can be swayed by a cool framework or hosting.
First off, let's compare what you get for free. Bear in mind that Azure is free until the end of January, but since this is a CTP and won't end soon, I'm going to exclude it. Google's free quota currently has no time restrictions.
| Windows Azure | Google App Engine |
| CPU Hours | - | 6.5hrs/day |
| Bandwidth (out) | - | 1GB/day |
| Bandwidth (in) | - | 1GB/day |
| Storage (DB) | - | 1GB |
| Storage Transactions | - | 10,368,000/day |
Well, for free, I think we have a clear winner. If you can run your website/app within the limits above, then you can do it for free with Google. It's worth mentioning that Google let you have 10 apps per account (though you may not balance a single site/app across app instances - they are specifically for separate projects).
But what if you're bigger than that? What if you get Slashdotted or Dugg a lot? You might find you quickly break out of the free limits. How do prices compare?
| Windows Azure | Google App Engine |
| CPU | $0.12/hour | $0.10/hour |
| Note that MS bill "per hour app is running" whereas Google bill "per CPU hour consumed" |
| Bandwidth (out) | $0.15/GB | $0.12/GB |
| Bandwidth (in) | $0.10/GB | $0.10/GB |
| Storage (Files) | $0.15/GB/month | Pricing unavailable (Blobstore) |
| Storage (DB) | $9.99/month (SQL Server up to 1GB) | $0.15/GB/month ($0.005/GB/day) |
| Storage Transactions | $0.01/10,000 | ? |
| I can't find any prices for Google App Engine storage transactions, so it's possible there is no charge (though a limit of 140,000,000/day applies) |
Well, that's interesting. I was going to try and calculate at what point Azure would become cheaper, but looking at those prices, it just isn't going to happen. Now it's worth pointing out that not all of the comparisons are fair. Google bill per actual CPU hour (so if nobody visits your site, it's not costing you), whereas Microsoft are billing for each hour your app is live and able to respond. There's also a significant difference between SQL Server and App Engine Datastore (and depending on what you're doing, one will have advantages over the other).
I really hope Microsoft re-evaluate their pricing for small apps. It's too expensive to play around with small prototypes at those prices, whereas Google's offering will let me get started completely free, until my app is churning a considerable amount of traffic, and even then, it'll work our cheaper for the same processing/transfer.
Sorry Microsoft. I love .NET and Visual Studio, but Google App Engine is just so easy and cheap that it's going to be my "toy of choice" for my hobby coding for the immediate future!
Related Reading
Over the years, I've written (and re-written) many blog engines with the intention of hosting my blog on my own code. I'm a programmer, that's what we do. We don't like the thought of other people writing our HTML!
If you've been following my blog over the last twelve months, you'll probably know what my language/framework of choice would be when writing a web app, based on my previous posts...
As a .NET developer by trade, I'm experienced with C#, .NET, ASP.NET MVC etc. and it's always been the logical choice. There's nothing I like to write more than C#/.NET
So why are you hosted on Blogger?
An interesting question :) Unfortuantely the answer is not interesting. The answer is simply: Hosting. Windows hosting is a pain in the ass. I've had many bad Windows hosts that have dodgy control panels, poor performance or a lack of required features. Most of this is addressed with IIS 7 because we can now do most things via XML config files, but it still leaves one issue: Price. Prices seem to vary wildly, and it's such a pain to set up that I'm often put off signing up in case it turns out to be a lemon. This is the reason I have a fully working .NET MVC blog engine ready to roll in my Documents folder that's never made it to the big cloud in the sky.
What about Azure?
A few months ago I was really excited about Azure. It looked ideal for what I wanted, and looking at how EC2 is priced, I suspected it would be cheap if you're only getting a few hundred visitors per day. Then Microsoft announced the prices... To run a no-to-low traffic blog would cost more than getting a virtual server! On top of that, it seemed quite hacky to get MVC working, and it's still only in preview.
Enter, Google App Engine
While playing around in Google Wave, I downloaded the Google App Engine SDK and had a play. While Python isn't exactly my language of choice (I've never written it before!), it struck me as quite a good deal. Five million page views per month... for free! It's hosted on Google's infrastructure and scales well, and there's no way I'd hit those limits anytime soon.
So, now I'm having thoughts... Do I become a hacky Python programmer, putting aside all the .NET experience I have, for free hosting with Microsoft's biggest competitor?
If anyone has any experience with running blogs on Google App Engine, I'd be very interested in hearing from them. Should I run with it, or should I stop being tight-fisted and just pay for some Windows hosting?
To be continued!
Apologies if this is all I seem to be blogging about lately, but it's the only interesting thing I've been doing!
I've just pushed out a small update to my Google Wave Notifier application (v0.6). You can read about it here.
New features include the ability to play the Windows "New Mail" sound when you get new messages, the ability to change the interval it polls for new messages and some general tidying up and bug fixes!
I'm sure I don't need to tell you how bad serving a Yellow Screen of Death to your users is. Nonetheless, it seems to be pretty common practice across the web. One of the first things I do when setting up a new ASP.NET project is set up custom error pages and ensure all exceptions are logged (who wants to find out about their errors from their clients?). Since things work slightly differently in ASP.NET MVC I thought I'd dig in and find the best way to do the same thing.
The HandleError Attribute
The HandleError attribute (which appears on the default controllers in an MVC project) tells the framework that if an unhandled exception occurs in your controller that rather than showing the default Yellow Screen of Death it should instead serve up a view called Error. The controller-specific View folder will be checked first (eg. Views/Home/Error.aspx) and if it's not found, the Shared folder (Views/Home/Error.aspx) will be used.
But How Do I Log Exceptions?
You might've spotted the problem with HandleError. It just outputs a view, and doesn't let you run any code. This might be fine if you don't want users to see errors but don't really care for fixing them. Hopefully you think this isn't acceptable and you want to investigate all exceptions!
The OnException Method
The System.Web.Mvc.Controller class contains a method called OnException which is called whenever an exception occuts within an action. This does not rely on the HandleError attribute being set. If you're being a good coder and have your own base Controller class you can override this method in one place to handle/log all errors for your site. You might choose to send emails and/or detect duplicate exceptions and discard them. For now, I'm just going to write them all to a text file in my App_Data folder.
protected override void OnException(ExceptionContext filterContext)
{
WriteLog(Settings.LogErrorFile, filterContext.Exception.ToString());
}
/// <summary>
/// Logs a message to the given log file
/// </summary>
/// <param name="logFile">The filename to log to</param>
/// <param name="text">The message to log</param>
static void WriteLog(string logFile, string text)
{
//TODO: Format nicer
StringBuilder message = new StringBuilder();
message.AppendLine(DateTime.Now.ToString());
message.AppendLine(text);
message.AppendLine("=========================================");
System.IO.File.AppendAllText(logFile, message.ToString());
}
This works great, but it still shows our user an unhandled exception message, even if we use the HandleError attribute. This makes the HandleError attribute look rather useless, so I've removed it. We can easily show the friendly error ourselves with the following code:
filterContext.ExceptionHandled = true;
this.View("Error").ExecuteResult(this.ControllerContext);
It's important to set ExceptionHandled to true, otherwise you'll still see the default unhandled exception message. The OnException method returns void so we must Execute the view and pass in the ControllerContext ourselves.
How Do I see my own Errors During Development?
It's a little inconvenient to open log files or keep commenting out your error handling code while developing to see exceptions and stack traces. You might remember ASP.NET has a nice web.config setting that configures custom errors. This property is exposed via MVC, so we can set up our config to show friendly errors to remote users only:
<customErrors mode="RemoteOnly" />
Then all we need to do in our OnException method is check this value and serve up the custom error view only if it returns true.
protected override void OnException(ExceptionContext filterContext)
{
WriteLog(Settings.LogErrorFile, filterContext.Exception.ToString());
// Output a nice error page
if (filterContext.HttpContext.IsCustomErrorEnabled)
{
filterContext.ExceptionHandled = true;
this.View("Error").ExecuteResult(this.ControllerContext);
}
}
It's worth noting that IsCustomErrorEnabled will resolve the RemoteOnly option for you, you don't need to check where the user is coming from. Now out site serves up friendly errors to users and logs all exceptions without us losing the ability to see stack traces during development.
Related Reading
Tuesday, 14 April 2009
2 comments .NET ASP.NET MVC Over the last few days I've been rewriting this blog in ASP.NET MVC. As it gets closer to a state where I can upload it, I found myself needing to implement security for the administration section (adding, editing posts, etc.). I don't want yet another username/password to remember, and I don't want to IP-restrict it because that's not very flexible (and I don't know how static my IP is!), so what are my options?
OpenID
OpenID is nothing new, it's been around since late 2005. I've been aware of what it did and how it worked, but never really played with it. I did, however, get the impression it might solve my problem. Especially having seen that you can use your Google account as an OpenID!
What's OpenID? Why is it Cool?
OpenID is a standard for authentication, allowing you to use the same identitiy/login for multiple services. It is not the same as using the same username/password at multiple websites (that's a very bad idea). Let's see an example.
I want to be able to login to my blog to edit posts. I don't want another username/password. As Google now works as an identity provider, my blog can redirect me to Google and let them authenticate me. Google will then return me to my blog saying "Yes, this is definitely Danny Tuppeny". This means I don't need any user tables, login forms, or anything else on my blog!
This might sounds complicated, but as with most things, there's a nice .NET library called dotnetopenid to hide the complexity. Let's see some code!
On the first request, dotnetopenid will return a null response. After logging in at the identity providers website, the user will be redirected back (to the same page by default, but this can be changed) with a token on the query string. This will cause dotnetopenid to return a response. The basic code looks like this:
var openId = new OpenIdRelyingParty();
if (openId.Response == null)
{
// No response means this is the first page load
}
else
{
// This means we're been redirected back after authentication
if (openId.Response.Status == AuthenticationStatus.Authenticated)
// User was logged in (as someone!)
}
On the first page load, we would usually ask the user for their OpenID Identifier/URL, however since in my case it's always going to be Google, I'm going to hard-code this as a single value.
dotnetopenid supports adding claim requests so that you can request (or even demand) specific pieces of information. In my case I only care about authenticating me, I don't need to request my name or email address. As such, I'm just going to fire a simple request off without any claim requests.
openId.CreateRequest("https://www.google.com/accounts/o8/id").RedirectToProvider();
In the else block we need to check the response. We want to make sure that the status is Authenticated and the ClaimedIdentifier matches the known identifier for my own login.
// We got a response - check it's valid
if (openId.Response.Status == AuthenticationStatus.Authenticated
&& openId.Response.ClaimedIdentifier.ToString() == "http://google.com/blah/blah/blah")
{
Session["Admin"] = true;
return Redirect("/posts/edit");
}
else
return Content("Go away, you're not me.");
The ClaimedIdentifier will be unique to each Google account. You can run the code once and examine the returned value to find out your own, and then you can check against it.
If we put all this together into a controller action, it'll look something like this:
public ActionResult Login()
{
var openId = new OpenIdRelyingParty();
// If we have no response, start
if (openId.Response == null)
{
// Create a request and redirect the user
openId.CreateRequest(Settings.AdminOpenIDIdentifier).RedirectToProvider();
return null;
}
else
{
// We got a response - check it's valid and that it's me
if (openId.Response.Status == AuthenticationStatus.Authenticated
&& openId.Response.ClaimedIdentifier.ToString() == Settings.AdminClaimedIdentifier)
{
Session["Admin"] = true;
return Redirect("/posts/edit");
}
else
return Content("Go away, you're not me.");
}
}
That's really all there is to it. Now when I hit the Login action I'll be redirected to Google's login page. After logging in, I end up back at /posts/edit on my blog with the correct session variable set. Of course, you could instead call the built-in ASP.NET authentication methods, or look up a user from your database based on their ClaimedIdentifier. There are a lot of ways you can extend this, and I'll cover using OpenID for blog comments in a future article!
Related Reading
By default, LINQ to SQL lazy-loads its relationships. This means it won't go fetching entire trees of objects when you're only using the top ones. However, this might not always be desirable. Imagine if every time you output a post for your blog, you include tagsa. You might write something like this:
foreach(var post in db.Posts)
{
Response.Write("<h1>{0}</h1>", post.Title);
foreach(var Tag in post.Tags)
{
Response.Write("<a href=\"{0}\">{1}</a>",
Html.Encode(tag.FullUrl),
Html.Encode(tag.Name)
);
}
}
This code will work fine, but if you were to examine the SQL being generated, you'd see n+1 SELECT queries. One for fetching the posts, and one for fetching the tags for each posts - individually.
What can we do about it?
LINQ to SQL allows us to specify a set of DataLoadOptions that dictate this behaviour. One of the methods of the DataLoadOptions is LoadWith<T> which allows us to say "whenever you load x, always include y". E.g.
// Create DataLoadOptions
DataLoadOptions dlo = new DataLoadOptions();
// Always fetch tags when we get posts
dlo.LoadWith<Post>(p => p.Tags);
// Set these options on the DataContext
db.LoadOptions = dlo;
If we re-run the original query, we'll now find a JOIN to the Tags table and just a single query to fetch all the data we require.
Simple! However, bear in mind that LINQ to SQL might not always generate joins. I've got a few cases where the LoadWith seems to be ignored. As soon as I figure out why, I'll be sure to update this post!
Related Reading
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