I am using IIS to develop some web applications. I used to believe that every application should have a entry point. But it seems a web application doesn't have one.
I have read many books and articles addressing how to build an ASP.NET application under IIS, but they are just not addressing the most obvious and basic thing that I want to know.
So could anyone tell me how is a web application started? What's the difference between a traditional desktop application and a web application in terms of their working paradigm, such as the starting and terminating logic.
Many thanks.
Update - 1 - 23:14 2011/1/4
My current understanding is:
When some request arrives, the URL contained in the request will be extracted by the IIS. I guess IIS must have maintained some kind of a internal table which maps a URL to corresponding physical directory on disk. Let's take the following URL as an example:
http://myhost/webapp/page1.aspx
With the help of the aforementioned internal table, IIS will locate the page1.aspx file on disk. And then this file is checked and the code-behind code file is located. And then proper page class instance will be contructed and its methods defined in the code-behind file will be invoked in a pre-defined order. The output of the series of method invoking will be the response sent to the client.
Update - 2 - 23:32 2011/1/4
The URL is nothing but an identifier that serves as an index into the aforementioned internal table. With this index, IIS (or any kind of web server technology) could find the physical location of the resource. Then with some hint (such as file extension name like *.aspx), the web server knows what handler (such as the asp.net ISAPI handler) should be used to process that resource. That chosen handler will know how to parse and execute the resource file.
So this also explains why a web server should be extensible.
It depends what language and framework you are using, but broadly there are a number of entry points that will be bound to HTTP requests (e.g. by URL). When the server receives a request that matches one of these bindings, the bound code is executed.
There may also be various filter chains and interceptors that are executed based on other conditions of the request. There will probably also be some set-up code that the server executes when it starts up. Ultimately, there is still a single entry-point - the main() function of the server - but from the web application's perspective it is the request bindings that matter.
Edit in response to question edits
I have never used IIS, but I would assume there is no "lookup table", but instead some lookup rules. I shall talk you through the invocation of a .jsp page on an Apache server, which should be basically the same process.
The webapp is written and placed in the file system - e.g. C:/www/mywebapp
The web server is given a configuration rule telling it that the URL path /webapp/ should be mapped to C:/www/mywebapp
The web server is also configured to recognise .jsp files as being JSP servlets
The web server receives a request for /webapp/page1.jsp, this is dispatched to a worker thread
The web server uses its mapping rules to locate C:/www/mywebapp/page1.jsp
The web server wraps the code in the JSP file in a class with method serveRequest(request, response) and compiles it (if not already done so)
The web server calls the serveRequest function, which is now the entry point of the user code
When the user code is finished, the web server sends the response to the client, and the worker thread terminates
This is the most basic system - resource-based servlets (i.e. .jsp or .aspx files). The binding rules become much more complicated when using technologies like MVC frameworks, but the essential concepts are the same.
Similar to what OrangeDog mentioned in his answer, there is plenty that goes on when serving these pages Before you even get to your code.
Not only in asp.net mvc, but in asp.net in general there are various pieces that come into play when you're executing a request.
There is code like modules, handlers, etc that again do processing Before it gets to the code of the page. Additionally you can map the same page to be able to process different urls.
The concept of handler in asp.net is important, as there are various handlers that are responsible of processing requests that match extensions and/or http verbs (get, head, post). If you take a look into %systemroot%\Microsoft.NET\Framework64\v4.0.30319\Config\web.config, you can see a section. You can also see the handlers in IIS (these can be changed x site).
For example, the HttpForbiddenHandler is one that just rejects the request. It is configured to be called for special files like the sources "*.cs".
You can define your own handler, that is nothing more than a class that implements an IHttpHandler interface. So it has 2 methods: ProcessRequest and IsReusable. This is more similar to your cgi program, as the implementation is mainly a method that produces HTML or any other type of output based on the information in the request.
Asp.net pages build on top of that, and have plenty of extra features meant to make it easier for you to develop pages. You implement a class that inherits from Page, and there are 2 code files associated to it (.aspx and .cs). The same can be said for asp.net mvc, but it is structured differently. There is much more than it, if you want to take advantage of it you'd need to learn about it.
The downside of those abstractions, is that it makes some developers lose track of the context they're at / about the underlying. The context is still the same, you're producing an application that takes a request and produces an output. The difference is that there is plenty more code in place intended to make it easier.
In terms of a more detailed list of IIS's ASP.NET Request Lifecycle, there are a quite a few stages in the HTTPApplication Pipeline. Faily recently there was a good blog post that I thought summarized them very concisely and well. It's "HTTP Request Lifecycle Events in IIS Pipeline that every ASP.NET Developer Should Know" by Suprotim Agarwal.
For a more detailed explanation you should check out the MSDN article on the subject. This will also go into information on what happens before that pipeline.
Related
I wish to make a progressive web app for a domain www.xyz.com and another progressive web app for the domain www.xyz.com/abc. How should I go about it and what will be the behaviour of service workers in both the cases? Will there be 2 service worker registrations or a single one will work for both the PWAs? Also, should I make 2 manifest files for them?
You can have only one PWA for both URLs. When you create your service worker, its scope covers the current folders and the relative children.
If you place it at the root level, you can use one service worker for both URLs, without the need to make thinks more complex introducing nested constructions.
You can define different caching strategies within the same service worker with ease.
If you want to deepen the PWA topic, you can have a look at the articles I wrote about them, starting from basic concepts and then going deeper with more advanced themes.
Update
The scope property of the manifest file determines which HTTP calls can be intercepted by the Service Worker (SW).
If you have scope: '/', your SW will intercept all HTTP requests made by your app. If it would be /user, the SW couldn't intercept a request that doesn't fall within its scope (e.g. /orders/code.js), but it would intercept all GET calls under the user root, like /user/details.
In your case you can have therefore two SWs (even on the same page) where you can define different scopes to intercept, you have just to be careful in not overlapping the scopes among them.
If you plan to cache also static assets, keep it in mind that the scope for the SW is given by the folder where the SW file is stored and its subfolders.
About multiple manifest files, Jeff gave an answer about it on SO.
I'm a project manager not a developer, and we stood up a really basic site in windows azure, We've now been asked to track usage of the site, and I'm curious what a request is. The site is accessed through a mobile device and performs a basic calculation. So I believe that there is only one request per visit, changing numbers you enter in various fields to what if the calculation doesn't seem to refresh the page. Is that a fair assumption or are there some basic checks I can do to understand if I need to aggregate requests to really track or interpret usage of the site.
Whenever your web browser fetches a file (a page, a picture, etc) from
a web server, it does so using HTTP - that's "Hypertext Transfer
Protocol". HTTP is a request/response protocol, which means your
computer sends a request for some file (e.g. "Get me the file
'home.html'"), and the web server sends back a response ("Here's the
file", followed by the file itself).
That request which your computer sends to the web server contains all
sorts of (potentially) interesting information. We'll now examine the
HTTP request your computer just sent to this web server, see what it
contains, and find out what it tells me about you.
http://djce.org.uk/dumprequest
tip: add google analytics to your site. It will give to you the number of views and unique users.
I have a custom HTTP server written in C# that provides specialized application services in my application domain, such as rendering a dashboard with graphing. I am not using IIS; the server is completely written in C# using the HttpListener class to bind directly to the port(s) that it serves.
I would like to use ServiceStack to add in a RESTful API for pulling data to browser-side code to improve the user experience, using the same web server (so it can bind to the same HTTPS port, and share my security module).
All of the example code on the web that I have found assumes either that IIS owns the web port, or that Service Stack owns the web port. In my use case, my custom application owns the web port, and wants to delegate certain HTTP requests to Service Stack.
Is there a simple way to pass off a single HttpListenerContext off to Service Stack to handle? I could not find documentation examples using google, since all of the key words seem to be too common.
In the context of my custom code, I will have already evaluated the URL, determined that the user has permission to access it, and just need to have HttpListenerResponse generated.
Simple sample code or a pointer to a web article would be fantastic.
We've never tested doing this before, but the AppHostHttpListenerBase.ProcessRequest entry point accepts a HttpListenerContext.
You would still need to call new AppHost().Init() but you shouldn't need to start it.
I have my site hosted on IIS hosting. Site has feature that needs calling WCF service and then return result. The issue is that site is processing calling to WCF service another web site calling is freezing and not return content fast (this is just static content). I setup two chrome instances with different imacros' scripts, which one is calling page that requests wcf service and another one page is just static content. So here I can just see that when first page that requests wcf services freezes, another one page also freezes and when first is released the second is too.
Do I need reconfigure something in my Web.Config or do should I do something else to get possible to get static content immediately.
I think that there are two seperate problems here:
Why does the page that uses the WCF service freeze
Why does the static content page freeze
On the page that calls the WCF service a common problem is that the WCF client is not closed. By default there are 10 WCF connections with a timeout of 1 min. The first 10 calls go fine (say they execute i 2 secs), then the 11th call comes, there are no free wcf connections it must therefore wait 58 secs for a connection to timeout and become available.
On why your static page freezes. It could be that your client only allows one connection to the site, the request for the static page is not sent untill the request for the page with the wcf services is complete.
You should check the IIS logs to see how must time IIS is reporting that the request is taking.
I would say that this is a threading issue. This MSDN KB article has some suggestions on how to tune your ASP.NET threading behavior:
http://support.microsoft.com/kb/821268
From article - ...you can tune the following parameters in your Machine.config file to best fit your situation:
maxWorkerThreads
minWorkerThreads
maxIoThreads
minFreeThreads
minLocalRequestFreeThreads
maxconnection
executionTimeout
To successfully resolve these problems, do the following:
Limit the number of ASP.NET requests that can execute at the same time to approximately 12 per CPU.
Permit Web service callbacks to freely use threads in the ThreadPool.
Select an appropriate value for the maxconnections parameter. Base your selection on the number of IP addresses and AppDomains that are used.
etc...
Consider such scenario: when you make a request to IIS your app changes, deletes or creates some file outside of App_Data folder. This often tends to be a log file which is mistakenly was put at bin folder of the app. The file system changes lead to AppDomain reloading by IIS as it thinks that app was changed, hence the experienced delay. This may or may not apply to your issue, but it is a common mistake in ASP.NET apps.
Well, maybe there is no problem...
It may be just the browser's same domain simultaneous requests limit.
Until the browser not finished the request to the first page (the WCF page), it won't send the request to the second page (the static).
Try this:
Use different browsers for each page (for example chrome/firefox).
Or open the second page in chrome in incognito window (Ctrl + Shift + N).
Or try to access each page from different computer.
You could try to use AppFabric and see what is wrong with your WCF services http://msdn.microsoft.com/en-us/windowsserver/ee695849
I have what I thought was a simple(ish) problem. I'm writing a SCORM package for an external learning resource. It's basically an iframe in a HTML page that the clients install in their LMS (Learning Management System).
The external resource needs to be able to tell the LMS that the user has completed the content. Because the LMS and resource are on different domains, there's obviously a JS security wall stopping me communicating directly. So when the user reaches the end of the content, the external resources sets its URL to have an anchor so the url goes from http://url to http://url#complete
Now I'm trying to get the location from the iframe and I'm failing miserably. I've tried iframe.location and iframe.window.location (.window is nothing too). I can't seem to get a handle on the right thing.
iframe.src shows me the original source URL, but it doesn't change when the iframe updates to the #complete version.
Any tips? Any alternatives? Although I control both pages, unless there's a javascript method to set cross-domain communication, I can't set the http header to allow it because I don't control the LMS server - it just pushes out my static page.
Edit: As an alternative, I'm considering storing the completed event in the session (a cookie would work too, I guess) at the resource end and then making another page that outputs that as a JSONP statement. I think it would be quite easy to do but it's a lot more fuss for something that should be simple. I literally need to flip one switch on the LMS code from the external site.
Use easyXDM, it should make this fairly easy.
Using it you can do cross-domain RPC with no server-side interaction. The readme at github is pretty good.