I need to add a file upload function to an ASP.NET website and would like to be able to read a small portion of the file on the server while it's still uploading. A peek or preview type function so I can determine contents and give some feedback to the user while it is still uploading (we're talking about large files here). Is there any way to do this? I'm thinking worst case of writing a custom control which uploads only a fixed number of bytes of the file once chosen and then under the covers starts another upload of the full file. Not totally sure even this is possible, but I'm looking for a more elegant solution anyway... Thanks!
It sounds like you want to avoid the "white screen of death" during large file uploads. If so, you might want to look into Telerik's RadUpload control , which provides a progress bar during upload.
If you want to roll your own, I'd decompile their trial copy for ideas. I've peeked at their source in this way, and they accomplish the progress bar through a combination of a custom HttpModule and HttpHandler along with their control. The handler routes the file in a streamed fashion while the module provides "percent complete" information--or the other way round; it's been a few years since I looked at it.
Edit:
Actually, I'm trying to do server-side processing as the file is still being uploaded. I want to import user data via HTTP, but want to present the user with preview/options of how we'll process their data while the file is still uploading (column definitions, etc.). No matter what, we'll take the file as is, so the upload doesn't need to be interrupted. Given that I actually want interaction during the upload based on reading a relatively small portion of the file as it is being uploaded, would you still recommend the same approach?
Well... it'd be very difficult to do, and it might not work cross-browser, but it could be done with this approach.
Since it's entirely possible to work with the incoming file as a stream as I mentioned, you could have your intial processing update some state as part of that stream processing. If you don't process as a stream, you have to wait for the full file upload before you can do anything with it.
The problem is this: during the file upload, you cannot have any more HTML-based interaction. The post must continue unabated or the upload will fail. The control I linked only works at all because most browsers allow javascript to continue to execute and update page DOM during the post.
So in order to make this work, you have to update some standardized state server-side during your file processing in the HttpModule, which is transmitted back to the client via XmlHttpRequest calls handled by the HttpHandler. You have to use pure javascript/DOM to update the UI for the user.
So, as I said, it's complex and likely to be buggy cross-browser, but it could theoretically be done.
There are alernatives that might be more stable, but might not necessarily be feasible: you could build an ActiveX control or a Click-Once .NET application that pre-processes the file before upload, and maybe even asynchronously transfers the file while the user continues browsing. Some users may not like that option, and I don't know the particulars of your deployment scenario, but it's an option.
There is an HTTP HEAD method but not PEEK.
HEAD will give you information and headers about the file.
Of course you can make a special request handler that does anything you want. You don't have to work with static resources, you can dynamically create any response you want.
Related
How do I know what are all the Javascript and CSS files is called by the clients from IIS server? Can this be done via httpmodule?
Basically what I want to know is that when the client is accessing the server i want to know what are the files that are consumed mostly along with their size and time taken to serve the request.
I think the quickest way to do this is like this: In IIS Management console, make sure logging is enabled, and set it to the place you want. After a short delay, the log files will appear, import them to a database and start analyzing. You can choose which fields you want to save.
Alternatively if you want to have more control and do this in real time, you could create a handler or module, but you will also have to make sure all requests, including static content, go through the asp processor, which will create quite some overhead. Very much not recommended for dev time and performance, but it will work.
I'm trying to download a file using a servlet. If I make use of Content Disposition response Header,an open/save dialog box would appear. Is there a way that I could save the file directly to a folder instead of selecting the destination from the dialog box. I would need this approach since. the file is being downloaded from a batch rather than a webapp.
If it were possible, any arbitrary website would theoretically be able to silently write malware to visitor's disk without any notification. Would you as being the visitor appreciate it?
I don't think so.
It's fortunately not possible to write anything to visitor's disk without confirmation by standard HTTP/HTML means. The world wide web would have looked very different.
If you have really a hard head in this, then your best bet is creating a signed(!) Java applet for the job of file downloading and saving. You see this also often on those "large" websites as so-called "Download Managers" which can easily annoy endusers. Again, do this only if you have really a hard head in this.
Yes, I'm still using Classic ASP.
I'm about to write a script that checks a directory on the server, every 5 minutes, for newly uploaded photos, by my office, and to transfer the photos to another location. I'm using ASP and the FileSystemObject as the application and a Windows Schedule calls it.
What I would like to know is: If the user is sending 150 photos, by FTP, my application is not going to know if the user has finished uploading, or not. So then the application will go through the files one-by-one and transfer them. If my user has a slower connection than the speed of my application, the script may eventually come across the file that is currently being uploaded...
Will my application grab that file thinking it's complete or will it know that it's in the middle of upload and leave it alone? If it DOES grab it and transfers half a photo, how can I stop this from happening?
There is no good way to test for that, much depends on how the uploader is working.
Its highly unlikely that a file currently open for write access while the uploader creates it is going to allow your code to move it. An attempt to move it will result in a sharing violation or similar error. So protecting that section of code with an On Error Resume Next would do it. Have your code skip that file in the knowledge that it will be picked up again when the next poll comes round.
I do not really understand how Google Code handles file versioning.
I am building a jQuery plugin that anyone can access. Like so:
<script type="text/javascript" src="http://jquery-old-browser-warning.googlecode.com/files/jquery.browser-warning.js"></script>
This script accesses other files on the same project (via ajax).
The problem is, that when I upload a new file, it just seems like there aren't any changed to it. Google recommends that new files should have new names.
But then I would have to change the filenames that the script loads.
But then I would have to change the script file as well, and that would break everybodys implementation (with the script-tag above)
Is there a way to force a file to change when uploading with the same filename?
PS: If I go directly to the project page's file list. Then I do get the file with the updated content. But as I said, not when getting it through ajax.
The cheapest trick in the book to prevent caching is adding some random content to a GET parameter:
www.example.com/resources/resource.js?random=1234567
You can for example use the current timestamp for this.
This, however, causes any and every access to re-fetch the content, and invalidates any client-side caching mechanism as well. I would use this only as a last resort. If Google are that stringent about caching, I'd rather develop a workflow that allows for easy renaming of files.
I don't know your workflow, but maybe you can work with versioned directories?
Like so:
www.example.com/50/resources/resource.js
www.example.com/51/resources/resource.js
that would keep whatever caching the client employs intact, but whenever there's a change from your end, the browser would reload the content.
I think Its just a cache on the browsers, So when you request file from ajax, just add random parameters or version number.
For example, Stackoverflow add version parameter to static contents like
http://sstatic.net/so/all.css?v=6638
Are you talking about uploading files to the "Downloads" area? Those should have distinct filenames, for example they should be versioned. If you're uploading the script code, that should be submitted by the version control system you're using, and should most definitely keep the same name across revisions.
Edit: your code snippet didn't show up on my page, misunderstood what you're trying. Don't imagine Google would be happy with you referencing the SVN repository every time some client page is loaded :)
An architect at my work recently read Yahoo!'s Exceptional Performance Best Practices guide where it says to use a far-future Expires header for resources used by a page such as JavaScript, CSS, and images. The idea is you set a Expires header for these resources years into the future so they're always cached by the browser, and whenever we change the file and therefore need the browser to request the resource again instead of using its cache, change the filename by adding a version number.
Instead of incorporating this into our build process though, he has another idea. Instead of changing file names in source and on the server disk for each build (granted, that would be tedious), we're going to fake it. His plan is to set far-future expires on said resources, then implement two HttpModules.
One module will intercept all the Response streams of our ASPX and HTML pages before they go out, look for resource links and tack on a version parameter that is the file's last modified date. The other HttpModule will handle all requests for resources and simply ignore the version portion of the address. That way, the browser always requests a new resource file each time it has changed on disk, without ever actually having to change the name of the file on disk.
Make sense?
My concern relates to the module that rewrites the ASPX/HTML page Response stream. He's simply going to apply a bunch of Regex.Replace() on "src" attributes of <script> and <img> tags, and "href" attribute of <link> tags. This is going to happen for every single request on the server whose content type is "text/html." Potentially hundreds or thousands a minute.
I understand that HttpModules are hooked into the IIS pipeline, but this has got to add a prohibitive delay in the time it takes IIS to send out HTTP responses. No? What do you think?
A few things to be aware of:
If the idea is to add a query string to the static file names to indicate their version, unfortunately that will also prevent caching by the kernel-mode HTTP driver (http.sys)
Scanning each entire response based on a bunch of regular expressions will be slow, slow, slow. It's also likely to be unreliable, with hard-to-predict corner cases.
A few alternatives:
Use control adapters to explicitly replace certain URLs or paths with the current version. That allows you to focus specifically on images, CSS, etc.
Change folder names instead of file names when you version static files
Consider using ASP.NET skins to help centralize file names. That will help simplify maintenance.
In case it's helpful, I cover this subject in my book (Ultra-Fast ASP.NET), including code examples.
He's worried about stuff not being cached on the client - obviously this depends somewhat on how the user population has their browsers configured; if it's the default config then I doubt you'd need to worry about trying to second guess the client caching, it's too hard and the results aren't guaranteed, also it's not going to help new users.
As far as the HTTP Modules go - in principle I would say they are fine, but you'll want them to be blindingly fast and efficient if you take that track; it's probably worth trying out. I can't speak on the appropriateness of use RegEx to do what you want done inside, though.
If you're looking for high performance, I suggest you (or your architect) do some reading (and I don't mean that in a nasty way). I learnt something recently which I think will help -let me explain (and maybe you guys know this already).
Browsers only hold a limited number of simultaneous connections open to a specific hostname at any one time. e.g, IE6 will only do 6 connections to say www.foo.net.
If you call your images from say images.foo.net you get 6 new connections straight away.
The idea is to seperate out different content types into different hostnames (css.foo.net, scripts.foo.net, ajaxcalls.foo.net) that way you'll be making sure the browser is really working on your behalf.
http://code.google.com/p/talifun-web
StaticFileHandler - Serve Static Files in a cachable, resumable way.
CrusherModule - Serve compressed versioned JS and CSS in a cachable way.
You don't quite get kernel mode caching speed but serving from HttpRuntime.Cache has its advantages. Kernel Mode cache can't cache partial responses and you don't have fine grained control of the cache. The most important thing to implement is a consistent etag header and expires header. This will improve your site performance more than anything else.
Reducing the number of files served is probably one of the best ways to improve the speed of your website. The CrusherModule combines all the css on your site into one file and all the js into another file.
Memory is cheap, hard drives are slow, so use it!