I have a flash file uploader that allows uploading multiple files in one shot.
Now on one click how many times will the hanlder is supposed to be called?
I am seeing that the ProcessRequest() of the HttpHandler is getting called for each of the files I upload. If I upload 5 files, then the Process request gets called 5 times.
This seems odd. I would expect the handler to be called just once where I will loop the
Can anyone confirm this behavior or I am missing something?
The Flash uploader and the ASP.Net HTTPHandler are not related. If the Flash uploader calls the HTTPHandler 5 times, you will see ProcessRequest() called 5 times.
If the Flash uploader serializes the data, and passes the entire string to the HTTPHandler for deserialization and processing, you will see ProcessRequest() called once.
Related
The user selects some options then clicks "download". At that point, my php script starts preparing the file, and it can take 5-10 minutes before the file is ready and starts downloading. I want to notify the user with a sound that the download has started.
How can I do that?
According to this question:
Is there a way to detect the start of a download in JavaScript?
There is no programmatic way to detect when a download begins. That question is six years old now, so perhaps it is out of date, but I could not find any more recent information to contradict it.
An alternative approach would be to break the download process into two parts so that you can control when the actual data transfer begins:
Instead of initiating the download immediately, have the button send an AJAX request to the server asking it to prepare the file for download.
The server should not reply to the AJAX immediately, but should prepare the file and save it in a temporary file storage area with a unique generated name/ID.
Once the file is ready, the server should reply to the AJAX with the name/ID of the file.
On the client, the AJAX completion callback can play the sound, since it knows the download is about to begin.
It then uses window.open() to request the file from the server.
Now the server can respond with the appropriate headers as you used to do.
Finally, the server can delete the file from temporary storage (or just wait for a cron job to do it).
In my Lotus Notes web application, I have file upload functionality. Here I want to validate the attachment file size before uploading which I did through webquerysave. My problem is that whenever the attached file size exceeds the limitation, which is configured in server document, it throws the server error page like “HTTP: 500 Invalid POST Request Exception”.
I tried some methods to resolve this, but they’re not working:
In domcfg.nsf, I mapped the target form called "CustomGeneralErrorForm".
I created "$$ReturnGeneralError" from to show error page.
In Notes.ini, I added "HTTPMultiErrorPage=/error.html"
How can I resolve this issue?
I suppose there's no way. I've tried several time to catch that error but I think the only way is to test files size with javascript; Obviously it works only with html5 browsers as you can find in this post:
Using jQuery, Restricting File Size Before Uploading
So... you have to write code to detect browser features and use javascript code with html5 browser and find alternative ways for old browser.
For example you can use Flash plugin and post tu server-side code depending on your backend.
Uploadify is a very good chance (http://www.uploadify.com/) to work just one time, but make a internet search and choose the best for you.
In this way you can stop user large posts, but if you need to upload large size file (>10Mb default) you must set a secondary internet site server document with greater post size limit.
In my content script, I want to monitor which file a is getting uploaded to a web application.
I monitor "change" event for any "input:file" element. It works on any site (such as Gmail) that uses "input:file".
However sites like imgur, use SWFUpload mechanism. I tried to capture "fileQueued" event on element that I suspected to be swfupload. But that did not work.
How can I capture file upload event for sites that use swfupload?
Are there any other plugins that manage file uploading that I would need to take care in my content script?
Is there any generic mechanism to tackle this problem?
(I am aware of drag-n-drop mechanism, but I have not handled that case so far.
I have also read following relevant question on SO:
Grab file with chrome extension before upload)
It's probably worth your time to experiment with the chrome.webRequest API; it appears that the onBeforeRequest event contains info about file uploads. It's a complex API with extra parameters to addListener; read the docs thoroughly.
Expressjs has bodyParser middleware which can handle file-uploads and can even store them in a directory given in options. But in my app I want to store the files in Amazon S3, so I basically want to stream the file straight to S3 without having to store it locally at all.
But the problem is validation of the file. How can I be sure that these files are all images. Checking the content-type isn't good enough option coz that can be faked. I want to know is it ok if I do the validation after streaming the file to S3?? I am asking from the security point of view.
After storing the image, I need to retrieve it for creating thumbnails, How can I do it asynchronously after giving the response after file upload?
You have contradictory goals of not wanting to store it locally during upload but then also wanting to download it needlessly again to make thumbnails. If you want to go for technical slickness awards, you can simultaneously stream the file upload request body to a local temporary file as well as S3. Or you can do what the rest of the industry does and store it in a local temporary file and then thumbnail it, and then upload all sizes to S3. Either of these approaches alleviates any need to immediately download it from S3 to make thumbnails.
How exactly do you intend to validate that it's really an image? You could look at the first chunk of file data and validate for the file type's magic number if that gives you warm fuzzies, but ultimately it's untrusted user data. The second half of the supposed image file could be virus code and that is just as easily faked at the Content-Type header. Sounds like your security concerns are mostly driven by FUD as opposed to specific threats you intend to defend against. As long as you don't take the user's uploaded data, mark it executable and run it as root on your server, any non-image data is just going to be corrupt and fail to render correctly in a browser (and/or cause your thumbnailer program to exit with an error or perhaps crash in an extreme case).
Regarding validation can I just try to create a thumbnail and if I can't then its not a valid image and delete it. Is this way fine?
Most of the time, yes. There will be edge cases where your thumbnailer cannot process an image but a browser can as thumbnailers are not perfect and some images are partially corrupt. For example, I have found some animated GIFs that render and animate fine in a web browser but graphicsmagick crashes trying to process them. Not sure there's anything that can be done about those 0.01% edge cases.
And for uploads part, can I send a response to the user and than carry on with the thumbnail creation and storing it in S3?
Yes, that is generally the best approach so the user knows their upload succeeded. Generally image processing is usually architected as a "work queue" model where you just record that there's work to do and then proceed and a separate process or processes take work off the queue and complete it.
Im having problems uploading files to a node.js application using restify.
This is my upload code https://gist.github.com/maumercado/7ab5cbbfd27c6b825044
Apparently the events are not being triggered, but I dont really know the reason, also the files are being created, but once I see the size info it says 0 bytes.
also this is the server.js file https://gist.github.com/maumercado/ecf948b4b8fc7d39e69e
Im using a post request in order to upload the file and node 0.10.7.
What can be wrong with the code??
Thank you
It looks like restify.bodyParser() works the same as express.bodyParser(), in that it will handle the upload for you (and in the process consume the body data passed with the request, so there's nothing left to read once your handler is called – hence, no events either).
The uploaded data is written to a temporary file, req.files.selfie.path in your case.
As for what you're intending to do (upload progress), I don't think it's possible, unless you implement the functionality of bodyParser() itself. But I'm not overly familiar with the inner workings of Restify to be 100% sure about that.
If you're working with a browser as a client, you could implement upload progress there instead.