Browser data storage location for "Choose File" button - file

Question

For web browsers (such as Chrome, IE, or Firefox), when you select a file using a "Choose File" button, where does the file's data get stored?
The file name shows in the browser, but does the data of the file get stored anywhere or is just a link to the file put somewhere, such as in the browser or a temporary file?
To clarify: I want to know where the file's data get's stored BEFORE submitting. JUST after the file is selected from the client's PC an not anything else is done.

Answer 1

After you select a file. I believe the client (browser) just stores a reference to the file location on the user's computer. It takes a combination of js and html to post the file to the server. Via a Multi/form-data Post.
In this case, on the server, you may have to store the file to a temp location of your choosing, until you're able to process it (i.e. transform and/or store to a Datastore).
In newer browsers you can use the FormData object and xhr to post to the server which is a lot cleaner.
This FormData object is used to construct the key/value pairs which form the data payload for the xhr request.
// Create a new FormData object.
var formData = new FormData();
In this case, once the file bytes are posted to the server, you can do whatever you want with that data. Typically I'll store it as a blob in the DB.
This approach will allow you to keep it all in memory. People make the mistake of trying to store on the server file system. In some multipart form post, you might have to do it this way, however.
Here's some of my web api upload code when using XHR.
I've also called this API route using an iframe (ugh!) in order to support IE8 and older. POS browsers!
/// <summary>
/// Upload the facility logo.
/// </summary>
/// <returns></returns>
[HttpPost]
[Route("logo")]
public HttpResponseMessage Logo()
{
int newImageId = -1;
var uploadedFiles = HttpContext.Current.Request.Files;
if (uploadedFiles.Count > 0)
{
var file = uploadedFiles[0];
if (!file.IsImage())
{
// "The uploaded file must be a .jpg, .jpeg, or .png"
return
Request.CreateResponse(HttpStatusCode.UnsupportedMediaType,
"unsupported");
}
var facilityRepository = new FacilityRepository();
var logoBytes =
StreamCopier.StreamToByteArray(file.InputStream, file.ContentLength);
newImageId = facilityRepository.InsertLogoImage(logoBytes);
}
return Request.CreateResponse(HttpStatusCode.OK,
newImageId);
}