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Re: File Upload Status ?

From: Garrett Smith <dhtmlkitchen@gmail.com>
Date: Mon, 11 Aug 2008 23:21:14 -0700
Message-ID: <c9e12660808112321r4987a1ecm4f19fd8f0ea34b6e@mail.gmail.com>
To: "Oliver Hunt" <oliver@apple.com>
Cc: "Web Applications Working Group WG" <public-webapps@w3.org>

On Mon, Aug 11, 2008 at 9:04 PM, Oliver Hunt <oliver@apple.com> wrote:
>>> Sorry, the "and browser" at the end was a typo.  I meant to say, "in the
>>> browser".  The reason synchronous access to the disk is a bad idea is
>>> that
>>> if the operation takes too long, a big file, a slow network home
>>> directory,
>>
>> Then:
>>
>> function readFile(file) {
>> // 1. Check the fileSize property.
>> if(file.fileSize > 100000) {
>>  generateFileWarning(file);
>>  return;
>> }
>> // 2. read file asynchronously.
>> setTimeout(readFile, 1);
>> }
>>
>> seems to completey address the problems you mentioned in only a few
>> lines of code.
>
> Alas this does not resolve the problem as you are making the implicit
> assumption that because a 100k file access may be fine on your local system,
> or even on a network drive on your local network it may not be for someone
> using a network drive over a the net or on an otherwise slow connection
> (this isn't necessarily an uncommon scenario, a person using a vpn on a 56k
> modem could hit this or a person with a poor wifi connection, etc).  The
> file limit being 100k is a magic number that could be replaced by any
> arbitrary value, but the simplest way to break any size assumption is to
> consider what would happen if the file you were attempting to load were on a
> network drive from a server that just fell over.
>

I missed the point with the server falling over.

> In general APIs that require the developer to make this sort of decision are
> poor as they tend to result in code that always uses the synchronous API
> (because it's "easy") because it works fine on the developers system, even
> though it may not be even remotely useful for many people.  The other
> scenario is that the developer does do some testing, but doesn't test every
> possible configuration, once again resulting in some people being unable to
> use the site/application.
>

The other alternative is to have a file sent to the server. The
downside here is when the user does not know that his jpg file that he
uploads is over 1mb. So there's a round trip and it's a slow U/X.

That's where the alert("you're file is too big.") provides faster
feedback than a round trip to a server (with a very large file on the
outbound).

> The other problem is that setTimeout does not result in async javascript
> execution it merely delays the synchronous execution of a script.

I've just tried to upload a 1.1mb log file from my hard drive and had
no issue reading. Using Firefox an older mac.

Reading a 46mb files was slow. I somewhat expected that.

Uploading large files will take time.

> In your
> example you are returning from readFile (to prevent your code from blocking
> the UI) and then the moment the timer is triggered a synchronous read of a
> definitely large file will occur, resulting in the UI being blocked.
>

That is not what the code was intended to do. I realize that I had a
recursive call in the function readFile. The intention is to
setTimeout(getFileContents, 1);

A useful error might be:
"error: file size over allowed limit."
Or in another context:
"warning: this file may take time to upload"

> The only way to prevent such UI blocking is to have an async api regardless
> as to whether you have a synchronous one, meaning that the synchronous api
> will only exist to either increase complexity (as developers will need to
> implement logic to fallback to, and implement, the async I/O in addition to
> the synchronous I/O logic as your above example would need to), or to
> produce sites that fail to account for non-fast I/O (which thus destroy the
> end user experience).
>

Sounds like async reads would avoid the problem of locking the UI.

Why don't you post up your ideas?

Garrett

> --Oliver
>
>
Received on Tuesday, 12 August 2008 06:21:49 GMT

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