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[FileReader API, ProgressEvents] Design patterns, FileWriter API

From: Marcin Hanclik <Marcin.Hanclik@access-company.com>
Date: Tue, 17 Nov 2009 10:40:11 +0100
To: WebApps WG <public-webapps@w3.org>, "public-device-apis@w3.org" <public-device-apis@w3.org>
Message-ID: <FAA1D89C5BAF1142A74AF116630A9F2C28942D7485@OBEEX01.obe.access-company.com>

This is a set of architectural comments to the FileReader API, ProgressEvents and the design patterns for DAP.

For DAP in [1] I propose the following consistency requirement (still [1] is a very early draft with bugs):
"All APIs MUST follow the same convention when handling callback functions (e.g. XHR / FileReaderAPI style with onreadystatechange, or ProgressEvents with EventTarget)."
There is currently discrepancy between XHR/FileReaderAPI and the ProgressEvents in terms of handling the same functionality differently.

The ProgressEvents specification proposes is the event firing order [2], that could be summarized as a firing grammar
(up to some lack of clarity around suspend and stalled events):

progressgrammar = loadstart working (error | abort | load) loadend
working         = *( progress | (progress suspend progress) | (progress stalled progress) )

In my opinion some part of the design from ProgressEvents is taken over in FileReader API too directly.
Specifically the event names are the same as within the ProgressEvents, but I assume they should be adjusted to the FileReader API.
Therefore instead of (forgetting the above issue with the callback model for now):

  attribute Function onloadstart;
  attribute Function onprogress;
  attribute Function onload;
  attribute Function onabort;
  attribute Function onerror;
  attribute Function onloadend;

we could have:

  attribute Function onreadstart;
  attribute Function onprogress;
  attribute Function onread;
  attribute Function onabort;
  attribute Function onerror;
  attribute Function onreadend;

Assuming that we will have an interface like FileWriter in the (near) future, we could already now anticipate that the interface would include e.g. the following:

  attribute Function onwritestart;
  attribute Function onprogress;
  attribute Function onwrite;
  attribute Function onabort;
  attribute Function onerror;
  attribute Function onwriteend;

Then, the ProgressEvents spec could act as a design pattern definition for lengthy, asynchronous operations.
To make it happen, the names of the events there could be changed to be generic:
loadstart -> start
load -> done
loadend -> end

Additionally the ProgressEvents spec could be divided (or split into two documents? ) to contain the section specific to the design pattern definition and to the section specific to data transfer / loading.

What to you think?


[1] http://dev.w3.org/cvsweb/~checkout~/2009/dap/design-patterns/Overview.html?rev=1.1&content-type=text/html;%20charset=iso-8859-1
[2] http://dev.w3.org/2006/webapi/progress/Progress.html#Event1

Marcin Hanclik
ACCESS Systems Germany GmbH
Tel: +49-208-8290-6452  |  Fax: +49-208-8290-6465
Mobile: +49-163-8290-646
E-Mail: marcin.hanclik@access-company.com


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Received on Tuesday, 17 November 2009 10:12:42 UTC

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