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you can actually do alot with javascript!

Reading binary files using Ajax April 6, 2008

Filed under: ajax,javascript — nagoon97 @ 2:18 pm
Tags: , , ,

A growing number of web applications are making more and more use of client-side technologies because thanks to Ajax, it is now possible to write more fluid and more responsive web applications using only client-side technologies.

Now, web developers from all around the globe are releasing really interesting utilities and applications using only client-side technologies, many of which used to be within the domain of server-side technologies.

But when it comes to binary files, helping hands from server-side technologies are often necessary.

So I googled around to see what I can do about binary files with Ajax and found this Marcus Granado’s post at http://mgran.blogspot.com/2006/08/downloading-binary-streams-with.html

What he posted there worked like a charm for FireFox and Safari but I couldn’t get it to work for IE.

But luckily, within the same page, someone had posted up a solution for IE as a comment, which is written in VBScript.

So I put them all together in this BinFileReader function, which provides cross-browser support and helper methods to easily access the binary contents.

 

* BinFileReader: http://www.heypage.com/nagoon97/BinFileReader/BinFileReader.js

getFileSize() Return the file size
getFilePointer() Return the reading position
movePointerTo(iTo) Move the reading position to iTo.
movePointer(iDirection) Move the reading position in iDirection.
For all the following read functions,
- The reading position will move to the end of where the content is last read
- When iFrom is ommited, current reading position is used
readNumber(iNumBytes, iFrom) Read and return iNumBytes-byte number starting at iFrom.
readString(iNumChars, iFrom) Read and return iNumChars characters starting at iFrom.
readUnicodeString(iNumChars, iFrom) Read and return iNumChars unicoded characters starting at iFrom.

 

* Example:
var bmpFile = new BinFileReader(“image.bmp”);
bmpFile.movePointerTo(18);
var width = bmpFile.readNumber(4);
var height = bmpFile.readNumber(4);

 
* Demo:
http://www.heypage.com/nagoon97/BinFileReader/BinFileReader_demo.html

http://www.heypage.com/nagoon97/BinFileReader/MosaicBuilder_demo.html

 

* Related Posts 

https://nagoon97.wordpress.com/2008/04/09/ajax-mosaic-builder/

 

 
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