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