Files and Checksums

[Rob]

Good afternoon,

Is it possible to have JavaScript do a checksum of a file a user has
chosen to upload via a multipart html form? I'd like have JavaScript
do a checksum on the client side, embedded the result in the form, and
then have a CGI on the server check to ensure the server-side checksum
matches the client. Is such a thing even possible?

Thanks in advance for any advice.

Rob

[Jim Dabell]

Rob wrote:

Is it possible to have JavaScript do a checksum of a file a user has
chosen to upload via a multipart html form? I'd like have JavaScript
do a checksum on the client side, embedded the result in the form, and
then have a CGI on the server check to ensure the server-side checksum
matches the client. Is such a thing even possible?

Part of your question is already mentioned in the FAQ:

<URL:http://jibbering.com/faq/#FAQ4_3>

Obviously, you'll need access to the filesystem to checksum the file.

On the other hand, what you describe is already provided for by HTTP. Look
into the Content-MD5 header:

<URL:http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.15>

I have no idea what browser support for this is like.
--
Jim Dabell