C CGI program, and CONTENT_TYPE and boundaries.

[Dino]

I'm writing my first CGI program, and it's in C. Right now, I'm just output all the environment variables and their values.

My question relates to the method="post" action="multipart/form-data" combination, and the boundary separators.

As seen in the attached image, the boundary indicator starts with 4 hyphens and end with an "M".

In the lower part of the image, (you can't see so good) I'm breaking up the attached file (a ruby script) at newline characters, and substituting a "<br />" in it's place so it will display properly.

However, it appears the boundary markers differ slightly. In the CONTENT_TYPE, when read from STDIN, the markers start with 6 hyphens.

And in the smaller image, you can see that the last boundary marker even has 2 trailing hyphens.

When I read the content, here is my loop:


for ( i = 0 ; i < clength ; ++i ) {
char c = fgetc(stdin) ;
if (c=='\n') printf("<br />") ;
else printf( "%c", c ) ;

}

clength is a straight atoi() of CONTENT_LENGTH, which leads me to think I'm reading the right amount of data.

Any ideas?

Thanks, Todd

[Dino]

I think I've come to a theory of operation for this question.

I think the way it is supposed to work is that if I find the boundary marker on any line (delimited by the newline character), then that is a separator "line" and marks the boundary from one set of data from another.

I was taking the boundary marker literally, and only ignoring those characters that comprise the boundary marker.

Is this correct?

Thanks, Todd

[arpsmack]

You should probably check out RFC 2045 (http://www.ietf.org/rfc/rfc2045.txt) and RFC 2046 (http://www.ietf.org/rfc/rfc2046.txt) for more info


The Content-Type field for multipart entities requires one parameter,
"boundary". The boundary delimiter line is then defined as a line
consisting entirely of two hyphen characters ("-", decimal value 45)
followed by the boundary parameter value from the Content-Type header
field, optional linear whitespace, and a terminating CRLF.


Those RFC's contain more information than I'd be willing to wade through, but I did find that snippet from doing a quick search for "boundary".

[Dino]

Thank you. That confirms what I had deduced.

Todd