[irahul]

> How is the CGI model fundamentally different from a servlet model,

Since both are web server to application server interfaces, they aren't fundamentally different - the difference is cgi was language independent and hence defined for the common minimum. cgi couldn't have been defined in request and response objects - it would have caused trouble for languages which doesn't have objects.

> where your application code is given a request as a parameter to a function, and must return a response?

cgi is not given a request parameter - the request parameters are passed in the environment. And cgi doesn't return a response object - whatever it writes to stdout constitutes the response. cgi had to cater to all sorts of implementation - assuming request/response objects wasn't a possibility.

Servlets and cgi aren't fundamentally different, but I guess we can agree they are sufficiently different.

[ianb]

To add/agree: I think the biggest difference is that CGI dealt in data, and did not have objects/APIs/etc. In many ways it would have been reasonable to skip even that, and pass an HTTP request in on stdin, and get an HTTP response on stdout, with just some minimal sanitizing promises; but I don't think I've ever seen that approach. Coincidence of history I suppose. Anyway, WSGI also carefully avoided any objects, only using standard data structures (dicts/hashes, strings, ints, ordered-associative-arrays, and iterable response). The result is a functional API without an opinions.