This document explains in as much details as possible the list of planned changes and work to be done on the Cowboy server. It is intended to be exhaustive but some elements might still be missing.
The main features that will be added to Cowboy 2.0 are support for HTTP/2.0 and Websocket permessage deflate compression.
A complete analysis of the httpbis set of specifications will be performed and extensive tests will be written to ensure maximum compatibility.
A number of backward incompatible changes are planned. These changes are individually small, but together should result in a large improvement in usability.
The interface of cowboy_req will be largely changed. The
number one complaint about Cowboy today is that you have
to keep track of the Req whenever you do anything. The new
interface will minimize that.
All functions will return a single term, excluding the body
reading functions body/{1,2}, body_qs/{1,2}, part/{1,2},
part_body/{1,2}.
Of the functions returning a single term, some of them will
return a Req object. This includes the functions that already
return Req: compact/1, delete_resp_header/2, set_meta/3,
set_resp_body/2, set_resp_body_fun/{2,3}, set_resp_cookie/4,
set_resp_header/3, and adds the chunked_reply/{2,3} and
reply/{2,3,4} functions to the list.
Of note is that this will allow chaining all the response functions if that's what you fancy.
The parse_header/{2,3} function will now only return the
parsed header value, and crash on error. It will also not
cache the parsed value anymore, except for headers that Cowboy
requires, like the connection header.
It is unsure what will become of the qs_val, qs_vals,
cookie and cookies functions. The main idea at this point
is to replace them with a parse_qs/2 and parse_cookies/2
that would return the parsed list, and let the user decide
how to access it.
The first argument of the init/3 function is too rarely used.
It will be removed.
The return value of the init/2 function will become
{http, Req, State} | {loop, Req, State} | {Module, Req, State}
with Module being cowboy_rest, cowboy_websocket or a
user provided module.
The rest_init and websocket_init callbacks will be removed
as they become unnecessary with the new init/2 interface.
Similarly, the rest_terminate and websocket_terminate
callbacks will be removed in favor of a unified terminate/3.
The terminate/3 callback will become optional.
The error tuple return value brings little value compared to the halt tuple. The error tuple will therefore be removed.
The onrequest hook will be removed. It can easily be replaced
by a middleware.
The interface of the onresponse hook will change. There has
been a number of issues and added complexity with the current
interface that warrant fixing. The main problem is that the
hook may be used to change the reply, by calling the reply
function again, forcing us to be careful not to reprocess
everything again.
To fix that, we will cut the reply mechanism in two steps,
one that is basically some preprocessing of the response
header to follow the protocol requirements, and then the
actual response. The onresponse hook will fit in the
middle, being called from the first step and calling the
second step itself.
If a body streaming function is provided, the hook will also receive it (unlike today). It will not be able to inspect its contents however.
This should greatly simplify the code and allow users to do any operation they wish.
A special chapter of the manual will document a low-level interface that may be used in middlewares or hooks (but nowhere else). This includes the Req access and update functions and the new response function described above.
The known_content_type callback has no purpose, so it
is going to be removed.
The documentation for all REST callbacks will be updated to describe whether they can have side effects. This will allows us to build introspection tools on top of a working REST API.
Range support will be added.
- Convenience API for extracting query string and body information, similar to PHP's $_GET, $_POST and $_FILES