netcgi1 programs to netcgi2
The library netcgi2 is a revised version of the old cgi library
which is now also referred to as netcgi1.
As any software, netcgi1 aged, and suffered more and more from
inadequate interfaces. Because of this it became necessary to
improve the interfaces from grounds up. The result is netcgi2,
a new major version that tries to continue the good parts of
netcgi1 while replacing its problematic edges.
When this text is written, netcgi2 is still being developed, and
subject of discussion.
Why porting and when?
It is not possible to use netcgi1 and netcgi2 at the same time in the
same application. This means that one cannot gradually upgrade from
netcgi1 to netcgi2 by using more and more of the netcgi2 features.
Instead of this, it is necessary to switch from netcgi1 to netcgi2
at one point in the lifetime of the web application.
The main benefit is that you have access to the newest netcgi2
features. There are already a number of connectors that are not
present in netcgi1 (newer AJP protocol version, SCGI). Furthermore,
new features will only be added to netcgi2.
However, if your application is already at or near its end of lifetime,
there is no need to port it to netcgi2. The netcgi1 library will
remain in Ocamlnet 2, and bugs will be fixed.
Module Organization
The new organization is very simple:
Netcgi defines all basic types. Previously, this was done in the
two modules Netcgi_env and Netcgi_typesNetcgi_c implementing
it. Especially the classic CGI connector is now in Netcgi_cgi.
Previously, the CGI connector was defined in Netcgi, and there
used to be several modules per connector.Netcgi_common defines service functions to define new connectors.Netcgi1_compat trying to ease porting. See
below for a discussion.
Interface Changes
Most of the types remain the same, or almost the same. A few changes have been done:
Netcgi.cgi_argument is no longer writable.
Furthermore, the list of arguments in a Netcgi.cgi_activation can no longer
be modified. There are some new service functions to modify lists
of arguments in case one needs such a list.Netcgi.Cookie.Netcgi_common.HTTP exception can be used to exit
from a processor at any time. There is the notion of an exception
handler for web-related exceptions.Netcgi.cgi_environment have been simplified.
It is only distinguished between two states: Output headers have been/
have not been sent. Other processing states are hidden by the
implementation.Netcgi.cgi_activation.at_exit
method.
Porting strategies
Strategy: Use new API
In the long term this is the best strategy. In principle, one has to distinguish between
netcgi values, andnetcgi application with the web
server.netcgi values do not change much. For example, the function
web_page for netcgi1
(* This is [netcgi1] code! *)
let web_page (cgi : Netcgi_types.cgi_activation) =
let webarg = cgi # argument_value "webarg" in
cgi # set_header();
cgi # output # output_string ("The argument is: " ^ webarg)
would read in the version for netcgi2 as follows:
(* This is [netcgi2] code! *)
let web_page (cgi : Netcgi.cgi_activation) =
let webarg = cgi # argument_value "webarg" in
cgi # set_header();
cgi # output # output_string ("The argument is: " ^ webarg)
The only change is that the type cgi_activation is now defined
in the module Netcgi and no longer in Netcgi_types. It is expected
that this simple way of porting applies to almost all parts of
netcgi applications.
By the way, the type cgi_activation can now be abbreviated as cgi,
as this is the type name that needs to be written down most
frequently.
The new CGI connector
In netcgi1, the CGI connector is selected by instantiating the class
Netcgi.std_activation, as in:
(* This is [netcgi1] code! *)
let cgi = new Netcgi.std_activation() in
process cgi
It is assumed that process is a function taking a cgi_activation
as argument, and processing the request.
The corresponding netcgi2 call is:
(* This is [netcgi2] code! *)
Netcgi_cgi.run process
As you see, Netcgi_cgi.run is now responsible for calling process.
The new FastCGI connector
In netcgi1 there are several ways of using FastCGI. The most common is
to call Netcgi_fcgi.serv as in:
(* This is [netcgi1] code! *)
Netcgi_fcgi.serv process optype
It is assumed that process is a function taking a cgi_activation
as argument, and processing the request. optype is a valid
operating type.
The corresponding netcgi2 call is:
(* This is [netcgi2] code! *)
let process' cgi = process (cgi :> Netcgi.cgi_activation) in
Netcgi_fcgi.run ~output_type:optype process'
Note that the argument of process' is a slightly extended version
of cgi_activation, so you usually need the coercion to cut off the
additional part of the object interface.
The new AJP connector
The new connector supports now the AJP version 1.3 - this is the default
version used by Jakarta and mod_jk. In netcgi1, only version 1.2 of
the AJP protocol was supported. The new protocol version is no big
improvement, however. It uses a slightly more compact representation
of the data. The biggest plus is better support of SSL.
In netcgi1 there was some special machinery around the AJP connector
to create worker processes. This code has been completely removed
in favor of netplex, the new general-purpose server framework.
Because of that, porting AJP applications is probably a bit of work,
and we cannot give a receipt here how to do that.
Strategy: Use
Netcgi1_compat
If you want to use the new connectors but currently do not have time
to check all your code for changes, there is a special helper module
called Netcgi1_compat that provides a netcgi1-compatible API
on top of either netcgi1 or netcgi2.
Because Netcgi1_compat is available in both netcgi1 and netcgi2
you can write code that can be compiled for both versions without
needing to change anything. Note, however, that this module is not
100% identical in both versions - the netcgi2 version includes some
additional functions that converts values from their netcgi1
representation to their netcgi2 representation and vice versa.
Unfortunately, this makes the two versions of this module
binary-incompatible, so you have to recompile your code for either
netcgi1 or netcgi2.
The Netcgi1_compat module simply contains the relevant parts of
the netcgi1 API as submodules. That means you can access
netcgi1 version of the module Netcgi_types as
Netcgi1_compat.Netcgi_typesnetcgi1 version of the module Netcgi_env as
Netcgi1_compat.Netcgi_envnetcgi1 version of the module Netcgi as Netcgi1_compat.Netcginetcgi1 are not covered by the compatibility API.
In Netcgi, the custom_activation class has been left out.
You can usually port code to using this API by either
Netcgi1., e.g.
new Netcgi.std_activation() would be turned into
new Netcgi1_compat.Netcgi.std_activation()Netcgi1 at the beginning of each .ml and .mli
file by an open Netcgi1_compat.Netcgi.std_activation, the netcgi1 way of creating a
connector for classic CGI, there are no connectors in the
compatibility API. If you need one, you must take it directly
from either netcgi1 or netcgi2. For example, to connect using
FastCGI:
(* This is code for both [netcgi1] and [netcgi2]! *)
let process (cgi : Netcgi1_compat.Netcgi.cgi_activation) =
...
(* This is [netcgi2] code! *)
let process_netcgi2 cgi2 =
let cgi1 = Netcgi1_compat.Netcgi_types.to_compat_activation cgi2 in
process cgi1
Netcgi_fcgi.run ~output_type process'
