A few words about this and that...
Organization of Ocamlnet
Ocamlnet has grown a lot, and it may look a bit confusing to beginners. Fortunately, Ocamlnet follows a few organizational principles:
String routines are often factored out
String routines like URL parsing, buffer handling, message decoding etc. are often not directly included in the protocol interpreter, but defined in separate modules. Actually, there is a whole library, Netstring, only consisting of string functions.
The advantage is obvious: String functions can be reused, for example from within clients and servers, but also from user code wishing to do certain string manipulations directly.
Common types ease plugging parts together
It is encouraged that one can plug together various parts of Ocamlnet to create new functionality. Ocamlnet tries to use the same types for the same kind of values throughout the whole library to make this easier. Examples:
Netmime defines mail messages, but as this data format is also
used in HTTP, Http_client represents requests and responses
with the same classesNetchannels defines object-oriented I/O channels. These are
used almost everywhere in Ocamlnet.All Ocamlnet modules use this infrastructure:
Netlog is a simple logging module and redirectorNetexn provides extended support for exception printingNetsys_signal is a little framework for coordinating signal handlersPreference of asynchronous protocol interpreters
A number of protocol interpreters are written in asynchronous style.
This is generally preferred because of better timeout and error
handling, but also because it makes it possible to run several
instances of these protocol interpreters in the same thread
concurrently (i.e. it is a kind of micro-threading). Ocamlnet
includes the Equeue library as support library for asynchronous
network programming (see Equeue_intro for more information).
Nevertheless, nobody is forced to use these protocol interpreters asynchronously. There is always also a simple way for synchronous calls (i.e. where the execution of the caller blocks until the network function is completely done).
Parallelization is done at a single place
In other network environments, often every protocol interpreter defines functions for parallelizing its use, e.g. by using thread pools. In Ocamlnet we avoid that. For parallelization there is only the Netplex library which supports both multi-threading and multi-processing.
It is easy to use Netplex with the available server implementations:
Nethttpd_plex allows it to run a webserver inside NetplexRpc_netplex can run SunRPC servers inside NetplexNetcgi_plex can run FCGI, SCGI, and AJP connectors inside Netplexnetplex-admin.
Second, one does not need to develop the parallelization code anew for each protocol implementation. It is difficult enough.
Third, this approach makes it first possible to provide a serious implementation of multi-processing. For this kind of parallelism, more coordination between the interacting components is required than for multi-threading. For example, when child processes are forked off, it must be clear which protocol interpreter are run within them.
At Mylife, we have developed a server program that integrates dozens of different protocols under the same roof. The Netplex approach is scalable!
Pick what you like, and omit things you don't understand
Ocamlnet is modular enough that one can cherry-pick the parts one needs. After all, it is only a library, i.e. a collection of Ocaml modules, and by using one module there is no strict requirement to use another module.
Of course, there is also a "use hierarchy" in Ocamlnet - the HTTP code uses Equeue, for instance. However, the user of HTTP needs not to know this or care about it. Equeue is then simply an internally used helper library.
Future Directions
Ocamlnet is already focused on Internet protocols. Current activities especially try to
There a number of libraries using and extending Ocamlnet:
