Interface description
=====================

All Modelverse components communicate with each other through the use of sockets.
On these sockets, XML/HTTP Requests are used for communication.
In this brief section, we describe the form of these requests.

MvS server
----------

The MvS server listens to a fixed set of commands.
All commands have a fully defined signature and result.
Note that commands are encoded: a decoding table is presented below.

==== ======================
Code Description
==== ======================
CN   create_node
CE   create_edge
CNV  create_nodevalue
CD   create_dict
RV   read_value
RO   read_outgoing
RI   read_incoming
RE   read_edge
RD   read_dict
RDN  read_dict_node
RDNE read_dict_node_edge
RDE  read_dict_edge
RRD  read_reverse_dict
RR   read_root
RDK  read_dict_keys
DE   delete_edge
DN   delete_node
==== ======================

Requests are sent as POST requests (*i.e.*, in the data of a HTTP request).
They have the following form::

    op=CODE&params=PARAMS

In this case, *CODE* is one of the codes mentioned above, and the value of *PARAMS* is a JSON encoded list of Modelverse identifiers.
The choice of what is a Modelverse identifier is left to the MvS itself.

The result will be a JSON serialized list containing as first element the response to the request, and as second element the statuscode.
If the statuscode is 200, the first element will be correct.
Otherwise, the statuscode indicates the error, and the first element is set to *null*.

MvK server
----------

The communication with the MvK is a lot easier, as there is only a very minimal interface: the actual interface needs to be explicitly modelled in action language.
Requests have the following form::

    op=OPERATION&username=USERNAME&value=VALUE

Here, *OPERATION* defines the operation to execute, of which only two exist:

1. *set_input*, which adds the sent value to the input queue of the user;
2. *get_output*, which blocks until there is a value in the output queue of the user.

Obviously, *USERNAME* specifies the name of the user for which the operation needs to happen.

The *VALUE* is just a JSON encoded value which will be added to the input queue of the Modelverse.
This is ignored when the *get_output* operation is used.
Note that there are some minor differences between our encoding and JSON encoding.

The supported types are shown below.

======= ===================
Type    Example
======= ===================
Integer 1
Float   1.0
Boolean true
String  "abc"
Action  if
======= ===================

While this list mostly resembles JSON, there are some important differences:

* Lists and objects are not supported;
* Null object is not supported;
* Action type is new, and contains a string representation (without quotes!) of the action language construct to add

Performance notes
^^^^^^^^^^^^^^^^^

For performance reasons, sending a huge amount of data to the Modelverse (*e.g.*, a compiled program), should not happen with individual requests for each line.
To allow for packed messages, users can ignore the *value* parameter, and use the *data* parameter instead.
The content of this parameter should be a JSON encoded list of all individual values to be inserted.