## OSC Messages

Many people have been using message passing not only to control Max/PD objects, but also to interact with processes living outside MAX/PD such as CSound, SuperCollider, etc.

To make their life easier, Antescofo comes with a builtin OSC server. The OSC protocol can be used to interact with external processes using UDP messages. It can also be used to make two Antescofo objects interact within the same patch. The management of OSC messages is achieved in Antescofo through 4 primitives.

### OSCSEND

This keyword introduces the declaration of a named OSC output channel of communication. The declaration takes the form:

              oscsend name host : port msg_prefix

where:

- `name` is a simple identifier and refers to the output channel (used later to send messages).

- `host` is the optional IP address (in the form `nn.nn.nn.nn` where `nn` is an integer) or the symbolic name of the host (in the form of a simple identifier or a string, like localhost or "test.ircam.fr"). If this argument is not provided, the localhost (that is, IP 127.0.0.1) is assumed.

- `port` is the mandatory number of the port where the message is routed (e.g. between 49152 and 65535, see List of TCP and UDP port numbers).

- `msg_prefix` is the OSC address in the form of a string that will prefix the OSC message send to this channel.

As soon as the OSC channel is declared, it is started and can be used to send messages. Note that sending a message before the definition of the corresponding output channel is interpreted as sending a message to MAX.

Sending an OSC message takes a form similar to sending a message to MAX or PD:

              name arg₁ arg₂ ...

This action construct and send the osc message

              msg_prefix arg₁ arg₂ ...

where `msg_prefix` is the OSC address declared for `name`. Note that to handle different message prefixes, different output channels have to be declared.

The character `/` is accepted in an identifier, so the usual hierarchical name used in OSC message prefixes can be used to identify the output channels. For instance, the declarations:

              oscsend extprocess/start test.ircam.fr : 3245 "start"
              oscsend extprocess/stop  test.ircam.fr : 3245 "stop"

can be used to later invoke

              0.0 extprocess/start "filter1"
              1.5 extprocess/stop "filter1"

### OSCRECEIVE

This keyword introduces the declaration of an input channel of communication. The declaration takes the form:

              oscrecv name port msg_prefix $v₁ $v₂ ...

where:

- `name` is the identifier of the input channel, and its used later to stop or restart the listening of the channel.

- `port` is the mandatory port number where the is received.

- On the previous port, the channel accepts messages with OSC address `msg_prefix`. Note that for a given input channel, the message prefixes have to be all different.

- When an OSC message is received, the argument are automatically assigned to the variables `$v₁`, `$v₂`... If there is less variables than arguments, the remaining arguments are simply thrown away (and an error message is emitted). Otherwise, if there is less arguments than variables, the remaining variables are untouched (and an error message is emitted).

Currently, Antescofo accepts only the following OSC types: bool, int32, int64, float, double, string and the arrays markers bracketing sequence of these values (nested arrays are allowed). These value are converted respectively into boolean, integer, float, string and bracketed sequence are converted into tab.

A Whenever can be used to react to the reception of an OSC message: it is enough to put one of the variables `$vᵢ` as the condition of the whenever.

The reception is active as soon as the input channel is declared.

### OSCON and OSCOFF

These two commands take the name of an input channel. Switching off an input channel stops the listening and the message that arrives after, are ignored. Switching on restarts the listening. These commands have no effect on an output channel.

### Conversion between OSC types and Antescofo types

Sending (or receiving) an OSC message implies the conversion of an Antescofo value into an OSC value (or the reverse). The conversion is applied following the following mapping

Antescofo value | OSC value
--- | ---
bool | bool
int | int32
int | int64
Float | float
Float | double
string | string
string | symbol
tab | see function @set_osc_handling_tab

Antescofo value types that are not present in the table are not handled (e.g. proc or nim). The handling of tab can be changed using the @set_osc_handling_tab functions. By default, Antescofo sends the elements of a tab as the successive arguments of a message, without using the OSC array facilities. A call to `@set_osc_handling_tab(true)` switches the behavior to rely on the array feature present in OSC v1.1. A call to `@set_osc_handling_tab(false)` switches to the default behavior (tab flattening).

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