Small-OSC

Small-OSC is a minimal Open Sound Control (OSC) library written in C. The typical use case is to parse a raw buffer received directly from a socket. Given the limited nature of the library it also tends to be quite fast. It doesn't hold on to much state and it doesn't do much error checking. If you have a good idea of what OSC packets you will receive and need to process them quickly, this library might be for you.

TinyOSC

Small-OSC was forked from tinyosc on 18.06.2026.

The goals:

• implement the fixes distributed over all the various forks and put them into one repository
• use it in OpenMixerControl

MicroOSC

There is also MicroOsc: https://github.com/thomasfredericks/MicroOsc

Supported Features

Due to its tiny or small nature, Small-OSC does not support all standard OSC features. Currently it supports:

• message parsing
• message writing
• bundle parsing
• bundle writing
• timetag
• matching
• Types
  • b: binary blob
  • f: float
  • d: double
  • i: int32
  • h: int64
  • s: string
  • m: midi
  • t: timetag
  • T: true
  • F: false
  • I: infinitum
  • N: nil

Code Example

Reading Messages

#include"small-osc.h"tosc_messageosc; // declare the Small-OSC structurecharbuffer[1024]; // declare a buffer into which to read the socket contentsintlen=0; // the number of bytes read from the socketwhile ((len=READ_BYTES_FROM_SOCKET(buffer)) >0) {
// parse the buffer contents (the raw OSC bytes)// a return value of 0 indicates no errorif (!tosc_readMessage(&osc, buffer, len)) {
printf("Received OSC message: [%i bytes] %s %s ",
len, // the number of bytes in the OSC messagetosc_getAddress(&osc), // the OSC address string, e.g. "/button1"tosc_getFormat(&osc)); // the OSC format string, e.g. "f"for (inti=0; osc.format[i] !='\0'; i++) {
switch (osc.format[i]) {
case'f': printf("%g ", tosc_getNextFloat(&osc)); break;
case'i': printf("%i ", tosc_getNextInt32(&osc)); break;
// returns NULL if the buffer length is exceededcase's': printf("%s ", tosc_getNextString(&osc)); break;
default: continue;
}
}
printf("\n");
}
}

Writing Messages

// declare a buffer for writing the OSC packet intocharbuffer[1024];
// write the OSC packet to the buffer// returns the number of bytes written to the buffer, negative on error// note that tosc_write will clear the entire buffer before writing to itintlen=tosc_writeMessage(
buffer, sizeof(buffer),
"/ping", // the address"fsi", // the format; 'f':32-bit float, 's':ascii string, 'i':32-bit integer1.0f, "hello", 2);
// send the data out of the socketsend(socket_fd, buffer, len, 0);

Reading Bundles

Here is an example of the kind of message processing loop that you might have around a socket. The buffer should first be inspected to see if it contains a bundle or not, at which point messages are parsed independently along with an optional timetag.

voidreceive(char*buffer, intlen) {
// see if the buffer contains a bundle or an individual messageif (tosc_isBundle(buffer)) {
tosc_bundlebundle;
tosc_parseBundle(&bundle, buffer, len);
constuint64_ttimetag=tosc_getTimetag(&bundle);
tosc_messageosc;
while (tosc_getNextMessage(&bundle, &osc)) {
tosc_printMessage(&osc);
}
} else {
tosc_printOscBuffer(buffer, len);
}
}

Writing Bundles

charbuffer[1024];
tosc_bundlebundle;
tosc_writeBundle(&bundle, buffer, sizeof(buffer));
tosc_writeNextMessage(&bundle, "/ping", "fsi", 1.0f, "hello", 3);
tosc_writeNextMessage(&bundle, "/pong", "TTF");
// etc.send(buffer, tosc_getBundleLength(&bundle));

main.c

A small example program is included in main.c. Build it using the included shell script build.sh, and run it with small-osc. The program simply opens a UDP socket on port 9000 and prints out received OSC messages. Press Ctrl+C to stop. Try it with any OSC client, such as TouchOSC. This program is also an example for how Small-OSC is expected to be used.

Sample Output

Starting write tests:
[56 bytes] /address fsibTFNI 1 hello world -1 [8]001080F0011181F1 true false nil inf
done.
small-osc is now listening on port 9000.
Press Ctrl+C to stop.

License

Small-OSC is published under the ISC license. Please see the LICENSE file included in this repository.