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OOCSI library for ESP (Arduino IDE)
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matsfunk - ONE library again for ESP32 and ESP8266
 - migrated to ArduinoJson (new dependency)
 - added long and string array support
 - fixed connection logic
 - less dynamic memory consumption
 - library size is now 60% only
Latest commit 67d95b4 Jun 1, 2019


The OOCSI mission is to create a simple systems-interaction fabric for use by designers.

There are two basic components that form an OOCSI network: the client and the server. While the server can be started from the command line (see here), the client interface need to be embedded in other code and allows this code to access the OOCSI network, to send and receive data in a simple way.

THe OOCSI for ESP library is made for the Arduino IDE and it allows to directly use most of the OOCSI functionality in small-scale systems. We tested this library with the ESP32 and ESP8266.


Module Arduino board name ESP variant v1.2.1 v1.3.1
Sparkfun ESP32 Thing ESP32 DEV Module 32 OK OK
Sparkfun ESP32 Thing Sparkfun ESP32 Thing 32 OK OK
Sparkfun ESP8266 Thing Sparkfun ESP8266 Thing 8266 OK UR
WeMos D1 mini LOLIN(WEMOS) D1 R2 & mini 8266 OK UR
WeMos D1 v3.0.0 LOLIN(WEMOS) D1 R2 & mini 8266 OK UR
WeMos D1 v3.0.0 LOLIN(WEMOS) D1 mini Lite 8266 OK UR
NodeMCU (AI-Thinker) NodeMCU 1.0 8266 OK OK
NodeMCU (AI-Thinker) NodeMCU 0.9 8266 - -
Adafruit Feather HUZZAH Adafruit Feather HUZZAH ESP8266 8266 UR -

OK = sending / receiving all fine; UR = unstable run, might crash

Check the table above for compatilibity with different ESPs. Version v1.2.1 is more basic and can only deal with first level event data. v1.3.1 can parse JSON properly, but needs more memory, making it less stable on some low-memory modules. Both versions are available from If you are not sure which module to get, go for the ESP32!

How to install

To install the library, download the library archive from the latest release and unpack into the libraries folder of your Arduino IDE (usually here: Documents/Arduino/libraries/). After this, restart the Arduino IDE and check whether a new examples category "OOCSI" is shown. If yes, all fine, start coding. If not, check again that the library is in the right folder. Make sure that you have downloaded the library archive and not the source archive of the release.

How to use

To use OOCSI for ESP, please check out the example code that is packaged with the library. Below, the different functions of the library will be explained divided into the following parts: connecting to a network, sending data to the network and receiving data from the network. We will use similar code as in the library examples.


To connect to an OOCSI network, that is, a running OOCSI server, you first need to create an OOCSI reference:

OOCSI oocsi = OOCSI();

This will not yet connect to the network. To connect, you have to use the connect function which takes five parameters: the unique handle of the client in the OOCSI network (this is important to identify itself and receive direct messages), the address of the OOCSI server, the name and password of the Wifi network to use and a reference to a function that will be called to process incoming messages.

oocsi.connect(OOCSIName, hostserver, ssid, password, processOOCSI);
void processOOCSI() {
	// event data processing here...

When running this code, the library will start by connecting to the Wifi ssid and, if that is successful, then to the OOCSI server at hostserver. The progress will be logged on the Serial console. To better understand how to process incoming messages, refer to the Receiving data section below.

Sending data

Sending data to one or more recipients in the OOCSI network works in three steps: creating a new message, adding data to the message, and sending the message out.

Creating a new message

A new message is always created for a channel (broadcast) or the handle of another client (direct message). In the example below, the new message is created to be sent to the channel "testchannel", that is, to all clients subscribing to that channel (see below how to do that).


After this command, data can be added to the message. Please note that the ESP library can currently only work with one outgoing message at a time, which should be fine for more use-cases.

Adding data to a message

A message is empty at first. While it is certainly possible to send an empty message (for instance, as a "heartbeat" or "ping" signal), adding data makes it more useful. A message in OOCSI consists of several pairs of each a key and a value. The key identifies and labels the data. With the key the recipient of the message can easily retrieve it. The value that is given with the key, can be of many types. In this library, only a few basic types are implemented, which should cover 95% of all cases: int, long, float, and string.

oocsi.addInt("int", 40)
oocsi.addLong("long", 5000000);
oocsi.addFloat("float", 50.6);
oocsi.addString("text", "value as string");

It is also possible to chain the commands to add data:

oocsi.addInt("int", 40).addLong("long", (long) 51250220);

Sending the message

After the message is complete, we can send it out:


Again, it is possible to chain all commands for sending a message:

oocsi.newMessage("testchannel").addInt("number", 6).sendMessage();

To see what was actually sent out, you can use the printMessage command:


Receiving data

Receiving data from OOCSI works with a processing function that is called whenever new data has arrived. This function is referenced in the beginning when connecting to the network.

void processOOCSI() {
	// event data processing here...

Subscribing to a channel

If we just want to receive direct messages, we do not need to subscribe to a channel. Nevertheless, it is good practice to send data via a channel, so others can subscribe and make use of my data. Subscribing to ta channel is straight-forward:


We can subscribe to as many channels as we want; if data is sent to these channels, we receive it. See below for receiving messages from mutliple channels.

Getting data out

There are similar functions to adding data, for getting out. Commonly, the data type is identified by the command, the first parameter provides the key and the last parameter provides a default value that is used in case the key could not be found in the message. In the examples below we use -200 as the default value (anything is possible actually).

int ivalue = oocsi.getInt("integer", -200);
float fvalue = oocsi.getFloat("float", -200.0);
long lvalue = (long) oocsi.getInt("long", -200);
string svalue = oocsi.getString("string", "-200");

There is an exception for the long data type, where we use getInt and cast to long.

Getting message meta-data

A message always contains meta-data, the sender handle, the recipient which is either a channel or the unique handle of the receiving client and a timestamp.

string sender = oocsi.getSender();
string recipient = oocsi.getRecipient();
long timestamp = oocsi.getTimeStamp();

Before using a key, we can also check whether the message contains data with the given key:

if(oocsi.has("integer")) {
	// get data out

Receiving data from multiple channels and directly

Sometimes we would like to subscribe to multiple channels at the same time. All messages will arrive via the processing function that we have registered before. We can use the message recipient to distinguish between message coming from different channels (or directly).

void processOOCSI() {
	// event data processing here...
	if (oocsi.getRecipient() == "channel1") {
		// extract data for this message from channel "channel1"
	} else if (oocsi.getRecipient() == "channel2") {
		// extract data for this message from channel "channel2"

If we have registered the client with a specific handle when connecting to OOCSI, we can also compare with this handle to filter messages that were sent directly to this client only.

if (oocsi.getRecipient() == "myhandle") {
	// extract data for this direct message

Other functions

There are more functions in the OOCSI for ESP library. There will be explained here briefly.


The library will log its output to Serial. If this is too noisy, we can switch OOCSI for ESP to silently mode:


To switch logging on again, use:


Activity LED

The library can use an LED to signal activity. Use this by switching the respective pin to OUTPUT and tell the library about which pin to use:

pinMode(5, OUTPUT);

More --> Tbd.


Initial development: Jort Band Stable version and maintenance: Mathias Funk Testing and support: Henk Apeldoorn, Geert van den Boomen, Dirk van de Mortel

Find the OOCSI mothership project at

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