ZeroMQ

ZeroMQ enables ffgac, ffedit, and fflive to do many kinds of network communication and messaging. It’s possible to use tcp connections to communicate across the network, and it’s also possible to use inter-process communication to allow separate scripts to communicate with each other easily and quickly.

The "zmq" module is built-in to the quickjs engine. It is a simple wrapper around ZeroMQ functionality. It can be imported with:

import * as zmq from "zmq";

The "zmq" module provides the Context() constructor to create Context objects, and the Poller() constructor to create Poller objects. The Context object provides the socket() method to create Socket objects.

This page is mostly based on the ZMQ API reference itself.

---

zmq.version()

This function is used to obtain the version of the underlying ZeroMQ library.

Syntax

zmq.version()

Return value

An Array with the [ major, minor, patch ] version of ZeroMQ.

Examples

import * as zmq from "zmq";
const version = zmq.version();
console.log(version);
// 4,3,6

---

zmq.has()

This function is used to detect whether a certain capability (transport or security option) is available in the underlying ZeroMQ library. The following capabilities are defined:

• "ipc" - the library supports the ipc:// protocol
• "pgm" - the library supports the pgm:// protocol
• "tipc" - the library supports the tipc:// protocol
• "norm" - the library supports the norm:// protocol
• "vmci" - the library supports the vmci:// protocol
• "curve" - the library supports the CURVE security mechanism
• "gssapi" - the library supports the GSSAPI security mechanism
• "draft" - the library is built with the draft api

Syntax

zmq.has(capability)

Parameters

capability is the capability to be probed.

Return value

1 if the capability is provided, 0 otherwise.

Examples

import * as zmq from "zmq";
const has_ipc  = zmq.has("ipc");
const has_vmci = zmq.has("vmci");
console.log(`has_ipc:  ${has_ipc}`);
// has_ipc:  1
console.log(`has_vmci: ${has_vmci}`);
// has_vmci: 0

---

Context Constructor

The new zmq.Context() constructor is used to create a new Context object.

The Context is the main object for using ZeroMQ.

This is a wrapper around zmq_ctx_new().

Syntax

new zmq.Context()

Return value

The new Context object.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();

---

zmq.Context.prototype.socket()

The socket() function is used to create a new Socket object within the given Context object.

This is a wrapper around zmq_socket().

Syntax

socket(type)

Parameters

The type argument specifies the socket type, which determines the semantics of communication over the socket.

The available socket types are:

• zmq.PAIR
• zmq.PUB
• zmq.SUB
• zmq.REQ
• zmq.REP
• zmq.DEALER
• zmq.ROUTER
• zmq.PULL
• zmq.PUSH
• zmq.XPUB
• zmq.XSUB
• zmq.STREAM

Return value

The new Socket object. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
const socket = ctx.socket(zmq.PUSH);

---

zmq.Context.prototype.set()

The set() function shall set the option specified by the option_name argument to the value of the option_value argument.

This is a wrapper around zmq_ctx_set().

Syntax

set(option_name, option_value)

Parameters

Please refer to the zmq_ctx_set() documentation for the available values for option_name and option_value.

The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_BLOCKY becomes zmq.BLOCKY.

Return value

0 on success. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
ctx.set(zmq.BLOCKY, 0);

---

zmq.Context.prototype.get()

The get() function shall return the option specified by the option_name argument.

This is a wrapper around zmq_ctx_get().

Syntax

get(option_name)

Parameters

Please refer to the zmq_ctx_get() documentation for the available values for option_name.

The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_MAX_MSGSZ becomes zmq.MAX_MSGSZ.

Return value

A number on success. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
const max_msg_size = ctx.get(zmq.MAX_MSGSZ);

---

zmq.Context.prototype.shutdown()

The shutdown() function shall shutdown the Context.

This is a wrapper around zmq_ctx_shutdown().

Syntax

shutdown()

Return value

0 on success. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
ctx.shutdown();

---

zmq.Context.prototype.term()

The term() function shall destroy the Context.

This is a wrapper around zmq_ctx_term().

Note: it is not necessary to call this function. The garbage collection takes care of destroying the Contexts. There is no harm in calling it though.

Syntax

term()

Return value

0 on success. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
ctx.term();

---

Poller Constructor

The new zmq.Poller() constructor is used to create a new Poller object.

This is a wrapper around zmq_poller_new().

Syntax

new zmq.Poller()

Return value

The new Poller object.

Examples

import * as zmq from "zmq";
const poller = new zmq.Poller();

---

zmq.Poller.prototype.size()

This is a wrapper around zmq_poller_size().

Syntax

size()

Return value

A number with the amount of sockets or file descriptors registered with a poller.

Examples

const size = poller.size();

---

zmq.Poller.prototype.add()

This is a wrapper around zmq_poller_add().

Syntax

add(socket, events, user_data)

Parameters

socket is the Socket object (created with Context.prototype.socket()) to be polled.

events is a combination of the following values:

• zmq.POLLIN
• zmq.POLLOUT
• zmq.POLLERR
• zmq.POLLPRI

user_data is an optional parameter that will be passed back for all events that are processed.

Return value

0 on success. Throws an exception on error.

Examples

poller.add(socket, zmq.POLLIN);

---

zmq.Poller.prototype.modify()

This is a wrapper around zmq_poller_modify().

Syntax

modify(socket, events)

Parameters

socket is the Socket object (which must have already been add()ed to the poller).

events is a combination of the following values:

• zmq.POLLIN
• zmq.POLLOUT
• zmq.POLLERR
• zmq.POLLPRI

Return value

0 on success. Throws an exception on error.

Examples

poller.modify(socket, zmq.POLLOUT);

---

zmq.Poller.prototype.remove()

This is a wrapper around zmq_poller_remove().

Syntax

remove(socket)

Parameters

socket is the Socket object (which must have already been add()ed to the poller).

Return value

0 on success. Throws an exception on error.

Examples

poller.remove(socket);

---

zmq.PollerEvent

A PollerEvent object is returned for every event that is polled.

The object contains 3 key-value pairs:

• "socket": the Socket object that originated the event;
• "user_data": the user_data parameter passed to the zmq.Poller.prototype.add() function;
• "events": a combination of the following values:
  • zmq.POLLIN
  • zmq.POLLOUT
  • zmq.POLLERR
  • zmq.POLLPRI

---

zmq.Poller.prototype.wait()

This is a wrapper around zmq_poller_wait().

Syntax

wait(timeout)

Parameters

timeout is the maximum time (in milliseconds) the function shall wait. A timeout of -1 is an infinite timeout.

Return value

A PollerEvent object if any event hapenned within the specified timeout, null otherwise. Throws an exception on error.

Examples

// wait up to 1000 milliseconds
const event = poller.wait(1000);

---

zmq.Poller.prototype.poll()

This is a wrapper around zmq_poller_wait() with the timeout parameter set to 0.

Syntax

poll()

Return value

A PollerEvent object if any event is immediately available, null otherwise. Throws an exception on error.

Examples

// immediate return
const event = poller.poll();

---

zmq.Poller.prototype.wait_all()

This is a wrapper around zmq_poller_wait_all().

Syntax

wait_all(n_events, timeout)

Parameters

n_events is the maximum number of events the function shall return.

timeout is the maximum time (in milliseconds) the function shall wait. A timeout of -1 is an infinite timeout.

Return value

An Array of PollerEvent objects with all events that hapenned within the specified timeout, null otherwise. Throws an exception on error.

Examples

// wait up to 1000 milliseconds for up to 4 events
const events = poller.wait_all(4, 1000);

---

zmq.Poller.prototype.poll_all()

This is a wrapper around zmq_poller_wait_all() with the timeout parameter set to 0.

Syntax

poll_all(n_events)

Parameters

n_events is the maximum number of events the function shall return.

Return value

An Array of PollerEvent objects with all events that are immediately available, null otherwise. Throws an exception on error.

Examples

// immediate return, up to 4 events
const events = poller.poll_all(4);

---

zmq.Socket.prototype.bind()

This is a wrapper around zmq_bind().

Syntax

bind(endpoint)

Parameters

The endpoint is a string consisting of a transport:// followed by an address. The transport specifies the underlying protocol to use. The address specifies the transport-specific address to bind to.

Return value

0 on success. Throws an exception on error.

Examples

socket.bind("tcp://*:5555");

---

zmq.Socket.prototype.unbind()

This is a wrapper around zmq_unbind().

Syntax

unbind(endpoint)

Parameters

The endpoint is a string consisting of a transport:// followed by an address. The transport specifies the underlying protocol to use. The address specifies the transport-specific address to unbind from.

Return value

0 on success. Throws an exception on error.

Examples

socket.unbind("tcp://*:5555");

---

zmq.Socket.prototype.connect()

This is a wrapper around zmq_connect().

Syntax

connect(endpoint)

Parameters

The endpoint is a string consisting of a transport:// followed by an address. The transport specifies the underlying protocol to use. The address specifies the transport-specific address to connect to.

Return value

0 on success. Throws an exception on error.

Examples

socket.connect("tcp://localhost:5555");

---

zmq.Socket.prototype.disconnect()

This is a wrapper around zmq_disconnect().

Syntax

disconnect(endpoint)

Parameters

The endpoint is a string consisting of a transport:// followed by an address. The transport specifies the underlying protocol to use. The address specifies the transport-specific address to disconnect from.

Return value

0 on success. Throws an exception on error.

Examples

socket.disconnect("tcp://localhost:5555");

---

zmq.Socket.prototype.send()

This is a wrapper around zmq_send().

Syntax

send(data, flags)

Parameters

The data parameter can be either of the following:

• null: an empty message is sent
• number or boolean: a 32-bit integer is sent
• BigInt: a 64-bit integer is sent
• string: a string is sent (it may contain \0 characters)
• Uint8FFArray: a uint8_t buffer is sent

The flags parameter is optional. It is 0 by default if not specified. The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_DONTWAIT becomes zmq.DONTWAIT.

Return value

A number with the amount of bytes in the message if successful, undefined if non-blocking mode was requested and the message could not be sent at the moment. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
const socket = ctx.socket(zmq.REQ);
socket.connect("tcp://localhost:5555");
socket.send(null);
socket.send(10);
socket.send(true);
socket.send("apfelstrudel");
const data = new Uint8FFArray(10);
data.forEach((_, i) => { data[i] = i; });
socket.send(data, zmq.DONTWAIT);

---

zmq.Socket.prototype.recv()

This is a wrapper around zmq_recv().

It returns binary data in an Uint8FFArray. Note: more specialized functions (for types such as 32-bit and 64-bit integers or strings) are available and will be described below.

Syntax

recv(flags)

Parameters

The flags parameter is optional. It is 0 by default if not specified. The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_DONTWAIT becomes zmq.DONTWAIT.

Return value

An Uint8FFArray with the message if successful, undefined if non-blocking mode was requested and the message could not be received at the moment. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
const socket = ctx.socket(zmq.REP);
socket.bind("tcp://*:5555");
// assuming there is already data received
const data = socket.recv(zmq.DONTWAIT);
// blocking wait for data
data = socket.recv();
socket.send(null);

---

zmq.Socket.prototype.recv_int()

The recv_int() function is similar to recv() above, but it only receives 32-bit integers.

Return value

A 32-bit number with the message if successful, undefined if non-blocking mode was requested and the message could not be received at the moment. Throws an exception on error or if the received message was not a 32-bit integer.

---

zmq.Socket.prototype.recv_bigint()

The recv_bigint() function is similar to recv() above, but it only receives 64-bit integers.

Return value

A 64-bit BigInt number with the message if successful, undefined if non-blocking mode was requested and the message could not be received at the moment. Throws an exception on error or if the received message was not a 64-bit integer.

---

zmq.Socket.prototype.recv_str()

The recv_str() function is similar to recv() above, but it only receives strings.

Return value

A String with the message if successful, undefined if non-blocking mode was requested and the message could not be received at the moment. Throws an exception on error.

---

zmq.Socket.prototype.recv_uint8ffarray()

The recv_uint8ffarray() function the same as recv() above, but the name is more explicit.

Return value

An Uint8FFArray with the message if successful, undefined if non-blocking mode was requested and the message could not be received at the moment. Throws an exception on error.

---

zmq.Socket.prototype.close()

The close() function shall destroy the Socket.

This is a wrapper around zmq_close().

Note: it is not necessary to call this function. The garbage collection takes care of destroying the Sockets. There is no harm in calling it though.

Syntax

close()

Return value

0 on success. Throws an exception on error.

Examples

import * as zmq from "zmq";
const ctx = new zmq.Context();
const socket = ctx.socket(zmq.REP);
socket.close();

---

zmq.Socket.prototype.getsockopt()

The getsockopt() function shall retrieve the value for the option specified by the option_name argument.

This is a wrapper around zmq_getsockopt().

Note: more specialized functions (for types such as 32-bit and 64-bit integers or strings) are available and will be described below.

Note2: if no specialized function is used, this function will try to treat the options as these types in the following order: string, int, bigint.

Syntax

getsockopt(option_name)

Parameters

Please refer to the zmq_getsockopt() documentation for the available values for option_name.

The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_MAXMSGSIZE becomes zmq.MAXMSGSIZE.

Return value

Either a string, an int, a BigInt, or undefined. Throws an exception on error.

---

zmq.Socket.prototype.getsockopt_int()

The getsockopt_int() function is similar to getsockopt() above, but it only works if the option is a 32-bit integer.

Return value

A 32-bit number with the option value if successful, undefined otherwise. Throws an exception on error or if the option was not a 32-bit integer.

---

zmq.Socket.prototype.getsockopt_bigint()

The getsockopt_bigint() function is similar to getsockopt() above, but it only works if the option is a 64-bit integer.

Return value

A 64-bit BigInt with the option value if successful, undefined otherwise. Throws an exception on error or if the option was not a 64-bit integer.

---

zmq.Socket.prototype.getsockopt_str()

The getsockopt_str() function is similar to getsockopt() above, but it only works if the option is a string.

Return value

A string with the option value if successful, undefined otherwise. Throws an exception on error or if the option was not a string.

---

zmq.Socket.prototype.getsockopt_uint8ffarray()

The getsockopt_uint8ffarray() function is similar to getsockopt() above, but it only works if the option is an Uint8FFArray.

Return value

An Uint8FFArray with the option value if successful, undefined otherwise. Throws an exception on error or if the option was not an Uint8FFArray.

---

zmq.Socket.prototype.setsockopt()

The setsockopt() function shall set the option specified by the option_name argument to the value pointed to by the option_value argument.

This is a wrapper around zmq_setsockopt().

Syntax

setsockopt(option_name, option_value)

Parameters

Please refer to the zmq_setsockopt() documentation for the available values for option_name.

The option names are defined in the zmq module, without the ZMQ_ prefix as in the documentation above. e.g.: ZMQ_SUBSCRIBE becomes zmq.SUBSCRIBE.

Return value

0 on success. Throws an exception on error.

---

Full Example

This example consists of three scripts:

• producer.js, which connects to the server in zmq.PUSH mode and sends data from the command line parameters
• subscriber.js, which connects to the server in zmq.SUB mode and waits for data
• server.js, which acts as a server that forwards data sent from producers to subscribers

server.js:

import * as zmq from "zmq";
function main()
{
  const ctx = new zmq.Context();
  const producer_socket = ctx.socket(zmq.PULL);
  producer_socket.bind("tcp://*:5555");
  const subscriber_socket = ctx.socket(zmq.PUB);
  subscriber_socket.bind("tcp://*:5556");
  const poller = new zmq.Poller();
  poller.add(producer_socket, zmq.POLLIN);
  while ( 42 )
  {
    const event = poller.wait(-1); // infinite wait
    if ( !event )
      continue;
    const socket = event.socket; // should be producer_socket
    const data = socket.recv_str();
    subscriber_socket.send(data);
    console.log(`Forwarded "${data}"`);
  }
  subscriber_socket.close();
  producer_socket.close();
  ctx.term();
}
try {
  main();
} catch (e) {
  console.log("Uncaught exception!");
  console.log(e);
  if ( e.stack )
    console.log(e.stack);
}

subscriber.js:

import * as zmq from "zmq";
function main()
{
  const ctx = new zmq.Context();
  const socket = ctx.socket(zmq.SUB);
  socket.connect("tcp://localhost:5556");
  socket.setsockopt(zmq.SUBSCRIBE, "");
  while ( true )
  {
    const data = socket.recv_str();
    console.log(`Received "${data}"`);
  }
  socket.close();
  ctx.term();
}
try {
  main();
} catch (e) {
  console.log("Uncaught exception!");
  console.log(e);
  if ( e.stack )
    console.log(e.stack);
}

producer.js:

import * as zmq from "zmq";
function main(argv)
{
  const ctx = new zmq.Context();
  const socket = ctx.socket(zmq.PUSH);
  socket.connect("tcp://localhost:5555");
  argv.forEach((data) => {
    socket.send(data);
    console.log(`Sent "${data}"`);
  });
  socket.close();
  ctx.term();
}
try {
  main(scriptArgs.slice(1));
} catch (e) {
  console.log("Uncaught exception!");
  console.log(e);
  if ( e.stack )
    console.log(e.stack);
}

In one terminal, leave the server running:

$ qjs server.js

On another terminal, leave the subscriber running:

$ qjs subscriber.js

On yet another terminal, send messages using the producer:

$ qjs producer.js hello world
Sent "hello"
Sent "world"

On the producer terminal, you should now see:

Sent "hello"
Sent "world"

On the subscriber terminal, you should now see:

Received "hello"
Received "world"

On the server terminal, you should now see:

Forwarded "hello"
Forwarded "world"