net-socket-messaging

npm install net-socket-messaging

Implementation of a simple messaging protocol by monkey-patching a net.Socket. The protocol is the simplest I could think of:

• The head consists of 4 bytes which encodes an unsigned 32 int written in little endian.
• The body is a string of bytes which encodes a string in utf8 and whose byte length is defined by the head.

Example

const socket = require("net").connect();
// `registerSocket` monkey-patches a net.Socket
// with the `send` method and the `message` event.
require("net-socket-messaging").monkeyPatch(socket);
// Once monkey-patched, the socket should not be
// directly used to read or write data.
const message = "foo";
socket.send(message);
// The `message` event is emitted only if there is a
// least one listener registered.
socket.on("message", (message) => {
  console.log("Received:", message);
});

API

NetSocketMessaging.patch(socket)

• socket <net.Socket>: the socket to monkey-patch.
• Returns <undefined>: I'm not a big fan of artificial chain callings, you should assume your side effects!

NetSocketMessaging.getMaxByteLength()

• Returns <integer>: the maximum length of messages.

socket.send(message)

Send a message through the net.Socket.

• message <string>: the message to send. Sending a string longer than 256 * 2^20 characters will fire an 'error' event on the socket. There is two motivations for this limit:
  1. It ensures that the body is under 1GiB (as a single utf16 character may be encoded in as much as 4 bytes). There is two reasons why we want to limit the length of the body. First, the maximum number encoded by the head is 2^32. Second, the stream.readable.read(size) does not accept a size argument greater than 2^30.
  2. JS engines impose a limit to the length of strings. Although the ECMAScript 2016 specification states that the maximum length of a string is 2^53 - 1, many engines opted for a smaller limit. A length of 256 * 2^20 is a conservative limit which most JS engines support.
• Returns <null> | <boolean>: null if the message is too big to be sent and a <boolean> as per the return value of new.Socket.write(buffer).

Event 'message'

Emitted when a message has been fully received.

• message <string>: the received message. Neither the length of the body nor the length of the message is checked. If the engine supports it, a message as long as 2^32 characters could be provided.