mTCPJSONRPC

Module with classes to make remote procedure calls using JSON over TCP.

Getting Started

1. Install mTCPJSONRPC via NPM.

npm install mtcpjsonrpc

Optionally: rename mtcpjsonrpc to mTCPJSONRPC: npm is unable to handle the complexity of uppercase characters in a module name. Node.js on Windows does not have this problem, so renaming the folder is not required for you to use the module.

1. Require mTCPJSONRPC in your project.

var mTCPJSONRPC = require("mTCPJSONRPC");

1. Instantiate a cServer to accept connections and request/perform remote procedure calls.

var dfProcedures = {
  "test": function(oConnection, xData, fCallback) {
    console.log("test argument: " + JSON.stringify(xData));
    fCallback(undefined, "test result");
  },
};
var oServer = new mTCPJSONRPC.cServer({"dfProcedures": dfProcedures});
oServer.on("connect", function (oConnection) {
  oConnection.fCall("test", "test argument", fHandleCallResult);
});
function fHandleCallResult(oError, xResult) {
  if (oError) {
    console.log("test failed:", oError);
  } else {
    console.log("test succeeded " + JSON.stringify(xResult));
  };
};

1. Instantiate a cConnection to a server and request/perform remote procedure calls.

var oConnection = new mTCPJSONRPC.fConnect({"dfProcedures": dfProcedures});
oConnection.fCall("test", "test argument", fHandleCallResult);

Notes

The code in the above two examples shows how both a client and a server can make RPC calls: both produce cConnection instances, that can handle remote procedure calls as well as be used to make them. Whether the client and server actually offer any procedures to be executed depends on the dfProcedures property of the dxOptions argument (see cConnection below for details).

The server and client can be on the same machine or on two different machines. By default cServer instances bind to IP address that is associated with the computer name and fConnect connects to that IP address. Use localhost or 127.0.01 as the hostname to allow only local connections in a server and connect to that server from the same machine.

Protocol

Information is exchanged using the JSON over TCP protocol as described in the mTCPJSON module. When a connection is established, the ''client'' will request a version using the following message:

{"initialize": "TCP JSON RPC version request", "version": "0.1"}

If the server receives this message and can handle the version, it should respond with the following message:

{"initialize": "TCP JSON RPC version accept", "version": "0.1"}

The server can then start making calls. If the server receives a ''version request'' message and can not handle the version, it should respond with the following message:

{"initialize": "TCP JSON RPC version reject", "version": "0.2"}

Where "0.2" is any other version the server would like the client to use.

The server can not make calls at this point, as the protocol version has not been established. The server instead waits for the client to close the connection or send another ''version request'' message with a different version number.

If the client receives a ''version accept'' message, it will emit the initialize event, after which you can start making remote procedure calls. If the client receives a ''version reject'' message, it will close the connection, and emit an error event.

Once a ''version accept'' message is received by the client, both parties can make a remote procedure call by sending a message in the following format:

{"call":"procedure name", "data": ..., "id": 0}

The call field specifies the name of the remote procedure to call and must be a string. The data field specifies the argument to be passed to the procedure and can by any value encoded as JSON. The id field is optional and must be a positive integer and should have been used in any ''call'' message before. The id field is only populated if the caller would like to have a result returned. When a remote procedure has been executed, the result can returned to the caller by sending a message in the following format:

{"result": {"error": {...}, "data": ..., "id": 0}

The error field specifies any error that may have occurred during execution of the procedure. if it is undefined the data field specifies any data that the procedure would like to return to the caller.

API

class cServer

Can be used to accept connections, through which you can send values as JSON.

Constructors:

[new] mTCPJSON.cServer(Object dxOptions);

Where dxOptions is an object that can have the following properties:

• Number uIPVersion: IP version to use (valid values: 4 (default), 6).
• String sHostname: Network device to bind to (default: computer name, use localhost if you want to accept connections only from scripts running on the same machine).
• Number uPort: port number to send to (default: 28876).
• Number uConnectionKeepAlive: Enable sending TCP keep-alive packets every uConnectionKeepAlive milliseconds.
• Object dfProcedures: associative array of procedures that the server will execute at the request of a connected client. See cConnection below for details.

Events:

error, parameter: Error oError

Emitted when there is a network error.

start

Emitted when the cServer instance is ready to receive connections.

connect, parameter: cConnection oConnection

Emitted when a connection to the server is established.

stop

Emitted when the cServer instance has stopped receiving connections. This can happen when there is a network error or after you tell the sender to stop.

Methods:

undefined fStop(bDisconnect)

Stop the cServer instance. If bDisconnect is false, the server stops accepting new connections and will wait for existing connections to close. If bDisconnect is true, the server will also disconnect all existing connections. The server will emit a stop event as soon as it no longer accepts new connections and there are no more open connections.

`undefined fConnect(Function fCallback, Object dxOptions)

Where dxOptions is an object that can have the following properties:

• Number uIPVersion: IP version to use (valid values: 4 (default), 6).
• String sHostname: Target computer (default: connect to local computer).
• Number uPort: port number to connect to (default: 28876).
• Number uConnectionKeepAlive: Enable sending TCP keep-alive packets every uConnectionKeepAlive milliseconds.
• Object dfProcedures: associative array of procedures that the server will execute at the request of a connected client. See cConnection below for details. fConnect attempts to establish a connection of a cServer instance using the provided dxOptions. fCallback(Error oError, cConnection oConnection) is called when a connection cannot be established (oError will contain details) or when a connection has been established (oError will be undefined).

class cConnection

Represent connections through which data can be transmitted as JSON messages. Instances of cConnection are emitted through the connect event of cServer instances, and passed to the callback of the fConnect function. You should not need to instantiate this class yourself unless you are doing some serious re-purposing of the code.

Events:

error, parameter: Error oError

Emitted when there is a network error.

initialize

Emitted when the cConnection instance has been initialize, i.e. the client and server have negotiated an TCP JSON TPC version and the connection can be used to make calls.

disconnect

Emitted when the cConnection instance has stopped receiving messages. This happens when there is a network error or after you tell the connection to disconnect.

Methods:

undefined fCall(String sProcedureName, Any xData[, Function fCallback])

Request a remote procedure call for the procedure with the given name. Any value provided in xData is passed to the remote as an argument to be provided to the procedure. If fCallback is not undefined, fCallback(cConnection oConnection, Error oError, Any xData) is called when the remote procedure call is finished and the remote has return the result. In this case the remote procedure can return any error in oError or if oError is undefined, return a result value in xData. If the remote procedure call fails for some reason, the callback is also called with oError containing details. If the result is not returned before a timeout, the callback is also called with oError containing details.

undefined fDisconnect()

Disconnect the cConnection instance.

object mTCPJSON.oErrorCodes

Contains a list of common error codes used to identify errors in the RPC layer.

Properties:

iConnectionFailed = -1

This error code is used to indicate the network connection failed. E.g. the connection was closed or the network is down.

iInvalidJSON = -2

This error code is used to indicate the remote sent an invalid JSON message. E.g. the remote sent "{", which is not valid JSON.

iInvalidJSONRPC = -3

This error code is used to indicate a number of situations:

• the remote sent an invalid JSON message that is an invalid JSON RPC message. (e.g. "0", "[]" or "{}").
• the remote sent a JSON RPC version negotiation message after version negotiation is finished.
• the remote sent a JSON RPC version negotiation message that is invalid for the current stage of version negotiation. (e.g. rejecting or accepting a version before a request is made).
• the remote sent an invalid JSON RPC version negotiation message (e.g. rejecting or accepting a version that was not requested).
• the remote rejected all acceptable JSON RPC versions.

iProcedureNotFound = -4

This error code is used to indicate that the remote does not know the requested procedure name and therefore cannot execute the call.

iInvalidId = -5

This error code is used to indicate that the remote does not know the id for which a result was sent back. This can happen when local stub is broken, or if a procedure call did not return its result before the remote assumed it had timed out.

iProcedureFailed = -6

This error code is used to indicate that the remote procedure threw an unhandled exception.

iResultTimeout = -7

This error code is used to indicate that the remote assumes the requested procedure call has timed out and will not return a result.

---

License

This code is licensed under CC0 v1.0 Universal.