INTRODUCTION

The following example performs a simple IPC between two processes one client and the other server. The "Server" process acts as Remote Command Server, it waits to receive a request by the "Client" and serves it.

This example is composed by four parts, each one of them stored in an own folder:

• libzipc: it contains the IPC logic, this component utilizes ZeroMQ library to implement the ipc channel
• libdaemon: it contains the service logic
• client: it utilises libdaemon to perfome the service request
• server: it utilises libdaemon to perfome the service response

libdaemon example implements only one service 'getServerPid( )' is utilised by the server to return to client its process ID (PID). The libdaemon source code is articulated to semplify the library exstention and to privide the developer with a standard service structure and for this reason the logic of REQUEST/RESPONCE is stored in the same function '__getServerPid( )'.

Libzipc

The library libzipc exposes the only one function:

IPC_RESULT ipc_call (IPC_ROLE role, const char *lib, const char *func, void *in, size_t in_size, void **out, size_t *out_size, int *ret_val);

• this fuction is utilised by both server and client; the first call it specifing the IPC_SERVER role the second as IPC_CLIENT.
• func and lib parameters are instead utilised by the client to specify the function name that the server must execute and the shared library where this function is stored.
• in, in_size, out and out_size are the parameters utilized to specify an input and an out parameter structure for the function.
• finally, the remote function return is passed to the client by ret_val.

Libdaemon

The library libdaemon specifies the logic of the service; inside there are:

• the function startServer () that rappresents the function invoked by the server to start.
• the function getServerPid (), just wrapper for the function __getServerPid() to adapt/mask the function parameters to the format:

int function_name (IPC_ROLE role, void *in, size_t in_size, void **out, size_t * out_size, int *retval);

• the function __getServerPid() that perform the service and it is called by both server and client, the body of this function is composed by two section:
  • the IPC_CLIENT part, called only by the client during the request.
  • the IPC_SERVER part, called only by the server when the command request is received to process the data for the responce.

usually, the IPC_SERVER part allocate the return struct value and the IPC_CLIENT part process and dellocate it.

INSTALLATION

• The only dependency of this example is the ZeroMQ library for C (https://zeromq.org/download/).

UBUNTU :

sudo apt install libzmq3-dev

cd libzipc

mkdir build && cd build

cmake .. && cmake --build . && sudo make install