phyunsj/oncrpc-api-design

Generate ONCRPC middle-layer to simplify RPC application development (for my own reference)

ONC/RPC API Design

• Example 1 rls (remote ls - original version)

• Example 2 rls_v2 (revised)

• Example 3 calc

Example 3 calc

ONCRPC restricted us to remote procedures that accept a single parameter and return a single parameter. (Might not be true now but stick to this restriction)

Instead of starting with IDL (like Example 1 & 2), start wtih API.h and generate ONCRPC middle-layer automatically. Keep (or share) the same local implementation between RPC server and RPC client.

Similar to non-RPC application, the below files are manaully created. Create RPC middle-layer to integrate the local APIs defined in cl_calc.h. Use the same API locally or remotely.

cl_calc.c/h : functions declaration, definition.

cl_client.c : client main program

cl_common.c/h : RPC Client handler

cl_return_t CL_CALC_WRITE ( HANDLER *remote , cl_msg_t in, cl_bus_t *out )  
{

  if ( remote != NULL && remote->clnt != (CLIENT *)NULL ) {

    ...    
    res = cl_calc_write_func_1( &req, remote->clnt );
    ...
    
    return ret;
  } else {

    return cl_calc_write( in,out );

  }

}

CL is an imaginary product name for example 3.

1. cpp cl_calc.h -o cl_calc.i
2. pycparser to generate AST
3. AST visitor extracts typdef & *** fucntion declaration *** out of AST
4. generate IDL & RPC middle-layer Interface

The following files are generated from cl_calc.h

• CL.x (ONCRPC IDL)
• CL_proc.c (Client Middlelayer)
• CL_svc_proc.c (Server Middlelayer)
• CL_proc.h

CL.x generates :

• CL.h
• CL_svc.c
• CL_clnt.c
• CL_xdr.c

Accessing AST

generated by pycparser ( Complete C99 parser in pure Python )

pycparser installation. ( powered by PLY )

pip install --index-url=https://pypi.python.org/simple/ pycparser

from pycparser import c_parser, c_ast, parse_file

class FuncCallVisitor(c_ast.NodeVisitor):
    def __init__(self):
        ...

    def visit_FuncDecl (self, node):
        ...

if __name__ == "__main__":

    ast = parse_file(args.filename, use_cpp=False)
    v = FuncCallVisitor()
    v.visit(ast)