import json
import sys

##################################################
# User defined methods go here
##################################################
def addMeth(args):
    a = float(args[0])
    b = float(args[1])
    return [a + b]

def multMeth(args):
    a = float(args[0])
    b = float(args[1])
    return [a * b]

def echoMeth(args):
    return args

methods = {}
methods["add"] = addMeth
methods["mult"] = multMeth
methods["echo"] = echoMeth
##################################################
# End of user defined methods
##################################################


#Begining of JSON RPC server code

class RPCError(Exception):
    def __init__(self, message, id, code):
        self.message = message
        self.id = id
        self.code = code

    def __str__(self):
        return "Request id: " + str(self.id) + ' Error: ' + self.message

def processRequest(req):
    id = None
    if "id" in req:
        id = req["id"]

    if type(id) != int and type(id) != float:
        raise RPCError("Invalid id field", None, -32600)

    if not "jsonrpc" in req:
        raise RPCError("Missing jsonrpc field", id, -32600)
    if req["jsonrpc"] != "2.0":
        raise RPCError("Invalid jsonrpc value: " + str(req["jsonrpc"]), id, -32600)
    if not "method" in req:
        raise RPCError("Missing method field", id, -32600)
    methName = req["method"]
    if not methName in methods:
        raise RPCError("Unknown method: " + methName, id, -32602)
    if not "params" in req:
        raise RPCError("Missing params field", id, -32600)
    params = req["params"]

    meth = methods[methName]
    result = meth(params)
    response = {"jsonrpc": "2.0", "id": id, "result": result}
    return response


# main loop
for line in sys.stdin:
    try:
        req = json.loads(line)
        res = processRequest(req)
        print(json.dumps(res))
        sys.stdout.flush()
    except RPCError as err:
        res = {"jsonrpc": "2.0", "id": err.id, "error" : { "message": err.message, "code" : err.code}}
        print(json.dumps(res))
        sys.stdout.flush()