async_ssl_calculator_client.py

#!/usr/bin/env python3

import argparse
import asyncio
import os
import ssl
import socket

import capnp
import calculator_capnp


this_dir = os.path.dirname(os.path.abspath(__file__))


class PowerFunction(calculator_capnp.Calculator.Function.Server):
    """An implementation of the Function interface wrapping pow().  Note that
    we're implementing this on the client side and will pass a reference to
    the server.  The server will then be able to make calls back to the client."""

    async def call(self, params, **kwargs):
        """Note the **kwargs. This is very necessary to include, since
        protocols can add parameters over time. Also, by default, a _context
        variable is passed to all server methods, but you can also return
        results directly as python objects, and they'll be added to the
        results struct in the correct order"""

        return pow(params[0], params[1])


def parse_args():
    parser = argparse.ArgumentParser(
        usage="Connects to the Calculator server at the given address and does some RPCs"
    )
    parser.add_argument("host", help="HOST:PORT")

    return parser.parse_args()


async def main(host):
    addr, port = host.split(":")

    # Setup SSL context
    ctx = ssl.create_default_context(
        ssl.Purpose.SERVER_AUTH, cafile=os.path.join(this_dir, "selfsigned.cert")
    )

    # Handle both IPv4 and IPv6 cases
    try:
        print("Try IPv4")
        stream = await capnp.AsyncIoStream.create_connection(
            addr, port, ssl=ctx, family=socket.AF_INET
        )
    except Exception:
        print("Try IPv6")
        stream = await capnp.AsyncIoStream.create_connection(
            addr, port, ssl=ctx, family=socket.AF_INET6
        )

    client = capnp.TwoPartyClient(stream)

    # Bootstrap the Calculator interface
    calculator = client.bootstrap().cast_as(calculator_capnp.Calculator)

    """Make a request that just evaluates the literal value 123.

    What's interesting here is that evaluate() returns a "Value", which is
    another interface and therefore points back to an object living on the
    server.  We then have to call read() on that object to read it.
    However, even though we are making two RPC's, this block executes in
    *one* network round trip because of promise pipelining:  we do not wait
    for the first call to complete before we send the second call to the
    server."""

    print("Evaluating a literal... ", end="")

    # Make the request. Note we are using the shorter function form (instead
    # of evaluate_request), and we are passing a dictionary that represents a
    # struct and its member to evaluate
    eval_promise = calculator.evaluate({"literal": 123})

    # This is equivalent to:
    """
    request = calculator.evaluate_request()
    request.expression.literal = 123

    # Send it, which returns a promise for the result (without blocking).
    eval_promise = request.send()
    """

    # Using the promise, create a pipelined request to call read() on the
    # returned object. Note that here we are using the shortened method call
    # syntax read(), which is mostly just sugar for read_request().send()
    read_promise = eval_promise.value.read()

    # Now that we've sent all the requests, wait for the response.  Until this
    # point, we haven't waited at all!
    response = await read_promise
    assert response.value == 123

    print("PASS")

    """Make a request to evaluate 123 + 45 - 67.

    The Calculator interface requires that we first call getOperator() to
    get the addition and subtraction functions, then call evaluate() to use
    them.  But, once again, we can get both functions, call evaluate(), and
    then read() the result -- four RPCs -- in the time of *one* network
    round trip, because of promise pipelining."""

    print("Using add and subtract... ", end="")

    # Get the "add" function from the server.
    add = calculator.getOperator(op="add").func
    # Get the "subtract" function from the server.
    subtract = calculator.getOperator(op="subtract").func

    # Build the request to evaluate 123 + 45 - 67. Note the form is 'evaluate'
    # + '_request', where 'evaluate' is the name of the method we want to call
    request = calculator.evaluate_request()
    subtract_call = request.expression.init("call")
    subtract_call.function = subtract
    subtract_params = subtract_call.init("params", 2)
    subtract_params[1].literal = 67.0

    add_call = subtract_params[0].init("call")
    add_call.function = add
    add_params = add_call.init("params", 2)
    add_params[0].literal = 123
    add_params[1].literal = 45

    # Send the evaluate() request, read() the result, and wait for read() to finish.
    eval_promise = request.send()
    read_promise = eval_promise.value.read()

    response = await read_promise
    assert response.value == 101

    print("PASS")

    """
    Note: a one liner version of building the previous request (I highly
    recommend not doing it this way for such a complicated structure, but I
    just wanted to demonstrate it is possible to set all of the fields with a
    dictionary):

    eval_promise = calculator.evaluate(
{'call': {'function': subtract,
          'params': [{'call': {'function': add,
                               'params': [{'literal': 123},
                                          {'literal': 45}]}},
                     {'literal': 67.0}]}})
    """

    """Make a request to evaluate 4 * 6, then use the result in two more
    requests that add 3 and 5.

    Since evaluate() returns its result wrapped in a `Value`, we can pass
    that `Value` back to the server in subsequent requests before the first
    `evaluate()` has actually returned.  Thus, this example again does only
    one network round trip."""

    print("Pipelining eval() calls... ", end="")

    # Get the "add" function from the server.
    add = calculator.getOperator(op="add").func
    # Get the "multiply" function from the server.
    multiply = calculator.getOperator(op="multiply").func

    # Build the request to evaluate 4 * 6
    request = calculator.evaluate_request()

    multiply_call = request.expression.init("call")
    multiply_call.function = multiply
    multiply_params = multiply_call.init("params", 2)
    multiply_params[0].literal = 4
    multiply_params[1].literal = 6

    multiply_result = request.send().value

    # Use the result in two calls that add 3 and add 5.

    add_3_request = calculator.evaluate_request()
    add_3_call = add_3_request.expression.init("call")
    add_3_call.function = add
    add_3_params = add_3_call.init("params", 2)
    add_3_params[0].previousResult = multiply_result
    add_3_params[1].literal = 3
    add_3_promise = add_3_request.send().value.read()

    add_5_request = calculator.evaluate_request()
    add_5_call = add_5_request.expression.init("call")
    add_5_call.function = add
    add_5_params = add_5_call.init("params", 2)
    add_5_params[0].previousResult = multiply_result
    add_5_params[1].literal = 5
    add_5_promise = add_5_request.send().value.read()

    # Now wait for the results.
    assert (await add_3_promise).value == 27
    assert (await add_5_promise).value == 29

    print("PASS")

    """Our calculator interface supports defining functions.  Here we use it
    to define two functions and then make calls to them as follows:

      f(x, y) = x * 100 + y
      g(x) = f(x, x + 1) * 2;
      f(12, 34)
      g(21)

    Once again, the whole thing takes only one network round trip."""

    print("Defining functions... ", end="")

    # Get the "add" function from the server.
    add = calculator.getOperator(op="add").func
    # Get the "multiply" function from the server.
    multiply = calculator.getOperator(op="multiply").func

    # Define f.
    request = calculator.defFunction_request()
    request.paramCount = 2

    # Build the function body.
    add_call = request.body.init("call")
    add_call.function = add
    add_params = add_call.init("params", 2)
    add_params[1].parameter = 1  # y

    multiply_call = add_params[0].init("call")
    multiply_call.function = multiply
    multiply_params = multiply_call.init("params", 2)
    multiply_params[0].parameter = 0  # x
    multiply_params[1].literal = 100

    f = request.send().func

    # Define g.
    request = calculator.defFunction_request()
    request.paramCount = 1

    # Build the function body.
    multiply_call = request.body.init("call")
    multiply_call.function = multiply
    multiply_params = multiply_call.init("params", 2)
    multiply_params[1].literal = 2

    f_call = multiply_params[0].init("call")
    f_call.function = f
    f_params = f_call.init("params", 2)
    f_params[0].parameter = 0

    add_call = f_params[1].init("call")
    add_call.function = add
    add_params = add_call.init("params", 2)
    add_params[0].parameter = 0
    add_params[1].literal = 1

    g = request.send().func

    # OK, we've defined all our functions.  Now create our eval requests.

    # f(12, 34)
    f_eval_request = calculator.evaluate_request()
    f_call = f_eval_request.expression.init("call")
    f_call.function = f
    f_params = f_call.init("params", 2)
    f_params[0].literal = 12
    f_params[1].literal = 34
    f_eval_promise = f_eval_request.send().value.read()

    # g(21)
    g_eval_request = calculator.evaluate_request()
    g_call = g_eval_request.expression.init("call")
    g_call.function = g
    g_call.init("params", 1)[0].literal = 21
    g_eval_promise = g_eval_request.send().value.read()

    # Wait for the results.
    assert (await f_eval_promise).value == 1234
    assert (await g_eval_promise).value == 4244

    print("PASS")

    """Make a request that will call back to a function defined locally.

    Specifically, we will compute 2^(4 + 5).  However, exponent is not
    defined by the Calculator server.  So, we'll implement the Function
    interface locally and pass it to the server for it to use when
    evaluating the expression.

    This example requires two network round trips to complete, because the
    server calls back to the client once before finishing.  In this
    particular case, this could potentially be optimized by using a tail
    call on the server side -- see CallContext::tailCall().  However, to
    keep the example simpler, we haven't implemented this optimization in
    the sample server."""

    print("Using a callback... ", end="")

    # Get the "add" function from the server.
    add = calculator.getOperator(op="add").func

    # Build the eval request for 2^(4+5).
    request = calculator.evaluate_request()

    pow_call = request.expression.init("call")
    pow_call.function = PowerFunction()
    pow_params = pow_call.init("params", 2)
    pow_params[0].literal = 2

    add_call = pow_params[1].init("call")
    add_call.function = add
    add_params = add_call.init("params", 2)
    add_params[0].literal = 4
    add_params[1].literal = 5

    # Send the request and wait.
    response = await request.send().value.read()
    assert response.value == 512

    print("PASS")


if __name__ == "__main__":
    # Using asyncio.run hits an asyncio ssl bug
    # https://bugs.python.org/issue36709
    # asyncio.run(main(parse_args().host), loop=loop, debug=True)
    loop = asyncio.get_event_loop()
    loop.run_until_complete(capnp.run(main(parse_args().host)))