tests: add a test case for custom server json encoding class

Add a new test file to verify that the json_encoder_cls argument
can be given to the Service to specify a custom encoder.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Author: phlogistonjohn

varlink/tests/org.example.encoding.varlink

@@ -0,0 +1,27 @@
+# Example Varlink service
+interface org.example.encoding
+
+type State (
+  start: ?bool,
+  progress: ?int,
+  end: ?bool
+)
+
+type Shipment (
+  name: string,
+  description: string,
+  size: int,
+  weight: ?int
+)
+
+type Order (
+  shipments: []Shipment,
+  order_num: int,
+  customer: string
+)
+
+# Returns the same string
+method Ping(ping: string) -> (pong: string)
+
+# Returns a fake order given an order number
+method GetOrder(num: int) -> (order: Order)

varlink/tests/test_server_encoding.py

@@ -0,0 +1,124 @@
+#!/usr/bin/env python
+
+"""Test custom JSON encoding by subclassing VarlinkEncoder and
+passing it to a server Service.
+"""
+
+import dataclasses
+import os
+import threading
+import time
+import typing
+import unittest
+
+import varlink
+import varlink.error
+
+
+@dataclasses.dataclass
+class Shipment:
+    name: str
+    description: str
+    size: int
+    weight: typing.Optional[int] = None
+
+
+@dataclasses.dataclass
+class Order:
+    shipments: list[Shipment]
+    order_num: int
+    customer: str
+
+
+@dataclasses.dataclass
+class GetOrderResult:
+    order: Order
+
+
+class VDCEncoder(varlink.error.VarlinkEncoder):
+    def default(self, obj):
+        if dataclasses.is_dataclass(obj):
+            return dataclasses.asdict(obj)
+        return super().default(obj)
+
+
+service = varlink.Service(
+    vendor="Varlink",
+    product="Varlink Encoding Example",
+    version="1",
+    url="http://varlink.org",
+    interface_dir=os.path.dirname(__file__),
+    json_encoder_cls=VDCEncoder,
+)
+
+
+class ServiceRequestHandler(varlink.RequestHandler):
+    service = service
+
+
+@service.interface("org.example.encoding")
+class EncodingExample:
+    sleep_duration = 1
+
+    def Ping(self, ping):
+        return {"pong": ping}
+
+    def GetOrder(self, num):
+        order = Order(
+            shipments=[
+                Shipment(
+                    name="Furniture",
+                    description="Furniture by Ferb",
+                    size=1000,
+                    weight=400,
+                ),
+                Shipment(
+                    name="Electronics",
+                    description="Electronics by Earl",
+                    size=588,
+                ),
+            ],
+            order_num=num,
+            customer="Joe's Discount Store",
+        )
+        return GetOrderResult(order=order)
+
+
+class TestService(unittest.TestCase):
+    address = "tcp:127.0.0.1:23451"
+
+    @classmethod
+    def setUpClass(cls):
+        cls._server = varlink.ThreadingServer(cls.address, ServiceRequestHandler)
+        cls._server_thread = threading.Thread(target=cls._server.serve_forever)
+        cls._server_thread.start()
+        time.sleep(0.1)
+
+    @classmethod
+    def tearDownClass(cls):
+        cls._server.shutdown()
+        cls._server.server_close()
+        cls._server_thread.join()
+
+    def test_ping(self):
+        client = varlink.Client.new_with_address(self.address)
+        with client.open("org.example.encoding") as conn:
+            response = conn.Ping("Foo")
+        self.assertEqual(response["pong"], "Foo")
+
+    def test_get_order(self):
+        client = varlink.Client.new_with_address(self.address)
+        with client.open("org.example.encoding") as conn:
+            response = conn.GetOrder(4638547)
+        # response will be a dict represenation of GetOrderResult
+        self.assertIn("order", response)
+        order = response["order"]
+        self.assertEqual(order.get("order_num"), 4638547)
+        self.assertEqual(order.get("customer"), "Joe's Discount Store")
+        self.assertEqual(len(order.get("shipments", [])), 2)
+        shipment1 = order["shipments"][0]
+        self.assertEqual(shipment1.get("name"), "Furniture")
+        self.assertIsNotNone(shipment1.get("weight"))
+        shipment2 = order["shipments"][1]
+        self.assertEqual(shipment2.get("name"), "Electronics")
+        self.assertIsNone(shipment2.get("weight"))