ctx.random() and ctx.uuid() for deterministic random and uuid. (#120)

Author: slinkydeveloper

examples/example.py

@@ -15,12 +15,14 @@
 import restate
 
 from greeter import greeter
+from random_greeter import random_greeter
 from virtual_object import counter
 from workflow import payment
 from pydantic_greeter import pydantic_greeter
 from concurrent_greeter import concurrent_greeter
 
 app = restate.app(services=[greeter,
+                            random_greeter,
                             counter,
                             payment,
                             pydantic_greeter,

examples/random_greeter.py

@@ -0,0 +1,39 @@
+#
+#  Copyright (c) 2023-2024 - Restate Software, Inc., Restate GmbH
+#
+#  This file is part of the Restate SDK for Python,
+#  which is released under the MIT license.
+#
+#  You can find a copy of the license in file LICENSE in the root
+#  directory of this repository or package, or at
+#  https://github.com/restatedev/sdk-typescript/blob/main/LICENSE
+#
+"""example.py"""
+# pylint: disable=C0116
+# pylint: disable=W0613
+
+from restate import Service, Context
+
+random_greeter = Service("random_greeter")
+
+@random_greeter.handler()
+async def greet(ctx: Context, name: str) -> str:
+
+    # ctx.random() returns a Python Random instance seeded deterministically.
+    # By using ctx.random() you don't write entries in the journal,
+    # but you still get the same generated values on retries.
+
+    # To generate random numbers
+    random_number = ctx.random().randint(0, 100)
+
+    # To generate random bytes
+    random_bytes = ctx.random().randbytes(10)
+
+    # Use ctx.uuid() to generate a UUID v4 seeded deterministically
+    # As with ctx.random(), this won't write entries in the journal
+    random_uuid = ctx.uuid()
+
+    return (f"Hello {name} with "
+            f"random number {random_number}, "
+            f"random bytes {random_bytes!r} "
+            f"and uuid {random_uuid}!")

python/restate/context.py

@@ -14,6 +14,8 @@
 """
 
 import abc
+from random import Random
+from uuid import UUID
 from dataclasses import dataclass
 from typing import Any, Awaitable, Callable, Dict, List, Optional, TypeVar, Union, Coroutine, overload, ParamSpec
 import typing
@@ -219,6 +221,21 @@ def request(self) -> Request:
         Returns the request object.
         """
 
+    @abc.abstractmethod
+    def random(self) -> Random:
+        """
+        Returns a Random instance inherently predictable, deterministically seeded by Restate.
+
+        This instance is useful to generate identifiers, idempotency keys, and for uniform sampling from a set of options.
+        """
+
+    @abc.abstractmethod
+    def uuid(self) -> UUID:
+        """
+        Returns a random UUID, deterministically seeded.
+
+        This UUID will be stable across retries and replays.
+        """
 
     @typing_extensions.deprecated("`run` is deprecated, use `run_typed` instead for better type safety")
     @overload

python/restate/server_context.py

@@ -18,12 +18,14 @@
 
 import asyncio
 import contextvars
+from random import Random
 from datetime import timedelta
 import inspect
 import functools
 from typing import Any, Awaitable, Callable, Dict, List, Optional, TypeVar, Union, Coroutine
 import typing
 import traceback
+from uuid import UUID
 
 from restate.context import DurablePromise, AttemptFinishedEvent, HandlerType, ObjectContext, Request, RestateDurableCallFuture, RestateDurableFuture, RunAction, SendHandle, RestateDurableSleepFuture, RunOptions, P
 from restate.exceptions import TerminalError
@@ -278,6 +280,7 @@ def __init__(self,
         self.invocation = invocation
         self.attempt_headers = attempt_headers
         self.send = send
+        self.random_instance = Random(invocation.random_seed)
         self.receive = receive
         self.run_coros_to_execute: dict[int,  Callable[[], Awaitable[None]]] = {}
         self.request_finished_event = asyncio.Event()
@@ -471,6 +474,12 @@ def request(self) -> Request:
             attempt_finished_event=ServerTeardownEvent(self.request_finished_event),
         )
 
+    def random(self) -> Random:
+        return self.random_instance
+
+    def uuid(self) -> UUID:
+        return UUID(int=self.random_instance.getrandbits(128), version=4)
+
     # pylint: disable=R0914
     async def create_run_coroutine(self,
                                    handle: int,