From 8177e63f41af666bb401482f56d0b9d38af9c8a5 Mon Sep 17 00:00:00 2001
From: Stefan Thomas <justmoon@members.fsf.org>
Date: Tue, 10 Sep 2024 08:43:10 -0400
Subject: [PATCH] feat(reactive): provide deterministic randomness

---
 .../src/test/mocks/test-environment.ts        |  5 ++--
 packages/lib-reactive/src/index.ts            |  4 +++
 .../src/mocks/deterministic-crypto.ts}        | 18 ++++++-------
 .../src/test/deterministic-crypto.test.ts     | 25 +++++++++++++++++++
 4 files changed, 41 insertions(+), 11 deletions(-)
 rename packages/{lib-protocol-stream/src/test/mocks/crypto-context.ts => lib-reactive/src/mocks/deterministic-crypto.ts} (75%)
 create mode 100644 packages/lib-reactive/src/test/deterministic-crypto.test.ts

diff --git a/packages/lib-protocol-stream/src/test/mocks/test-environment.ts b/packages/lib-protocol-stream/src/test/mocks/test-environment.ts
index f5ae918f..b24f1a17 100644
--- a/packages/lib-protocol-stream/src/test/mocks/test-environment.ts
+++ b/packages/lib-protocol-stream/src/test/mocks/test-environment.ts
@@ -17,14 +17,15 @@ import {
   type Crypto,
   type DisposableScope,
   createMockClock,
+  createMockDeterministicCrypto,
   createScope,
   createTopic,
 } from "@dassie/lib-reactive"
+import { createCrypto } from "@dassie/lib-reactive-io"
 
 import type { StreamProtocolContext } from "../../context/context"
 import { DEFAULT_POLICY, type StreamPolicy } from "../../context/policy"
 import { getPskEnvironment } from "../../crypto/functions"
-import { createMockCryptoContext } from "./crypto-context"
 
 interface EnvironmentOptions {
   // Environment options
@@ -67,7 +68,7 @@ export function createTestEnvironment({
   maxPacketsInFlight = Infinity,
   scope = createScope("test-environment"),
   logger = createLogger("das:test:stream"),
-  crypto = createMockCryptoContext(),
+  crypto = createMockDeterministicCrypto(createCrypto()),
   clock = createMockClock(),
   policy = DEFAULT_POLICY,
 }: EnvironmentOptions = {}) {
diff --git a/packages/lib-reactive/src/index.ts b/packages/lib-reactive/src/index.ts
index 52eaf8ce..0b062e4d 100644
--- a/packages/lib-reactive/src/index.ts
+++ b/packages/lib-reactive/src/index.ts
@@ -35,6 +35,10 @@ export {
   MockClockImplementation,
   DEFAULT_MOCK_CLOCK_TIME,
 } from "./mocks/clock"
+export {
+  createMockDeterministicCrypto,
+  Xoshiro128PlusPlus,
+} from "./mocks/deterministic-crypto"
 export { delay, delayWithAbortSignal } from "./tools/delay"
 
 export type { Topic, ReadonlyTopic, InferTopicType } from "./topic"
diff --git a/packages/lib-protocol-stream/src/test/mocks/crypto-context.ts b/packages/lib-reactive/src/mocks/deterministic-crypto.ts
similarity index 75%
rename from packages/lib-protocol-stream/src/test/mocks/crypto-context.ts
rename to packages/lib-reactive/src/mocks/deterministic-crypto.ts
index 8f40cc3b..83ce05fc 100644
--- a/packages/lib-protocol-stream/src/test/mocks/crypto-context.ts
+++ b/packages/lib-reactive/src/mocks/deterministic-crypto.ts
@@ -1,14 +1,16 @@
-import type { Crypto } from "@dassie/lib-reactive"
-import { createCrypto } from "@dassie/lib-reactive-io"
+import type { Crypto } from "../types/base-modules/crypto"
 
 const DEFAULT_SEED = new Uint32Array([
   0x13_67_bd_3b, 0x83_31_fa_de, 0x7b_96_f6_b5, 0xb4_9e_9f_58,
 ])
 
-export function createMockCryptoContext(): Crypto {
-  const randomGenerator = new Xoshiro128PlusPlus()
+export function createMockDeterministicCrypto(
+  crypto: Crypto,
+  seed: Uint32Array = DEFAULT_SEED,
+): Crypto {
+  const randomGenerator = new Xoshiro128PlusPlus(seed)
 
-  return Object.assign(createCrypto(), {
+  return Object.assign(crypto, {
     getRandomBytes: (length: number) => {
       const data = new Uint32Array(Math.ceil(length / 4))
 
@@ -16,14 +18,12 @@ export function createMockCryptoContext(): Crypto {
         data[index] = randomGenerator.next()
       }
 
-      const result = new Uint8Array(data.buffer)
-
-      return result.subarray(0, length)
+      return new Uint8Array(data.buffer, 0, length)
     },
   })
 }
 
-class Xoshiro128PlusPlus {
+export class Xoshiro128PlusPlus {
   private state: Uint32Array
 
   constructor(seed: Uint32Array = DEFAULT_SEED) {
diff --git a/packages/lib-reactive/src/test/deterministic-crypto.test.ts b/packages/lib-reactive/src/test/deterministic-crypto.test.ts
new file mode 100644
index 00000000..6ec5d3a9
--- /dev/null
+++ b/packages/lib-reactive/src/test/deterministic-crypto.test.ts
@@ -0,0 +1,25 @@
+import { uint8ArrayToHex } from "uint8array-extras"
+import { describe, test } from "vitest"
+
+import { createMockDeterministicCrypto } from "../mocks/deterministic-crypto"
+import type { Crypto } from "../types/base-modules/crypto"
+
+describe("Deterministic Crypto", () => {
+  test("should generate (not so) random bytes", ({ expect }) => {
+    const crypto = createMockDeterministicCrypto({} as Crypto)
+    const randomNumber = crypto.getRandomBytes(32)
+    expect(uint8ArrayToHex(randomNumber)).toMatchInlineSnapshot(
+      `"1f0796160c164e1fdcc306caed8497f7c424a4e4d66f5653f50d1f35e47638d9"`,
+    )
+  })
+
+  test("should generate (not so) random bytes of a length that is not a multiple of 4", ({
+    expect,
+  }) => {
+    const crypto = createMockDeterministicCrypto({} as Crypto)
+    const randomNumber = crypto.getRandomBytes(31)
+    expect(uint8ArrayToHex(randomNumber)).toMatchInlineSnapshot(
+      `"1f0796160c164e1fdcc306caed8497f7c424a4e4d66f5653f50d1f35e47638"`,
+    )
+  })
+})