feat(errors): retryFailures and prependErrorMessageWith

deps.ts

@@ -4,6 +4,7 @@ export * as colors from 'https://deno.land/[email protected]/fmt/colors.ts'
 export * as base64 from 'https://deno.land/[email protected]/encoding/base64.ts'
 export * as streamUtils from 'https://deno.land/[email protected]/streams/mod.ts'
 export * as hexEncodingUtils from 'https://deno.land/[email protected]/encoding/hex.ts'
+export * as asyncUtils from 'https://deno.land/[email protected]/async/mod.ts'
 
 // Third party
 export * as jwtCore from 'https://deno.land/x/[email protected]/mod.ts'

errors.test.ts

@@ -1,5 +1,5 @@
 import { asserts } from './deps.ts'
-import { bindErrorRecovery, withAsyncErrorRecovery, withErrorRecovery } from './errors.ts'
+import { bindErrorRecovery, prependErrorMessageWith, retryFailures, withAsyncErrorRecovery, withErrorRecovery } from './errors.ts'
 
 Deno.test('bindErrorRecovery works', () => {
 	function foo(error: boolean) {
@@ -60,3 +60,51 @@ Deno.test('withAsyncErrorRecovery works', async () => {
 		13,
 	)
 })
+
+Deno.test('retryFailures retries correct number of times', async () => {
+	let didRun = 0
+
+	await retryFailures(
+		() => {
+			didRun++
+
+			if (didRun < 10) throw new Error('Test error')
+		},
+		5,
+		10,
+	)
+
+	asserts.assertEquals(didRun, 10)
+})
+
+Deno.test('retryFailures stops retrying on success', async () => {
+	let didRun = 0
+
+	const result = await retryFailures(
+		() => {
+			didRun++
+
+			if (didRun < 5) throw new Error('Test error')
+
+			return 45
+		},
+		5,
+		10,
+	)
+
+	asserts.assertEquals(result, 45)
+	asserts.assertEquals(didRun, 5)
+})
+
+Deno.test('prependErrorMessageWith prepends error messages with', () => {
+	asserts.assertThrows(
+		() => {
+			const error = new Error('Test error')
+			prependErrorMessageWith(error, 'prepend stuff')
+
+			throw error
+		},
+		Error,
+		'prepend stuff Test error',
+	)
+})

errors.ts

@@ -1,3 +1,5 @@
+import { asyncUtils } from './deps.ts'
+
 export class UserError extends Error {
 	code = 'USER_FAULT'
 }
@@ -110,3 +112,30 @@ export async function withAsyncErrorRecovery<T, O>(fn: () => Promise<T>, recover
 		return recoverWith
 	}
 }
+
+/** Call `fn`. If it throws, delay for `delayTime`, then call it again, up to `retryCount` times. */
+export async function retryFailures<T>(fn: () => Promise<T> | T, delayTime = 3000, retryCount = 3): Promise<T> {
+	let triedTime = 0
+	let lastError: unknown
+
+	while (triedTime <= retryCount) {
+		triedTime++
+
+		try {
+			return await fn()
+		} catch (error) {
+			lastError = error
+			await asyncUtils.delay(delayTime)
+		}
+	}
+
+	prependErrorMessageWith(lastError, `After ${retryCount} retries, the error remains:`)
+
+	throw lastError
+}
+
+/** Modifies the `message` field of `error` to be prepended with `prepend` */
+export function prependErrorMessageWith(error: unknown, prepend: string): void {
+	// @ts-ignore we want to append some info to the error message if it exists
+	if (error.message) error.message = `${prepend} ${error.message}`
+}