Add ky.retry() to force retries from afterResponse hooks

readme.md

@@ -489,6 +489,8 @@ Default: `[]`
 
 This hook enables you to read and optionally modify the response. The hook function receives normalized request, options, a clone of the response, and a state object. The return value of the hook function will be used by Ky as the response object if it's an instance of [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response).
 
+You can also force a retry by returning [`ky.retry(options)`](#kyretryoptions). This is useful when you need to retry based on the response body content, even if the response has a successful status code. The retry will respect the `retry.limit` option and be observable in `beforeRetry` hooks.
+
 The `state.retryCount` is `0` for the initial request and increments with each retry. This allows you to distinguish between initial requests and retries, which is useful when you need different behavior for retries (e.g., showing a notification only on the final retry).
 
 ```js
@@ -518,6 +520,20 @@ const response = await ky('https://example.com', {
 				}
 			},
 
+			// Or force retry based on response body content
+			async (request, options, response) => {
+				if (response.status === 200) {
+					const data = await response.clone().json();
+					if (data.error?.code === 'RATE_LIMIT') {
+						// Retry with custom delay from API response
+						return ky.retry({
+							delay: data.error.retryAfter * 1000,
+							code: 'RATE_LIMIT'
+						});
+					}
+				}
+			},
+
 			// Or show a notification only on the last retry for 5xx errors
 			(request, options, response, {retryCount}) => {
 				if (response.status >= 500 && response.status <= 599) {
@@ -842,6 +858,142 @@ const response = await ky.post('https://example.com', options);
 const text = await ky('https://example.com', options).text();
 ```
 
+### ky.retry(options?)
+
+Force a retry from an `afterResponse` hook.
+
+This allows you to retry a request based on the response content, even if the response has a successful status code. The retry will respect the `retry.limit` option and skip the `shouldRetry` check. The forced retry is observable in `beforeRetry` hooks, where the error will be a `ForceRetryError` with the error name `'ForceRetryError'`.
+
+#### options
+
+Type: `object`
+
+##### delay
+
+Type: `number`
+
+Custom delay in milliseconds before retrying. If not provided, uses the default retry delay calculation based on `retry.delay` configuration.
+
+**Note:** Custom delays bypass jitter and `backoffLimit`. This is intentional, as custom delays often come from server responses (e.g., `Retry-After` headers) and should be respected exactly as specified.
+
+##### code
+
+Type: `string`
+
+Error code for the retry.
+
+This machine-readable identifier will be included in the error message passed to `beforeRetry` hooks, allowing you to distinguish between different types of forced retries.
+
+```js
+return ky.retry({code: 'RATE_LIMIT'});
+// Resulting error message: 'Forced retry: RATE_LIMIT'
+```
+
+##### cause
+
+Type: `Error`
+
+Original error that caused the retry. This allows you to preserve the error chain when forcing a retry based on caught exceptions. The error will be set as the `cause` of the `ForceRetryError`, enabling proper error chain traversal.
+
+```js
+try {
+	const data = await response.clone().json();
+	validateBusinessLogic(data);
+} catch (error) {
+	return ky.retry({
+		code: 'VALIDATION_FAILED',
+		cause: error  // Preserves original error in chain
+	});
+}
+```
+
+##### request
+
+Type: `Request`
+
+Custom request to use for the retry.
+
+This allows you to modify or completely replace the request during a forced retry. The custom request becomes the starting point for the retry - `beforeRetry` hooks can still further modify it if needed.
+
+**Note:** The custom request's `signal` will be replaced with Ky's managed signal to handle timeouts and user-provided abort signals correctly. If the original request body has been consumed, you must provide a new body or clone the request before consuming.
+
+#### Example
+
+```js
+import ky, {isForceRetryError} from 'ky';
+
+const api = ky.extend({
+	hooks: {
+		afterResponse: [
+			async (request, options, response) => {
+				// Retry based on response body content
+				if (response.status === 200) {
+					const data = await response.clone().json();
+
+					// Simple retry with default delay
+					if (data.error?.code === 'TEMPORARY_ERROR') {
+						return ky.retry();
+					}
+
+					// Retry with custom delay from API response
+					if (data.error?.code === 'RATE_LIMIT') {
+						return ky.retry({
+							delay: data.error.retryAfter * 1000,
+							code: 'RATE_LIMIT'
+						});
+					}
+
+					// Retry with a modified request (e.g., fallback endpoint)
+					if (data.error?.code === 'FALLBACK_TO_BACKUP') {
+						return ky.retry({
+							request: new Request('https://backup-api.com/endpoint', {
+								method: request.method,
+								headers: request.headers,
+							}),
+							code: 'BACKUP_ENDPOINT'
+						});
+					}
+
+					// Retry with refreshed authentication
+					if (data.error?.code === 'TOKEN_REFRESH' && data.newToken) {
+						return ky.retry({
+							request: new Request(request, {
+								headers: {
+									...Object.fromEntries(request.headers),
+									'Authorization': `Bearer ${data.newToken}`
+								}
+							}),
+							code: 'TOKEN_REFRESHED'
+						});
+					}
+
+					// Retry with cause to preserve error chain
+					try {
+						validateResponse(data);
+					} catch (error) {
+						return ky.retry({
+							code: 'VALIDATION_FAILED',
+							cause: error
+						});
+					}
+				}
+			}
+		],
+		beforeRetry: [
+			({error, retryCount}) => {
+				// Observable in beforeRetry hooks
+				if (isForceRetryError(error)) {
+					console.log(`Forced retry #${retryCount}: ${error.message}`);
+					// Example output: "Forced retry #1: Forced retry: RATE_LIMIT"
+				}
+			}
+		]
+	}
+});
+
+const response = await api.get('https://example.com/api');
+```
+
 ### HTTPError
 
 Exposed for `instanceof` checks. The error has a `response` property with the [`Response` object](https://developer.mozilla.org/en-US/docs/Web/API/Response), `request` property with the [`Request` object](https://developer.mozilla.org/en-US/docs/Web/API/Request), and `options` property with normalized options (either passed to `ky` when creating an instance with `ky.create()` or directly when performing the request).

source/core/Ky.ts

@@ -1,5 +1,6 @@
 import {HTTPError} from '../errors/HTTPError.js';
 import {NonError} from '../errors/NonError.js';
+import {ForceRetryError} from '../errors/ForceRetryError.js';
 import type {
 	Input,
 	InternalOptions,
@@ -21,6 +22,7 @@ import {
 	maxSafeTimeout,
 	responseTypes,
 	stop,
+	RetryMarker,
 	supportsAbortController,
 	supportsAbortSignal,
 	supportsFormData,
@@ -44,17 +46,31 @@ export class Ky {
 			let response = await ky.#fetch();
 
 			for (const hook of ky.#options.hooks.afterResponse) {
+				// Clone the response before passing to hook so we can cancel it if needed
+				const clonedResponse = ky.#decorateResponse(response.clone());
+
 				// eslint-disable-next-line no-await-in-loop
 				const modifiedResponse = await hook(
 					ky.request,
 					ky.#getNormalizedOptions(),
-					ky.#decorateResponse(response.clone()),
+					clonedResponse,
 					{retryCount: ky.#retryCount},
 				);
 
 				if (modifiedResponse instanceof globalThis.Response) {
 					response = modifiedResponse;
 				}
+
+				if (modifiedResponse instanceof RetryMarker) {
+					// Cancel both the cloned response passed to the hook and the current response
+					// to prevent resource leaks (especially important in Deno/Bun)
+					// eslint-disable-next-line no-await-in-loop
+					await Promise.all([
+						clonedResponse.body?.cancel(),
+						response.body?.cancel(),
+					]);
+					throw new ForceRetryError(modifiedResponse.options);
+				}
 			}
 
 			ky.#decorateResponse(response);
@@ -90,8 +106,9 @@ export class Ky {
 			return response;
 		};
 
-		const isRetriableMethod = ky.#options.retry.methods.includes(ky.request.method.toLowerCase());
-		const result = (isRetriableMethod ? ky.#retry(function_) : function_())
+		// Always wrap in #retry to catch forced retries from afterResponse hooks
+		// Method retriability is checked in #calculateRetryDelay for non-forced retries
+		const result = ky.#retry(function_)
 			.finally(async () => {
 				const originalRequest = ky.#originalRequest;
 				const cleanupPromises = [];
@@ -166,7 +183,7 @@ export class Ky {
 	readonly #options: InternalOptions;
 	#originalRequest?: Request;
 	readonly #userProvidedAbortSignal?: AbortSignal;
-	#cachedNormalizedOptions?: NormalizedOptions;
+	#cachedNormalizedOptions: NormalizedOptions | undefined;
 
 	// eslint-disable-next-line complexity
 	constructor(input: Input, options: Options = {}) {
@@ -262,11 +279,7 @@ export class Ky {
 				throw new Error('Request streams are not supported in your environment. The `duplex` option for `Request` is not available.');
 			}
 
-			const originalBody = this.request.body;
-			if (originalBody) {
-				// Pass original body to calculate size correctly (before it becomes a stream)
-				this.request = streamRequest(this.request, this.#options.onUploadProgress, this.#options.body);
-			}
+			this.request = this.#wrapRequestWithUploadProgress(this.request, this.#options.body ?? undefined);
 		}
 	}
 
@@ -297,6 +310,16 @@ export class Ky {
 		// Wrap non-Error throws to ensure consistent error handling
 		const errorObject = error instanceof Error ? error : new NonError(error);
 
+		// Handle forced retry from afterResponse hook - skip method check and shouldRetry
+		if (errorObject instanceof ForceRetryError) {
+			return errorObject.customDelay ?? this.#calculateDelay();
+		}
+
+		// Check if method is retriable for non-forced retries
+		if (!this.#options.retry.methods.includes(this.request.method.toLowerCase())) {
+			throw error;
+		}
+
 		// User-provided shouldRetry function takes precedence over all other checks
 		if (this.#options.retry.shouldRetry !== undefined) {
 			const result = await this.#options.retry.shouldRetry({error: errorObject, retryCount: this.#retryCount});
@@ -371,6 +394,16 @@ export class Ky {
 			// Only use user-provided signal for delay, not our internal abortController
 			await delay(ms, this.#userProvidedAbortSignal ? {signal: this.#userProvidedAbortSignal} : {});
 
+			// Apply custom request from forced retry before beforeRetry hooks
+			// Ensure the custom request has the correct managed signal for timeouts and user aborts
+			if (error instanceof ForceRetryError && error.customRequest) {
+				const managedRequest = this.#options.signal
+					? new globalThis.Request(error.customRequest, {signal: this.#options.signal})
+					: new globalThis.Request(error.customRequest);
+
+				this.#assignRequest(managedRequest);
+			}
+
 			for (const hook of this.#options.hooks.beforeRetry) {
 				// eslint-disable-next-line no-await-in-loop
 				const hookResult = await hook({
@@ -380,9 +413,8 @@ export class Ky {
 					retryCount: this.#retryCount,
 				});
 
-				// If a Request is returned, use it for the retry
 				if (hookResult instanceof globalThis.Request) {
-					this.request = hookResult;
+					this.#assignRequest(hookResult);
 					break;
 				}
 
@@ -418,14 +450,14 @@ export class Ky {
 				{retryCount: this.#retryCount},
 			);
 
-			if (result instanceof Request) {
-				this.request = result;
-				break;
-			}
-
 			if (result instanceof Response) {
 				return result;
 			}
+
+			if (result instanceof globalThis.Request) {
+				this.#assignRequest(result);
+				break;
+			}
 		}
 
 		const nonRequestOptions = findUnknownOptions(this.request, this.#options);
@@ -449,4 +481,17 @@ export class Ky {
 
 		return this.#cachedNormalizedOptions;
 	}
+
+	#assignRequest(request: Request): void {
+		this.#cachedNormalizedOptions = undefined;
+		this.request = this.#wrapRequestWithUploadProgress(request);
+	}
+
+	#wrapRequestWithUploadProgress(request: Request, originalBody?: BodyInit): Request {
+		if (!this.#options.onUploadProgress || !request.body) {
+			return request;
+		}
+
+		return streamRequest(request, this.#options.onUploadProgress, originalBody ?? this.#options.body ?? undefined);
+	}
 }