feat: support non-standard retry-after header formats (#713)

Add support for non-standard retry-after header formats used by
CivicPlus and other services that use "30s" or "1m30s" notation
instead of the standard seconds or HTTP date format.

Changes:
- Extract retry-after parsing logic into parseRetryAfter() method
- Add regex support for "Xs" and "XmYs" time formats
- Add tests for non-standard formats (3s, 1m1s)
- Fix missing redirect parameter in 405 and fallback GET requests

Closes #556



🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: JustinBeckwith

src/index.ts

@@ -297,6 +297,7 @@ export class LinkChecker extends EventEmitter {
 				response = await makeRequest('GET', options.url.href, {
 					headers: options.checkOptions.headers,
 					timeout: options.checkOptions.timeout,
+					redirect: redirectMode,
 				});
 				if (this.shouldRetryAfter(response, options)) {
 					return;
@@ -321,6 +322,7 @@ export class LinkChecker extends EventEmitter {
 				response = await makeRequest('GET', options.url.href, {
 					headers: options.checkOptions.headers,
 					timeout: options.checkOptions.timeout,
+					redirect: redirectMode,
 				});
 				if (this.shouldRetryAfter(response, options)) {
 					return;
@@ -554,6 +556,30 @@ export class LinkChecker extends EventEmitter {
 		}
 	}
 
+	/**
+	 * Parse the retry-after header value into a timestamp.
+	 * Supports standard formats (seconds, HTTP date) and non-standard formats (30s, 1m30s).
+	 * @param retryAfterRaw Raw retry-after header value
+	 * @returns Timestamp in milliseconds when to retry, or NaN if invalid
+	 */
+	private parseRetryAfter(retryAfterRaw: string): number {
+		// Try parsing as seconds
+		let retryAfter = Number(retryAfterRaw) * 1000 + Date.now();
+		if (!Number.isNaN(retryAfter)) return retryAfter;
+
+		// Try parsing as HTTP date
+		retryAfter = Date.parse(retryAfterRaw);
+		if (!Number.isNaN(retryAfter)) return retryAfter;
+
+		// Handle non-standard formats like "30s" or "1m30s"
+		const matches = retryAfterRaw.match(/^(?:(\d+)m)?(\d+)s$/);
+		if (!matches) return Number.NaN;
+
+		return (
+			(Number(matches[1] || 0) * 60 + Number(matches[2])) * 1000 + Date.now()
+		);
+	}
+
 	/**
 	 * Check the incoming response for a `retry-after` header.  If present,
 	 * and if the status was an HTTP 429, calculate the date at which this
@@ -572,14 +598,9 @@ export class LinkChecker extends EventEmitter {
 			return false;
 		}
 
-		// The `retry-after` header can come in either <seconds> or
-		// A specific date to go check.
-		let retryAfter = Number(retryAfterRaw) * 1000 + Date.now();
+		const retryAfter = this.parseRetryAfter(retryAfterRaw);
 		if (Number.isNaN(retryAfter)) {
-			retryAfter = Date.parse(retryAfterRaw);
-			if (Number.isNaN(retryAfter)) {
-				return false;
-			}
+			return false;
 		}
 
 		// Check to see if there is already a request to wait for this host

test/test.retry.ts

@@ -99,6 +99,46 @@ describe('retries', () => {
 		assert.ok(results.passed);
 	});
 
+	it('should retry 429s with non-standard seconds format (3s)', async () => {
+		const mockPool = mockAgent.get('http://example.invalid');
+		mockPool.intercept({ path: '/', method: 'GET' }).reply(429, '', {
+			headers: { 'retry-after': '3s' },
+		});
+		mockPool.intercept({ path: '/', method: 'GET' }).reply(200, '');
+
+		const { promise, resolve } = invertedPromise();
+		const checker = new LinkChecker().on('retry', resolve);
+		const clock = vi.useFakeTimers({ shouldAdvanceTime: true });
+		const checkPromise = checker.check({
+			path: 'test/fixtures/basic',
+			retry: true,
+		});
+		await promise;
+		await clock.advanceTimersByTime(3000);
+		const results = await checkPromise;
+		assert.ok(results.passed);
+	});
+
+	it('should retry 429s with non-standard minutes and seconds format (1m1s)', async () => {
+		const mockPool = mockAgent.get('http://example.invalid');
+		mockPool.intercept({ path: '/', method: 'GET' }).reply(429, '', {
+			headers: { 'retry-after': '1m1s' },
+		});
+		mockPool.intercept({ path: '/', method: 'GET' }).reply(200, '');
+
+		const { promise, resolve } = invertedPromise();
+		const checker = new LinkChecker().on('retry', resolve);
+		const clock = vi.useFakeTimers({ shouldAdvanceTime: true });
+		const checkPromise = checker.check({
+			path: 'test/fixtures/basic',
+			retry: true,
+		});
+		await promise;
+		await clock.advanceTimersByTime(61_000);
+		const results = await checkPromise;
+		assert.ok(results.passed);
+	});
+
 	it('should detect requests to wait on the same host', async () => {
 		const mockPool = mockAgent.get('http://example.invalid');
 		mockPool.intercept({ path: '/1', method: 'GET' }).reply(429, '', {