From d27c2d364f1d0b44521177965708583b16cb175a Mon Sep 17 00:00:00 2001
From: astrobot-houston <fred+astrobot@astro.build>
Date: Mon, 6 Jul 2026 02:53:21 +0000
Subject: [PATCH] fix(routing): prevent trailing slash on file extension
 endpoint paths in stringifyParams

When trailingSlash is 'always', stringifyParams (via getRouteGenerator)
was appending a trailing slash to endpoint paths with file extensions
(e.g. /og/foo.png/). But the route pattern for such endpoints is
generated with trailingSlash 'never' by trailingSlashForPath() in
create-manifest.ts (e.g. /^\/og\/(.*?)\.png$/). This mismatch caused
getParams() to fail matching, leading to NoMatchingStaticPathFound
during static builds.

Apply the same trailingSlashForPath logic in stringifyParams: when the
route is an endpoint with a file extension, force trailingSlash to
'never'.

Fixes #17306
---
 packages/astro/src/core/routing/params.ts     |  9 ++++
 .../test/units/routing/get-params.test.ts     | 45 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/packages/astro/src/core/routing/params.ts b/packages/astro/src/core/routing/params.ts
index 0f9bae073cfb..4603dde72489 100644
--- a/packages/astro/src/core/routing/params.ts
+++ b/packages/astro/src/core/routing/params.ts
@@ -1,3 +1,4 @@
+import { hasFileExtension } from '@astrojs/internal-helpers/path';
 import type { GetStaticPathsItem } from '../../types/public/common.js';
 import type { AstroConfig } from '../../types/public/index.js';
 import type { RouteData } from '../../types/public/internal.js';
@@ -15,6 +16,14 @@ export function stringifyParams(
 	route: RouteData,
 	trailingSlash: AstroConfig['trailingSlash'],
 ) {
+	// Endpoint routes with file extensions (e.g. [slug].png.ts) should never
+	// append a trailing slash, matching the pattern generated in create-manifest.ts
+	// by trailingSlashForPath(). Without this, the generated path (e.g. /og/foo.png/)
+	// won't match the route pattern (e.g. /^\/og\/(.*?)\.png$/) and getParams() fails.
+	if (route.type === 'endpoint' && hasFileExtension(route.route)) {
+		trailingSlash = 'never';
+	}
+
 	// validate parameter values then stringify each value
 	const validatedParams: Record<string, string> = {};
 	for (const [key, value] of Object.entries(params)) {
diff --git a/packages/astro/test/units/routing/get-params.test.ts b/packages/astro/test/units/routing/get-params.test.ts
index 648e72d0b39f..c8c4e43e9117 100644
--- a/packages/astro/test/units/routing/get-params.test.ts
+++ b/packages/astro/test/units/routing/get-params.test.ts
@@ -3,6 +3,7 @@ import { describe, it } from 'node:test';
 import * as cheerio from 'cheerio';
 import { createComponent, render } from '../../../dist/runtime/server/index.js';
 import { getParams } from '../../../dist/core/render/params-and-props.js';
+import { stringifyParams } from '../../../dist/core/routing/params.js';
 import { dynamicPart, makeRoute, spreadPart, staticPart } from './test-helpers.ts';
 import { createTestApp, createPage } from '../mocks.ts';
 
@@ -167,6 +168,50 @@ describe('getParams', () => {
 	});
 });
 
+describe('stringifyParams', () => {
+	it('should not append trailing slash for file extension endpoint routes with trailingSlash always (issue #17306)', () => {
+		const route = makeRoute({
+			route: '/og/[...slug].png',
+			segments: [[staticPart('og')], [spreadPart('...slug'), staticPart('.png')]],
+			trailingSlash: 'never',
+			pathname: undefined,
+			type: 'endpoint',
+		});
+
+		const result = stringifyParams({ slug: '概率论/参数估计' }, route, 'always');
+		assert.equal(result, '/og/概率论/参数估计.png');
+		// Verify the generated path matches the route pattern
+		assert.ok(route.pattern.test(result), 'generated path should match route pattern');
+	});
+
+	it('should not append trailing slash for single dynamic file extension endpoint', () => {
+		const route = makeRoute({
+			route: '/api/[name].json',
+			segments: [[staticPart('api')], [dynamicPart('name'), staticPart('.json')]],
+			trailingSlash: 'never',
+			pathname: undefined,
+			type: 'endpoint',
+		});
+
+		const result = stringifyParams({ name: 'bar' }, route, 'always');
+		assert.equal(result, '/api/bar.json');
+		assert.ok(route.pattern.test(result), 'generated path should match route pattern');
+	});
+
+	it('should still append trailing slash for endpoints without file extensions', () => {
+		const route = makeRoute({
+			route: '/api/[name]',
+			segments: [[staticPart('api')], [dynamicPart('name')]],
+			trailingSlash: 'always',
+			pathname: undefined,
+			type: 'endpoint',
+		});
+
+		const result = stringifyParams({ name: 'bar' }, route, 'always');
+		assert.equal(result, '/api/bar/');
+	});
+});
+
 describe('Params rendered via App', () => {
 	const paramPage = createComponent((result: any, props: any, slots: any) => {
 		const Astro = result.createAstro(props, slots);