Add support for custom non-html route encoding (#4549)

* Add custom encoding support for non-html routes

* Add changeset

* Add tests for png and json routes

11 files changed, 93 insertions, 3 deletions

diff --git a/.changeset/stale-camels-invent.md b/.changeset/stale-camels-invent.md
new file mode 100644
index 000000000..e3d88bc33
--- /dev/null
+++ b/.changeset/stale-camels-invent.md
@@ -0,0 +1,5 @@
+---
+'astro': minor
+---
+
+Allow specifying custom encoding when using a non-html route. Only option before was 'utf-8' and now that is just the default.
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index b2347c410..c358d63e7 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -1085,6 +1085,7 @@ export interface APIContext {
 
 export interface EndpointOutput {
 	body: Body;
+	encoding?: BufferEncoding;
 }
 
 export type APIRoute = (
diff --git a/packages/astro/src/core/build/generate.ts b/packages/astro/src/core/build/generate.ts
index 406186a21..b6ebf4697 100644
--- a/packages/astro/src/core/build/generate.ts
+++ b/packages/astro/src/core/build/generate.ts
@@ -391,6 +391,7 @@ async function generatePath(
 	};
 
 	let body: string;
+	let encoding: BufferEncoding | undefined;
 	if (pageData.route.type === 'endpoint') {
 		const result = await callEndpoint(mod as unknown as EndpointHandler, options);
 
@@ -398,6 +399,7 @@ async function generatePath(
 			throw new Error(`Returning a Response from an endpoint is not supported in SSG mode.`);
 		}
 		body = result.body;
+		encoding = result.encoding;
 	} else {
 		const response = await render(options);
 
@@ -413,5 +415,5 @@ async function generatePath(
 	const outFile = getOutFile(astroConfig, outFolder, pathname, pageData.route.type);
 	pageData.route.distURL = outFile;
 	await fs.promises.mkdir(outFolder, { recursive: true });
-	await fs.promises.writeFile(outFile, body, 'utf-8');
+	await fs.promises.writeFile(outFile, body, encoding ?? 'utf-8');
 }
diff --git a/packages/astro/src/core/endpoint/index.ts b/packages/astro/src/core/endpoint/index.ts
index 9e974ee36..73c96ae64 100644
--- a/packages/astro/src/core/endpoint/index.ts
+++ b/packages/astro/src/core/endpoint/index.ts
@@ -21,6 +21,7 @@ type EndpointCallResult =
 	| {
 			type: 'simple';
 			body: string;
+			encoding?: BufferEncoding;
 	  }
 	| {
 			type: 'response';
@@ -52,5 +53,6 @@ export async function call(
 	return {
 		type: 'simple',
 		body: response.body,
+		encoding: response.encoding,
 	};
 }
diff --git a/packages/astro/test/fixtures/non-html-pages/package.json b/packages/astro/test/fixtures/non-html-pages/package.json
new file mode 100644
index 000000000..c3a215d98
--- /dev/null
+++ b/packages/astro/test/fixtures/non-html-pages/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "@test/non-html-pages",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/non-html-pages/src/images/placeholder.png b/packages/astro/test/fixtures/non-html-pages/src/images/placeholder.png
new file mode 100644
index 000000000..62841efdb
--- /dev/null
+++ b/packages/astro/test/fixtures/non-html-pages/src/images/placeholder.png
diff --git a/packages/astro/test/fixtures/non-html-pages/src/pages/about.json.ts b/packages/astro/test/fixtures/non-html-pages/src/pages/about.json.ts
new file mode 100644
index 000000000..af61847f3
--- /dev/null
+++ b/packages/astro/test/fixtures/non-html-pages/src/pages/about.json.ts
@@ -0,0 +1,11 @@
+// Returns the file body for this non-HTML file.
+// The content type is based off of the extension in the filename,
+// in this case: about.json.
+export async function get() {
+	return {
+		body: JSON.stringify({
+			name: 'Astro',
+			url: 'https://astro.build/',
+		}),
+	};
+}
diff --git a/packages/astro/test/fixtures/non-html-pages/src/pages/placeholder.png.ts b/packages/astro/test/fixtures/non-html-pages/src/pages/placeholder.png.ts
new file mode 100644
index 000000000..0c2d3806b
--- /dev/null
+++ b/packages/astro/test/fixtures/non-html-pages/src/pages/placeholder.png.ts
@@ -0,0 +1,17 @@
+import { promises as fs } from 'node:fs';
+
+import type { APIRoute } from 'astro';
+
+export const get: APIRoute = async function get() {
+	try {
+		// Image is in the public domain. Sourced from
+		// https://en.wikipedia.org/wiki/File:Portrait_placeholder.png
+		const buffer = await fs.readFile('./test/fixtures/non-html-pages/src/images/placeholder.png');
+		return {
+			body: buffer.toString('binary'),
+			encoding: 'binary',
+		} as const;
+	} catch (error: unknown) {
+		throw new Error(`Something went wrong in placeholder.png route!: ${error as string}`);
+	}
+};
diff --git a/packages/astro/test/non-html-pages.test.js b/packages/astro/test/non-html-pages.test.js
new file mode 100644
index 000000000..e1b89ee6a
--- /dev/null
+++ b/packages/astro/test/non-html-pages.test.js
@@ -0,0 +1,38 @@
+import { expect } from 'chai';
+import { loadFixture } from './test-utils.js';
+
+describe('Non-HTML Pages', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({ root: './fixtures/non-html-pages/' });
+		await fixture.build();
+	});
+
+	describe('json', () => {
+		it('should match contents', async () => {
+			const json = JSON.parse(await fixture.readFile('/about.json'));
+			expect(json).to.have.property('name', 'Astro');
+			expect(json).to.have.property('url', 'https://astro.build/');
+		});
+	});
+
+	describe('png', () => {
+		it('should not have had its encoding mangled', async () => {
+			const buffer = await fixture.readFile('/placeholder.png', 'base64');
+
+			// Sanity check the first byte
+			const hex = Buffer.from(buffer, 'base64').toString('hex');
+			const firstHexByte = hex.slice(0, 2);
+			// If we accidentally utf8 encode the png, the first byte (in hex) will be 'c2'
+			expect(firstHexByte).to.not.equal('c2');
+			// and if correctly encoded in binary, it should be '89'
+			expect(firstHexByte).to.equal('89');
+
+			// Make sure the whole buffer (in base64) matches this snapshot
+			expect(buffer).to.equal(
+				'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'
+			);
+		});
+	});
+});
diff --git a/packages/astro/test/test-utils.js b/packages/astro/test/test-utils.js
index c6150b26b..59a925314 100644
--- a/packages/astro/test/test-utils.js
+++ b/packages/astro/test/test-utils.js
@@ -146,8 +146,8 @@ export async function loadFixture(inlineConfig) {
 			const previewServer = await preview(config, { logging, telemetry, ...opts });
 			return previewServer;
 		},
-		readFile: (filePath) =>
-			fs.promises.readFile(new URL(filePath.replace(/^\//, ''), config.outDir), 'utf8'),
+		readFile: (filePath, encoding) =>
+			fs.promises.readFile(new URL(filePath.replace(/^\//, ''), config.outDir), encoding ?? 'utf8'),
 		readdir: (fp) => fs.promises.readdir(new URL(fp.replace(/^\//, ''), config.outDir)),
 		glob: (p) =>
 			fastGlob(p, {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 5e7d1dce1..e5c2a6f1e 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1666,6 +1666,12 @@ importers:
   packages/astro/test/fixtures/multiple-renderers/renderers/two:
     specifiers: {}
 
+  packages/astro/test/fixtures/non-html-pages:
+    specifiers:
+      astro: workspace:*
+    dependencies:
+      astro: link:../../..
+
   packages/astro/test/fixtures/page-format:
     specifiers:
       astro: workspace:*