Fix incorrect addition of the "Vary: Accept-Encoding" header

packages/sirv/index.mjs

@@ -187,7 +187,13 @@ export default function (dir, opts={}) {
 			return res.end();
 		}
 
-		if (gzips || brots) {
+		// When a users "requests" a file, sirv may "choose" a different (compressed) version based
+		// on the current options (gzip, brotli), request headers ("Accept-Encoding"), and available files.
+		// We should only set "Vary: Accept-Encoding" if a compressed version of the requested file exists
+		// and was chosen instead of the requested file.
+		const isChosenFileCompressed = !!data.headers['Content-Encoding'];
+		const doesChosenFileMatchRequestedFile = data.abs.endsWith(pathname);
+		if (isChosenFileCompressed && !doesChosenFileMatchRequestedFile) {
 			res.setHeader('Vary', 'Accept-Encoding');
 		}
 

tests/public/no-compressed-version.txt

@@ -0,0 +1 @@
+no-compressed-version.txt

tests/sirv.mjs

@@ -820,6 +820,51 @@ brotli('should be preferred when "Accept-Encoding" allows both', async () => {
 	}
 });
 
+brotli('should set "Vary: Accept-Encoding" when a compressed version of the requested file exists', async () => {
+	let server = utils.http({ brotli: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/index.html', { headers });
+		assert.is(res.headers['content-type'], 'text/html;charset=utf-8');
+		assert.is(res.headers['vary'], 'Accept-Encoding');
+		assert.is(res.data, 'brotli html\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
+brotli('should not set "Vary: Accept-Encoding" when a compressed file is requested directly', async () => {
+	let server = utils.http({ brotli: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/index.html.br', { headers });
+		assert.is(res.headers['content-type'], 'text/html;charset=utf-8');
+		assert.is(res.headers['vary'], undefined);
+		assert.is(res.data, 'brotli html\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
+brotli('should not set "Vary: Accept-Encoding" when a compressed version of the requested file does not exist', async () => {
+	let server = utils.http({ brotli: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/no-compressed-version.txt', { headers });
+		assert.is(res.headers['content-type'], 'text/plain');
+		assert.is(res.headers['vary'], undefined);
+		assert.is(res.data, 'no-compressed-version.txt\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
 brotli.run();
 
 // ---
@@ -885,6 +930,51 @@ gzip('should defer to brotli when "Accept-Encoding" allows both', async () => {
 	}
 });
 
+gzip('should set "Vary: Accept-Encoding" when a compressed version of the requested file exists', async () => {
+	let server = utils.http({ gzip: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/index.html', { headers });
+		assert.is(res.headers['content-type'], 'text/html;charset=utf-8');
+		assert.is(res.headers['vary'], 'Accept-Encoding');
+		assert.is(res.data, 'gzip html\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
+gzip('should not set "Vary: Accept-Encoding" when a compressed file is requested directly', async () => {
+	let server = utils.http({ gzip: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/index.html.gz', { headers });
+		assert.is(res.headers['content-type'], 'text/html;charset=utf-8');
+		assert.is(res.headers['vary'], undefined);
+		assert.is(res.data, 'gzip html\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
+gzip('should not set "Vary: Accept-Encoding" when a compressed version of the requested file does not exist', async () => {
+	let server = utils.http({ gzip: true });
+	let headers = { 'Accept-Encoding': 'br,gzip' };
+
+	try {
+		let res = await server.send('GET', '/no-compressed-version.txt', { headers });
+		assert.is(res.headers['content-type'], 'text/plain');
+		assert.is(res.headers['vary'], undefined);
+		assert.is(res.data, 'no-compressed-version.txt\n');
+		assert.is(res.statusCode, 200);
+	} finally {
+		server.close();
+	}
+});
+
 gzip.run();
 
 // ---