Fix it incorrectly modifying the original response

And correctly remove `content-length` header.

Fixes #28 (comment)

Fixes #37

index.js

@@ -9,9 +9,11 @@ export default function decompressResponse(response) {
 		return response;
 	}
 
-	delete response.headers['content-encoding'];
-
 	let isEmpty = true;
+	let finalStream = new PassThroughStream();
+
+	// Clone headers to avoid modifying the original response headers
+	const headers = {...response.headers};
 
 	function handleContentEncoding(data) {
 		const decompressStream = contentEncoding === 'br'
@@ -51,7 +53,7 @@ export default function decompressResponse(response) {
 		},
 	});
 
-	const finalStream = new PassThroughStream({
+	finalStream = new PassThroughStream({
 		autoDestroy: false,
 		destroy(error, callback) {
 			response.destroy();
@@ -60,6 +62,10 @@ export default function decompressResponse(response) {
 		},
 	});
 
+	delete headers['content-encoding'];
+	delete headers['content-length'];
+	finalStream.headers = headers;
+
 	mimicResponse(response, finalStream);
 	response.pipe(checker);
 

test/test.js

@@ -153,3 +153,17 @@ test('passthrough on non-compressed data', async t => {
 
 	t.is(await getStream(response), fixture);
 });
+
+test('original response retains content-encoding and content-length headers', async t => {
+	const originalResponse = await httpGetP(server.url);
+	const decompressedResponse = decompressResponse(originalResponse);
+
+	t.is(originalResponse.headers['content-encoding'], 'gzip');
+	t.truthy(originalResponse.headers['content-length']);
+	t.is(decompressedResponse.headers['content-encoding'], undefined);
+	t.is(decompressedResponse.headers['content-length'], undefined);
+
+	decompressedResponse.setEncoding('utf8');
+
+	t.is(await getStream(decompressedResponse), fixture);
+});