fix: avoid Buffer re-encode during compression (#184)

If the data is already a Buffer then just compress it, don't convert it to a string and back to a Buffer again before compressing it.

A test with Buffer input is added. The input is chosen carefully to ensure that if it was assumed to be UTF-8 encoded it would not be the same when decompressed and added an additional assertion for the decompressed data to match the original.

lib/request-wrapper.ts

@@ -444,6 +444,8 @@ export class RequestWrapper {
       if (isStream(data)) {
         const streamData = await streamToPromise(data);
         reqBuffer = Buffer.isBuffer(streamData) ? streamData : Buffer.from(streamData);
+      } else if (Buffer.isBuffer(data)) {
+        reqBuffer = data;
       } else if (data.toString && data.toString() !== '[object Object]' && !Array.isArray(data)) {
         // this handles pretty much any primitive that isnt a JSON object or array
         reqBuffer = Buffer.from(data.toString());

test/unit/request-wrapper.test.js

@@ -908,6 +908,19 @@ describe('gzipRequestBody', () => {
     expect(headers['Content-Encoding']).toBe('gzip');
   });
 
+  it('should compress buffer data into a buffer', async () => {
+    // Use an invalid UTF-8 overlong encoding as example binary data
+    const originalData = Buffer.from('f08282ac', 'hex');
+    const headers = {};
+
+    const data = await requestWrapperInstance.gzipRequestBody(originalData, headers);
+    expect(data).toBeInstanceOf(Buffer);
+    expect(gzipSpy).toHaveBeenCalled();
+    expect(headers['Content-Encoding']).toBe('gzip');
+    // If UTF-8 has been assumed the data will not match
+    expect(zlib.gunzipSync(data)).toEqual(originalData);
+  });
+
   it('should log an error and return data unaltered if data cant be stringified', async () => {
     let data = { key: 'value' };
     data.circle = data;