[Unity][Android] API compression does not work

Edit: Tests with Fiddler show that the SDK claims it's umcompressed, but the response is clearly compressed. Technically a bug, but any user can ignore this bug.

API compression work in the editor (2020.3.8 LTS Platform Android), but not on the device.

• Using UnityWebRequest. PlayFabSDK: UnitySDK-2.108.210511.
• Headers, URL, payload is the same in both.
• Request compression works fine on both (makes it even weirder!).
• Response is compressed properly in the editor, but not on the device!
• Editor respose bytes: 31 & 139
• Device response bytes: 123 & 34
• No errors or warnings at any time. Response is fine on the device, just not compressed.

I've tried various things, but none helped. I even tried other Unity versions and other projects, but the result was the same. It's a mystery to me. Nothing indicates that the server even know it's a device making the call, yet he delivers different responses.

Try it for yourself with an APK. Sample project can be provided upon request.

Here's what I did in PlayFabUnityHttp.cs to find out about the issue (the rest of the project is a simple LoginWithCustomIDRequest and nothing more):

public void MakeApiCall(object reqContainerObj)
        {
            CallRequestContainer reqContainer = (CallRequestContainer)reqContainerObj;
            reqContainer.RequestHeaders["Content-Type"] = "application/json";
            Debug.Log("Payload before compressing: " + System.Text.Encoding.UTF8.GetString(reqContainer.Payload));

            Debug.Log("Compression: "+ PlayFabSettings.CompressApiData);
#if !UNITY_WSA && !UNITY_WP8 && !UNITY_WEBGL
            if (PlayFabSettings.CompressApiData)
            {
                reqContainer.RequestHeaders["Content-Encoding"] = "gzip"; //GZIP
                reqContainer.RequestHeaders["X-Accept-Encoding"] = "gzip"; // UpperLower case doesn't change anything

                using (var stream = new MemoryStream())
                {
                    using (var zipstream = new Ionic.Zlib.GZipStream(stream, Ionic.Zlib.CompressionMode.Compress,
                        Ionic.Zlib.CompressionLevel.BestCompression))
                    {
                        zipstream.Write(reqContainer.Payload, 0, reqContainer.Payload.Length);
                    }
                    reqContainer.Payload = stream.ToArray();
                }
            }
#endif

            Debug.Log("Payload after compressing: " + System.Text.Encoding.UTF8.GetString(reqContainer.Payload));

            Debug.Log("FullUrl: "+reqContainer.FullUrl);
            Debug.Log("ApiEndpoint: " + reqContainer.ApiEndpoint);
            string headers = "";
            foreach(var h in reqContainer.RequestHeaders)
            {
                headers += h.Key + ": " + h.Value + "; ";
            }
            Debug.Log(headers);


            // Start the www corouting to Post, and get a response or error which is then passed to the callbacks.
            PlayFabHttp.instance.StartCoroutine(Post(reqContainer));
        }

        private IEnumerator Post(CallRequestContainer reqContainer)
        {
#if PLAYFAB_REQUEST_TIMING
            var stopwatch = System.Diagnostics.Stopwatch.StartNew();
            var startTime = DateTime.UtcNow;
#endif

            var www = new UnityWebRequest(reqContainer.FullUrl)
            {
                uploadHandler = new UploadHandlerRaw(reqContainer.Payload),
                downloadHandler = new DownloadHandlerBuffer(),
                method = "POST"
            };

            foreach (var headerPair in reqContainer.RequestHeaders)
            {
                if (!string.IsNullOrEmpty(headerPair.Key) && !string.IsNullOrEmpty(headerPair.Value))
                    www.SetRequestHeader(headerPair.Key, headerPair.Value);
                else
                    Debug.LogWarning("Null header: " + headerPair.Key + " = " + headerPair.Value);
            }

#if UNITY_2017_2_OR_NEWER
            yield return www.SendWebRequest();
#else
            yield return www.Send();
#endif

#if PLAYFAB_REQUEST_TIMING
            stopwatch.Stop();
            var timing = new PlayFabHttp.RequestTiming {
                StartTimeUtc = startTime,
                ApiEndpoint = reqContainer.ApiEndpoint,
                WorkerRequestMs = (int)stopwatch.ElapsedMilliseconds,
                MainThreadRequestMs = (int)stopwatch.ElapsedMilliseconds
            };
            PlayFabHttp.SendRequestTiming(timing);
#endif
            Debug.Log("Result:");
            if (!string.IsNullOrEmpty(www.error))
            {
                OnError(www.error, reqContainer);
            }
            else
            {
                try
                {
                    byte[] responseBytes = www.downloadHandler.data;
                    Debug.Log(www.url);
                    Debug.Log("Payload before decompressing: "+System.Text.Encoding.UTF8.GetString(responseBytes));
                    bool isGzipCompressed = responseBytes != null && responseBytes[0] == 31 && responseBytes[1] == 139;
                    Debug.Log("responseBytes[0]=" + responseBytes[0] + ", responseBytes[1]=" + responseBytes[1]);
                    Debug.Log("isGzipCompressed: " + isGzipCompressed);
                    string responseText = "Unexpected error: cannot decompress GZIP stream.";
                    if (!isGzipCompressed && responseBytes != null)
                        responseText = System.Text.Encoding.UTF8.GetString(responseBytes, 0, responseBytes.Length);

                    Debug.Log("responseText before decompressing: " + responseText);
#if !UNITY_WSA && !UNITY_WP8 && !UNITY_WEBGL
                    if (isGzipCompressed)
                    {
                        Debug.Log("Decompressing!");
                        var stream = new MemoryStream(responseBytes);
                        using (var gZipStream = new Ionic.Zlib.GZipStream(stream, Ionic.Zlib.CompressionMode.Decompress, false))
                        {
                            var buffer = new byte[4096];
                            using (var output = new MemoryStream())
                            {
                                int read;
                                while ((read = gZipStream.Read(buffer, 0, buffer.Length)) > 0)
                                    output.Write(buffer, 0, read);
                                output.Seek(0, SeekOrigin.Begin);
                                var streamReader = new StreamReader(output);
                                var jsonResponse = streamReader.ReadToEnd();
                                //Debug.Log(jsonResponse);
                                Debug.Log("Payload after decompressing: " + jsonResponse);
                                OnResponse(jsonResponse, reqContainer);
                                //Debug.Log("Successful UnityHttp decompress for: " + www.url);
                            }
                        }
                    }
                    else
#endif
                    {
                        Debug.Log("Payload after decompressing: " + responseText);
                        OnResponse(responseText, reqContainer);
                    }
                }
                catch (Exception e)
                {
                    OnError("Unhandled error in PlayFabUnityHttp: " + e, reqContainer);
                }
            }
            www.Dispose();
        }