CreateFile.cs

        public async Task<bool> CreateFileAsync(string filesystem, string path, 
            string fileName, Stream stream)
        {           
            var operationResult = await this.CreateEmptyFileAsync(filesystem, path, fileName);
            if (operationResult)
            {
                var tokenInfo = await tokenProvider.GetAccessTokenV2EndpointAsync();
                var headers = Statics.Http.DefaultRequestHeaders;
                headers.Clear();
                headers.Add("Authorization", $"Bearer {tokenInfo.access_token}");
                headers.Add(API_VERSION_HEADER_NAME, API_VERSION_HEADER_VALUE);

                using (var streamContent = new StreamContent(stream))
                {
                    var resourceUrl = $"{baseUri}{filesystem}{path}{fileName}?action=append&timeout={this.Timeout}&position=0";
                    var msg = new HttpRequestMessage(new HttpMethod("PATCH"), resourceUrl);
                    msg.Content = streamContent;
                    var response = await Statics.Http.SendAsync(msg);

                    //flush the buffer to commit the file
                    var flushUrl = $"{baseUri}{filesystem}{path}{fileName}?action=flush&timeout={this.Timeout}&position={msg.Content.Headers.ContentLength}";
                    var flushMsg = new HttpRequestMessage(new HttpMethod("PATCH"), flushUrl);
                    response = await Statics.Http.SendAsync(flushMsg);

                    return response.IsSuccessStatusCode;
                }
            }
            return false;
        }