I’m trying to upload a big file (~500MB), 100 MB each chunk and tries with startupload, continueupload and finishupload SharePoint APIs.

The following code takes long time to execute and prints the console messages properly. But finally written 0 byte only. Not sure what i’m missing here. Any help is much appreciated. Thanks.

    HttpClient client = new HttpClient();
    client.Timeout = TimeSpan.FromMinutes(15);
    client.DefaultRequestHeaders.Add("Authorization", $"Bearer {accessToken}");

    string fileName = Path.GetFileName(sourcePath);
    string createFileRequestUrl = $"{baseURL}/_api/web/getfolderbyserverrelativeurl('{targetFolderUrl}')/files/add(url='{fileName}',overwrite=true)";
    HttpResponseMessage response = await client.PostAsync(createFileRequestUrl, null);

    if (response.IsSuccessStatusCode)
    {
        await response.Content.ReadAsStringAsync();
    }

    var targetUrl = Path.Combine(targetFolderUrl, fileName);
    var firstChunk = true;
    var uploadId = Guid.NewGuid();
    var offset = 0L;

    using (FileStream fileStream = File.OpenRead(sourcePath))

    using (BinaryReader reader = new BinaryReader(fileStream))
    {
        var endpointUrl = "";
        var buffer = new byte[chunkSizeBytes];
        int bytesRead;

        while ((bytesRead = reader.Read(buffer, 0, buffer.Length)) > 0)
        {
            if (firstChunk)
            {
                endpointUrl = $"{baseURL}/_api/web/getfilebyserverrelativeurl('{targetUrl}')/startupload(uploadId=guid'{uploadId}')";
                response = await client.PostAsync(endpointUrl, new ByteArrayContent(buffer));
                firstChunk = false;
            }
            else if (reader.BaseStream.Position == reader.BaseStream.Length)
            {
                endpointUrl = $"{baseURL}/_api/web/getfilebyserverrelativeurl('{targetUrl}')/finishupload(uploadId=guid'{uploadId}',fileOffset='{offset}')";
                var finalBuffer = new byte[bytesRead];
                Array.Copy(buffer, finalBuffer, finalBuffer.Length);
                response = await client.PostAsync(endpointUrl, new ByteArrayContent(finalBuffer));
            }
            else
            {
                endpointUrl = $"{baseURL}/_api/web/getfilebyserverrelativeurl('{targetUrl}')/continueupload(uploadId=guid'{uploadId}',fileOffset='{offset}')";
                response = await client.PostAsync(endpointUrl, null);
            }
            offset += bytesRead;
            chunkUploaded(offset, reader.BaseStream.Length);
        }
    }