Thin Thin → Future

If i want to transmit a encrypted file i am missing bytes. It happens not to all Files. But it is reproduce able with the attached file. Which is 4001 bytes long, but i get only 4000 in the xhr.response.
There is some special border by 4000 bytes, but it happens to larger files at "random" positions.
I use this code to retrive the file from thin.

function requestFile(filename) {
  var xhr = new XMLHttpRequest();
  xhr.open('POST', '/request', true);
  xhr.responseType = 'arraybuffer';
  xhr.onloadend = function(e) {
    if (this.status == 200) {
      console.log("OK, got ArrayBuffer");
      decrypted.ciphertext = new DataView(xhr.response); 
    };
  }

  var formData = new FormData();
  formData.append('filename', filename);
  xhr.send(formData);
}

I attach the code for thin and my test file.

I all so have seen in wireshark that all 0x0d bytes are changed to 0x0a but i dont know why. I have set the contentype to octet-stream.

Please request if a am not clear enought or if more testfiles needed, longer files tend to loose more bytes. A 1 MB test file lose 12 bytes.