Problem with FS.writeFile

[Stefan Meier]

Hi,

I have a small problem with the following code which aims to download a binary file from a server ans save it to the virtual FS with the FS.writeFile. No matter what I try the file doesn't get written, so perhaps I am doing something substancially wrong. Can anyone provide a hint what I need to correct?

JS code:

                xhr = new XMLHttpRequest();
                xhr.open("GET", "dtest", true);
                xhr.responseType = "arraybuffer";
                xhr.overrideMimeType("application/octet-stream");
                xhr.onreadystatechange = function () {
                    if (xhr.readyState === 4 && xhr.status === 200) {
                       console.log(xhr.response);
                       blob = new Blob([new Uint8Array(xhr.response)], {type: "application/octet-stream"});
                       console.log(blob);
                       FS.writeFile('/dtest', [blob], { encoding: "binary" });
                       console.log('dtest: '+(FS.stat('/dtest')).size);
                       refreshSGList();
                   }
                };
                xhr.send();

From the console output I guess that the download from the file is working, the size is the expected:

ArrayBuffer { byteLength: 11667 }
Blob { size: 11667, type: "application/octet-stream" }
"dtest: 1"

But the size that is reported back from FS.stat is wrong and the file is unusable, so I think it is not written eventually.

I am using this with emscripten sdk 1.25 on OSX 10.8.5.

Many thanks for your help!
Stefan

[Alon Zakai]

Can you please make a complete standalone testcase showing the issue, that is runnable in node? Much easier to debug that way.

- Alon

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[Stefan Meier]

Hi Alon,
thanks for offering your help! I have never worked with node before, but when writing the testcase I recognized the error I had in my source. Just in case somebody has a use for it (downloading custom binary data from a server and storing it to the virtual FS). This is the slightly modified version that works as expected (probably needs to be adapted to responseType blob when all browsers support it):

xhr = new XMLHttpRequest();
xhr.open("GET", "/msa2/dtest", true);

xhr.responseType = "arraybuffer";
xhr.overrideMimeType("application/octet-stream");
xhr.onreadystatechange = function () {
  if (xhr.readyState === 4 && xhr.status === 200) {
      console.log(xhr.response);

      FS.writeFile('/dtest', new Uint8Array(xhr.response), { encoding: "binary" });

      console.log('dtest: '+(FS.stat('/dtest')).size);
  }

};
xhr.send();

Thanks again for caring!
Stefan