Just messing around with node.js, I am trying to get a file uploader working that chunks the file on the client side, sends pieces to the server via socket.io, and reassembles. It's a rather naive implementation, but just trying to learn. Currently if I submit a text file, it moves over and is reassembled correctly, but if I try to upload say an image file, the encoding is messed up and the file is corrupt.

I am reading on the client side as binary string, and the node fs encoding is set to binary. What else needs to happen?

Client Code

while(start < fileSize)
{
    var reader = new FileReader();
    reader.onload = function(e){
        var data = {
            "data" : e.target.result,
            "sequence" : chunkCount++
        };
        socket.emit("sendChunk", data, function(data){
            console.log("Confirmation recieved");
        });
        console.log("Log: Sent");
    };

    reader.onerror = function(e){
        alert(e.getMessage());
    };

    var blob = file.slice(start, end);
    reader.readAsBinaryString(blob);
    start = end;
    end = end + chunkSize;

}

Server Code

socket.on('sendChunk', function (data) {
    fs.appendFileSync(path + fileName, data.data, 'binary');
    console.log(data.sequence + ' - The data was appended to file ' + fileName);
});

Update

With the suggestion given, I updated the code to use base64 decoding. There is still some sequencing issues going on sometimes, but for the most part files are transferring correctly.

Client Code:

var data = {
    "data" : window.btoa(e.target.result),
    "sequence" : chunkCount++
};
socket.emit("sendChunk", data, function(data){
    console.log("Confirmation recieved");
});

Server Code:

var decoded =  new Buffer(data.data, 'base64').toString('binary');
fs.appendFileSync(path + fileName, decoded, 'binary');