I’ve already wrote an article about file uploads in Node.js before. However Node.js is in rapid development and so many things have changed since then.

So, I decided to do an updated version, which accommodates for such changes:

• events module was removed
• posix module was replaced by fs
• various changes into HTTP request/response API
• multipart module refactored into separate project
• convenient fs.createWriteStream instead of low-level API

See the code snippet under the cut, or on github. Special thanks goes to Felix Geisendörfer for some useful suggestions.

Please note that you’ll need to install multipart module for the code to work.

To make it clear, Node.js version used was v. 0.1.91.

UPD: Fixed stream.onData handler. It was writing corrupted data (UTF-8 character were translated) because of binary mode not being used. Thanks to Ron Ward for suggesting solution.

var http = require("http");
var url = require("url");
var multipart = require("multipart");
var sys = require("sys");
var fs = require("fs");

var server = http.createServer(function(req, res) {
    // Simple path-based request dispatcher
    switch (url.parse(req.url).pathname) {
        case '/':
            display_form(req, res);
            break;
        case '/upload':
            upload_file(req, res);
            break;
        default:
            show_404(req, res);
            break;
    }
});

// Server would listen on port 8000
server.listen(8000);

/*
 * Display upload form
 */
function display_form(req, res) {
    res.sendHeader(200, {"Content-Type": "text/html"});
    res.write(
        '<form action="/upload" method="post" enctype="multipart/form-data">'+
        '<input type="file" name="upload-file">'+
        '<input type="submit" value="Upload">'+
        '</form>'
    );
    res.close();
}

/*
 * Create multipart parser to parse given request
 */
function parse_multipart(req) {
    var parser = multipart.parser();

    // Make parser use parsed request headers
    parser.headers = req.headers;

    // Add listeners to request, transfering data to parser

    req.addListener("data", function(chunk) {
        parser.write(chunk);
    });

    req.addListener("end", function() {
        parser.close();
    });

    return parser;
}

/*
 * Handle file upload
 */
function upload_file(req, res) {
    // Request body is binary
    req.setBodyEncoding("binary");

    // Handle request as multipart
    var stream = parse_multipart(req);

    var fileName = null;
    var fileStream = null;

    // Set handler for a request part received
    stream.onPartBegin = function(part) {
        sys.debug("Started part, name = " + part.name + ", filename = " + part.filename);

        // Construct file name
        fileName = "./uploads/" + stream.part.filename;

        // Construct stream used to write to file
        fileStream = fs.createWriteStream(fileName);

        // Add error handler
        fileStream.addListener("error", function(err) {
            sys.debug("Got error while writing to file '" + fileName + "': ", err);
        });

        // Add drain (all queued data written) handler to resume receiving request data
        fileStream.addListener("drain", function() {
            req.resume();
        });
    };

    // Set handler for a request part body chunk received
    stream.onData = function(chunk) {
        // Pause receiving request data (until current chunk is written)
        req.pause();

        // Write chunk to file
        // Note that it is important to write in binary mode
        // Otherwise UTF-8 characters are interpreted
        sys.debug("Writing chunk");
        fileStream.write(chunk, "binary");
    };

    // Set handler for request completed
    stream.onEnd = function() {
        // As this is after request completed, all writes should have been queued by now
        // So following callback will be executed after all the data is written out
        fileStream.addListener("drain", function() {
            // Close file stream
            fileStream.end();
            // Handle request completion, as all chunks were already written
            upload_complete(res);
        });
    };
}

function upload_complete(res) {
    sys.debug("Request complete");

    // Render response
    res.sendHeader(200, {"Content-Type": "text/plain"});
    res.write("Thanks for playing!");
    res.end();

    sys.puts("\n=> Done");
}

/*
 * Handles page not found error
 */
function show_404(req, res) {
    res.sendHeader(404, {"Content-Type": "text/plain"});
    res.write("You r doing it rong!");
    res.end();
}

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