buggy3.js

// rm aa; node buggy3.js | fgrep WTF | wc -l
// different results for each run
// writes are sequential

function FileWriterQueue(file) {
    this.file  = file;
    this.queue = [];
}

FileWriterQueue.prototype.write = function(buffer, offset, callback) {
    this.queue.push([buffer, offset, callback]);
    if (this.queue.length > 1) {
        return;
    }

    this.process();
};

FileWriterQueue.prototype.process = function() {
    var self  = this,
        write = self.queue[0];

    if (!write) {
        return console.log("requested write with empty queue!");
    }

    console.log("[pwrite]", write[1], write[0].length);
    fs.write(self.file, write[0], 0, write[0].length, write[1], function(error) {
        console.log("[pwrite finished]", write[1], "->", write[1] + write[0].length);
        write[2] && write[2](error);

        self.queue.shift();
        if (self.queue.length) {
            self.process();
        }
    });
};

var fs   = require("fs"),
    file = fs.openSync("aa", "a+"),
    bufs = {},
    off  = fs.fstatSync(file).size,
    offs = {},
    queue = new FileWriterQueue(file);



Object.keys(offs).forEach(function(o) {
    offs[o] += off;
});

function calc_offset(size, from) {
    var result = 0;
    while (from < size) {
        result += from;
        from++;
    }

    return result;
}

function buf(size) {
    if (!bufs[size]) {
        bufs[size] = new Buffer(size);
        for (var i = 0; i < size; i++) {
            bufs[size][i] = i % 256;
        }
    }

    return bufs[size];
}

function write_with_offset(size, from, callback) {
    var offset = calc_offset(size, from);
    queue.write(buf(size), offset, callback);
}

function reader() {
    console.log("reader is here");
    console.log(bufs);
    console.log(offs);
    Object.keys(bufs).forEach(function(size) {
        size = +size;
        var offset = offs[size],
            test   = new Buffer(size);
        fs.read(file, test, 0, test.length, offset, function() {
            if (test.toString("base64") != buf(size).toString("base64")) {
                console.log("WTF? " + test.length + ":" + buf(size).length);
                console.log(buf(size).slice(0,4).toString("base64"), test.slice(0, 4).toString("base64"))
            }
        });
    });
}

//for (var i = 4000; i >= 3900; i--) {
//    write_with_offset(i, 3900);
//}

for (var i = 9; i <= 100; i++) {
    console.log(i);
    write_with_offset(i, 9);
}

setTimeout(reader, 1000);