dracoblue.net

While working with Node.JS and dbslayer today, I was facing a weird issue with escaping strings.

Best thing would have been, if I could have forced my server to use NO_BACKSLASH_ESCAPES as sql-mode and then just escape the ' to ''.

But since this server is also used by other programs and NO_BACKSLASH_ESCAPES option cannot be set by option for dbslayer I had to turn it off again.

I ended up with this tiny escape string method:

var db_escape_string = function(string) {
	return string.replace(/([\\\n\r])/g, "\\$&").replace("'", "''", 'g');
};

It replaces ** (backslash), newline and carriage return with \, \n and \r. Since also single quote needs to be escaped, I finally replace all ' with ''.

You may wonder why I do not escape ". The issue is, that a " appearing within a string in between ' does not need to be escaped.

'this is a test"2' => 'this is a test\"2'

That's why I sticked to the rule to put strings within single quote and do not escape those question marks at all.

A while back I explained how to mount sftp/ssh folders in eclipse.

When working with eclipse or zend studio on remote systems, there are times when I get the message "Operation failed. File system input or output error" very often.

Even though several posts in zend forums suggest, that you should restart your IDE in this case, I tried to track down what causes the issue.

I ended up with the following: The ssh-host has already closed the connection, but eclipse thinks it's still available. So it tries to use the connection, but fails.

Whenever I get this issue now, I go into "Remote Systems"-View, right-click the Connection and choose "Disconnect" from the context menu. Right after that, I open that context menu again and press "Connect". Problem resolved.

This is an PHP-Tokenizer error, which just wants to tell you that there are two colons. ;)

If one develops with Node.JS and wants to use the full event-loop power, you got to use callbacks for everything.

That said, it looks ugly to do that:

posix.rename("/tmp/hello", "/tmp/world").addCallback(function () {
  posix.stat("/etc/passwd").addCallback(function (stats) {
    sys.puts("stats: " + JSON.stringify(stats));
  });
});

The

api advices to use:

posix.rename("/tmp/hello", "/tmp/world").wait();
var stats = posix.stat("/etc/passwd").wait();
sys.puts("stats: " + JSON.stringify(stats));

but this is a problem, too. Why? Because you can't do that too often (just ~10 times) at the same time.

That's why I created two little helper methods:

chain and group.

Today I ran into the problem, that I had a graph full of data points, which obviously did not form a straight line.

There is a method called

Linear least squares to calculate the straight line with least difference to the original data points.

Since I needed the method in javascript, here is what I came up with in the end.

function findLineByLeastSquares(values_x, values_y) {
    var sum_x = 0;
    var sum_y = 0;
    var sum_xy = 0;
    var sum_xx = 0;
    var count = 0;
    
    /*
     * We'll use those variables for faster read/write access.
     */
    var x = 0;
    var y = 0;
    var values_length = values_x.length;

    if (values_length != values_y.length) {
        throw new Error('The parameters values_x and values_y need to have same size!');
    }
    
    /*
     * Nothing to do.
     */
    if (values_length === 0) {
        return [ [], [] ];
    }
    
    /*
     * Calculate the sum for each of the parts necessary.
     */
    for (var v = 0; v < values_length; v++) {
        x = values_x[v];
        y = values_y[v];
        sum_x += x;
        sum_y += y;
        sum_xx += x*x;
        sum_xy += x*y;
        count++;
    }
    
    /*
     * Calculate m and b for the formular:
     * y = x * m + b
     */
    var m = (count*sum_xy - sum_x*sum_y) / (count*sum_xx - sum_x*sum_x);
    var b = (sum_y/count) - (m*sum_x)/count;
    
    /*
     * We will make the x and y result line now
     */
    var result_values_x = [];
    var result_values_y = [];
    
    for (var v = 0; v < values_length; v++) {
        x = values_x[v];
        y = x * m + b;
        result_values_x.push(x);
        result_values_y.push(y);
    }
    
    return [result_values_x, result_values_y];
}