code-diesel » functions

Unpacking binary data in PHP

sameer — Tue, 21 Sep 2010 09:38:48 +0000

To set the stage we will start with a programming problem, this will keep the discussion anchored to a relevant context. The problem is this : We want to write a function that takes a image file as an argument and tells us whether the file is a GIF image; irrelevant with whatever the extension the file may have. We are not to use any GD library functions.

A GIF file header

With the requirement that we are not allowed to use any graphics functions, to solve the problem we need to get the relevant data from the GIF file itself. Unlike a HTML or XML or other text format files, a GIF file and most other image formats are stored in a binary format. Most binary files carry a header at the top of the file which provides the meta information regarding the particular file. We can use this information to find out the type of the file and other things, such as height an width in case of a GIF file. A typical raw GIF header is shown below, using a hex editor such as WinHex.

The detailed description of the header is given below.

Offset   Length   Contents
  0      3 bytes  "GIF"
  3      3 bytes  "87a" or "89a"
  6      2 bytes  
  8      2 bytes  
 10      1 byte   bit 0:    Global Color Table Flag (GCTF)
                  bit 1..3: Color Resolution
                  bit 4:    Sort Flag to Global Color Table
                  bit 5..7: Size of Global Color Table: 2^(1+n)
 11      1 byte   
 12      1 byte   
 13      ? bytes  
         ? bytes  
         1 bytes   (0x3b)

So to check if the image file is a valid GIF, we need to check the starting 3 bytes of the header, which have the ‘GIF’ marker, and the next 3 bytes, which give the version number; either ’87a’ or ’89a’. It is for tasks such as these that the unpack() function is indispensable. Before we look at the solution, we will take a quick look at the unpack() function itself.

Using the unpack() function

unpack() is the complement of pack() – it transforms binary data into an associative array based on the format specified. It is somewhat along the lines of sprintf, transforming string data according to some given format. These two functions allow us to read and write buffers of binary data according to a specified format string. This easily enables a programmer to exchange data with programs written in other languages or other formats. Take a small example.

$data = unpack('C*', 'codediesel');
var_dump($data);

This will print the following, decimal codes for ‘codediesel’ :

array
  1 => int 99
  2 => int 111
  3 => int 100
  4 => int 101
  5 => int 100
  6 => int 105
  7 => int 101
  8 => int 115
  9 => int 101
  10 => int 108

In the above example the first argument is the format string and the second the actual data. The format string specifies how the data argument should be parsed. In this example the first part of the format ‘C’, specifies that we should treat the first character of the data as a unsigned byte. The next part ‘*’, tells the function to apply the previously specified format code to all the remaining characters.

Although this may look confusing, the next section provides a concrete example.

Grabbing the header data

Below is the solution to our GIF problem using the unpack() function. The is_gif() function will return true if the given file is in a GIF format.

function is_gif($image_file)
{
 
    /* Open the image file in binary mode */
    if(!$fp = fopen ($image_file, 'rb')) return 0;
 
    /* Read 20 bytes from the top of the file */
    if(!$data = fread ($fp, 20)) return 0;
 
    /* Create a format specifier */
    $header_format = 'A6version';  # Get the first 6 bytes

    /* Unpack the header data */
    $header = unpack ($header_format, $data);
 
    $ver = $header['version'];
 
    return ($ver == 'GIF87a' || $ver == 'GIF89a')? true : false;
 
}
 
/* Run our example */
echo is_gif("aboutus.gif");

The important line to note is the format specifier. The ‘A6′ characters specifies that the unpack() function is to get the the first 6 bytes of the data and interpret it as a string. The retrieved data is then stored in an associate array with the key named ‘version’.

Another example is given below. This returns some additional header data of the GIF file, including the image width and height.

function get_gif_header($image_file)
{
 
    /* Open the image file in binary mode */
    if(!$fp = fopen ($image_file, 'rb')) return 0;
 
    /* Read 20 bytes from the top of the file */
    if(!$data = fread ($fp, 20)) return 0;
 
    /* Create a format specifier */
    $header_format = 
            'A6Version/' . # Get the first 6 bytes
            'C2Width/' .   # Get the next 2 bytes
            'C2Height/' .  # Get the next 2 bytes
            'C1Flag/' .    # Get the next 1 byte
            '@11/' .       # Jump to the 12th byte
            'C1Aspect';    # Get the next 1 byte

    /* Unpack the header data */
    $header = unpack ($header_format, $data);
 
    $ver = $header['Version'];
 
    if($ver == 'GIF87a' || $ver == 'GIF89a') {
        return $header;
    } else {
        return 0;
    }
}
 
/* Run our example */
print_r(get_gif_header("aboutus.gif"));

The above example will print the following when run.

Array
(
    [Version] => GIF89a
    [Width1] => 97
    [Width2] => 0
    [Height1] => 33
    [Height2] => 0
    [Flag] => 247
    [Aspect] => 0
)

Below we will go into the details of how the format specifier works. I’ll split the format, giving the details for each character.

$header_format = 'A6Version/C2Width/C2Height/C1Flag/@11/C1Aspect';

A - Read a byte and interpret it as a string. 
    Number of bytes to read is given next
6 - Read a total of 6 bytes, starting from position 0
Version - Name of key in the associative array where data 
    retrieved by 'A6' is stored
 
/ - Start a new code format
C - Interpret the next data as an unsigned byte
2 - Read a total of 2 bytes
Width - Key in the associative array
 
/ - Start a new code format
C - Interpret the data as an unsigned byte
2 - Read a total of 2 bytes
Height- Key in the associative array
 
/ - Start a new code format
C - Interpret the data as an unsigned byte
1 - Read a total of 2 bytes
Flag - Key in the associative array
 
/ - Start a new code format
@ - Move to the byte offset specified by the following number.
      Remember that the first position in the binary string is 0. 
11 - Move to position 11
 
/ - Start a new code format
C - Interpret the data as an unsigned byte
1 - Read a total of 1 bytes
Aspect - Key in the associative array

More format options can be found here. Although I’ve only shown a small example, the pack/unpack is capable of much complex work than presented here.

Easy way to build GET query strings in php

sameer — Thu, 13 Nov 2008 14:10:58 +0000

Passing variables with a url is such a frequent thing programmers do that most of you may think this post is unwarranted. We call this method of passing variables as GET, the other being POST. It is one of those things which can be easily done in php. Lets take an example. You are to query a database and for that you need to send three variables via GET – city, id, paid.
The common way to pass them via GET is to construct a query string as below:

/* assume we want to pass this variables */
$city_name = "new york";
$invoice_id = 3456;
$paid = 1;
 
$query_string = "city={$city_name}&id={$invoice_id}&paid={$paid}";
$url = "http://www.example.com?" . $query_string;

The problem is that most php programmers get stuck using the above method. The method is fine for three to four variables, but for more than that the code gets hard to read and maintain, introducing subtle bugs in the constructed query.

The best way to pass GET variables is to use the http_build_query() function available from php version 5; which takes an array of variables and builds a nice URL encoded string which you can append to a url. And example is shown below.

$city_name = "new york";
$invoice_id = 3456;
$paid = 1;
 
$fields = array('city' => $city_name,
                'id' => $invoice_id,
                'paid' => $paid);
 
$url = "http://www.example.com?" . http_build_query($fields, '', "&");

In the above example the array contained the variable names and their values. You can also pass an array containing only values and let the function fill the variable name using the array index and a variable you supply (as a second parameter). For example if you want to pass an array of six cities than you can do the following, the second parameter of the function being the query variable.

$fields = array('paris',
                'new york',
                'florence',
                'london',
                'berlin',
                'delhi');
 
$url = "http://www.example.php?" .
        http_build_query($fields, 'city', "&");

The generated url will look like this:

http://www.example.php/?city0=paris&city1=new+york&city2=florence&city3=london&city4=berlin&city5=delhi

The third parameter to the function is not necessary as the function defaults to using ‘&’ as a separator. But I prefer making it explicit.
You can also easily pass a complex array as below:

$city_name      = "new york";
$invoice_id     = 3456;
$currency_name  = "euro";
$total          = 345;
$receipt_no     = "fgf44545";
 
$fields = array('city' => $city_name,
                'id' => $invoice_id,
                'paid' => array('currency' => $currency_name,
                                'amount' => $total,
                                'receipt' => $receipt_no)                
                );
 
$url = "http://www.example.php?" .
        http_build_query($fields, '', "&");

Which will create a url encoded query as following:

http://www.example.com?city=new+york&id=3456&paid%5Bcurrency%5D=euro&paid%5Bamount%5D=345&paid%5Breceipt%5D=fgf44545

To go the reverse way, we can parse the encoded url above using the code below:

$url_to_parse = "http://www.example.com?city=new+york&id=3456&paid%5Bcurrency%5D=euro&paid%5Bamount%5D=345&paid%5Breceipt%5D=fgf44545";
$parsed_url = parse_url($url_to_parse);
print_r($parsed_url);
 
/* This will output the following array */
Array
(
    [scheme] => http
    [host] => www.example.com
    [query] => city=new+york&id=3456&paid%5Bcurrency%5D=euro&paid%5Bamount%5D=345&paid%5Breceipt%5D=fgf44545
)

Now we can further parse the url query string stored in the ‘query’ variable above:

$url_query = $parsed_url['query'];
parse_str($url_query, $out);
print_r($out);
 
/* This will output the following array */
Array
(
    [city] => new york
    [id] => 3456
    [paid] => Array
        (
            [currency] => euro
            [amount] => 345
            [receipt] => fgf44545
        )
 
)

As can be seen the http_build_query() function really makes constructing GET queries simple.

Simple Pagination in PHP tutorial

sameer — Fri, 24 Oct 2008 05:03:48 +0000

Pagination is a frequent requirement in web development projects. Most PHP developers must have already implementated paging in one form or other in their projects. In this post we will see how to add pagination the easy way using PEAR’s Pager class. Note that in all the posts I use PHP 5.x.x, so if you are still stuck at version 4.x.x, its already time to upgrade.

Its always nice to see some working code first, before getting into the details. So here goes.

require_once 'Pager/Pager.php';
/* We will bypass the database connection code ... */
$sqlQuery = "SOME SQL QUERY";
$result = mysql_query($sqlQuery);
$totalRows = mysql_num_rows($result);
 
$pager_options = array(
'mode'       => 'Sliding',
'perPage'    => 10,
'delta'      => 4,
'totalItems' => $totalRows,
);
$pager = Pager::factory($pager_options);
echo $pager->links;

The above code will return the following pagination links.

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 » [10]

Assuming the page where the above code is included is named ‘dataPage.php’; the pager links will have a url like follows:

dataPage.php?pageID=n

where n is the page number.

You can see how easy it is using the Pager class. All the link building is handled by the class. Now lets go into the details.

1. Installation

If you are installing using the Pear installer, enter the following at the command prompt to install Pager.

c:\pear install Pager

Or else you can just download the module from here and then copy it to your Pear includes directory, which will probably be ‘c:\your php installation directory\Pear’.

2. A simple example

In the following example we will create a pagination for a ‘logs’ table.

/* Include the Pear::Pager file */
require_once ('Pager/Pager.php');
 
/* Replace this with your database details */
$connection = mysql_connect("localhost", username, password);
mysql_select_db(database name, $connection);
 
/* First we need to get the total rows in the table */
$result=mysql_query("SELECT count(*) AS total FROM logs", $connection);
$row = mysql_fetch_array($result);
 
/* Total number of rows in the logs table */
$totalItems = $row['total'];
 
/* Set some options for the Pager */
$pager_options = array(
'mode'       => 'Sliding',   // Sliding or Jumping mode. See below.
'perPage'    => 10,   // Total rows to show per page
'delta'      => 4,   // See below
'totalItems' => $totalItems,
);
 
/* Initialize the Pager class with the above options */
$pager = Pager::factory($pager_options);
 
/* Display the links */
echo $pager->links;
 
/* The following code will retreive the result using the pager options */
 
/* The function below will get the page offsets to be used with
the database query. For e.g if we are on the third page then the
$from variable will have the value of '21' (we are showing 10 items per 
page, remember) and the $to variable will have the value of '30'.
*/
list($from, $to) = $pager->getOffsetByPageId();
/* The MySQL 'LIMIT' clause index starts from '0', 
    so decrease the $from by 1 */
$from = $from - 1;
 
/* The number of rows to get per query */
$perPage = $pager_options['perPage'];
 
$result = mysql_query("SELECT * FROM alogs LIMIT $from , $perPage",
$connection);
 
while($row = mysql_fetch_array($result))
{
/* Do something with the query results */
}

In the Pager class there are two modes to display the pagination: Sliding & Jumping.

With Pager in “Sliding” mode the pagination links change smoothly, and the current page is always shown at the center of the “window” (except for the start and end pages). When in Sliding mode the delta option implies how many links to show on the left and right of the current page link.
For e.g with a delta set to ’3′ the links are displayed as shown below, page 10 being the current page:

[1] « 7 | 8 | 9 | 10 | 11 | 12 | 13 » [13]

With delta option set to ’4′ the links are shown as below. As you can see there are four links to the left and right of the current page.

[1] « 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 » [13]

With the Pager in “Jumping” mode and delta set to ’4′ the Pager always shows the same 4 page links while you are on one of these pages.
For e.g with a delta set to ’4′ the links are displayed as shown below, page 5 being the current page:

[1] << Back 5 6 7 8 Next >> [13]

If you are on page ’9′ the links displayed are as below:

[1] << Back 9 10 11 12 Next >> [13]

3. More options

You can also change the default separator to any character or image you like.

$pager_options = array(
'mode'       => 'Sliding',
'perPage'    => 10,
'delta'      => 4,
'separator' => ',',
'totalItems' => $totalItems,
);

This will output the following:
[1] « 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 » [13]

If you would like to add images to the ‘next’ and ‘previous’ links, use the following options:

$pager_options = array(
'mode'       => 'Sliding',
'perPage'    => 10,
'delta'      => 4,
'nextImg'    => '',
'prevImg'    => '',
'totalItems' => $totalItems,
);

Which will display the links as shown below:

The default number of spaces before each separator is three. To change the number of spaces use the ‘spacesBeforeSeparator’ option. For e.g:

.
.
'spacesBeforeSeparator' => 1,
.

4. Styling

You can style the links by putting them in a div tag and applying a css. A example css and its output is shown below.

Add a div tag:

.
.
echo '';
echo $pager->links;
echo '
';

Apply CSS:

.pager {
    font-family: Arial;
    font-size: 14px;
}
 
.pager a {
    font-family: Arial;
    font-size: 14px;
    text-decoration: none;
    width: 17px;
    height: 17px;
    border: 1px solid #000;
    background-color: #0C74BA;
    text-align: center;
    color: #fff;
}
 
.pager a:hover {
    background-color: #c0c0c0;
}

The output:

That’s it. There are many other options you can use with the Pager class, the details which you can find in the Pager documentation.

WHOIS directory lookup in PHP

sameer — Sat, 13 Sep 2008 12:23:11 +0000

Net_Whois lets you query a internet name directory service in a easy to use manner. WHOIS is a protocol which is widely used to determine the owner of a domain name, an IP address by querying an official name database. One possible application I can think of is to see if DNS servers are set correctly for various domains I handle regularly.

Installation

Net_Whois being a Pear package we will use the Pear installer as below. I recommend to always use the Pear installer to download packages rather than downloading it manually as the Pear installer automatically downloads any dependent packages.

pear install Net_Whois-1.0.2

Usage

The current library uses the following servers to execute the query:
whois.crsnic.net
whois.networksolutions.com
whois.nic.mil
whois.nic.gov
whois.arin.net
whois.ripe.net
whois.apnic.net
whois.ripn.net
whois.ra.net
.whois-servers.net
whois.6bone.net
whois.registro.br

A example code is shown below.


 
    require_once "Net/Whois.php";
 
    $whois = new Net_Whois();
    /* You can add other NIC server as a second parameter. */
    $info = $whois->query('example.com');
    echo($info);
 
?>

Note that the class returns a string, so you would need to use regular expressions to get to the relevant information.

Ping a server using PHP

sameer — Sat, 13 Sep 2008 11:58:05 +0000

PEAR’s Net_Ping is a niffty wrapper class for executing ping calls from PHP. You can use it to check if a remote server is responding correctly. The library can be download from here.

Installation

Net_Ping being a Pear package we will use the Pear installer to download and install it. I recommend to always use the Pear installer to download packages rather than downloading it manually as the Pear installer automatically downloads any dependent packages.

pear install Net_Ping-2.4.4

Usage

A example of using Net_Ping is given below.


 
    require_once "Net/Ping.php";
 
    $ping = Net_Ping::factory();
 
    if(PEAR::isError($ping))
      echo $ping->getMessage();
    else
    {
      /* Number of packets to send */
      $ping->setArgs(array('count' => 4));
      $rawData = $ping->ping('google.com');
      print_r($rawData);
    }
 
?>

The output of the same is shown below.

Net_Ping_Result Object
(
    [_icmp_sequence] => Array
        (
            [1] => 310
            [2] => 300
            [3] => 318
            [4] => 301
        )
 
    [_target_ip] => 64.233.167.99
    [_bytes_per_request] => 32
    [_bytes_total] => 128
    [_ttl] => 238
    [_raw_data] => Array
        (
            [0] => 
            [1] => Pinging google.com [64.233.167.99] with 32 bytes of data:
            [2] => 
            [3] => Reply from 64.233.167.99: bytes=32 time=310ms TTL=238
            [4] => Reply from 64.233.167.99: bytes=32 time=300ms TTL=238
            [5] => Reply from 64.233.167.99: bytes=32 time=318ms TTL=238
            [6] => Reply from 64.233.167.99: bytes=32 time=301ms TTL=238
            [7] => 
            [8] => Ping statistics for 64.233.167.99:
            [9] =>     Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
            [10] => Approximate round trip times in milli-seconds:
            [11] =>     Minimum = 300ms, Maximum = 318ms, Average = 307ms
        )
 
    [_sysname] => windows
    [_round_trip] => Array
        (
            [min] => 300
            [max] => 318
            [avg] => 307
        )
 
    [_transmitted] => 4
    [_received] => 4
    [_loss] => 0
)

Reading raw POST data in PHP

sameer — Fri, 12 Sep 2008 07:00:55 +0000

A quick tip for reading raw http POST data in PHP. For example if we have a xml posted to a page, we can read the raw data with the following code.

$xml = file_get_contents('php://input');

We could use $HTTP_RAW_POST_DATA instead, but many times it does not work due to some php.ini settings. Note that ‘php://input’ does not work with enctype=”multipart/form-data”.

Google Pagerank in PHP

sameer — Sat, 19 Apr 2008 08:59:08 +0000

Due to recent changes made by Google in its Page Rank processing the following library doesn’t work. However you can try to use the following api made available by fusionswift.com:
http://fusionswift.com/201004/google-pagerank-script-in-php/

Mark Woodman has created a nifty class which lets you query Google pagerank info in PHP 5 and above. The complete classes are available here.

The minimum classes required are ‘cacher.class.php‘ and ‘google_pagerank.class.php‘.

Sample code is shown below.

require_once("popstats/google_pagerank.class.php");
 
$rankObject = new GooglePageRank("http://www.someDomain.com");
 
$pageRank = $rankObject->pagerank;
 
echo $pageRank;

The class also supports result caching on the local machine, so if a second query arrives within the cache time limit the result saved in the local file is returned rather then going out and querying Google.

The ‘GooglePageRank’ class accepts cache time as a second parameter. So if you want to cache the result for 6 hours you set the second parameter for 21600 seconds (6 * 60 * 60):

$rankObject = new GooglePageRank("http://www.someDomain.com", 21600);

The default is set to 24 hours, which is more then adequate for most purposes.