Compiling Server Software From Source¶

Introduction¶

The Internet is operating on the IP protocol. IP addresses, like this one: 74.125.225.115, mark each participating system.
Each website name can be translated into an IP address. This is called DNS (Domain Name Services)
The software used in Internet applications can be separated into client-side software and server-side software.
A web browser or SSH client are examples of client-side software.
Apache, MySQL are examples of server-side software. The server-side software can be accessed via the IP protocol anywhere in the world.

Web Components¶

CGI ³¶

CGI stands for Common Gateway Interface.
The CGI defines the abstract parameters, known as meta-variables that describe a client’s request.
meta-variable: A named parameter which carries information from the server to the script.
server: The application program that invokes the script in order to service requests from the client.
CGI and a concrete programmer interface specify a platform-independent interface between the script and the HTTP server.
The server is responsible for managing connection, data transfer, transport and network issues related to the client request.
CGI script handles the application issues, such as data access and document processing.
How CGI works:
1. The client sends a request to the server. Then server acts as an application gateway.
2. Server receives the request from the client.
3. Server selects a CGI script to handle the request.
4. Server converts the client request to a CGI request.
5. Server executes the CGI script passing the CGI request as input. expects the CGI script to produce a CGI response.
6. Server converts the CGI response into a response for the client (depending on the request http, udp, socket, json, text ..etc).
7. Server responds to the client.

PHP Installation and Configuration ²¶

Way to use PHP:
1. Server-side scripting: you need 3 things: a web server, a PHP interpreter (Parser), and a web browser. You can access the PHP script via the web browser.
2. Command-line scripting: you need 2 things: a PHP interpreter (Parser), and a command-line interface. You can access the PHP script via the command-line interface typing php ./fileName.php.
3. Desktop applications: PHP-GTK is a PHP extension that allows you to create desktop applications (and/or cross-platform applications) using PHP.
PHP works as either:
1. a module: a shared library that can be loaded into a web server (Apache, IIS, etc.) to extend its functionality.
2. a CGI processor: a program that runs as a separate process and communicates with the web server via standard input/output.
SAPI (Server Application Programming Interface):
- is a layer between the web server and the PHP interpreter.
- SAPI is a module that interfaces between the web server and the PHP interpreter.
- SAPI -by default- supports all famous web servers (Apache, IIS, etc.).
- If your web server is not supported by SAPI, you can use CGI executable of PHP (a file named php-cgi.exe on windows, similar files on other OSes) directly. In this case, PHP will be used as a CGI processor and it will execute the PHP script as a separate process, then returns back to the client directly -no server in the middle-.
- see this

PHP Tutorial ¹¶

PHP is an acronym for “PHP: Hypertext Preprocessor“
current version: PHP 7 (released on 3 Dec 2015).
In PHP, keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are not case-sensitive. echo = ECHO = Echo = eChO = eCHo = etc.
Variable names are case-sensitive. $color = "red"; $COLOR = "blue"; $Color = "green";
comments: // or # or /* */
string concatenation: . (dot) or += (plus-equals) or “string interpolation” (PHP 5.3+) as in echo "Hello $name"; or echo "Hello {$name}"; or echo "Hello {$name}s";.
PHP is a Loosely Typed Language:
- PHP automatically associates a data type to the variable, depending on its value.
- In PHP 7, type declarations were added.
- If PHP runs on strict it will not perform type juggling, and throw a TypeError exception instead.
PHP has three different variable scopes:
1. local: declared inside a function, only accessible within that function
2. global:
  - variable defined outside a function has global scope and can only be accessed outside a function.
  - global keyword: to access a global variable from within a function, use the global keyword before the variables (inside the function).
  - PHP also stores all global variables in an array called $GLOBALS[index]
3. static:
  - declares a static variable, which retains its value between function calls.
Data Types: string, integer, float, boolean, array, object, NULL, resource.
PHP Resource:
- The special resource type is not an actual data type.
- It is the storing of a reference to functions and resources external to PHP.
constants:
- defined by this syntax: define(variable_name: string, value: any, case-insensitive: boolean = false);
- constants are global by default.
reference for built-in functions
strict mode:
- turned on by declare(strict_types=1); at the beginning of the script.
- if a function is called with the wrong number of arguments, an ArgumentCountError will be thrown…etc.
Passing arguments to functions:
- usually PHP passes arguments by value, so the function will not change the value of the argument.
- to pass arguments by reference, use the & operator in the function declaration.
PHP SuperGlobals: variables that are always available in all scopes.
- $GLOBALS - global scope
- $_SERVER - server and execution environment information
- $_REQUEST - HTTP request variables
- $_POST - HTTP POST variables
- $_GET - HTTP GET variables
- $_FILES - HTTP File Upload variables
- $_ENV - environment variables
- $_COOKIE - HTTP Cookies
- $_SESSION - session variables

// ----------------------- strings -----------------------
$str = "Hello World!";
strlen($str); // 12
str_word_count($str); // 2 // (Hello, World!)
strrev($str); // !dlroW olleH // (reverse)
strpos($str, "World"); // 6 // search for "World" in $str
str_replace("World", "Dolly", $str); // Hello Dolly! // replace "World" with "Dolly" in $str
// php string functions: http://php.net/manual/en/ref.strings.php

// ----------------------- numbers -----------------------
$x = 5985;
is_int($x); // true // check if the type of a variable is integer
is_float($x); // false // (is_double)
is_integer($x); // true // alias of is_int()
is_long($x); // true // alias of is_integer()

$s1 = "10.5";
is_numeric($s1); // true // (is_int or is_float on a string)

$d = 10.5;
$int_cast = (int)$d; // 10 // cast float to int
$int_cast = intval($d); // 10 // cast float to int

$x = acos(8);
var_dump($x); // NAN // (Not a Number) since it is impossible to calculate the arc cosine of 8

// ----------------------- math -----------------------
pi(); // 3.1415926535898
min(0, 150, 30, 20, -8, -200); // -200
max(0, 150, 30, 20, -8, -200); // 150
abs(-6.7); // 6.7 // absolute value
sqrt(64); // 8 // square root
round(0.60); // 1 // round to nearest integer
rand(); // 456 // random integer
rand(0, 10) // random integer between 0 and 10

// -----------------------  operators -----------------------
$x = 10;
$y = 6;

// arithmetic
echo $x <> $y; // 1 // (not equal)
echo $x <=> $y; // 1 // (spaceship) returns 0 if values of $x and $y are equal, 1 if $x is greater than $y, -1 otherwise
++$x; // 11 //  pre-increment : increments $x by one, then returns $x
$x++; // 10 // post-increment : returns $x, then increments $x by one

// logical
$x and $y; // true // and same as &&
$x or $y; // true // or same as ||
$x xor $y; // false // xor

// arrays
$x = array("a" => "red",);
$y = array("c" => "blue",);

echo $x + $y; // { "a": "red", "c": "blue" } // union of $x and $y
echo $x == $y; // false // equality, returns true if $x and $y have the same key/value pairs
echo $x === $y; // false // identity, returns true if $x and $y have the same key/value pairs in the same order and of the same types
echo $x != $y; // true // inequality, returns true if $x is not equal to $y // same as <>

// conditional assignment
$x = NULL;
$y = $x ?? 200; // 200 // Null coalescing
$y = $x ?: 200; // 200 // Ternary operator // same as $y = ($x != NULL) ? $x : 200;

// -----------------------  loops -----------------------
// while
while (condition is true) {
 code to be executed;
}

// do...while
do {
  code to be executed;
} while (condition is true);

// for
for (init counter; test counter; increment counter) {
  code to be executed for each iteration;
  works as long as the test counter is true
}

// foreach
foreach ($array as $key => $value) {
  code to be executed;
}

// -----------------------  functions -----------------------
function addNumbers(int $a, int $b): int {
  return $a + $b;
}

// pass by reference
$x = 0;
function addFive(&$num) {
  $num += 5;
}
addFive($x); // $x is now 5

// -----------------------  arrays -----------------------
// associative array
$array = array("foo" => "bar", 12 => true); // { "foo": "bar", "12": true }
// indexed array
$arr = array ("a", "b", "c", "d", "e"); // { "0": "a", "1": "b", "2": "c", "3": "d", "4": "e" }
// multidimensional array
$multi = array(
  array(1,2,3),
  array(4,5,6),
  array(7,8,9)
);

$arr = array(1,2,3)
count($arr); // 5 // count elements in array
sort($arr); // { "0": 1, "1": 2, "2": 3 } // sort arrays in ascending order
rsort($arr); // { "0": 3, "1": 2, "2": 1 } // sort arrays in descending order
asort($arr); // { "0": 1, "1": 2, "2": 3 } // sort associative arrays in ascending order, according to the value
ksort($arr); // { "0": 1, "1": 2, "2": 3 } // sort associative arrays in ascending order, according to the key
arsort($arr); // { "0": 3, "1": 2, "2": 1 } // sort associative arrays in descending order, according to the value
krsort($arr); // { "0": 3, "1": 2, "2": 1 } // sort associative arrays in descending order, according to the key


// -----------------------  objects -----------------------
class Car {
    public $color;
    private $model;
    static $wheels = 4;
    function __construct($color, $model) {
        $this->color = $color;
        $this->model = $model;
    }

}
$carObj = new Car('red', 'myModel'); // create object

// -----------------------  regular expressions -----------------------
$re = '/[a-z]/'; // match any lowercase letter
$str = 'Hee';
$matches = array();
// preg_match(pattern, subject, matches)
preg_match($re, $str, $matches); // 1 // 1 match found $matches = array("e")
// preg_match_all(pattern, subject, matches)
preg_match_all($re, $str, $matches); // 8 // 8 matches found $matches = array("e", "e")
// preg_replace(pattern, replacement, subject)
preg_replace($re, 'X', $str); // 'HXX' // returns a new string with all matches replaced by the replacement string

References¶

PHP 5 Tutorial. (n.d.). w3schools.com. Retrieved from https://www.w3schools.com/php/default.asp ↩
Cowburn, P. (Ed.). (2018). PHP manual. PHP Documentation Group. Retrieved from http://php.net/manual/en/install.php ↩
RFC 3875 https://www.rfc-editor.org/rfc/rfc3875.html ↩

Compiling Server Software From Source¶

Introduction¶

Web Components¶

CGI 3¶

PHP Installation and Configuration 2¶

PHP Tutorial 1¶

References¶

CGI ³¶

PHP Installation and Configuration ²¶

PHP Tutorial ¹¶