13. Exercise IMPOTS with XML

In this exercise, which we have already studied many times, the server returns the results to the client in the form of a XML stream.

13.1. The server (impots_05B_web)

The tax calculation web service written earlier has a layered architecture:

In the previous example, the web service sent one of the following two lines to its clients:

<erreur>message d'error</error>
<impot>montant de l'tax</tax>

This is not a well-formed XML document because it lacks a root tag. The new web service will send its response in the following format:

<reponse><erreur>message d'error</error></response>

or

<reponse><impot>montant de l'tax</tax></answer>

In both cases, the response is a well-formed XML document that can be processed by the [simpleXML] module.

In the three-layer schema, only the [web] layer needs to be modified. Its code [impots_05B_web] becomes the following:


<?php
 
// business layer
require_once "impots_05_metier.php";
 
// error management
ini_set("display_errors", "off");
 
// uTF-8 header
header("Content-Type: text/plain; charset=utf-8");
 
// ------------------------------------------------------------------------------
// tax web service
// definition of constants
$HOTE = "localhost";
$PORT = 3306;
$BASE = "dbimpots";
$USER = "root";
$PWD = "";
// the data required to calculate the tax has been placed in table mysqL $TABLE
// belonging to the $BASE database. The table has the following structure
// limits decimal(10,2), coeffR decimal(6,2), coeffN decimal(10,2)
// taxable person parameters (marital status, number of children, annual salary)
// are sent by the customer in the form params=marital status, number of children, annual salary
// results (marital status, number of children, annual salary, tax payable) are returned to the customer
// in the form <impot>impot</impot>
// or as <error>error</error>, if parameters are invalid
// retrieve the [business] layer in the session
session_start();
if (!isset($_SESSION['metier'])) {
// instantiation of layer [dao] and layer [métier]
  try {
    $_SESSION['metier'] = new ImpotsMetier(new ImpotsDaoWithMySQL($HOTE, $PORT, $BASE, $USER, $PWD));
  } catch (ImpotsException $ie) {
    print "<reponse><erreur>Erreur : " . utf8_encode($ie->getMessage() . "</erreur></reponse>");
    exit;
  }
}
$metier = $_SESSION['metier'];
 
// retrieve the line sent by the client
$params = utf8_encode(htmlspecialchars(strtolower(trim($_POST['params']))));
//print "parameters received --> $params\n";
$items = explode(",", $params);
// there must be only 3 parameters
if (count($items) != 3) {
  print "<reponse><erreur>[$params] : nombre de paramètres invalides</erreur></reponse>\n";
  exit;
}//if
// first parameter (marital status) must be yes/no
$marié = trim($items[0]);
if ($marié != "oui" and $marié != "non") {
  print "<reponse><erreur>[$params] : 1er paramètre invalide</erreur></reponse>\n";
  exit;
}//if
// the second parameter (number of children) must be an integer
if (!preg_match("/^\s*(\d+)\s*$/", $items[1], $champs)) {
  print "<reponse><erreur>[$params] : 2ième paramètre invalide</erreur></reponse>\n";
  exit;
}//if
$enfants = $champs[1];
// the third parameter (salary) must be an integer
if (!preg_match("/^\s*(\d+)\s*$/", $items[2], $champs)) {
  print "<reponse><erreur>[$params] : 3ième paramètre invalide</erreur></reponse>\n";
  exit;
}//if
$salaire = $champs[1];
// tax calculation
$impôt = $metier->calculerImpot($marié, $enfants, $salaire);
// return the result
print "<reponse><impot>$impôt</impot></reponse>\n";
// end
exit;

The format of the web service response is modified on lines 35, 47, 53, 58, 64, and 71.

13.2. The client (client_impots_05b_web)

The client is modified to account for the new response format. We use [simpleXML] to process it:


<?php
 
// tax client
// error management
ini_set("display_errors", "off");
 
// ---------------------------------------------------------------------------------
// a class of utility functions
class Utilitaires {
...
}
 
// main -----------------------------------------------------
// definition of constants
$DATA = "data.txt";
$RESULTATS = "resultats.txt";
// server data
$HOTE = "localhost";
$PORT = 80;
$urlServeur = "/exemples-web/impots_05B_web.php";
 
...
exit;
 
function calculerImpot($HOTE, $PORT, $urlServeur, &$cookie, $params) {
  // connects client to ($HOTE,$PORT,$urlServeur)
// sends the $cookie cookie if it is non-empty. $cookie is passed by reference
// sends $params to the server
// exploits the result line
...
  // read line result
  $ligne = fgets($connexion, 1000);
  // close the connection
  fclose($connexion);
  // result calculation
  $xml = new SimpleXMLElement($ligne);
  $erreur = isset($xml->erreur) ? $xml->erreur : "";
  $impôt = isset($xml->impot) ? $xml->impot : "";
  // return
  return array($erreur, $impôt);
}

line 32: the server response is read. It is a XML document.
line 36: a SimpleXML object is constructed from the received XML document.
line 37: any error message
line 38: the tax amount, if any