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Friday, January 12, 2007

Implementing Web Services with Open Source Software

Today many services are available (both internal and external to a company) as Web Services, more specifically as SOAP. Companies like Microsoft, IBM or Sun have heavily invested in this field and made many of their products compatible with it (as a client and/or as a server). In this article I will study the different possibilities of implementing a SOAP server with Open Source solutions.

The specific requirements are:

  • It should use the HTTP transport layer (the most commonly used in SOAP)
  • It should either have an embedded HTTP server or be usable with Apache
  • It should be platform independent

But let me step back for a moment and ask: why would you want to go this route? Why not use the product of well known companies which offer integration with developer tools and in some cases are available for free? While those products are certainly more mature and easier to use, when going the OSS route you have:

  • more flexibility (because you have the full source code available - and even if you don't want to actively participate in the development process, it helps a lot for debugging),
  • more deployment options (just think how many webhosts offer Apache / MySQL / PHP / Perl as opposed to IIS, WebSphere or Java)
  • when extending the possible interfacing options of a product written for this platform (adding a SOAP API for a wiki for example) it is easier to use something like this rather than requiring the installation of a whole new framework
  • and finally the issue of the cost: while not a big problem because (a) academic institutions already have or can get free licenses for much of the products and (b) the companies themselves distribute their products (or at least some versions) free, it may still be an argument.

By doing research following these guidelines the following three possibilities emerged:

  • The SOAP::Lite library for Perl


    • Very easy to use
    • Available across platforms (both from the CPAN and PPM repositories)
    • Has an extensive "cookbook" (set of short HOWTOs):
    • Runs in Apache (either as CGI or with mod_perl - in the later case you may need to replace SOAP::Transport::HTTP::CGI with SOAP::Transport::HTTP::Apache in the examples)
    • Has tracing functionality (to enable it at the client side, use the following way to include the library: use SOAP::Lite +trace => 'all'; and then redirect the stderr output (where the tracing info is dumped) to a file like this 2>debug-info.txt


    • Does not support automatic generation of the WSDL file
    • Sometimes it insists on sending the variables as a certain type (integer) even though I would like to send them as string
  • The SOAP library included with PHP


    • Usually readily included with PHP
    • Cross platform
    • Under active development


    • Does not support automatic generation of the WSDL file
    • There are few tutorials for it
    • Very basic debugging support. PHP has a weak debugging support out of the box, but the fact that the majority of the functions are implemented in a binary library makes things even worse (because you would need a hybrid PHP/binary debugger for proper debugging)
  • The NuSOAP project for PHP


    • Cross platform (written in PHP)
    • Automatic WSDL generation
    • When accessed with a browser, it presents a friendly HTML interface which lists all the published methods / objects and their parameters
    • Distributed as PHP source files which can be easily installed to most hosts (the user doesn't need to ask the server administrator to load extra binary modules)
    • While PHP has no integrated debugging support, the library itself tries to output debugging information. To activate this mode set the debug variable to 1 (like this: $debug = 1;). The debugging information will be appended to the reponse XML as a comment.


    • Not very well maintained (probably because of the existence of the "official" PHP SOAP module)
    • Few examples and many of the examples don't work. For working examples go to the authors webiste
    • Conflicts with the official PHP SOAP module. If you get an error saying something along the lines of can not redefine class soap_client, you have to unload the PHP SOAP module. An other option would be to go through the source and rename this class.
    • No real debugging support (because PHP doesn't have one).

The final choice was NuSOAP. The deciding factor was the (semi)automatic - because you have to give it hints about the parameter types - WSDL generation. This is essential if you wish to make your service available to the largest possible audience, especially those using statically typed languages. A perfect example is the .NET / Visual Studio environment, which needs the WSDL file to automatically generate the stub for the web service.

A little side note: if your web service is accessed through SSL / HTTPS and the certificate authority who signed the certificate of the server is not trusted (ie. it's not Verisign), you get some warnings while generating the stub in Visual Studio and the final program will halt with an exception saying something like Could not establish a trusted connection over this SSL/TLS connection. The most common cause of this is the fact that the developer uses a self-signed certificate for the server. As far as I know there is no way to stop this from happening from inside the framework. However, because the framework shares its network access architecture with Internet Explorer, you can correct it from there. First you will need the certificate from the server (a .crt file, server.crt). Then go to Tools->Internet Options and select the Content tab. Click on Certificates, go to the Trusted Root Certification Authorities and select Import. Point it to the server certificate and answer affirmatively to the confirmation dialog. From now on that certificate will also be considered a trusted root certificate, you won't get warnings while browsing sites with it (and those sites might even have elevated privileges - depending on your Internet Explorer configuration), but most importantly your .NET client side code will work just fine.

The test project was to implement a web service which simulated some simple state machine(s). The project was implemented on the following platform:

The test was done on a Windows XP Pro machine using XAMPP to quickly install all the required components, however there is nothing platform specific in the code or the components, so it should be easy to replicate it on a different platform (Linux for example). The PHP code for the server side can be seen in Appendix A and an example for a state machine definition file can be found in Appendix B. An example client program written in C# can be seen in Appendix C.

The structure of a state machine definition file is as follows:

  • The root node is stateMachine. It has one mandatory parameter: initialState which specifies the initial state it is in
  • In the messages section it defines all possible messages (identified by name) which can be sent to this machine. This enumeration is needed to be able to check the validity of the message names provided later to guard against miss-typing.
  • The list of states identified by name. The states can be of two type: auto and message. Those of type auto automatically advance from the current state to the next state depending on the contained action elements. Those of type message wait for a message to advance.
  • The action elements contain the following attributes:
    • nextState - mandatory, the name of the text state if this action is chosen
    • waitBefore and waitAfter - optional, the amount of period to pause before and after executing this actions, in milliseconds. If omitted, zero is assumed. It must be a positive integer.
    • probability - a number greater than 0 but less or equal to 1.0. Determines the probability of this action being chosen. 0 means never and 1 means always. The sum of probabilities for a group (state element for auto states and message element for message states) must be 1.0. If some probabilities are omitted, the remaining probability is distributed amongst them (so if we have 5 action items and the first has a probability of 0.1, the second one of 0.3 and the rest are omitted, the last three will each have a probability of 0.2)

The exported functions by the server are:

  • postMessage(stateMachineName: string, message: string): string

    posts a message to the state machine identified by the stateMachineName. The definition for this state machine must be stored on the server in the file <stateMachineName>.xml. It is assumed that there is only one instance "running" of each server. This is guaranteed by the fact that the state of them is stored in a database table protected by write locks during the transitions. The method is synchronous and returns the name of the current state resulted from processing the message and any other automatic steps (states of type auto) which followed. One thing to keep in mind is that if you specify a state of type auto for the initial state, this will also be evaluated at the first message posted. On error it returns an empty string and you can use the getErrorMessage function to get the error message.

  • getMachineState(stateMachineName: string): string

    Gets the current state of the given state machine. It's asynchronous (with respect to the state machine, not the caller). If an error has occurred in the state machine it returns the empty string. You can use the getErrorMessage function to get the error message.

  • getErrorMessage(stateMachineName: string): string

    Returns the error message for the given state machine or empty if no error exists

  • resetMachineState(stateMachineName: string): void

    Resets the machine to its initial state (as specified by the initialState attribute of the correspoding definition file)

  • resetAllMachines: void

    Resets all the state machines to their initial state

Appendix A - PHP Server side code

To install it you would need the following items:

  • The NuSOAP library in the lib subdirectory (or anywhere else, just be sure to adjust the include directive accordingly)
  • The PearDB package for database access
  • Adjust the $data_directory variable so that it points to directory where the XML files describing the state machines are located. Important: include the trailing slash or backslash depending on the platform
  • Create two database tables to store the current state of the automatas (the second table is for locking purposes only, because MySQL doesn't support writing while in a read lock). The SQL statements to create these tables are (you might need to tweak these a little bit to get them to work if you are using something other than MySQL or a different version of it):
    CREATE TABLE `state_machines`.`state_machines` (
    `machine_name` VARCHAR(255) NOT NULL DEFAULT '',
    `machine_state` VARCHAR(255) NOT NULL DEFAULT '',
    `error_message` VARCHAR(255) NOT NULL DEFAULT '',
    PRIMARY KEY(`machine_name`)
    CREATE TABLE `state_machines`.`lock_table` (
     PRIMARY KEY(`dummy_column`)
  • Adjust the connection string accordingly in the DB::connect call
  require_once 'lib/nusoap.php';
  require_once 'DB.php';
  $server = new soap_server();
  $server->configureWSDL('statemachine', 'urn:statemachine');
  $data_directory = "C:\\xampp\\htdocs\\webservice\\data\\";  
  $db_connection = DB::connect("mysql://state_machine:password@localhost/state_machines");
  if (DB::isError($db_connection)) 
    stopWithErrorMessage("failed to connect to the database - " . $db_connection->getMessage());
  // Register the methods to expose
      array('stateMachineName' => 'xsd:string', 'message' => 'xsd:string'),
      array('return' => 'xsd:string'),
      'send a message to a given state machine. returns the new state'      
      array('stateMachineName' => 'xsd:string'),
      array('return' => 'xsd:string'),
      'returns the current state of the automaton'      
      array('stateMachineName' => 'xsd:string'),
      array('return' => 'xsd:string'),
      'returns the error message for a given state machine ("" if no error exists)'      
      array('stateMachineName' => 'xsd:string'),
      'resets the given state machine'      
      'resets all the state machines'      


  //send a message to a given state machine. returns the new state
  function postMessage($stateMachineName, $message) {
    if (!preg_match('/^[\w\-\s]+$/', $stateMachineName)) 
      stopWithErrorMessage('state machine name contains illegal characters');
    global $data_directory;
    if (!is_file($data_directory . $stateMachineName . ".xml")) 
      stopWithErrorMessage('specified state machine does not exists');
    //load up the state machine
    $stateMachine = loadStateMachineFromFile($data_directory . $stateMachineName . ".xml");
    global $db_connection;
    //from now on we need to be synchronized with other threads - lock the database table
    $db_connection->query('LOCK TABLE lock_table WRITE');
    //synchronize it with the database
    $stateMachine = synchronizeStateMachine($stateMachine, $stateMachineName);
    //now post the message to the state machine
    $stateMachine = postMessageWhilePossible($stateMachine, $message);
    if (is_string($stateMachine)) {
      //an error has occured! store the error message and return the empty string
      $db_connection->query('REPLACE INTO state_machines (machine_state, error_message) VALUES ("", "' . addslashes($stateMachine['currentState']) . 
        '") WHERE machine_name="' . addlashes($stateMachineName) . '"');
      $db_connection->query('UNLOCK TABLES');
      return '';
    } else {
      //everything went ok, store the new state and return it
      $db_connection->query('REPLACE INTO state_machines (machine_state, error_message) VALUES ("' . addslashes($stateMachine['currentState']) . 
        '", "") WHERE machine_name="' . addslashes($stateMachineName) . '"');
      $db_connection->query('UNLOCK TABLES');
      return $stateMachine['currentState'];
  //returns the current state of the automaton
  function getMachineState($stateMachineName) {
    if (!preg_match('/^[\w\-\s]+$/', $stateMachineName)) 
      stopWithErrorMessage('state machine name contains illegal characters');
    global $data_directory;
    if (!is_file($data_directory . $stateMachineName . ".xml")) 
      stopWithErrorMessage('specified state machine does not exists');
    //load up the state machine
    $stateMachine = loadStateMachineFromFile($data_directory . $stateMachineName . ".xml");
    //synchronize it with the database
    $stateMachine = synchronizeStateMachine($stateMachine, $stateMachineName);
    //return the current state
    return $stateMachine['currentState'];
  //returns the error message for a given state machine ('' if no error exists)
  function getErrorMessage($stateMachineName) {
    if (!preg_match('/^[\w\-\s]+$/', $stateMachineName)) 
      stopWithErrorMessage('state machine name contains illegal characters');
    global $db_connection;
    return $db_connection->getOne("SELECT error_message FROM state_machines WHERE machine_name=\"" . addslashes($stateMachineName) . "\"");
  //resets the given state machine
  function resetMachineState($stateMachineName) {
    if (!preg_match('/^[\w\-\s]+$/', $stateMachineName)) 
      stopWithErrorMessage('state machine name contains illegal characters');
    global $db_connection;
    $db_connection->query('DELETE FROM state_machines WHERE machine_name="' . addslashes($stateMachineName) . '"');
  //resets all the state machines
  function resetAllMachines() {
    global $db_connection;
    $db_connection->query('DELETE FROM state_machines');
  //internal helper function which outputs the error message to the header and then exits
  function stopWithErrorMessage($error_message) {
    header("HTTP/1.1 500 Internal Server Error: " . $error_message, true, 500);
  //internal helper function - synchronizes the state of a an automaton with the one stored in the databas
  //(if it's stored there)
  function synchronizeStateMachine($state_machine, $stateMachineName) {
    global $db_connection;
    $machine_state = $db_connection->getRow("SELECT * FROM state_machines WHERE machine_name=\"" . addslashes($stateMachineName) . "\"");
    if (is_array($machine_state)) {
      //it is present in the database, try to synchronize with it
      if ( ('' == $machine_state['machine_state']) || array_key_exists($machine_state['machine_state'], $state_machine['states'])) {
        $state_machine['currentState'] = $machine_state['machine_state'];
        return $state_machine;
      } else {
        stopWithErrorMessage("Erroneous state in the database: " . $machine_state['machine_state']);        
    //it's not present in the database, leave it as it is
    return $state_machine;
  //internal helper function. Checks if the given node has the specified attribute
  //if not, returns null, if it does, it returns it
  function getAttributeOrNull($node, $attr_name) {
    if ($node->hasAttribute($attr_name))
      return $node->getAttribute($attr_name);
    return null;      
  //internal helper function. Extract and validate the action elements from
  //a node (message or state). Return an array structure on success,
  //an error messag (string) on failure
  function extractActions($parent_node, $states_list, $state_name, $message_name) {
    //process the probable actions - make sure that the sum of the probabilities if 1.0
    //when no probaility is specified, the remaining probability is distributed between them
    $error_message_suffix = ('' == $message_name) ? '' : " at message '$message_name'";
    $actions = $parent_node->getElementsByTagName('action');
    $result = array();
    $probability_sum = 0.0; $actions_with_no_probability = 0;
    foreach ($actions as $action) {
      $new_action = array();
      if (null !== ($action_probability = getAttributeOrNull($action, 'probability'))) {
        if ($action_probability <= 0)
          return "Negative probability of action in state '$state_name'$error_message_suffix";
        $probability_sum += 0.0 + $action_probability;
        $new_action['probability'] = 0.0 + $action_probability;
      } else {
      if (null === ($action_wait_before = getAttributeOrNull($action, 'waitBefore'))) {
        $new_action['waitBefore'] = 0;
      } else {
        if ($action_wait_before < 0)
          return "Negative 'waitBefore' of action in state '$state_name'$error_message_suffix";
        $new_action['waitBefore'] = intval($action_wait_before);
      if (null === ($action_wait_after = getAttributeOrNull($action, 'waitAfter'))) {
        $new_action['waitAfter'] = 0;
      } else {
        if ($action_wait_after < 0)
          return "Negative 'waitAfter' of action in state '$state_name'$error_message_suffix";
        $new_action['waitAfter'] = intval($action_wait_after);
      if (null === ($action_next_state = getAttributeOrNull($action, 'nextState')))
        return "Unspecified nextState in state '$state_name'$error_message_suffix";
      if (!array_key_exists($action_next_state, $states_list))
        return "Invalid nextState specified in action at state '$state_name'$error_message_suffix: '$action_next_state'";
      $new_action['nextState'] = $action_next_state;
      $result[] = $new_action;
    //now redistribute the remaining probability :)
    if ($actions_with_no_probability > 0) {
      foreach (array_keys($result) as $action_key) {
        if (!array_key_exists('probability', $result[$action_key])) {
          $result[$action_key]['probability'] = (1.0 - $probability_sum) / $actions_with_no_probability;
    //finally sum up the probability and check it (must be 1.0)
    $probability_sum = 0.0;
    foreach ($result as $action)
      $probability_sum += $action['probability'];
    if (abs(1.0 - $probability_sum) > 0.001)
      return "The sum of probabilities for state '$state_name'$error_message_suffix is way off from 1.0"; 
    return $result;

  //returns a structure which completly describes the state machine
  //returns a string with an error message if the XML failed to follow
  //the rules
  function loadStateMachine($state_machine_xml) {
    $doc = new DOMDocument();
    //this will be the result is all goes well
    $result = array();
    //find all the valid message
    $xpath = new DOMXPath($doc);
    $valid_messages = array();
    foreach ($xpath->query('//stateMachine/messages/message') as $valid_message) {
      if (null === getAttributeOrNull($valid_message, 'name'))
        return "Found message element which doesn't have the 'name' attribute!";
      $valid_messages[getAttributeOrNull($valid_message, 'name')] = 1;
    if (0 >= count($valid_messages))
      return 'No valid message names found!';   
    //now parse states
    $result['states'] = array();
    $states = $doc->getElementsByTagName('state');
    if (0 >= $states->length)
      return 'No state elements found!';
    //first store the state names so that we can validate them later on
    foreach ($states as $state) {
      if (null === ($state_name = getAttributeOrNull($state, 'name')))
        return 'Found state with no name!';
      if (array_key_exists($state_name, $result['states']))
        return "Found state with duplicate name: '$state_name'";
      $result['states'][$state_name] = array();
    foreach ($states as $state) {
      //validate the basic parameters for the state
      $state_name = getAttributeOrNull($state, 'name');
      if (null === ($state_type = getAttributeOrNull($state, 'type')))
        return 'Found state with no type!';
      if ( ('message' != $state_type) && ('auto' != $state_type) )
        return "Found state with invalid type: '$state_type'";
      //save the validated stuff
      $result['states'][$state_name]['type'] = $state_type;
      //process the available state transitions
      if ('message' == $state_type) {
        $messages = $state->getElementsByTagName('message');
        $result['states'][$state_name]['messages'] = array();
        foreach ($messages as $message) {
          //message name: - it should exists, - it should be valid and - it shouldn't be used before (in this state)
          if (null === ($message_name = getAttributeOrNull($message, 'name')))
            return "Found message with no name in state '$state_name'";
          if (!array_key_exists($message_name, $valid_messages))
            return "Found invalid message name '$message_name' in state '$state_name'";
          if (array_key_exists($message_name, $result['states'][$state_name]['messages']))          
            return "Found duplicate message name '$message_name' in state '$state_name'";
          $result['states'][$state_name]['messages'][$message_name] = array();
          $result['states'][$state_name]['messages'][$message_name]['actions'] = 
            extractActions($message, $result['states'], $state_name, $message_name);
          if (is_string($result['states'][$state_name]['messages'][$message_name]['actions']))
            //an error has occured
            return $result['states'][$state_name]['messages'][$message_name]['actions'];
      } else {
        //load the actions we can chose from
        $result['states'][$state_name]['actions'] = 
          extractActions($state, $result['states'], $state_name, '');
        if (is_string($result['states'][$state_name]['actions']))
          //an error has occurred
          return $result['states'][$state_name]['actions'];
    //get the starting state and make sure that it's a valid state
    if (null === ($initial_state = getAttributeOrNull($doc->documentElement, 'initialState')))
      return 'Document has no initial state!';      
    if (!array_key_exists($initial_state, $result['states']))
      return 'Initial state is invalid!';   
    $result['currentState'] = $initial_state;   
    return $result;
  function loadStateMachineFromFile($file_machine) {
    $xml_file_contents = file_get_contents($file_machine);
    if (get_magic_quotes_gpc()) $xml_file_contents = stripslashes($xml_file_contents);
    return loadStateMachine($xml_file_contents);
  //applies a given message to a given state machine. it executes the specified waits
  //returns the modified state machine. If an error occured, the currentState will be set to ''
  function internalPostMessage($state_machine, $message = '') {
    //print "Applying message: '$message'\n";
    //print "Current state: $state_machine[currentState]\n";
    //we are in an invalid state - we can't do anything
    if (!array_key_exists($state_machine['currentState'], $state_machine['states']))
      return $state_machine;
    if ('message' == $state_machine['states'][$state_machine['currentState']]['type']) {
      if (!array_key_exists($message, $state_machine['states'][$state_machine['currentState']]['messages'])) {
        //this message can not be applied now
        $state_machine['currentState'] = '';
        return $state_machine;
      $actions = $state_machine['states'][$state_machine['currentState']]['messages'][$message]['actions'];
    } else {
      $actions = $state_machine['states'][$state_machine['currentState']]['actions'];
    //now chose an action, by "throwing a dice"
    $rand_value = rand(0, 32768) / 32768;
    $action_to_execute = null;
    foreach ($actions as $action) {
      $action_to_execute = $action;
      if ($rand_value <= $action['probability'])        
      $rand_value -= $action['probability'];
    //print "Going to state $action[nextState]\n";
    //now execute the action        
    sleep(intval($action['waitBefore'] / 1000 + 0.5));
    $state_machine['currentState'] = $action['nextState'];    
    sleep(intval($action['waitAfter'] / 1000 + 0.5));
    //print "Gone to state $action[nextState]\n";   
    return $state_machine;
  //the same as above, however it continues while possible after the first move
  //(while the current state is an automatic one)
  function postMessageWhilePossible($state_machine, $message) {
    //process any automatic statest BEFORE
    while ( ('' != $state_machine['currentState']) &&
      ('auto' == $state_machine['states'][$state_machine['currentState']]['type']) ) {
      $state_machine = internalPostMessage($state_machine);
    if ('' != $state_machine['currentState'])
      $state_machine = internalPostMessage($state_machine, $message);
    //process any automatic statest AFTER
    while ( ('' != $state_machine['currentState']) &&
      ('auto' == $state_machine['states'][$state_machine['currentState']]['type']) ) {
      $state_machine = internalPostMessage($state_machine);
    return $state_machine;

Appendix B - Example state machine file

<stateMachine initialState="Off">
    <message name="Flip" />
  <state name="Off" type="message">
    <message name="Flip">
      <action probability="0.5" nextState="Transient" />
      <action probability="0.5" nextState="Off" />
  <state name="Transient" type="auto">
    <action probability="0.9" nextState="On" waitBefore="1000" />
    <action probability="0.1" nextState="Off" waitBefore="1000" />  
  <state name="On" type="message">
    <message name="Flip">
      <action nextState="Off" />  

Appendix C - Example client program in .NET (C#, VB .NET, Delphi and Managed C++)

Before you can use these examples, you have to add a Web Reference to your project. You can do this by right-clicking on your Reference folder in your Visual Studio and selecting Web Reference. You should put in the link with a ?wsdl appended (to get the WSDL file). For example if you are hosting the service locally, you would put in http://localhost/webservice/index.php?wsdl

private static void Main(string[] args)
      Console.WriteLine("Startin up...");
      statemachine statemachine1 = new statemachine();
      Console.WriteLine("Startup done...");
      for (int num1 = 0; num1 < 10; num1++)
            Console.WriteLine("The current state is: " + statemachine1.getMachineState("testAutomata"));
            Console.WriteLine("Passing message: Flip");
            Console.WriteLine("Test automata returned: " + statemachine1.postMessage("testAutomata", "Flip"));
      Console.WriteLine("Press any key to exit...");
Private Shared Sub Main(ByVal args As String())
      Console.WriteLine("Startin up...")
      Dim statemachine1 As New statemachine
      Console.WriteLine("Startup done...")
      Dim num1 As Integer = 0
      Do While (num1 < 10)
            Console.WriteLine(("The current state is: " & statemachine1.getMachineState("testAutomata")))
            Console.WriteLine("Passing message: Flip")
            Console.WriteLine(("Test automata returned: " & statemachine1.postMessage("testAutomata", "Flip")))
            num1 += 1
      Console.WriteLine("Press any key to exit...")
End Sub
procedure Program.Main(args: string[]);
      Console.WriteLine('Startin up...');
      statemachine1 := statemachine.Create;
      Console.WriteLine('Startup done...');
      num1 := 0;
      while ((num1 < 10)) do
            Console.WriteLine(string.Concat('The current state is: ', statemachine1.getMachineState('testAutomata')));
            Console.WriteLine('Passing message: Flip');
            Console.WriteLine(string.Concat('Test automata returned: ', statemachine1.postMessage('testAutomata', 'Flip')));
      Console.WriteLine('Press any key to exit...');
Managed C++
private: static void __gc* Main(System::String __gc* args __gc [])
      System::Console::WriteLine(S"Startin up...");
      ContactWebservice::stateMachine::statemachine __gc* statemachine1 = __gc new ContactWebservice::stateMachine::statemachine();
      System::Console::WriteLine(S"Startup done...");
      for (System::Int32 __gc* num1 = 0; (num1 < 10); num1++)
            System::Console::WriteLine(System::String::Concat(S"The current state is: ", statemachine1->getMachineState(S"testAutomata")));
            System::Console::WriteLine(S"Passing message: Flip");
            System::Console::WriteLine(System::String::Concat(S"Test automata returned: ", statemachine1->postMessage(S"testAutomata", S"Flip")));
      System::Console::WriteLine(S"Press any key to exit...");

Appendix D - Example client written in Perl

use warnings;
use diagnostics;
use SOAP::Lite +trace => 'all';

print ">>" . SOAP::Lite
  -> uri('')
  -> proxy('http://localhost/webservice/index.php')
  -> getMachineState("testAutomata")
  -> result;


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