A No So-Useful Echolalia Client and Server

As our first full-blown code example of the ground covered in this chapter, we will create an echolalia server and client. Echolalia is a psychiatric disorder in which causes those afflicted to mechanically repeat the uttering of other people, kinda of like a ditto-head, ``Johnson, we should buy more shares of SCO.'' ``Yes boss, we should by more shares of SCO.'', but much more insidious.

Our echolalia server will simply repeat everything ``said'' by our echolalia client, and our echolalia client will ``say'' only those things pass to it via the command line. So, for example, we would first start the echolalia server as follows

% echolaliaserver

After the echolalia server is up and running we could start the echolalia client as follows

% echolaliaclient

The echolalia client will then wait for user input. For example, the user my type in the following, then hit return

Hey, you repeat everything I say.

The server would then print out

Hey, you repeat everything I say.

The idea is relatively simple, though it can be of use in tracking networking problems between a server and client. Let us now move on to code.

The full code for the echolalia client is as follows

#include <string.h>
#include <stdio.h>
#include "GAT.h"

static GATPipe Obtain_GATPipe( void );
static void Send_Messages( GATPipe pipe );

int main( int argc, char *argv[] )
{
  GATPipe pipe;
  
  /* Obtain  GATPipe */
  pipe = Obtain_GATPipe();
  
  /* Send Messages on GATPipe */
  if( NULL != pipe )
    Send_Messages( pipe );
  
  /* Return to OS */
  return 1;
}

static GATPipe Obtain_GATPipe( void )
{
  GATPipe pipe;
  GATResult result;
  const char *path;
  GATObject object;
  GATList_String paths;
  GATString stringPath;
  GATContext context;
  GATTable description;
  GATList_String_Iterator beginning;
  GATAdvertService advertService;
  
  /* Set GATPipe */
  pipe = NULL;
  
  /* Create GATContext */
  context = GATContext_Create();
  
  /* Check GATContext creation */
  if( NULL != context )
  {
    /* Create GATAdvertService */
    advertService = GATAdvertService_Create( context, NULL );
    
    /* Check GATAdvertService creation */
    if( NULL != advertService )
    {
      /* Create GATTable */
      description = GATTable_Create();
      
      /* Check GATTable creation */
      if( NULL != description )
      {
        /* Add Meta-Data to GATTable */
        result = GATTable_Add_String( description, 
                                      (const void *) "name", 
                                      "echolalia" );
        
        /* Check last call */
        if( GAT_SUCCEEDED( result ) )
        {
          /* Find GATPipe */
          result = GATAdvertService_Find( advertService, description, &paths );
          
          /* Check last call */
          if( GAT_SUCCEEDED( result ) )
          {
            /* Obtain Beginning Iterator */
            beginning = GATList_String_Begin( paths );
            
            /* Check last call */
            if( NULL != beginning )
            {
              /* Check for non-empty list */
              if( beginning != GATList_String_End( paths ) )
              {
                /* Get path */
                path = GATList_String_Get( beginning );
                
                /* Create GATString */
                stringPath = GATString_Create( path, strlen( path ) + 1, "ASCII" );
                
                /* Check GATString creation */
                if( NULL != stringPath )
                {
                  /* Get Advertisable */
                  result = GATAdvertService_GetAdvertisable( advertService, 
                                                             stringPath, 
                                                             &object );
                  
                  /* Check Last Call */
                  if( GAT_SUCCEEDED( result ) )
                  {
                    /* Convert GATObject to GATPipe */
                    pipe = GATObject_ToGATPipe( object );
                  }
                
                  /* Destroy GATString */
                  GATString_Destroy( &stringPath );
                }
              }
            }
            
            /* Destroy GATList_String */
            GATList_String_Destroy( &paths );
          }
        }
      
        /* Destroy GATTable */
        GATTable_Destroy( &description );
      }
    
      /* Destroy GATAdvertService */
      GATAdvertService_Destroy( &advertService );
    }
    
    /* Destroy GATContext */
    GATContext_Destroy( &context );
  }
  
  /* Return to caller */
  return pipe;
}

static void Send_Messages( GATPipe pipe )
{
  GATuint32 size;
  char input[2048];
  GATResult result;
  GATObject object;
  GATuint32 writtenBytes;
  
  /* Convert GATPipe to GATObject */
  object = GATPipe_ToGATObject( pipe );
      
  /* Loop Forever */
  while( GATTrue == GATTrue )
  {
    /* Read Input from User */
    if( NULL != fgets( input, sizeof( input ), stdin ) )
    {
      /* Obtain size */
      size = (GATuint32) (strlen( input ) + 1);
      
      /* Write to GATObject */
      result = GATStreamable_Write( object, 
                                    (const void *) input,  
                                    size, 
                                    &writtenBytes );
      
      /* Check for Error */
      if( GAT_FAILED( result ) )
      {
        /* Print Error Message */
        printf( "An error occured in writing: %s\n", input );
      }
    }
    else
    {
      /* Print Error Message */
      printf( "An error occured in reading from stdin.\n" );
    }
  }
  
  /* Return to caller */
  return;
}

The full code for the echolalia server is as follows

#include <stdio.h>
#include <string.h>
#include "GAT.h"

static void Read_From_GATEndpoint( GATEndpoint endpoint );
static GATResult Advertise_GATEndpoint( GATContext context, GATEndpoint endpoint );

int main( int argc, char *argv[] )
{
  GATResult result;
  GATContext context;
  GATEndpoint endpoint;
  
  /* Create GATContext */
  context = GATContext_Create();
  
  /* Check GATContext creation */
  if( NULL != context )
  {
    /* Create GATEndpoint */
    endpoint = GATEndpoint_Create( context, NULL );
    
    /* Check GATEndpoint creation */
    if( NULL != endpoint )
    {
      /* Advertise GATEndpoint */
      result = Advertise_ GATEndpoint( context, endpoint );
      
      /* Check Last Call */
      if( GAT_SUCCEEDED( result ) )
      {
        /* Read GATEndpoint */
        Read_From_GATEndpoint( endpoint ); 
      }
    
      /* Destroy GATEndpoint */
      GATEndpoint_Destroy( &endpoint );
    }
  
    /* Destroy GATContext */
    GATContext_Destroy( &context );
  }

  /* Return to OS */
  return 1;
}

static GATResult Advertise_GATEndpoint( GATContext context, GATEndpoint endpoint )
{
  GATString path;
  GATResult result;
  GATObject object;
  GATTable description;
  GATAdvertService advertService;
  
  /* Set GATResult */
  result = GAT_MEMORYFAILURE;
  
  /* Create GATAdvertService */
  advertService = GATAdvertService_Create( context, NULL );
  
  /* Check GATAdvertService creation */
  if( NULL != advertService )
  {
    /* Convert GATEndpoint to GATObject */
    object = GATEndpoint_ToGATObject( endpoint );
    
    /* Create GATTable */
    description = GATTable_Create();
    
    /* Check GATTable create */
    if( NULL != description )
    {
      /* Create GATString */
      path = GATString_Create( "/usr/share/bin/echolaliad", 26, "ASCII" );
      
      /* Check GATString creation */
      if( NULL != path )
      {
        /* Add Meta-Data to GATTable */
        result = 
         GATTable_Add_String( description, (const void *) "name", "echolalia" );
      
        /* Check last call */
        if( GAT_SUCCEEDED( result ) )
        {
          /* Add GATEndpoint to GATAdvertService */
          result = 
           GATAdvertService_Add( advertService, object, description, path );
        }
        
        /* Destroy GATString */
        GATString_Destroy( &path );
      }
    
      /* Destroy GATTable */
      GATTable_Destroy( &description );
    }
    
    /* Destroy GATAdvertService */
    GATAdvertService_Destroy( &advertService );
  }
  
  /* Return to caller */
  return result;
}

static void Read_From_GATEndpoint( GATEndpoint endpoint )
{
  GATPipe pipe;
  GATResult result;
  char input[2048];
  GATObject object;
  GATuint32 readBytes;
  
  /* Wait For Incoming Call */
  result = GATEndpoint_Listen( endpoint, &pipe );
  
  /* Check last call */
  if( GAT_SUCCEEDED( result ) )
  {
    /* Convert GATPipe to GATObject */
    object = GATPipe_ToGATObject( pipe );
    
    /* Loop Until Failure */
    while( GAT_SUCCEEDED( result ) )
    {
      /* Read from GATObject */
      result = GATStreamable_Read( object, (void *) input, 2048, &readBytes );
      
      /* Check Last Call */
      if( GAT_SUCCEEDED( result ) )
      {
        /* Print Result */
        printf( "%s", input );
      }
    }
  
    /* Destroy GATPipe */
    GATPipe_Destroy( &pipe );
  }
  
  /* Return to caller */
  return;
}