Downloading Data from Multiple URLs

The Downloader application downloads data from multiple URLs in a predetermined order, and stores the data in multiple files. The application obtains the URLs that it downloads by reading a text file in which the URLs have been stored.

The Downloader application's main routine sets up the application's main event loop. It calls the getURL routine to read obtain a URL from a file of URLs and is ready to start downloading data.

Listing 2-10 The Downloader application's main routine



 
#include <Events.h>

#include <stdio.h>

#include "URLAccess.h"

#include "string.h"

#include "Memory.h"



void main (void)

{

    OSStatus err = noErr;

    char url[255];

    int count, fileCount = 0;

    EventRecord ev;

    // Call MaxApplZone, MoreMasters.

    // Initialize graph port, fonts, menus, cursor, and dialogs.

    // Clear the screen.



    while ( url != nil ) {

        // Handle Events through each loop

        WaitNextEvent(everyEvent, &ev, 0, nil);

        eventHandler( nil, &ev );



        // Obtain a URL from the file of URLs.

        result = getURL(url); // (Routine not shown.)

        if ( result == eofErr ) { // Handle error condition. }



 
        // Call Download routine.

        result = DoDownload( url );

        if ( result != noErr) { // Handle error condition. }

    }

    printf("\n All of the URLs have been downloaded.\n");

}

The DoDownload routine shown in Listing 2-11 does the actual work of downloading data from the URL. It creates a file specification for the data that is to be downloaded and a URL reference. It sets the open flags to replace an existing file (if any) with the downloaded data and to display a progress indicator during the download. Then the DoDownload routine calls URLDownload to download the data.

Listing 2-11 The Downloader application's DoDownload routine



 
void DoDownload (void)

{

    URLReference urlRef;

    FSSpec dest, *destPtr = nil;

    destPtr = &dest;

    Handle destHandle = nil;

    int openFlags = kURLReplaceExistingFlag + kURLDisplayProgressFlag;

    Str255 newFile;

        

    // Create the file specification for the download.

    sprintf((char*)newFile, "File %d", fileCount);

    c2pstr((char*)newFile);

    fileCount++;

    err = FSMakeFSSpec(0, 0, newFile, &dest);



 
    // Create the URLReference.

    err = URLNewReference( theURL, &urlRef );

    if (err != noErr) printf("URLNewReference failed\n");



 
    // Download the data.

    err = URLDownload( urlRef, destPtr, destHandle, openFlags, 

    &eventHandler, (void*)&fileCount );



    if (err != noErr) printf("URLDownload failed\n");



 
    // Clean up.

    err = URLDisposeReference( urlRef );

    if (err != noErr) printf("URLDisposeReference failed\n");

    return err;

}

The Downloader application uses the eventHandler routine as a general purpose event handling routine. In this example, the user context (context ) is an integer value.

Listing 2-12 The Downloader application's system event callback routine



 
pascal long eventHandler( void * userContext, EventRecord* eventPtr )

{

    EventRecord* ev;

    int what = 0;

    int context = 0;

    int* intPtr = nil;



 
// Convert the event pointer into an event record.

    ev = (EventRecord*)eventPtr;

    what = ev->what;

// Convert the void* to an integer.

    intPtr = (int*)userContext;

    context = *intPtr;

    if (context < 0 || context > 99)

        context = -1; // Unknown context

switch (what) {

    case 0 : // Null Event

        break;

    case mouseDown:

        printf("Handler Called: mouseDown  User Context: %d\n", context);

        // Call routine to handle event.

        break;

    case updateEvt:

        printf("Handler Called: updateEvt  User Context: %d\n", context);

        // Call routine to handle event.

        break;

    case activateEvt:

        printf("Handler Called: activateEvt  User Context: %d\n",

            context);

        // Call routine to handle event.

        break;

    case keyDown:

        printf("Handler Called: keyDown  User Context: %d\n", context);

        // Call routine to handle event.

        break;

    default:

        printf("Handler Called: Default  User Context: %d\n", context);

        break;

    }

    return nil;

}