So today, keeping in the theme of posting useful code snippets that do not rely on privileged SDK calls, let me show you how to Tweet. The API itself is really simple: you provide a user name, password and a Twitter message. What complicates this from an iPhone point of view is that you can't just assemble a URL and shoot it upstream to Twitter.com. The request requires POST.

The NSURLRequest class simplifies submitting form data. You can use synchronous requests with sendSynchronousRequest: returningResponse: error:. Synchronous requests mean you don't have handle threads and partial results. Instead, you send one (blocking) call, and when it returns you have your results.

The following source code demonstrates the entire process. First, it escapes the command line arguments, embedding them into the request URL and the form body. Then it builds the actual API request. The request parameters include POST as the method and x-www-form-urlencoded for the content type. Finally, it contacts the Twitter server and checks to see whether the request went through or whether there were authentication errors.

You can read more about Twitter's API at their website. It's a very nice Web service to get started with due to its simplicity and ease-of-use.

#import <CoreFoundation/CoreFoundation.h>
#import <Foundation/Foundation.h>
#import <stdio.h> 

int main(int argc, char **argv)
{
   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
   if (argc < 4) 
   { 
      printf("Usage: %s username password tweet\n", argv[0]);
      exit(-1);
   }

    // Convert the C-String arguments into Twitter-happy escaped format
    NSString *unpw = [[NSString stringWithFormat:@"%@:%@", 
                         [NSString stringWithCString:argv[1]
                            encoding:NSUTF8StringEncoding],
                         [NSString stringWithCString:argv[2] 
                            encoding:NSUTF8StringEncoding]]
         stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *tweet = [[NSString stringWithCString:argv[3]
                            encoding:NSUTF8StringEncoding] 
         stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *body = [NSString stringWithFormat: 
                        @"source=iTweet&status=%@", tweet];

    // Establish the Twitter API request
    id baseurl = [NSString stringWithFormat:
         @"http://%@@twitter.com/statuses/update.xml", unpw];
    NSURL *url = [NSURL URLWithString:baseurl];
    NSMutableURLRequest *urlRequest = [NSMutableURLRequest
                                         requestWithURL:url];

    if (!urlRequest)
    {
         printf("Error creating URL Request. Exiting.\n");
         exit(-1);
    }

    [urlRequest setHTTPMethod: @"POST"];
    [urlRequest setHTTPBody:[body dataUsingEncoding:NSUTF8StringEncoding]];
    [urlRequest setValue:@"application/x-www-form-urlencoded"
                forHTTPHeaderField:@"Content-Type"];
    [urlRequest setValue:@"iTweet" 
                forHTTPHeaderField:@"X-Twitter-Client"];

    // Contact Twitter and recover its response
    printf("Contacting Twitter Server. This may take up to a minute.\n");

    NSError *error;
    NSURLResponse *response;
    NSData* result = [NSURLConnection sendSynchronousRequest:urlRequest
                         returningResponse:&response error:&error];

    if (!result)
    {
       printf("Submission Error : %s\n", 
                  [[error localizedDescription] UTF8String]);
       exit(-1);
    }

    // Check to see if there was an authentication error. If so, report it.
    NSString *outstring = [[[NSString alloc] initWithData:result 
                             encoding:NSUTF8StringEncoding] autorelease];
    if ([outstring rangeOfString:@"uthentica"].location != NSNotFound)
         printf("%s\n", [outstring UTF8String]);
    else 
         printf("Done\n");
    exit(0);
}