Question

I’m trying to get a POST message working. I’ve seen a couple of posts describing doing so, such as this one, but I still cannot get it working. Below is my objective-c code:

NSString * urlString = @"http://magicthegatheringdatabase.com/test.php";
NSURL *aUrl = [NSURL URLWithString: urlString];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:aUrl
                                                       cachePolicy:NSURLRequestUseProtocolCachePolicy
                                                   timeoutInterval:60.0];

NSString *postString = [NSString stringWithFormat:@"tes1=%@&test2=%@",
                        [@"hello" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
                        [@"world" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
NSData * postBody = [postString dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody: postBody];

[request addValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"];

NSString *postLength = [NSString stringWithFormat:@"%d", postBody.length];
[request addValue: postLength forHTTPHeaderField:@"Content-Length"];

[request setHTTPMethod:@"POST"];

NSError * error = nil;
NSData *returnData = [NSURLConnection sendSynchronousRequest: request
                                           returningResponse: nil
                                                       error: &error];
NSLog(@"%p, %@", error, error.localizedDescription);

NSString * returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];
NSLog(@"Result: %@", returnString);

And here is my PHP:

<?php
  print_r($_REQUEST);
  print_r($_POST);
  print_r($_GET);

  echo file_get_contents( 'php://input' );
?>

If I run the code, I get the following logged:

2012-12-19 09:24:09.061 MTG Deck Builder[7921:570f] 0x0, (null)
2012-12-19 09:24:09.062 MTG Deck Builder[7921:570f] Result: Array
(
)
Array
(
)
Array
(
)

If I navigate directly to the url and append ?test1=hello&test2=world (using GET obviously instead of POST) I get:

Array
(
    [test1] => hello
    [test2] => world
    [phpbb3_5e63r_u] => 1
    [phpbb3_5e63r_k] => 
    [phpbb3_5e63r_sid] => 7ff37e188aa8e0ab57fae6a52f0d1f7b
    [__utma] => 86369156.392372889.1349352986.1352901458.1353328580.11
    [__utmz] => 86369156.1351935106.8.2.utmcsr=hankinsoft.com|utmccn=(referral)|utmcmd=referral|utmcct=/website/forum/10-mtg-magic-the-gathering-trading-card-game-tcg-da/634-new-forum.html
    [style_cookie] => null
)
Array
(
)
Array
(
    [test1] => hello
    [test2] => world
)

So I know my PHP is logging the get/requests properly, but I’m not sure why my POST via the objective-c code is not working. I’m pretty sure that I’m overlooking something stupid. Any suggestions on what I am missing?

Answer 1

This is because NSURLConnection doesn’t handle redirections properly.

When you send the POST request to the URL http://magicthegatheringdatabase.com/test.php, the server respond with 301 Moved Permanently and redirects to http://www.magicthegatheringdatabase.com/test.php.

Instead of sending the same request to the new URL, NSURLConnection creates a new GET request and discards the original request’s HTTPBody. THis behavior is due to the HTTP specifications that forbid the automatic redirection of requests other than HEAD and GET without a confirmation from the user. Changing the method to GET is erroneous but at least it is a safe method, which cannot harm the HTTP resource.

This problem can be solved with two options:

1. You may simply change the URL of the request to be http://www.magicthegatheringdatabase.com/test.php.

2. Or you may create an instance of NSURLConnection with a delegate and implement the connection:willSendRequest:redirectResponse: in order to handle the redirection properly as described in the answer to this question. This will work even if the redirection changes but requires you to write more code as you need to wait for the response, create a NSMutableData object, append the bytes as they come and handle everything asynchronously (see Apple Developer Documentation). However, performing tasks asynchronously is always a good idea: you can cancel them if needed and you don’t risk blocking your thread for a long a time (when you’re in the main thread, anything longer than 1 second is a long time).