NSData appendData: UIImageJPEGRepresentation() returns nil

Question

This has had me scratching for quite some time.

I am preparing a UIImage to post as part of a HTTP request . I am doing this with the following code:

[postData appendData:[[NSString stringWithFormat:@"--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
                        [postData appendData:[[NSString stringWithFormat:@"Content-Disposition: attachment; name=\"q%@\"; filename=\".jpg\"\r\n" , key] dataUsingEncoding:NSUTF8StringEncoding]];
                        [postData appendData:[@"Content-Type: application/octet-stream\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
                        [postData appendData:[NSData dataWithData:UIImageJPEGRepresentation(image, 1.0)]];
                        [postData appendData:[@"\r\n" dataUsingEncoding:NSUTF8StringEncoding]];

The problem I am having is that postData is null after running these lines.

Using NSLog I found out that [postData appendData:[NSData dataWithData:UIImageJPEGRepresentation(image, 1.0)]]; is the line which is causing this to happen. I then went on to see if the image was a the problem. UIImageJPEGRepresentation(image, 1.0) outputs a mass of data to the console and adding image to a UIImageView shows the .jpg I was expecting.

I am absolutely bamboozled. Please help >.< S

EDIT

After a bit of a debacle below I have realised that it is definitely posting the image .

NSLog(@"postData = %@",[postData length]);

shows 280861 (bytes?) but a PHP file with <?php print_r($_FILES); ?> <?php print_r($_FILES); ?> returns Array {} .

Answer 1

1. UIImageJPEGRepresentation(image, 1.0) returns a NSData object that can't be turned into a NSString. A jpeg does not consist of valid characters. And arbitrary data can't be converted to a valid string.

2. Even if UIImageJPEGRepresentation(image, 1.0) returns nil, the [NSData dataWithData:] call makes sure that the data you append to postData is not nil. [NSData dataWithData:nil]; returns an empty NSData instance, not nil.

3. Regarding your answer. nil is not a valid string encoding. The compiler should show a warning and you should see a warning in the console "Incorrect NSStringEncoding value 0x0000 detected. Assuming NSASCIIStringEncoding. Will stop this compatiblity mapping behavior in the near future.".

You can't convert postData back into a NSString. If you want to check that the image is part of the NSData object you could look at the length of postData.

Answer 2

Resolved with:

[postData appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[postData appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\";\r\nfilename=\"%@.jpeg\"\r\nContent-Type: image/jpeg\r\n\r\n", key,key] dataUsingEncoding:NSUTF8StringEncoding]];
[postData appendData:[NSData dataWithData:imageData]];
[postData appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];

The first newline after my already included data seems to have resolved this

Answer 3

How did you tell postData was null? Please note that you can't convert it to UTF8 string using some category/extension as below.

extension NSData { func to_string(encoding:UInt = NSUTF8StringEncoding) -> String? { return NSString(data:self, encoding:encoding) as? String } }