将图像从iOS应用程序上传到服务器时出错

Question

I am trying to do a simple task of uploading an image to server from iOS app. However I am receiving the following error message after running it:

Error: Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}

Any idea why? The following is my code for client side and server side respectively.

App side code:

-(void) uploadPhoto: (UIImage*) image{
    NSString *urlString = @"myServerDNS.com/upload.php";

    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/html"];

    NSData *imageData = UIImageJPEGRepresentation(image, 0.8);
    NSDictionary *parameters = @{@"foo":@"bar"};
    [manager POST:urlString
       parameters:parameters
constructingBodyWithBlock:^(id<AFMultipartFormData> formData)
     {[formData appendPartWithFormData:imageData name:@"file"];}
          success:^(AFHTTPRequestOperation *operation, id responseObject)
    {NSLog(@"Success: %@", responseObject);}
          failure:^(AFHTTPRequestOperation *operation, NSError *error)
    {NSLog(@"Error: %@", error);}
     ];
}

Server side php code:

<?php
$foo = $_POST["foo"];

$target_dir = "Folder/" . basename($_FILES["file"]["name"]);

if (move_uploaded_file($_FILES["file"]["tmp_name"], $target_dir)) 
{
echo json_encode([
"Message" => "The file ". basename( $_FILES["file"]["name"]). " has been uploaded.",
"Status" => "OK"
]);

} else {
echo json_encode([
"Message" => "Sorry, there was an error uploading your file.",
"Status" => "Error"
]);
}
?>

Answer 1

Okay, sorry I realised it was a stupid mistake causing the problem. It was simply because I added an echo "hello world"; at the start of the php script, causing it to trigger the JSON text error. Removed it and the error message went away.

Not corresponding to the error message stated in my question, but another bug that exists in my code was that I used appendPartWithFormData instead of appendPartWithFileData. After changing to the latter, image upload to server works.