Base64 Over HTTP POST losing data (Objective-C)

问题:

I currently have a HTTP POST Request and a Base64 Encoding Library, I encode my image to B64 then send it over HTTP via the POST method.

I output the Base64 to XCodes console, copy and paste it and it works perfectly. Although the Base64 I store within the Database (MongoDB, Plain Text File etc) always comes out corrupt on the other end.

Working Version (Copied and Pasted from XCode): http://dontpanicrabbit.com/api/working.php Broken Version (From MongoDB Database): http://dontpanicrabbit.com/api/grabimage.php

If you view the source you'll notice they are the same but there is added whitespace into the broken version.

The Objective-C code I am using is:

MyImage.image = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData *imageData = UIImageJPEGRepresentation(MyImage.image, 0);

    [Base64 initialize];
    NSString *encoded = [Base64 encode:imageData];

    NSString *urlPOST = encoded;
    //NSLog(@"%@",encoded);

    NSString *varyingString1 = @"picture=";
    NSString *varyingString2 = urlPOST;
    NSString *post = [NSString stringWithFormat: @"%@%@", varyingString1, varyingString2];
    NSLog(@"%@", post);
    //NSString *post = @"image=%@",urlPOST;
    NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];

    NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:@"url/api/insertimage.php"]];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postData];
    NSData *returnData = [NSURLConnection sendSynchronousRequest: request returningResponse: nil error: nil];
    NSString *strResult = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];

PHP -> MongoDB Storage

<?php
    try {
      // open connection to MongoDB server
      $conn = new Mongo('localhost');

      // access database
      $db = $conn->dablia;

      // access collection
      $collection = $db->images;

      // insert a new document
      $item = array(
        'picture' => $_POST['picture']
      );
      $collection->insert($item);
      echo 'Inserted document with ID: ' . $item['_id'];

      // disconnect from server
      $conn->close();
    } catch (MongoConnectionException $e) {
      die('Error connecting to MongoDB server');
    } catch (MongoException $e) {
      die('Error: ' . $e->getMessage());
    }
?>

Output Code:

<?php
try {
  // open connection to MongoDB server
  $conn = new Mongo('localhost');

  // access database
  $db = $conn->dablia;

  // access collection
  $collection = $db->images;

  // execute query
  // retrieve all documents
  $cursor = $collection->find();

  // iterate through the result set
  // print each document
  foreach ($cursor as $obj) {
    echo '<img src="data:image/jpeg;base64,'.trim($obj['picture']).'">';
  }

  // disconnect from server
  $conn->close();
} catch (MongoConnectionException $e) {
  die('Error connecting to MongoDB server');
} catch (MongoException $e) {
  die('Error: ' . $e->getMessage());
}
?>

I have no idea why I seem to be corrupting over POST?

回答1:

The problem is exactly what I suggested in my first comment. That is, base64 encoded data can contain '+' characters. In x-www-form-urlencoded data the receiver knows that '+' is an encoding of a space character. Thus since you aren't URL encoding your base64 value, any instances of '+' will cause the data to be corrupted when received.

The '+' characters in your initial data are turning into ' ' when received and stored. When you then output that value, it is invalid base64 encoded data.

If you examine the source of your working vs. non-working examples you'll see that the whitespace exists EXACTLY where there is a '+' in the original Base64 encoded value. Any newlines you're seeing are because whatever you're viewing the source in is wrapping lines at a ' ' character.

In your iOS code you need to properly encode the base64 encoded value, in your case all you really need to do is percent encode the '+' characters.

EDIT to add, in response to comment:

post = [post stringByReplacingOccurrencesOfString:@"+" withString:@"%2B"];