PHP json_encode() vs empty NSDictionary

Question

The gist of my question is: how can I convince PHP to encode/decode json without converting [NS]arrays or [NS]dictionaries to the other one?

I've got an app (iOS, though it shouldn't matter) that keeps a bunch of app data in an NSDictionary. Some of the data is nested a few levels, and some of the objects stored in my top-level dictionary are NSArray-s, or other NSDictionary-s, some of which contain additional NSArray-s or NSDictionary-s.

It's not really all that complicated, and the code traverses it all just fine, so that's all well & good.

I save this top-level dict to a server and, to do so, I use NSJSONSerialization, zip the resulting string and upload it. Later, the server sends back the zip file, I use NSJSONSerialization to decode, and we're all back in business -- again, all well & good.

The problem arrises in that, under certain circumstances, I want the server to unzip the file, json-decode the contents, alter the contents, json-encode the result, and re-zip before sending the data back to the app.

"So what's the problem?", I hear you ask. Aha!

The problem is: the server is PHP and uses json_encode() and json_decode() and, if my data contains empty dictionaries, they are converted to arrays, which makes my data-parsing code unhappy.

Further, if I use json_encode($foo, JSON_FORCE_OBJECT), that turns all arrays into dictionaries (keyed by index, if they didn't used to be dictionaries), which is every bit as bad.

So my question is:

Is there any way in PHP to encode/decode json such that what began life as an array remains an array (in the NSArray sense) and what began life as a dictionary (NSDictionary) remains a dictionary (PHP: "object"), regardless of whether the source data has contents or is empty?

Thanks!

(Yes, I googled around. That's how I learned about JSON_FORCE_OBJECT, but I was unable to find anything to help with this specific problem.)

VolkerK · Accepted Answer · 2015-08-07 13:11:54Z

Since there doesn't seem to be much activity on that question, here is a totally rudimentary/experimental idea:

<?php
abstract class JSONComplexType extends ArrayObject implements JsonSerializable {
    abstract protected function __key($key);
    abstract public function jsonSerialize();

    public function offsetSet ($key, $newval) {
        $offset = $this->__key($key);
        if ( is_null($offset) ) {
            trigger_error(get_class($this).': invalid key:'.var_export($key, true), E_USER_ERROR);
        }
        else {
            parent::offsetSet($offset, $newval);
        }
    }
}

class JSONArray extends JSONComplexType {
    protected function __key($key) {
        if ( is_null($key) ) {
            return $this->count();
        }
        else if ( !is_int($key) && !ctype_digit($key) ) {
            return null;
        }
        else {
            $key = intval($key);
            return $key <= $this->count() ? $key : null;
        }
    }

    public function jsonSerialize() {
        return $this->getArrayCopy();
    }
}

class JSONObject extends JSONComplexType {
    protected function __key($key) {
        return (string)$key;
    }

    public function jsonSerialize() {
        return (object)($this->getArrayCopy());
    }
}

function foo($in) {
    if ( is_object($in) ) {
        $retval = new JSONObject();
        foreach( get_object_vars($in) as $key=>$value ) {
            $retval[$key] =foo($value);
        }
    }
    else if ( is_array($in) ) {
        $retval = new JSONArray();
        foreach( array_values($in) as $key=>$value ) {
            $retval[$key] = foo($value);
        }
    }
    else {
        $retval = $in;
    }
    return $retval;
}

$in = '{
    "A":[
        {
            "X": 1,
            "Y": "z",
            "O": {},
            "AA":[ {},{},[],[1,2,3],{"I":"V"}]
        },
        {
            "X": 2,
            "Y": "Z",
            "AA": []
        }
    ]
}';

$json = foo( json_decode($in) );
echo "---- 1 ----\r\n", json_encode($json);

$json['A'][0]['AA'][1]['addObject']='New';
$json['A'][0]['AA'][2][]='New0';
$json['A'][0]['AA'][2][1]='New1';
$json['A'][0]['AA'][2][]='New2';
unset($json['A'][0]['AA'][3][0]);
unset($json['A'][0]['AA'][3][1]);
unset($json['A'][0]['AA'][3][2]);
unset($json['A'][0]['AA'][4]['I']);
echo "\r\n---- 2 ----\r\n", json_encode($json);

prints

---- 1 ----
{"A":[{"X":1,"Y":"z","O":{},"AA":[{},{},[],[1,2,3],{"I":"V"}]},{"X":2,"Y":"Z","AA":[]}]}
---- 2 ----
{"A":[{"X":1,"Y":"z","O":{},"AA":[{},{"addObject":"New"},["New0","New1","New2"],[],{}]},{"X":2,"Y":"Z","AA":[]}]}

The output seems to be ok, but the code would need quite some doing (and documentation ;-)). It's just something I came up with during lunch break...

Well, this is a bit wilder than what I was hoping for, but it's better than "it can't be done", so I'm going to accept it. FWIW, I ended up just doing validation on the receiving end. That is, I have code similar to NSDictionary *myDict = [otherDict objectForKey: @"hopeItsADict"]; if ([myDict count] == 0) { myDict = [NSDictionary new]; } // guard against json mangling (There's more to it, my dicts are mutable, etc., but that's the gist of it.)

Olie · Accepted Answer · 2015-08-24 15:47:35Z

0

(Just copying my code from comment to VolkerK into an answer, for easier reading & copy/paste.)

I ended up just doing validation on the receiving end. That is, I have code similar to:

NSDictionary *myDict = [otherDict objectForKey: @"hopeItsADict"];
if ([myDict count] == 0)      // guard against json mangling 
{
    myDict = [NSDictionary new];
}

There's more to it, my dicts are mutable, etc., but that's the gist of it. This works because both NSDictionary and NSArray respond to count, so the if-check doesn't care which one it is (nor if it's nil.)

answered Aug 24, 2015 at 15:47

Olie

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