JSON and PHP: formatting and validating
Formatting JSON to look all lovely
It's always a happy day when I manage to use JSON in PHP. As a JS developer, it sort of feels like I'm marrying the two technologies. Take that, serialised arrays - I'm using JSON.
PHP, of course, has support for encoding and decoding JSON via json_encode() and json_decode() respectively. What it can't do natively, though, is format JSON.
Why would you want to format JSON in PHP to make it look all nice and indented? Well, if the system you're building uses JSON for a config file, and you want users to be able to edit that config file within the system, in a textarea, say.
I then found this function, which largely does the job.
It can, however, get the indentation wrong sometimes. Also, it can leave whitespace at the end of lines. So I extended it slightly. The following three snippets should be inserted just before the final return statement.
Firstly, let's clear any whitespace left at the end of lines.
$result = preg_replace('/\t+\n/', "\n", $result);
Next, let's fix the indentation. What I noticed was that the script was indenting lines containing closing brackets/braces precisely double what it should be - so four tabs instead of two, for example. So, the following halves each case.
1function PR_callback($match) { return substr($match[1], 0, strlen($match[1]) / 2).$match[2]; }
2$result = preg_replace_callback('/^(\t+)(\]|\})/m', 'PR_callback', $result);
Note I'm using a callback on preg_replace() - this gives me greater control over the nature of my replacements. preg_replace() automatically forwards to my callback one argument - an array of the match. As ever, key 0 in the array contains the whole match and any subsequent keys contain any sub-matches my pattern looked for.
Lastly, either the script or (more probably) my hacks above end up killing some of the line breaks, so let's restore them.
$result = preg_replace('/([^\t]+)\t/', "$1\n\t", $result);
Et voila - nicely formatted JSON.
Make sure your JSON's valid
JSON and JavaScript Object Notation are not always the same thing. How so? Well, this is valid JS but INvalid JSON:
1var someObj = {
2 one: 'one',
3 two: 'two'
4}
...because the JSON spec demands that a) property names are quoted; b) property names and strings must be encased in double, not single quotes.
So if you end up with invalid JSON, how will you know? PHP >= 5.3 defines json_last_error(), which returns a flag saying what went wrong.
Confusingly, it returns something even if nothing went wrong - JSON_ERROR_NONE. It does not return false, so it is insufficient to check the validity of JSON with:
1$badJSON = '{one: "one"}';
2$array = json_decode($badJSON, true); //2nd param means we get back an assoc. array, not an object
3if (!json_last_error()) echo "All OK!";
Instead, the last line should be:
if (json_last_error() != JSON_ERROR_NONE) echo "All OK!";
PHP versions prior to 5.3
If you're running PHP prior to v.5.3, you won't have json_last_error(). Instead, you can simply check the truthy/falsy value of json_decode(), so:
1$array = json_decode($badJSON, true);
2if (!$array) echo "Problem!";
Obviously this approach is more crude and won't tell you what went wrong - just that something did.
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