仅验证一个图层

I want to verify a variable holding json only has one level simple format. Can someone provide an example where only one level is verified - not a multi-level verification?

   <?php
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
isValidOnlayer($json); // True
$json = '{
    "id": "0001",
    "type": "donut",
    "name": "Cake",
    "ppu": 0.55,
    "batters":
        {
            "batter":
                [
                    { "id": "1001", "type": "Regular" },
                    { "id": "1002", "type": "Chocolate" },
                    { "id": "1003", "type": "Blueberry" },
                    { "id": "1004", "type": "Devil's Food" }
                ]
        },
    "topping":
        [
            { "id": "5001", "type": "None" },
            { "id": "5002", "type": "Glazed" },
            { "id": "5005", "type": "Sugar" },
            { "id": "5007", "type": "Powdered Sugar" },
            { "id": "5006", "type": "Chocolate with Sprinkles" },
            { "id": "5003", "type": "Chocolate" },
            { "id": "5004", "type": "Maple" }
        ]
    }'
    isValidOnlayer($json); // False
?>

You can use this as a result of your function:

count(array_filter(json_decode($json, 1), 'is_array'))

$tmp = json_decode($json, true, 2); // depth=2, the array "itself" is level 1, its elements are level 2

if $tmp is null an error occurred. In case the depth limit was the problem json_last_error() will return JSON_ERROR_DEPTH