Support for disallow_unknown_properties option

[nicolaiarocci]

Support for disallow_unknown_properties option, available both in the validate method and in the SchemaValidator contstructor. Set to True to prevent injection of unwanted property/value pairs in your document. Defaults to False.

While you can achieve similar results by setting 'additionalProperties = False', that only works for 'object' types and not for the 'array' type. When an array's 'items' property is set to a schema, it will accept any number of incoming dicts (objects) making sure that known fields match the schema, but still allowing for unknown/unmatched fields (the 'additionalItems' property will only block multiple array items).

Look at the test_disallow_unknown_properties.py module for usage examples.

PS: as an alternative (more verbose, perhaps more coherent) solution would be to provide an array property that does what 'additionalProperty = False' does for 'object' types. Since 'additionalItems' does something else already, maybe something like 'allowUnknownProperties'...

[nicolaiarocci]

As I said in the original PR, additionalProperties=False works for object types, but there's no corresponding functionality for arrays. I know about additionalItems=False, but that will only prevent additional items in the list It won't stop from inserting unknown fields in each array item definition.

take the following schema definition:

    self.schema_complex = {
        "type": "object",
        "additionalProperties": False,
        "properties": {
            "inv_number": {"type": "string"},
            "rows": {
                "type": "array",
                "items": {
                    "sku": {"type": "string"},
                    "desc": {"type": "string"},
                    "price": {"type": "number"},
                },
            },
        },
    }

I don't want a row like this one:

    newrow = {"sku": "789", "desc": "catch me if you can", "price": 1, "rice": 666}

to be validated (the 'rice' field is unknown). If I set additionalItems=False on the 'rows' array it will prevent addition of multiple items, which is not the desired behavior in this case. I'm probably missing something here.

However what this patch does is preventing unknown fields (both in the main object and in the nested array in this case) to be validated. Maybe there's a better, different way to achieve this (see my PS note on the original PR comment).

[jamesturk]

again, sorry about the delay here- wasn't getting the notifications for this project somehow. I thought this over in more detail and went ahead and merged it, thanks!