Add validation mechanisms for writing JSON. Validate against a specification.

[stephenberry]

Discussed in #674

^{Originally posted by scalpel4k January 3, 2024}
Hi,

I see that the write operations are all noexcept. Is there a way to abort writing when some conditions fail using the custom serializers?

thx Michi

[stephenberry]

We should be able to support both compile time and runtime validation. Initially validation should be based off of JSON schema.

[stephenberry]

There are two approaches to runtime validation. We can perform validation on parse, or we can perform validation on C++ memory. The later will be much more performant and I think should be the first focus of Glaze. We will use the same glz::json_schema, but we can use these structs at runtime to validate the memory of the C++ objects.

my_struct obj{};
if (glz::schema_validate(obj)) {
   // true if the object matches the gz::json_schema
   // note that we don't use a buffer, instead we would first read in a JSON file
   // and then we would validate
}

This works with validating before a write or after a read.

[KarlHedlund]

I would be interested in compile time validation based on a schema if that is possible. Current use case is to require a struct to have a couple of properties and then support structs that add whatever else they want in an object struct. Something like:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Node",
  "type": "object",
  "properties": {
    "type": {
      "type": "string"
    },
    "description": {
      "type": "string"
    },
    "additionalInformation": {
      "type": "object"
    }
  },
  "required": ["type", "description"]
}

Which would be validated for both A and B:

struct A
{
  std::string type;
  std::string description;
}

struct Internal
{
  ...
}

struct B
{
  std::string type;
  std::string description;
  Internal additionalInformation;
}

[isaki]

I recently came across an instance where being able to validate the structs that will be converted to json against their glz::meta definitions would be awesome; especially the option where we do it in memory before ever creating JSON. Is this feature still on the roadmap?