openapi-schema-to-json-schema

Convert an OpenAPI 3.0 Schema Object into a JSON Schema draft-04 document.

OpenAPI 3.0 describes schemas with an extended subset of JSON Schema that is not itself valid draft-04. This crate bridges the gap. It is pure and in memory. It performs no I/O, no network access, and no $ref resolution.

Install

[dependencies]
openapi-schema-to-json-schema = "0.1"
serde_json = "1"

Use

use openapi_schema_to_json_schema::{from_schema, Options};
use serde_json::json;

let input = json!({ "type": "string", "nullable": true });
let output = from_schema(input, &Options::new()).unwrap();

assert_eq!(
    output,
    json!({
        "type": ["string", "null"],
        "$schema": "http://json-schema.org/draft-04/schema#"
    })
);

What it does

nullable: true adds "null" to type and appends null to an enum.
Strips OpenAPI-only keywords: nullable, discriminator, readOnly, writeOnly, xml, externalDocs, example, deprecated.
Maps numeric formats to bounds: int32, int64, float, double become minimum and maximum. byte becomes a base64 pattern. date becomes date-time when date_to_date_time is on.
Recurses combiners and structs: allOf, anyOf, oneOf, not, items, additionalProperties, and properties.
Prunes required of names no longer present in properties.
Rejects an invalid type in strict mode.

The root of the result carries "$schema". Nested schemas do not.

Parameters and responses

from_parameter converts a Parameter Object or Response Object. With a schema member it returns one JSON Schema. With a content member it returns a map keyed by MIME type, where each value is a JSON Schema with its own $schema.

use openapi_schema_to_json_schema::{from_parameter, Options};
use serde_json::json;

let param = json!({
    "name": "id",
    "in": "query",
    "schema": { "type": "string", "nullable": true }
});
let out = from_parameter(param, &Options::new()).unwrap();
assert_eq!(out["type"], json!(["string", "null"]));

Options

Option	Default	Effect
`date_to_date_time`	false	Rewrite `format: "date"` to `date-time`.
`clone_schema`	true	Kept for API parity. The crate owns its input, so conversion never mutates the caller's data.
`support_pattern_properties`	false	Move `x-patternProperties` to `patternProperties` and run the handler.
`keep_not_supported`	empty	Keep listed keywords that would otherwise be stripped.
`strict_mode`	true	Reject `type` values outside the draft-04 set.
`remove_read_only`	false	Drop properties marked `readOnly: true`.
`remove_write_only`	false	Drop properties marked `writeOnly: true`.
`pattern_properties_handler`	dedup handler	Replace the default `patternProperties` handler.
`definition_keywords`	empty	Dotted paths whose values hold named sub-schemas to convert.
`before_transform`	none	Hook run on each node before keyword processing.
`after_transform`	none	Hook run on each node after keyword processing.

License

Licensed under the MIT license.