noson 0.1.3

Generate random JSON values from a JSON Schema
Documentation

noson

A Rust library that generates example JSON data from a JSON Schema.

Given a JSON Schema as a serde_json::Value, noson produces a random JSON value that validates against it.

Installation

cargo add noson

Usage

The caller provides the random number generator, so output is reproducible when a seeded RNG is used.

use rand::SeedableRng;
use rand::rngs::StdRng;
use serde_json::json;

let schema = json!({
    "type": "object",
    "properties": {
        "name": { "type": "string", "minLength": 1, "maxLength": 20 },
        "age": { "type": "integer", "minimum": 0, "maximum": 120 },
        "active": { "type": "boolean" }
    },
    "required": ["name", "age"]
});

let mut rng = StdRng::seed_from_u64(42);
let example = noson::generate(&schema, &mut rng).unwrap();

// example is a random JSON value that validates against the schema
println!("{}", serde_json::to_string_pretty(&example).unwrap());

Required properties are always included; optional properties are included with 50% probability. Recursive schemas are supported up to a nesting depth of 16.

Supported Schema Features

  • Types: null, boolean, string, integer, number, object, array
  • Constraints: minimum/maximum, exclusiveMinimum/exclusiveMaximum, minLength/maxLength, minItems/maxItems
  • Format: date-time, date, time, duration
  • Enum / Const: enum, const
  • Composition: allOf, anyOf, oneOf
  • References: $ref resolved against $defs / definitions
  • Boolean schemas: true (any value) and false (error)

Not Supported

The following JSON Schema features are not currently handled. Schemas using them will either be silently ignored (the keyword has no effect on generation) or, in the case of external $ref, return an error.

  • String: pattern, contentEncoding, contentMediaType
  • Numeric: multipleOf
  • Object: additionalProperties, patternProperties, propertyNames, minProperties, maxProperties, unevaluatedProperties
  • Array: prefixItems, additionalItems, contains, minContains, maxContains, uniqueItems, unevaluatedItems
  • Composition: not, if/then/else
  • Dependencies: dependentRequired, dependentSchemas
  • References: external $ref (http/file URIs), $dynamicRef, $anchor
  • Type unions: "type": ["string", "null"] (array form of type)

Roadmap

  • Builder/configuration API -- customizable string length ranges, array sizes, max recursion depth
  • format generators -- email, uri, uuid, etc.
  • pattern support -- regex-based string generation via rand_regex
  • additionalProperties generation
  • prefixItems, contains
  • minProperties / maxProperties
  • multipleOf
  • if/then/else
  • not
  • dependentRequired / dependentSchemas
  • External $ref resolution (http/file references)

Development

This project was developed with the assistance of LLMs (Claude).