tinyjson

tinyjson is a library to parse/generate JSON format document.

Goals:

• Using Stable APIs; using no experimental APIs, no compiler plugin
• Reasonable simple JSON object interface
• No crate dependencies at runtime
• Well tested with famous JSON test suites
  • JSON checker in json.org
  • JSONTestSuite
  • JSON-Schema-Test-Suite
• My Rust practice :)

Requirements

Rust stable toolchain (no dependency).

Installation

Add this crate to dependencies section of your Cargo.toml

[dependencies]
tinyjson = "2"

Usage

Parse JSON

String is parsed to JsonValue struct via FromStr.

use tinyjson::JsonValue;

let s = r#"
    {
        "bool": true,
        "arr": [1, null, "test"],
        "nested": {
            "blah": false,
            "blahblah": 3.14
        },
        "unicode": "\u2764"
    }
"#;

let parsed: JsonValue = s.parse().unwrap();
println!("Parsed: {:?}", parsed);

str::parse() is available. It parses the target as JSON and creates tinyjson::JsonValue object. It represents tree structure of parsed JSON. JsonValue is an enum struct and allocated on stack. So it doesn't require additional heap allocation.

Access to JSON Value

JsonValue is an enum value. So we can access it with match statement.

let json = JsonValue::Number(42);
let v = match json {
    JsonValue::Number(n) => n, // When number
    JsonValue::Null => 0.0, // When null
    _ => panic!("Unexpected!"),
};

Each JSON types correspond to Rust types as follows:

JSON is a tree structure and it's boring to write nested match statement. So JsonValue implements std::ops::Index and std::ops::IndexMut traits in order to access to its nested values quickly.

let mut json: tinyjson::JsonValue = r#"
{
  "foo": {
    "bar": [
      {
        "target": 42
      },
      {
        "not target": 0
      }
    ]
  }
}
"#.parse().unwrap();

// Access with index operator
let target_value = json["foo"]["bar"][0]["target"];
println!("{:?}", target_value); // => JsonValue::Number(42.0)

// Modify value with index operator
json["foo"]["bar"][0]["target"] = JsonValue::Null;
println!("{:?}", json["foo"]["bar"][0]["target"]); // => JsonValue::Null

Index access with &str key is available when the value is an object. And index access with usize is available when the value is an array. They return the &JsonValue value if target value was found. And modifying inner value directly with index access at right hand side of = is also available. Note that it can modify value of objects but cannot add new key. In both cases, it will call panic! when the value for key or the element of index was not found.

get() and get_mut() methods are provided to dereference the enum value (e.g. JsonValue::Number(4.2) -> 4.2). get() method returns its dereferenced raw value. It returns Option<&T> (T is corresponding value that you expected). If None is returned, it means its type mismatched with your expected one. Which type get() should dereference is inferred from how the returned value will be handled. So you don't need to specify it explicitly.

use tinyjson::JsonValue;

let json: JsonValue = r#"{
  "num": 42,
  "array": [1, true, "aaa"]
}
"#.parse().unwrap();

// Refer mmutable inner value
let num: &f64 = json["num"].get().expect("Number value");
let arr: &Vec<_> = json["array"].get().expect("Array value");

let mut json: JsonValue = r#"
{
  "num": 42,
  "array": [1, true, "aaa"]
}
"#.parse().unwrap();

// Refer mutable inner value
let num: &mut f64 = json["num"].get_mut().expect("Number value");
num = JsonValue::Boolean(false);

JsonValue implements TryInto. It can convert JsonValue into inner value.

use tinyjson::JsonValue;
use std::convert::TryInto;

let json: JsonValue = r#"{ "num": 42 }"#.parse().unwrap();

// Move out inner value using try_into()
let num: f64 = json["num"].try_into().expect("Number value");

Equality of JsonValue

JsonValue derives PartialEq traits hence it can be checked with == operator.

let json: JsonValue = r#"{"foo": 42}"#.parse().unwrap();
assert!(json["foo"] == JsonValue::Number(42.0));

If you want to check its type only, there are is_xxx() shortcut methods in JsonValue instead of using match statement explicitly.

let json: tinyjson::JsonValue = r#"
{
  "num": 42,
  "array": [1, true, "aaa"],
  "null": null
}
"#.parse().unwrap();

assert!(json["num"].is_number());
assert!(json["array"].is_array());
assert!(json["null"].is_null());

Generate JSON

stringify() and format() methods can be used to create JSON string. stringify() generates a minified JSON text and format() generates pretty JSON text with indentation.

use tinyjson::JsonValue;

let s = r#"
    {
        "bool": true,
        "arr": [1, null, "test"],
        "nested": {
            "blah": false,
            "blahblah": 3.14
        },
        "unicode": "\u2764"
    }
"#;

let parsed: JsonValue = s.parse().unwrap();
println!("{}", parsed.stringify().unwrap());
println!("{}", parsed.format().unwrap());

For writing JSON outputs to io::Write instance, write_to() and format_to() methods are also available.

Examples

Working examples are put in examples directory. They can be run with cargo run --example.

echo '{"hello": "world"}' | cargo run --example parse
echo '["foo",  42,    null ]' | cargo run --example minify
cargo run --example json_value

TODO

• [x] Parser
• [x] Generator
• [x] Equality of JsonValue
• [x] Index access to JsonValue (array, object)
• [x] Tests
• [x] Fuzzing

Repository

https://github.com/rhysd/tinyjson

Development

# Run tests
cargo test

# Run linters
cargo clippy
cargo fmt -- --check

# Run fuzzer
cargo +nightly fuzz run parser

Tools:

• clippy
• rustfmt
• cargo-fuzz

License

the MIT License