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; not serialize/deserialize JSON format to some specific struct.
• Dependency free.
• My Rust practice :)

Requrements

Rust stable toolchain (no dependency).

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 trait in order to access to its value quickly.

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

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

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. When the value for key or the element of index was not found, it will call panic!.

get() method is provided to dereference the enum value (e.g. JsonValue::Number(4.2) -> 4.2).

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

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

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

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

// Move out inner value using try_into()
let num: f64 = json["num"].try_into().expect("Number value");
let arr: Vec<_> = json["array"].try_into().expect("Array value");
let null: () = json["null"].try_into().expect("Null value");

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 need not to specify it explicitly.

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() method can be used to create JSON string.

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();
let str = parsed.stringify().unwrap();
println!("{}", str);

TODO

• Parser
• Generator
• Equality of JsonValue
• Index access to JsonValue (array, object)
• Tests

Repository

https://github.com/rhysd/tinyjson

License

the MIT License