rspencer01/microjson

A feature-few, no-allocation JSON parser in `no_std` rust.

Small JSON Parser in no_std

This library reads and parses JSON strings.

Its intended use case is to read a JSON payload once.

It does not serialise data.

Sample usage

Simply put this in your Cargo.toml:

[dependencies]
microjson = "0.1"

You can read strings and integers easily:

# use microjson::{JSONValue, JSONParsingError};
# fn main() -> Result<(), JSONParsingError> {
let integer = JSONValue::load("42");

let value : isize = integer.read_integer()?;

let string = JSONValue::load("\"hello there\"");

let value : &str = string.read_string()?;
# Ok(())
# }

You can read arrays like this:

# use microjson::{JSONValue, JSONParsingError};
# fn main() -> Result<(), JSONParsingError> {
let input = r#" [0, 1, 2, 3, 4, 5] "#;

let array = JSONValue::load(input);

for (n, item) in array.iter_array()?.enumerate() {
    let value = item.read_integer()?;
    assert_eq!(value, n as isize);
}
# Ok(())
# }

And, of course, any combination of the above:

# use microjson::{JSONValue, JSONParsingError};
# fn main() -> Result<(), JSONParsingError> {
let input = r#" { "arr": [3, "foo", 3.625, false] } "#;

let object = JSONValue::load(input);

assert_eq!(
    object.get_key_value("arr")?.iter_array()?.nth(2).unwrap().read_float()?,
    3.625
);
# Ok(())
# }

If you are unsure what kind of data you have, you can query the [JSONValueType].

# use microjson::{JSONValue, JSONValueType, JSONParsingError};
# fn main() -> Result<(), JSONParsingError> {
let input = r#" 3.1415 "#;

let object = JSONValue::load(input);

match object.value_type {
    JSONValueType::String => {},
    JSONValueType::Number => {},
    JSONValueType::Object => {},
    JSONValueType::Array => {},
    JSONValueType::Bool => {},
    JSONValueType::Null => {},
    JSONValueType::Error => {},
}
# Ok(())
# }

Verifying Data

To load some JSON, you need only call

# use microjson::JSONValue;
let value = JSONValue::load(r#" [1,2,3,5"foo"] "#);

However, this data is malformed. [JSONValue::parse] will return an Ok result, as to determine that the data was corrupt would require scanning through the entire string. The error would only be reported when you attempted to iterate to the fourth item and parse it as a value.

If you need to know that the data is sound, use [JSONValue::verify]. Alternatively, you can parse and verify in one step.

# use microjson::JSONValue;
let value = JSONValue::load_and_verify(r#" [1,2,3,5"foo"] "#);

Feature Flags

These flags can be enabled using features.

Flag	Description
small_number_parsing	Replaces the core float parsing with a less accurate version that has a smaller code footprint.
std	Includes a marker to implement std::error::Error for JSONParsingError and use the standard library.