JSON Parser (Rust)

A small JSON parser written in Rust with a hand-built lexer and recursive-descent parser.

It can tokenise JSON text, parse it into a JsonValue tree, and print it back in normalized JSON form.

Features

• Tokenises JSON input into typed tokens ({}, [], strings, numbers, booleans, null)
• Parses nested objects and arrays
• Supports string escapes including Unicode (\uXXXX)
• Exposes both library functions and a binary example
• Includes tests for valid and invalid JSON scenarios

Project Layout

• src/tokeniser.rs - Lexer/tokeniser (tokenise)
• src/parser.rs - Recursive-descent parser (parse)
• src/error.rs - Shared parser/tokeniser error type
• src/value.rs - JsonValue enum and display formatting
• src/lib.rs - Public library exports
• src/bin/main.rs - Example binary entrypoint
• tests/mod.rs - Integration tests

Prerequisites

• Rust (stable) and Cargo

Build and Run

Build the project:

cargo build

Run the parser with JSON from a file:

cargo run --bin jsonparser -- input.json

Or pass JSON through standard input:

echo'{"name":"Soraya","age":30}'| cargo run --bin jsonparser --

Use - to explicitly read from standard input:

echo'{"active":true}'| cargo run --bin jsonparser -- -

Run tests:

cargo test

Library Usage

use jsonparser::{parse, tokenise,Result};fnmain() -> Result<()>{let input = r#"{"name":"Soraya","age":30,"active":true}"#;let tokens = tokenise(input)?;let value = parse(tokens)?;println!("{value}");Ok(())}

Supported JSON Values

• Objects
• Arrays
• Strings (with common escapes and \uXXXX)
• Numbers (parsed as f64)
• Booleans
• null

Current Limitations

• Numbers are parsed as f64
• Unicode escape parsing does not combine UTF-16 surrogate pairs