json-steroids 🚀

A high-performance, zero-copy JSON parsing and serialization library for Rust with derive macros for automatic implementation.

Features

Zero-copy parsing - Strings without escape sequences are borrowed directly from input, avoiding unnecessary allocations
Fast serialization - Pre-allocated buffers with efficient string escaping and number formatting
Derive macros - Automatically generate serializers and deserializers for your types
Minimal dependencies - Only uses itoa and ryu for fast number formatting
Full JSON support - Handles all JSON types including Unicode escape sequences and surrogate pairs
Pretty printing - Optional indented output for human-readable JSON
Dynamic values - Parse JSON into a flexible JsonValue type when structure is unknown

Installation

Add to your Cargo.toml:

[dependencies]
json-steroids = "0.1.0"

Quick Start

use json_steroids::{Json, to_string, from_str};

#[derive(Debug, Json, PartialEq)]
struct Person {
    name: String,
    age: u32,
    email: Option<String>,
}

fn main() {
    // Serialize
    let person = Person {
        name: "Alice".to_string(),
        age: 30,
        email: Some("alice@example.com".to_string()),
    };
    let json = to_string(&person);
    println!("{}", json);
    // Output: {"name":"Alice","age":30,"email":"alice@example.com"}

    // Deserialize
    let json_str = r#"{"name":"Bob","age":25,"email":null}"#;
    let person: Person = from_str(json_str).unwrap();
    println!("{:?}", person);
}

Derive Macros

`#[derive(Json)]`

The combined derive macro that implements both JsonSerialize and JsonDeserialize:

use json_steroids::Json;

#[derive(Json)]
struct User {
    id: u64,
    username: String,
    active: bool,
}

`#[derive(JsonSerialize)]` and `#[derive(JsonDeserialize)]`

Use these when you only need one direction:

use json_steroids::{JsonSerialize, JsonDeserialize};

#[derive(JsonSerialize)]
struct LogEntry {
    timestamp: u64,
    message: String,
}

#[derive(JsonDeserialize)]
struct Config {
    host: String,
    port: u16,
}

Field Renaming

Use the #[json(rename = "...")] attribute to customize field names in JSON:

use json_steroids::Json;

#[derive(Json)]
struct ApiResponse {
    #[json(rename = "statusCode")]
    status_code: u32,
    #[json(rename = "errorMessage")]
    error_message: Option<String>,
}

Enum Support

Enums are fully supported with different representations:

use json_steroids::Json;

// Unit variants serialize as strings
#[derive(Json)]
enum Status {
    Active,    // "Active"
    Inactive,  // "Inactive"
    Pending,   // "Pending"
}

// Tuple and struct variants use object notation
#[derive(Json)]
enum Message {
    Text(String),                    // {"Text":["hello"]}
    Coordinates { x: i32, y: i32 },  // {"Coordinates":{"x":10,"y":20}}
}

API Reference

Serialization Functions

// Compact JSON output
pub fn to_string<T: JsonSerialize>(value: &T) -> String;

// Pretty-printed JSON with 2-space indentation
pub fn to_string_pretty<T: JsonSerialize>(value: &T) -> String;

Deserialization Functions

// Parse from string slice
pub fn from_str<T: JsonDeserialize>(s: &str) -> Result<T>;

// Parse from bytes
pub fn from_bytes<T: JsonDeserialize>(bytes: &[u8]) -> Result<T>;

Dynamic Parsing

When the JSON structure isn't known at compile time:

use json_steroids::{parse, JsonValue};

let json = r#"{"name": "test", "values": [1, 2, 3]}"#;
let value = parse(json).unwrap();

// Access fields using indexing
assert_eq!(value["name"].as_str(), Some("test"));
assert!(value["values"].is_array());
assert_eq!(value["values"][0].as_i64(), Some(1));

// Check types
assert!(value.is_object());
assert!(value["missing"].is_null()); // Missing fields return null

JsonValue Type

The JsonValue enum represents any JSON value:

pub enum JsonValue {
    Null,
    Bool(bool),
    Integer(i64),
    Float(f64),
    String(String),
    Array(Vec<JsonValue>),
    Object(Vec<(String, JsonValue)>),
}

Methods available on JsonValue:

Type checking: is_null(), is_bool(), is_number(), is_string(), is_array(), is_object()
Value extraction: as_bool(), as_i64(), as_u64(), as_f64(), as_str(), as_array(), as_object()
Ownership: into_string(), into_array(), into_object()
Indexing: value["key"] for objects, value[0] for arrays

Supported Types

Primitives

Booleans: bool
Integers: i8, i16, i32, i64, isize, u8, u16, u32, u64, usize
Floats: f32, f64

Strings

String
&str (serialize only)
Cow<str>

Collections

Vec<T>
[T; N] (arrays, serialize only)
HashMap<K, V> (K must be string-like)
BTreeMap<K, V> (K must be string-like)

Wrapper Types

Option<T> - Serializes as null when None
Box<T>

Tuples

Tuples up to 8 elements are supported and serialize as JSON arrays:

let tuple = (1, "hello", true);
let json = to_string(&tuple); // [1,"hello",true]

Error Handling

The library provides detailed error messages:

use json_steroids::{from_str, JsonError};

let result: Result<i32, _> = from_str("not a number");
match result {
    Ok(value) => println!("Parsed: {}", value),
    Err(JsonError::ExpectedToken(expected, pos)) => {
        println!("Expected {} at position {}", expected, pos);
    }
    Err(e) => println!("Error: {}", e),
}

Error types include:

UnexpectedEnd - Input ended unexpectedly
UnexpectedChar(char, usize) - Unexpected character at position
ExpectedChar(char, usize) - Expected specific character
ExpectedToken(&str, usize) - Expected token (e.g., "string", "number")
InvalidNumber(usize) - Invalid number format
InvalidEscape(usize) - Invalid escape sequence
InvalidUnicode(usize) - Invalid Unicode escape
InvalidUtf8 - Invalid UTF-8 encoding
MissingField(String) - Required field missing during deserialization
UnknownVariant(String) - Unknown enum variant
TypeMismatch - Type mismatch during deserialization
NestingTooDeep(usize) - JSON nesting exceeds maximum depth (128)

Performance

json-steroids is designed for high performance:

Zero-Copy Parsing

Strings that don't contain escape sequences are borrowed directly from the input buffer using Cow<str>, avoiding allocation:

// This string has no escapes - zero allocation!
let json = r#"{"name": "hello world"}"#;

// This string has escapes - allocation needed to unescape
let json = r#"{"name": "hello\nworld"}"#;

Fast Number Formatting

Uses the itoa and ryu crates for extremely fast integer and floating-point formatting.

Efficient String Escaping

The serializer uses a fast path that checks if escaping is needed before processing:

// Fast path - no escaping needed
let s = "hello world";

// Slow path - escaping required
let s = "hello\nworld";

Pre-allocated Buffers

The JsonWriter pre-allocates buffer space to minimize reallocations during serialization.

Architecture

json-steroids/
├── src/
│   ├── lib.rs       # Public API and re-exports
│   ├── parser.rs    # Zero-copy JSON parser
│   ├── writer.rs    # Fast JSON serializer
│   ├── value.rs     # Dynamic JsonValue type
│   ├── traits.rs    # JsonSerialize/JsonDeserialize traits + impls
│   └── error.rs     # Error types
└── json-steroids-derive/
    └── src/
        └── lib.rs   # Procedural macros

Examples

Nested Structures

use json_steroids::Json;

#[derive(Json)]
struct Address {
    street: String,
    city: String,
    country: String,
}

#[derive(Json)]
struct Company {
    name: String,
    address: Address,
    employees: Vec<String>,
}

let company = Company {
    name: "Acme Corp".to_string(),
    address: Address {
        street: "123 Main St".to_string(),
        city: "Springfield".to_string(),
        country: "USA".to_string(),
    },
    employees: vec!["Alice".to_string(), "Bob".to_string()],
};

let json = to_string(&company);

Working with Optional Fields

use json_steroids::{Json, from_str};

#[derive(Json, Debug)]
struct UserProfile {
    username: String,
    bio: Option<String>,
    age: Option<u32>,
}

// Missing optional fields default to None
let json = r#"{"username": "alice"}"#;
let profile: UserProfile = from_str(json).unwrap();
assert!(profile.bio.is_none());
assert!(profile.age.is_none());

// Explicit null also becomes None
let json = r#"{"username": "bob", "bio": null, "age": 25}"#;
let profile: UserProfile = from_str(json).unwrap();
assert!(profile.bio.is_none());
assert_eq!(profile.age, Some(25));

Pretty Printing

use json_steroids::{Json, to_string_pretty};

#[derive(Json)]
struct Config {
    debug: bool,
    port: u16,
}

let config = Config { debug: true, port: 8080 };
let json = to_string_pretty(&config);
// Output:
// {
//   "debug": true,
//   "port": 8080
// }

Custom Serialization with JsonWriter

For advanced use cases, you can use JsonWriter directly:

use json_steroids::JsonWriter;

let mut writer = JsonWriter::new();
writer.begin_object();
writer.write_key("name");
writer.write_string("custom");
writer.write_comma();
writer.write_key("values");
writer.begin_array();
writer.write_i64(1);
writer.write_comma();
writer.write_i64(2);
writer.end_array();
writer.end_object();

let json = writer.into_string();
// {"name":"custom","values":[1,2]}

Running Benchmarks

cargo bench

Running Tests

cargo test

License

This project is licensed under the MIT License - see the LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

json-steroids 0.1.1