stream-json

A streaming, async-only JSON serialization framework for Rust.

Features

• Async-first poll-based serialization
• Streaming output in chunks
• Exact size() queries for supported values
• #[derive(IntoSerializer)] for structs and enums

Size Queries

IntoSerializer::size() returns the exact serialized byte size when known. Use it when you need a Content-Length-style value before streaming.

Examples:

use stream_json::serde::IntoSerializer;

assert_eq!("hello".size(), Some(7));
assert_eq!((42i64).size(), Some(2));

If a value cannot report its size, the default implementation returns None.

Base64 Embed

Base64EmbedFile::new(reader, expected_size, mime_type) validates the provided size and uses the provided mime_type.

use futures::io::Cursor;
use stream_json::Base64EmbedFile;

let embed = Base64EmbedFile::new(Cursor::new(vec![0u8; 16]), 16, "image/png".to_string())?;
assert!(embed.size().is_some());

Usage

use stream_json::serde::IntoSerializer;

#[derive(IntoSerializer)]
struct Person {
    name: String,
    age: i32,
}

let person = Person {
    name: "Alice".to_string(),
    age: 30,
};

assert_eq!(person.size(), Some(25));