"Smile" is a binary data format that defines a binary equivalent of standard JSON data format (*).

Format was specified in 2010 by Jackson JSON processor development team. First compliant implementation was included as a Jackson backend for Jackson version 1.6, released in September 2010.

(*) with following exceptions

• Number magnitude and precision are limited by length-indicators: so while for most practical purposes limits are never reached, there are theoretical limits. Specifically, "Big Integers" and "Big Decimals" (matching Java java.math.BigInteger and java.math.BigDecimal) are limited to encoded byte-lengths representable by 32-bit positive integers (about 2 GB).

Specification

Design documentation includes:

• Smile Format Specification describes format itself; how it works and what a compliant parser/generator implementations needs to do.
• Smile Format Design Goals explains rationale for design decisions concerning specification.

Community

• Smile format Google group

Documentation

• SmileFAQ
• Smile Wikipedia entry
• User documentation:
  • Understanding Smile data format

Implementations

Smile Codecs

• Clojure
  • Cheshire library offers support via Jackson jackson-dataformat-smile
• C
  • libsmile is a small C-library for reading and writing Smile data.
• Go
  • go-smile Smile decoder written in Golang.
• Java
  • Jackson provides Smile support through jackson-dataformat-smile modules) format codec
    • Full support: including streaming access, data binding and tree model (100% parity with textual JSON)
    • Jackson 2.9 added "non-blocking" ((aka "asynchronous") decoding for JSON and Smile format backends
  • Protostuff project supports Smile both as a low-level data format, and as format used for its RPC implementation
• Javascript
  • smile-js Smile decoder written in Javascript (only decodes (reads), does not encode (write))
• Kotlin Multiplatform
  • kotlinx-serialization-smile pure Kotlin Multiplatform implementation for kotlinx-serialization, supports JVM, Native, JS, etc
• Python
  • NewSmile Another Smile Format Decoder/Encoder for Python 3
  • PySmile Python codec
• Rust
  • serde-smile Serde serializer and deserializer written in Rust.

Frameworks, Systems that use Smile codec (encoder and decoder)

• Elastic Search uses Smile as transport format supports access using Smile encoding.
• Apache Solr can use Smile as the response format with the wt=smile parameter.

Related Publications

Here are some external articles, blog posts, research papers that may be of interest:

• A Survey of JSON-compatible Binary Serialization Specifications
• A Benchmark of JSON-compatible Binary Serialization Specifications