datavalue-rs

A bump-allocated JSON value type with a built-in zero-copy parser and serde_json::Value-style access.

Quick Example

use bumpalo::Bump;
use datavalue_rs::DataValue;

let arena = Bump::new();
let v = DataValue::from_str(r#"{"name":"alice","ages":[30,31]}"#, &arena).unwrap();

assert_eq!(v["name"].as_str(), Some("alice"));
assert_eq!(v["ages"][1].as_i64(), Some(31));
assert!(v["missing"].is_null()); // missing key indexes to Null, like serde_json

// Render back to JSON via Display.
println!("{v}");                    // compact: {"name":"alice","ages":[30,31]}
println!("{}", v.pretty());         // two-space indent, like serde_json::to_string_pretty

Building values inline

use datavalue_rs::{owned_json, OwnedDataValue};

let user = owned_json!({
    "name": "alice",
    "ages": [30, 31],
    "active": true,
    "tags": null,
});

assert_eq!(user["ages"][1].as_i64(), Some(31));

Packages

Resources

• Rust API (docs.rs)
• Benchmarks — full cross-library comparison (parse / serialize / access / mutate × twitter / citm / canada)
• datalogic-rs — JSONLogic engine that consumes this crate

Key Features

• Arena-Allocated — One Bump holds the entire value tree; reset between batches for amortized zero-allocation parsing.
• Zero-Copy Strings — String literals without escape sequences are borrowed directly from the input source.
• Native Integer Path — NumberValue distinguishes Integer(i64) from Float(f64); integer JSON stays on the integer fast path.
• serde_json::Value-Style Access — Index, get(), as_*/is_*, chained indexing returns Null on miss.
• Owned Counterpart — OwnedDataValue for cases where the value must outlive its arena (caches, return values, global state).
• Optional serde Integration — Serialize for both forms; DataValueSeed (DeserializeSeed) for arena targets, direct Deserialize for owned.
• Optional serde_json::Value Bridge — direct conversion to/from serde_json::Value for boundary interop (no string round-trip).
• Display + pretty() — println!("{v}") emits compact JSON; v.pretty() renders the same shape as serde_json::to_string_pretty.
• owned_json! Macro — serde_json::json!-style construction for OwnedDataValue.
• Optional datetime Extension — DateTime / Duration variants backed by chrono, mirroring datalogic-rs.

Performance

Highlights on the 631 KB twitter.json fixture from the serde-rs json benchmark suite (release build, single thread, criterion):

Full cross-library numbers (vs. simd-json, sonic-rs, json-rust) across twitter / citm_catalog / canada and across parse / serialize / access / mutate workloads live in BENCHMARKS.md. Reproduce with cargo bench --bench compare --features serde_json.

Owned Counterpart

Use OwnedDataValue when a value must escape its arena lifetime — long-lived caches, function return values, global state. Variants mirror DataValue one-for-one but use String / Vec<…> / Vec<(String, …)> instead of arena slices.

use bumpalo::Bump;
use datavalue_rs::{DataValue, OwnedDataValue};

// Parse fast path, then escape the arena.
let arena = Bump::new();
let v = DataValue::from_str(r#"{"x":42}"#, &arena).unwrap();
let owned: OwnedDataValue = v.to_owned();
drop(arena); // arena gone — `owned` keeps living.

assert_eq!(owned["x"].as_i64(), Some(42));

// Or: parse straight into owned form.
let owned2: OwnedDataValue = r#"{"x":42}"#.parse().unwrap();

// Rehydrate into a fresh arena when you need the borrowed shape again.
let arena2 = Bump::new();
let _borrowed = owned2.to_arena(&arena2);

OwnedDataValue implements Serialize + Deserialize directly (no seed required) since there's no arena lifetime to thread.

Cargo Features

Design Notes

• Strings: when a JSON string has no escape sequences, the parser borrows directly from the input — zero copy. Escaped strings are unescaped into the arena.
• Numbers: NumberValue natively distinguishes Integer(i64) from Float(f64). Integer-valued JSON numbers stay on the integer fast path through arithmetic and access.
• Objects: &'a [(&'a str, DataValue<'a>)]. Insertion order is preserved; lookup is a linear scan, which beats a hash map for the typical small object sizes seen in JSON.
• No coercion: as_i64, as_str, etc. return None when the variant doesn't match. There is no JSONLogic-style truthiness or cross-type coercion here; that belongs in the consumer crate.
• DateTime: JSON has no native datetime type, so the parser does not produce DateTime / Duration variants. Consumers upgrade strings at the operator boundary via DataDateTime::parse. Serialization back to JSON emits an ISO 8601 string or "1d:2h:3m:4s" duration string.

Status

0.1 — public API may shift before 1.0. Built to back hot paths in datalogic-rs and other Plasmatic crates.

Contributing

Contributions are welcome. Fork the repo, add tests for any new behavior, and open a PR.

About Plasmatic

Created by Plasmatic, building open-source tools for financial infrastructure and data processing.

License

Licensed under Apache 2.0. See LICENSE for details.