Canonical JSON serialization for Rust

This is an implementation for a canonical JSON serializer that tries to be compliant with the OLPC minimal specification for canonical JSON. Additionally, the implementation also tries to be fully compatible with the Go canonical JSON implementation used across the Docker and Notary ecosystem. If you find any inconsistencies with the result of the serialization, please open an issue.

Example - reading a JSON file and printing its canonical representation:

let res: serde_json::Value =
    serde_json::from_reader(input).expect("cannot deserialize input file");

println!(
    "{}",
    cjson::to_string(&res).expect("cannot write canonical JSON")
);

Note: this crate aims to always be compilable to the wasm32-unknown-unknown and wasm32-wasi targets.

Building and contributing

This project welcomes contributions of any kind, particularly additional test cases.

To build:

$ cargo build
$ cargo test

The testdata directory is structured in the following way:

• in the root of the directory are JSON files whose name is represented by the SHA256 digest of their canonical JSON representation, as calculated using the github.com/docker/go/canonical package. The test case will use compare the SHA256 digest obtained after serializing using this implementation, to the file name, and they are expected to be equal.

To add a new test case, you can use the canonjson binary, which is a CLI wrapper over the Go canonical JSON implementation:

$ go get github.com/technosophos/canonjson
$ canonjson target-file.json | sha256sum

At this point, rename target-file.json to the <computed-SHA256>.json, the move it in the root of the testdata directory.

• the errors sub-directory contains valid JSON files (if the files are not valid JSON files, the tests will fail), but which contain characters that are not permitted in canonical JSON - so trying to represent them in canonical JSON should produce an error.

Finally, the scripts/integration.sh script contains a very rudimentary test of the CLI from main.rs - and compares the digest of obtained there with the digest obtained from serializing with the Go implementation. Ideally, we would add more implementations of canonical JSON to test against. Note that you also need the canonjson binary used earlier to execute this script.

Notes and acknowledgement

• this implementation was initially based on the canonical JSON serialization used in the Rust TUF crate.