Instructions

If you have not used JSON as a wire format before, start with Why JSON. That page explains objects, arrays, numbers, strings, pretty-print, JSON Lines, Pointer, and Patch. Techniques explains how encode and decode are implemented.

Install Mojo 1.1.0

git clone https://github.com/leo-gan/gld-json.git
cd gld-json
pixi install
pixi run test

If pixi install fails with 401 on conda.modular.com, set PREFIX_API_KEY in a local .env (never commit that file) and run scripts/ci-setup.sh.

After a conda install from prefix.dev:

pixi add --channel https://prefix.dev/leo-gan/leo-gan mojo-json

That installs json.mojoc (plus wire / runtime / schema) and gld-jsongen-mojo.

Generate Mojo from JSON Schema

Write a JSON Schema document that uses the v1 subset (type, properties, required, items, local $ref, $defs, enum, const, two-branch null unions, named-object oneOf / anyOf). Then run the generator. After a conda install the command is gld-jsongen-mojo. In a checkout:

pixi run mojo run -I src src/codegen/cli.mojo -- \
  --schema testdata/schema/benchmark_v2.json --out tests/generated

pixi run generate rebuilds the in-tree types from every file under testdata/schema/.

A property that is not in required becomes Optional[T]. A two-branch type array {T, null} also becomes Optional[T].

Encode and decode

from json import encode, decode
from Message import Message

var m = Message()
m.f_int64 = Int64(150)
var buf = encode(m)
var m2 = decode[Message](buf)

from json import … resolves with mojo run -I src in a checkout, or from json.mojoc after the package is installed.

decode_jsonl_values reads zero or more compact values separated by newlines. pointer_get and pointer_set walk an RFC 6901 path. apply_patch applies RFC 6902 operations. merge_patch applies RFC 7396. Pretty-print uses EncodeOptions.pretty.

Schema-free values use JsonValue:

from json import decode_value, encode_value, EncodeOptions

var v = decode_value(buf)
var again = encode_value(v, EncodeOptions.pretty)