capnp-json

capnp-json

Represent structs from capnp-ts as enumerable json objects. This is designed to work with capnp-ts.

Installation

npm i --save capnp-json
or
yarn add capnp-json

Usage

const capnpJson = require('capnp-json');
const MyStructType = require('./schema/mytype.capnp');

// ...
// has a capnp-ts messages
var root = message.getRoot(MyStructType);
var json = capnpJson(root);

// json is now an enumerable json object
// every value is a getter which calls the get method on the original struct
// when a value is fetched it's cached forever, this structure is read only.
console.log(json.someMember);

API

capnpJson(struct) => Object

Scans through all of struct and creates a result object containing all of the data found in struct. Each value is added using Object.defineProperty such that the value is not parsed from the binary structure until it is actually fetched. It is recursively lazy, as well, in that if a member value is found that is also another capnp-ts struct the value returned when fetching it will be another lazy capnp-json object.

• struct: (capnp-ts Struct): The struct to convert into json.

NOTE: All 64-bit integers, signed or unsigned, will be converted to string at the time of fetching. Like all values, the result will be cached and the underlying structure will not call the getter again.

Why?

capnp-ts does a very poor job at letting you know which properties are available, and unforunately the slowest part of the library is the error handling code. By converting the structs into enumerable json objects we get rid of the ability to call getters which lack underlying data, avoiding these laggy awkward corner cases.

In my specific usecase I brought parsing time of a logfile down from 7 minutes to 7.8 seconds.

License

MIT