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                         infinitely
                           faster!

-- TypeScript Edition

This is a TypeScript implementation of the Cap'n Proto serialization protocol. Start with the Cap'n Proto Introduction for more detailed information on what this is about.

WARNING: THIS IS ALPHA QUALITY SOFTWARE. USE AT YOUR OWN RISK. AUTHORS ARE NOT RESPONSIBLE FOR LOSS OF LIMB, LIFE, SANITY, OR RETIREMENT FUNDS DUE TO USE OF THIS SOFTWARE.

• Packages
• Project Status
• Installation
• Implementation Notes
• Usage
  • Compiling Schema Files
  • Reading Messages
  • Usage with JavaScript
  • Usage in a Web Browser
• Building
  • Initial Setup
  • Build Tasks
• Testing
• Team

Packages

This repository is managed as a monorepo composed of separate packages.

Package	Version	Dependencies
capnp-ts
capnpc-ts
capnpc-js

• capnp-ts is the core Cap'n Proto library for Typescript. It is a required import for all compiled schema files, and the starting point for reading/writing a Cap'n Proto message.
• capnpc-ts is the schema compiler plugin for TypeScript. It is intended to be invoked by the capnp tool.
• capnpc-js is the schema compiler plugin for JavaScript. It is intended to be invoked by the capnp tool.

Project Status

This project is under active alpha stage development.

Until version 1.x.x lands expect that the top level API will change.

• Serialization: working, may be missing features
• Schema Compiler: working, may be missing features
• RPC Level 1: not implemented
• RPC Level 2: not implemented
• RPC Level 3: not implemented
• RPC Level 4: not implemented

Installation

Grab the latest library version from npm:

npm install --save capnp-ts

You will need the schema compiler as well (global installation recommended):

npm install -g capnpc-ts # For TypeScript
# OR
npm install -g capnpc-js # For JavaScript

The schema compiler is a Cap'n Proto plugin and requires the capnpc binary in order to do anything useful; follow the Cap'n Proto installation instructions to install it on your system.

Implementation Notes

These notes are provided for people who are familiar with the C++ implementation, or implementations for other languages. Those who are new to Cap'n Proto may skip this section.

This implementation differs in a big way from the C++ reference implementation: there are no separate Builder or Reader classes. All pointers are essentially treated as Builders.

This has some major benefits for simplicity's sake, but there is a bigger reason for this decision (which was not made lightly). Everything is backed by ArrayBuffers and there is no practical way to prevent mutating the data, even in a dedicated Reader class. The result of such mutations could be disastrous, and more importantly there is no way to reap much performance from making things read-only.

Usage

Compiling Schema Files

Run the following to compile a schema file into TypeScript source code:

capnpc -o ts path/to/myschema.capnp

Or for JavaScript:

capnpc -o js path/to/myschema.capnp

Running that command will create a file named path/to/myschema.capnp.ts (or .js).

These instructions assume capnpc-ts was installed globally and is available from $PATH. If not, change the -o option to something like -o node_modules/.bin/capnpc-ts or -o capnp-ts/packages/capnpc-ts/bin/capnpc-ts.js so it points to your local capnpc-ts install.

To write the compiled source to a different directory:

capnpc -o ts:/tmp/some-dir/ path/to/myschema.capnp

That will generate a file at /tmp/some-dir/path/to/myschema.capnp.ts.

Reading Messages

To read a message, do something like the following:

import * as capnp from "capnp-ts";

import { MyStruct } from "./myschema.capnp.js";

export function loadMessage(buffer: ArrayBuffer): MyStruct {
  const message = new capnp.Message(buffer);

  return message.getRoot(MyStruct);
}

Usage with JavaScript

JavaScript usage is nearly identical to the TypeScript version, except you won't get all of the type safety and code completion goodness in your editor.

Also, the name capnp-js is already reserved on npm from a previous attempt by another author so you'll be importing capnp-ts instead.

const capnp = require("capnp-ts");

const MyStruct = require("./myschema.capnp").MyStruct;

function loadMessage(buffer) {
  const message = new capnp.Message(buffer);

  return message.getRoot(MyStruct);
}

A larger example is located in the js-examples directory.

Usage in a Web Browser

Using a tool like webpack one should be able to bundle the library and compiled schema files for use in a web browser.

A deliberate effort was made to avoid using nodejs specific features (at the expense of performance) to maintain compatibility with browser environments.

Note that this library has not yet been tested in a web browser.

In the future a special nodejs version of the library may be released to take advantage of Buffer which gives access to unsafe malloc style allocation (as opposed to calloc style allocation in ArrayBuffer which always zeroes out the memory).

Building

Before building the source you will need a few prerequisites:

• nodejs (latest LTS or 8.x.x is recommended)
• yarn

nvm is highly recommended for managing multiple nodejs versions.

Initial Setup

Run yarn install to set up the node_modules directories for the monorepo and each package.

Build Tasks

The following package scripts are available for build tasks.

Using npm:

npm run build

---

benchmark

Runs all available benchmarks in packages/capnp-ts/test/benchmark.

build

Compiles the typescript sources and test files.

coverage

Generates a coverage report.

lint

Runs eslint and prints out any linter violations.

publish

Publish the latest release to NPM. Intended to only be run from CI.

release

Create a new release using standard-version; use this to trigger a continuous deployment run after pushing the new tag.

test

Runs the test suite and prints out a human-readable test result.

watch

Runs the test suite in a loop, recompiling any changes to the source as it is saved to disk.

Testing

Tests are written using node-tap and are located in the test/ subdirectory for each package. The goal for this repository is to reach 100% coverage on critical code. Exceptions may be made (e.g. for benchmark code) using special istanbul comments:

/* istanbul ignore next */ // ignore the next statement/block
/* istanbul ignore if */ // ignore an if branch
/* istanbul ignore else */ // ignore an else branch

Debugging

Some debug trace functionality is provided by the debug library.

To see trace messages in nodejs, export the following environment variable:

export DEBUG='capnp*'

When running in a web browser, use localStorage to enable debug output:

localStorage.debug = "capnp*";

Trace messages can get rather noisy, so tweak the DEBUG variable as you see fit.

All messages also have a handy .dump() method that returns a hex dump of the first 8 KiB for each segment in the message:

> console.log(message.dump());

================
Segment #0
================

=== buffer[64] ===
00000000: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ················
00000010: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ················
00000020: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ················
00000030: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 ················

Team

Check out the Humans Colophon for contributor credits.

License

MIT