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Snack

Snack lets you to run complete React Native projects in the browser. This is the web app for snack.expo.io.

Pre-requisites

Before running the web app, make sure to have the following packages installed globally on your system:

Make sure you have the environment variables available:

export SNACK_PORT=3011
export SNACK_SEGMENT_KEY=""
export SNACK_SENTRY_DSN=""
export SNACK_SERVER_HOST=snack.expo.test
export SNACK_SERVER_PROTOCOL=https
export API_SERVER_URL=https://staging.expo.io
export IMPORT_SERVER_URL=https://staging.snackager.expo.io

You can copy the above code to your .bashrc or .zshrc.

Getting started

Quick start

After cloning the repo, open a terminal in the directory and run following to install the dependencies and start the server:

# Install dependencies
yarn

# Start the server
yarn start

Now you can access the web app at localhost:3011.

Using the snack.expo.test domain

We develop Snack under snack.expo.test. We use hotel to do that. To set it up, open the file ~/.hotel/conf.json and make sure you have the tld set to test:

{
  "tld": "test"
}

Also add the following to ~/.hotel/servers/snack.expo.json:

{
  "target": "http://localhost:3011"
}

Configure your system to use configure proxies automatically following these instructions.

Now you should be able to access the snack server at http://snack.expo.test.

Setting up HTTPS with self-signed certifcate

The service worker needs HTTPS to work on the snack.expo.test domain. To set it up with Hotel, we need to add the cert.pem and key.pem files under the ~/.hotel directory. To create these files, first create a configuration file for the certificate with the following content (let's call it req.conf):

[req]
distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no
[req_distinguished_name]
C = US
ST = Oregon
L = Portland
O = Expo
OU = Org
CN = expo.test
[v3_req]
keyUsage = critical, digitalSignature, keyAgreement
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
[alt_names]
DNS.1 = expo.test
DNS.2 = snack.expo.test

Then run the following command in the same directory where you created the file to generate the certificate:

openssl req -x509 -newkey rsa:4096 -sha256 -keyout key.pem -out cert.pem -days 365 -nodes -config req.conf

Place the generated cert.pem and key.pem files under the ~/.hotel directory and hotel should be setup to work with SSL.

You'll also need to add the certificate to the system. Under Keychain Access > Certificates, drag and drop the cert.pem file to do that. Double click the certificate and mark it as trusted under the "Trust" section. You'll also need to add the certificate as an exception in the browser. You can do that by clicking the padlock in the URL bar.

Now you should be able to access the snack server at https://snack.expo.test.

File organization

The web server is under src/server/. The build scripts also generate a build subdirectory with the compiled JS; this is the JS that actually runs.

The code for the client is located under src/client/. The webpack build creates a dist/ folder which is ignored from version control.

Scripts related to deployment, like the Dockerfile, are under deploy. Note: even though the scripts are under deploy, you must run them from this directory; they are sensitive to cwd.

Files related to Jest tests, like the Jest configuration, are under jest.

Local environment variables for development are set up in .envrc.

Developing

The server uses a Koa server on production and webpack-serve in development.

To start the server, run yarn start. If you have access to the monorepo, to test with the local API server, you need to run yarn start in www/ in another terminal, and make sure the API_SERVER_URL environment variable is set to http://localhost:3000. Visit http://snack.expo.test or http://localhost:3011 in your browser to load the site.

yarn start runs a Gulp pipeline that compiles the server JavaScript, sets up a file watcher to compile changes on the fly, and starts a Koa server listening on port 3011 with Nodemon. The server is responsible for routing, serving the assets and running the weback server in development mode.

Nodemon is also configured with the --inspect flag, which lets you debug Node from Chrome. We use a non-default port for the inspector (9311 instead of 9229) since www's inspector uses the default port.

The client uses a service worker, which means you need some extra steps to get it setup for development.

Disabling cache with Service Worker

In chrome devtools, check "Bypass for network" under Application > Service workers to skip the service worker cache when working on the page.

Running the tests

We run unit tests with Jest. Run yarn test in another terminal to start Jest and have it continuously watch for changes. You also can run yarn jest if you want to run Jest without the watcher. Keep unit tests fast so that the feedback loop from them is fast.