♻️ Core server improvements

[wwilsman]

What is this?

This PR improves upon core's internal API server for future plans to incorporate cli-snapshot features into the core snapshot method. The most important feature is the static server, which is a concept used within several SDKs.

Currently, these SDKs use a third-party library to serve static directories while core's API server is a native Node server with basic routing built in. Initially, core's API server was adjusted to be able to stream files, including basic range support. Util functions from cli-snapshot were copied over to handle URL rewrites, and an additional helper function was created mirroring core's createPercyServer called createStaticServer. The additional helper created a server that rewrote request URLs, checked if a file existed, and served that static file.

While referencing Node docs, I noticed that the native http.createServer function accepts custom IncomingMessage and ServerResponse classes while the function itself was just a wrapper for new http.Server(). This inspired me to extend these classes for our desired features, and it actually ended up resulting in much more succinct server code!

Approach

http.IncomingMessage

This class is extended to automatically parse its own request URL and body. If the request content-type includes "json" the request body is parsed with JSON.parse.

http.ServerResponse

This class is extended to add express-like response methods.

#send([status][, headers], body) allows responding to requests with a status, headers, and a body.

#text([status], text) wraps send() with the text/plain content-type header.

#json([status], json) wraps send() with the application/json content-type header and stringifies provided json.

#file([status], filepath) streams file responses, including any requested ranges and appropriate file headers (content-type, disposition, etc).

http.Server

This class is extended to handle basic routing and middleware. Default middleware is pre-installed to handle CORS requests and CORS headers.

#route([method][, pathname], handler) installs a route handler/middleware. The handler function is called with IncomingMessage, ServerResponse, and a third argument next that can optionally be called to pass execution onto the next route handler (like middleware).

#serve([pathname], directory[, options]) installs middleware to serve the provided static directory's contents at the pathname. The options.cleanUrls option will strip index.html and .html from file URLs, and options.rewrites allows much finer control over rewrite rules.

#websocket([pathname], handler) installs a websocket handler for the specified route.

createPercyServer()

This function was moved into its own dedicated api.js file. The function utilizes the new server code from above to create the localhost:5338/percy API server, which works just as it did before. In the future, this file will also house a createStaticServer function which will handle creating static snapshot servers for SDKs in the same manner.

Tests

The core test server helper was updated to accept the old initialization and reply syntax. This way most tests can still remain as-is without having to undergo wider changes.

Existing API server tests were moved to an API specific test module. Server-specific tests were moved to and created in a new unit test module. Within this unit test a new package, quibble, is utilized for dependency mocking since our currently used dependency mocking library, mock-require, is now deprecated.

[Robdel12]

🏁 I dig quibble too!