restructure: move bin/ and tests/ to src/

Also add symlinks from the old `bin/` and `tests/` locations to avoid
breaking scripts and other tools.

Motivations:

  * Scripts and tests no longer have to do dubious things like:

        require('ep_etherpad-lite/node_modules/foo')

    to access packages installed as dependencies in
    `src/package.json`.

  * Plugins can access the backend test helper library in a non-hacky
    way:

        require('ep_etherpad-lite/tests/backend/common')

  * We can delete the top-level `package.json` without breaking our
    ability to lint the files in `bin/` and `tests/`.

    Deleting the top-level `package.json` has downsides: It will cause
    `npm` to print warnings whenever plugins are installed, npm will
    no longer be able to enforce a plugin's peer dependency on
    ep_etherpad-lite, and npm will keep deleting the
    `node_modules/ep_etherpad-lite` symlink that points to `../src`.

    But there are significant upsides to deleting the top-level
    `package.json`: It will drastically speed up plugin installation
    because `npm` doesn't have to recursively walk the dependencies in
    `src/package.json`. Also, deleting the top-level `package.json`
    avoids npm's horrible dependency hoisting behavior (where it moves
    stuff from `src/node_modules/` to the top-level `node_modules/`
    directory). Dependency hoisting causes numerous mysterious
    problems such as silent failures in `npm outdated` and `npm
    update`. Dependency hoisting also breaks plugins that do:

        require('ep_etherpad-lite/node_modules/foo')

src/tests/backend/specs/caching_middleware.js

@@ -0,0 +1,147 @@
+/**
+ * caching_middleware is responsible for serving everything under path `/javascripts/`
+ * That includes packages as defined in `src/node/utils/tar.json` and probably also plugin code
+ *
+ */
+
+const common = require('../common');
+const assert = require('assert').strict;
+const url = require('url');
+const queryString = require('querystring');
+const settings = require('../../../node/utils/Settings');
+
+let agent;
+
+/**
+ * Hack! Returns true if the resource is not plaintext
+ * The file should start with the callback method, so we need the
+ * URL.
+ *
+ * @param {string} fileContent the response body
+ * @param {URI} resource resource URI
+ * @returns {boolean} if it is plaintext
+ */
+function isPlaintextResponse(fileContent, resource) {
+  // callback=require.define&v=1234
+  const query = url.parse(resource).query;
+  // require.define
+  const jsonp = queryString.parse(query).callback;
+
+  // returns true if the first letters in fileContent equal the content of `jsonp`
+  return fileContent.substring(0, jsonp.length) === jsonp;
+}
+
+/**
+ * A hack to disable `superagent`'s auto unzip functionality
+ *
+ * @param {Request} request
+ */
+function disableAutoDeflate(request) {
+  request._shouldUnzip = function () {
+    return false;
+  };
+}
+
+describe(__filename, function () {
+  const backups = {};
+  const fantasyEncoding = 'brainwaves'; // non-working encoding until https://github.com/visionmedia/superagent/pull/1560 is resolved
+  const packages = [
+    '/javascripts/lib/ep_etherpad-lite/static/js/ace2_common.js?callback=require.define',
+    '/javascripts/lib/ep_etherpad-lite/static/js/ace2_inner.js?callback=require.define',
+    '/javascripts/lib/ep_etherpad-lite/static/js/pad.js?callback=require.define',
+    '/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define',
+  ];
+
+  before(async function () {
+    agent = await common.init();
+  });
+  beforeEach(async function () {
+    backups.settings = {};
+    backups.settings.minify = settings.minify;
+  });
+  afterEach(async function () {
+    Object.assign(settings, backups.settings);
+  });
+
+  context('when minify is false', function () {
+    before(async function () {
+      settings.minify = false;
+    });
+    it('gets packages uncompressed without Accept-Encoding gzip', async function () {
+      await Promise.all(packages.map(async (resource) => agent.get(resource)
+          .set('Accept-Encoding', fantasyEncoding)
+          .use(disableAutoDeflate)
+          .then((res) => {
+            assert.match(res.header['content-type'], /application\/javascript/);
+            assert.equal(res.header['content-encoding'], undefined);
+            assert.equal(isPlaintextResponse(res.text, resource), true);
+            return;
+          })));
+    });
+
+    it('gets packages compressed with Accept-Encoding gzip', async function () {
+      await Promise.all(packages.map(async (resource) => agent.get(resource)
+          .set('Accept-Encoding', 'gzip')
+          .use(disableAutoDeflate)
+          .then((res) => {
+            assert.match(res.header['content-type'], /application\/javascript/);
+            assert.equal(res.header['content-encoding'], 'gzip');
+            assert.equal(isPlaintextResponse(res.text, resource), false);
+            return;
+          })));
+    });
+
+    it('does not cache content-encoding headers', async function () {
+      await agent.get(packages[0])
+          .set('Accept-Encoding', fantasyEncoding)
+          .then((res) => assert.equal(res.header['content-encoding'], undefined));
+      await agent.get(packages[0])
+          .set('Accept-Encoding', 'gzip')
+          .then((res) => assert.equal(res.header['content-encoding'], 'gzip'));
+      await agent.get(packages[0])
+          .set('Accept-Encoding', fantasyEncoding)
+          .then((res) => assert.equal(res.header['content-encoding'], undefined));
+    });
+  });
+
+  context('when minify is true', function () {
+    before(async function () {
+      settings.minify = true;
+    });
+    it('gets packages uncompressed without Accept-Encoding gzip', async function () {
+      await Promise.all(packages.map(async (resource) => agent.get(resource)
+          .set('Accept-Encoding', fantasyEncoding)
+          .use(disableAutoDeflate)
+          .then((res) => {
+            assert.match(res.header['content-type'], /application\/javascript/);
+            assert.equal(res.header['content-encoding'], undefined);
+            assert.equal(isPlaintextResponse(res.text, resource), true);
+            return;
+          })));
+    });
+
+    it('gets packages compressed with Accept-Encoding gzip', async function () {
+      await Promise.all(packages.map(async (resource) => agent.get(resource)
+          .set('Accept-Encoding', 'gzip')
+          .use(disableAutoDeflate)
+          .then((res) => {
+            assert.match(res.header['content-type'], /application\/javascript/);
+            assert.equal(res.header['content-encoding'], 'gzip');
+            assert.equal(isPlaintextResponse(res.text, resource), false);
+            return;
+          })));
+    });
+
+    it('does not cache content-encoding headers', async function () {
+      await agent.get(packages[0])
+          .set('Accept-Encoding', fantasyEncoding)
+          .then((res) => assert.equal(res.header['content-encoding'], undefined));
+      await agent.get(packages[0])
+          .set('Accept-Encoding', 'gzip')
+          .then((res) => assert.equal(res.header['content-encoding'], 'gzip'));
+      await agent.get(packages[0])
+          .set('Accept-Encoding', fantasyEncoding)
+          .then((res) => assert.equal(res.header['content-encoding'], undefined));
+    });
+  });
+});