chore: cleanup puppeteer.connect({browserURL}) (#3766)

This patch:
- renames `browserUrl` into `browserURL`
- cleans up some code
- adds tests for error handling

References #3537

lib/Launcher.js

@@ -24,7 +24,7 @@ const {Connection} = require('./Connection');
 const {Browser} = require('./Browser');
 const readline = require('readline');
 const fs = require('fs');
-const {helper, debugError} = require('./helper');
+const {helper, assert, debugError} = require('./helper');
 const {TimeoutError} = require('./Errors');
 const WebSocketTransport = require('./WebSocketTransport');
 const PipeTransport = require('./PipeTransport');
@@ -278,33 +278,33 @@ class Launcher {
   }
 
   /**
-   * @param {!(Launcher.BrowserOptions & {browserWSEndpoint?: string, browserUrl?: string, transport?: !Puppeteer.ConnectionTransport})} options
+   * @param {!(Launcher.BrowserOptions & {browserWSEndpoint?: string, browserURL?: string, transport?: !Puppeteer.ConnectionTransport})} options
    * @return {!Promise<!Browser>}
    */
   async connect(options) {
     const {
       browserWSEndpoint,
-      browserUrl,
+      browserURL,
       ignoreHTTPSErrors = false,
       defaultViewport = {width: 800, height: 600},
       transport,
       slowMo = 0,
     } = options;
 
-    let connectionUrl;
-    let connectionTransport;
+    assert(Number(!!browserWSEndpoint) + Number(!!browserURL) + Number(!!transport) === 1, 'Exactly one of browserWSEndpoint, browserURL or transport must be passed to puppeteer.connect');
 
-    if (browserWSEndpoint)
-      connectionUrl = browserWSEndpoint;
-    else if (!browserWSEndpoint && browserUrl)
-      connectionUrl = await getWSEndpoint(browserUrl);
+    let connection = null;
+    if (transport) {
+      connection = new Connection('', transport, slowMo);
+    } else if (browserWSEndpoint) {
+      const connectionTransport = await WebSocketTransport.create(browserWSEndpoint);
+      connection = new Connection(browserWSEndpoint, connectionTransport, slowMo);
+    } else if (browserURL) {
+      const connectionURL = await getWSEndpoint(browserURL);
+      const connectionTransport = await WebSocketTransport.create(connectionURL);
+      connection = new Connection(connectionURL, connectionTransport, slowMo);
+    }
 
-    if (transport)
-      connectionTransport = transport;
-    else
-      connectionTransport = await WebSocketTransport.create(connectionUrl);
-
-    const connection = new Connection(connectionUrl, connectionTransport, slowMo);
     const {browserContextIds} = await connection.send('Target.getBrowserContexts');
     return Browser.create(connection, browserContextIds, ignoreHTTPSErrors, defaultViewport, null, () => connection.send('Browser.close').catch(debugError));
   }
@@ -393,45 +393,35 @@ function waitForWSEndpoint(chromeProcess, timeout, preferredRevision) {
 }
 
 /**
- * @param {string} browserUrl
+ * @param {string} browserURL
  * @return {!Promise<string>}
  */
-function getWSEndpoint(browserUrl) {
+function getWSEndpoint(browserURL) {
   let resolve, reject;
-  const endpointUrl = URL.resolve(browserUrl, '/json/version');
-  const requestOptions = Object.assign(URL.parse(endpointUrl), { method: 'GET' });
   const promise = new Promise((res, rej) => { resolve = res; reject = rej; });
 
-  function handleRequestEnd(data) {
-    try {
-      const {webSocketDebuggerUrl} = JSON.parse(data);
-      resolve(webSocketDebuggerUrl);
-    } catch (e) {
-      handleRequestError(e);
-    }
-  }
-
-  function handleRequestError(err) {
-    reject(new Error(`Failed to fetch browser webSocket url from ${endpointUrl}: ${err}`));
-  }
-
+  const endpointURL = URL.resolve(browserURL, '/json/version');
+  const requestOptions = Object.assign(URL.parse(endpointURL), { method: 'GET' });
   const request = http.request(requestOptions, res => {
     let data = '';
     if (res.statusCode !== 200) {
-      // consume response data to free up memory
+      // Consume response data to free up memory.
       res.resume();
-      handleRequestError(res.statusCode);
+      reject(new Error('HTTP ' + res.statusCode));
       return;
     }
     res.setEncoding('utf8');
     res.on('data', chunk => data += chunk);
-    res.on('end', () => handleRequestEnd(data));
+    res.on('end', () => resolve(JSON.parse(data).webSocketDebuggerUrl));
   });
 
-  request.on('error', handleRequestError);
+  request.on('error', reject);
   request.end();
 
-  return promise;
+  return promise.catch(e => {
+    e.message = `Failed to fetch browser webSocket url from ${endpointURL}: ` + e.message;
+    throw e;
+  });
 }
 
 /**