adds log-ios and log-android cli commands

Summary:
solves first part of #8186
Closes https://github.com/facebook/react-native/pull/8352

Differential Revision: D3475905

Pulled By: mkonicek

fbshipit-source-id: 99f6aa15b92ba3192fa0b812d369bd7020469573

docs/Debugging.md

@@ -54,9 +54,11 @@ YellowBoxes can be disabled during development by using `console.disableYellowBo
 
 ## Accessing logs
 
-To view detailed logs on iOS, open your app in Xcode, then Build and Run your app on a device or the iPhone Simulator. The console should appear automatically after the app launches. If your app is failing to build, check the Issues Navigator in Xcode.
+Run `react-native log-ios` in a terminal to display the logs for an iOS app running on a device or a simulator.
 
-Run `adb logcat *:S ReactNative:V ReactNativeJS:V` in a terminal to display the logs for an Android app running on a device or an emulator.
+You can also view the iOS logs in Xcode: open your app in Xcode, then Build and Run your app on a device or the iPhone Simulator. The console should appear automatically after the app launches. If your app is failing to build, check the Issues Navigator in Xcode.
+
+Run `react-native log-android` in a terminal to display the logs for an Android app running on a device or an emulator.
 
 ## Chrome Developer Tools
 

local-cli/cliEntry.js

@@ -19,7 +19,9 @@ const link = require('./rnpm/link/src/link');
 const path = require('path');
 const Promise = require('promise');
 const runAndroid = require('./runAndroid/runAndroid');
+const logAndroid = require('./logAndroid/logAndroid');
 const runIOS = require('./runIOS/runIOS');
+const logIOS = require('./logIOS/logIOS');
 const server = require('./server/server');
 const TerminalAdapter = require('yeoman-environment/lib/adapter.js');
 const yeoman = require('yeoman-environment');
@@ -49,7 +51,9 @@ const documentedCommands = {
   'new-library': [library, 'generates a native library bridge'],
   'android': [generateWrapper, 'generates an Android project for your app'],
   'run-android': [runAndroid, 'builds your app and starts it on a connected Android emulator or device'],
+  'log-android': [logAndroid, 'print Android logs'],
   'run-ios': [runIOS, 'builds your app and starts it on iOS simulator'],
+  'log-ios': [logIOS, 'print iOS logs'],
   'upgrade': [upgrade, 'upgrade your app\'s template files to the latest version; run this after ' +
                        'updating the react-native version in your package.json and running npm install'],
   'link': [linkWrapper, 'link a library'],

local-cli/logAndroid/logAndroid.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+const chalk = require('chalk');
+const child_process = require('child_process');
+const Promise = require('promise');
+
+/**
+ * Starts adb logcat
+ */
+function logAndroid() {
+  return new Promise((resolve, reject) => {
+    _logAndroid(resolve, reject);
+  });
+}
+
+function _logAndroid(resolve, reject) {
+  try {
+    const adbPath = process.env.ANDROID_HOME
+      ? process.env.ANDROID_HOME + '/platform-tools/adb'
+      : 'adb';
+
+    const adbArgs = ['logcat', '*:S', 'ReactNative:V', 'ReactNativeJS:V'];
+
+    console.log(chalk.bold(
+      `Starting the logger (${adbPath} ${adbArgs.join(' ')})...`
+    ));
+
+    const log = child_process.spawnSync(adbPath, adbArgs, {stdio: 'inherit'});
+
+    if (log.error !== null) {
+      throw log.error;
+    }
+
+  } catch (e) {
+    console.log(chalk.red(
+      'adb invocation failed. Do you have adb in your PATH?'
+    ));
+    reject();
+    return;
+  }
+}
+
+module.exports = logAndroid;

local-cli/logIOS/logIOS.js

@@ -0,0 +1,77 @@
+'use strict';
+
+const chalk = require('chalk');
+const child_process = require('child_process');
+const os = require('os');
+const path = require('path');
+const Promise = require('promise');
+
+/**
+ * Starts iOS device syslog tail
+ */
+function logIOS() {
+  return new Promise((resolve, reject) => {
+    _logIOS(resolve, reject);
+  });
+}
+
+function _logIOS(resolve, reject) {
+  let rawDevices;
+
+  try {
+    rawDevices = child_process.execFileSync(
+      'xcrun', ['simctl', 'list', 'devices', '--json'], {encoding: 'utf8'}
+    );
+  } catch (e) {
+    console.log(chalk.red(
+      'xcrun invocation failed. Please check that Xcode is installed.'
+    ));
+    reject(e);
+    return;
+  }
+
+  const { devices } = JSON.parse(rawDevices);
+
+  const device = _findAvailableDevice(devices);
+  if (device === undefined) {
+    console.log(chalk.red(
+      'No active iOS device found'
+    ));
+    reject();
+  }
+
+  tailDeviceLogs(device.udid, reject);
+}
+
+function _findAvailableDevice(devices) {
+  for (const key of Object.keys(devices)) {
+    for (const device of devices[key]) {
+      if (device.availability === '(available)' && device.state === 'Booted') {
+        return device;
+      }
+    }
+  }
+}
+
+function tailDeviceLogs(udid, reject) {
+  const logDir = path.join(
+    os.homedir(),
+    'Library',
+    'Logs',
+    'CoreSimulator',
+    udid,
+    'asl',
+  );
+
+  const log =
+    child_process.spawnSync('syslog', ['-w', '-F', 'std', '-d', logDir], {stdio: 'inherit'});
+
+  if (log.error !== null) {
+    console.log(chalk.red(
+      'syslog invocation failed.'
+    ));
+    reject(log.error);
+  }
+}
+
+module.exports = logIOS;