refactor(child-writer): add robot commands constant (#1332)

See: https://github.com/resin-io/etcher/pull/1295#discussion_r112463686
Signed-off-by: Juan Cruz Viotti <jviotti@openmailbox.org>

lib/child-writer/index.js

@@ -126,8 +126,6 @@ exports.write = (image, drive, options) => {
    * }));
    */
   const bridgeRobotMessage = (message) => {
-    const ROBOT_COMMAND_LOG = 'log';
-
     const parsedMessage = _.attempt(() => {
       if (robot.isMessage(message)) {
         return robot.parseMessage(message);
@@ -136,7 +134,7 @@ exports.write = (image, drive, options) => {
       // Don't be so strict. If a message doesn't look like
       // a robot message, then make the child writer log it
       // for debugging purposes.
-      return robot.parseMessage(robot.buildMessage(ROBOT_COMMAND_LOG, {
+      return robot.parseMessage(robot.buildMessage(robot.COMMAND.LOG, {
         message
       }));
 
@@ -157,9 +155,9 @@ exports.write = (image, drive, options) => {
       // The error object is decomposed by the CLI for serialisation
       // purposes. We compose it back to an `Error` here in order
       // to provide better encapsulation.
-      if (messageCommand === 'error') {
+      if (messageCommand === robot.COMMAND.ERROR) {
         emitError(robot.recomposeErrorMessage(parsedMessage));
-      } else if (messageCommand === ROBOT_COMMAND_LOG) {
+      } else if (messageCommand === robot.COMMAND.LOG) {
 
         // If the message data is an object and it contains a
         // message string then log the message string only.

lib/shared/robot/index.js

@@ -19,6 +19,33 @@
 const _ = require('lodash');
 const errors = require('../errors');
 
+/**
+ * @summary Robot commands
+ * @namespace COMMAND
+ * @public
+ */
+exports.COMMAND = {
+
+  /**
+   * @property {String} ERROR
+   * @memberof COMMAND
+   *
+   * @description
+   * This command is used to represent an error message.
+   */
+  ERROR: 'error',
+
+  /**
+   * @property {String} LOG
+   * @memberof COMMAND
+   *
+   * @description
+   * This command is used to represent a log message.
+   */
+  LOG: 'log'
+
+};
+
 /**
  * @summary Check whether we should emit parseable output
  * @function
@@ -154,7 +181,7 @@ exports.parseMessage = (string) => {
  * > 'foo'
  */
 exports.buildErrorMessage = (error) => {
-  return exports.buildMessage('error', errors.toJSON(error));
+  return exports.buildMessage(exports.COMMAND.ERROR, errors.toJSON(error));
 };
 
 /**
@@ -263,5 +290,5 @@ exports.printMessage = (message, data) => {
  * robot.log({ example: 'data' });
  */
 exports.log = (data) => {
-  exports.printMessage('log', data);
+  exports.printMessage(exports.COMMAND.LOG, data);
 };

tests/shared/robot.spec.js

@@ -22,6 +22,23 @@ const robot = require('../../lib/shared/robot');
 
 describe('Shared: Robot', function() {
 
+  describe('.COMMAND', function() {
+
+    it('should be a plain object', function() {
+      m.chai.expect(_.isPlainObject(robot.COMMAND)).to.be.true;
+    });
+
+    it('should only contain string values', function() {
+      m.chai.expect(_.every(_.values(robot.COMMAND), _.isString)).to.be.true;
+    });
+
+    it('should contain only unique values', function() {
+      const numberOfKeys = _.size(_.keys(robot.COMMAND));
+      m.chai.expect(_.size(_.uniq(_.values(robot.COMMAND)))).to.equal(numberOfKeys);
+    });
+
+  });
+
   describe('.isEnabled()', function() {
 
     it('should return false if ETCHER_CLI_ROBOT is not set', function() {
@@ -193,7 +210,7 @@ describe('Shared: Robot', function() {
       const message = robot.buildErrorMessage(error);
 
       m.chai.expect(JSON.parse(message)).to.deep.equal({
-        command: 'error',
+        command: robot.COMMAND.ERROR,
         data: {
           message: 'foo',
           stack: error.stack
@@ -207,7 +224,7 @@ describe('Shared: Robot', function() {
       const message = robot.buildErrorMessage(error);
 
       m.chai.expect(JSON.parse(message)).to.deep.equal({
-        command: 'error',
+        command: robot.COMMAND.ERROR,
         data: {
           message: 'foo',
           description: 'error description',
@@ -222,7 +239,7 @@ describe('Shared: Robot', function() {
       const message = robot.buildErrorMessage(error);
 
       m.chai.expect(JSON.parse(message)).to.deep.equal({
-        command: 'error',
+        command: robot.COMMAND.ERROR,
         data: {
           message: 'foo',
           code: 'MYERROR',