refactor(cli): make --robot option output JSON (#500)

The Etcher CLI `--robot` option outputs space separated lines including
useful information in a predefined order, for example:

```sh
progress write 50% 15s 65536
```

While this is very easy to parse, a stringified JSON line is much more
convenient since:

- We don't have to write any parsing logic.
- We don't have to guess the value types (string, number, boolean, etc).
- We don't have to hardcode property names.
- We don't have to extend the parsing code if we decide to send new
commands from the CLI, or make any change to the data we output.

Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

lib/cli/etcher.js

@@ -64,13 +64,15 @@ form.run([
   }, function(state) {
 
     if (options.robot) {
-      log.toStdout([
-        'progress',
-        state.type,
-        Math.floor(state.percentage) + '%',
-        state.eta + 's',
-        Math.floor(state.speed)
-      ].join(' '));
+      log.toStdout(JSON.stringify({
+        command: 'progress',
+        data: {
+          type: state.type,
+          percentage: Math.floor(state.percentage),
+          eta: state.eta,
+          speed: Math.floor(state.speed)
+        }
+      }));
     } else {
       progressBars[state.type].update(state);
     }
@@ -79,7 +81,13 @@ form.run([
 }).then(function(results) {
 
   if (options.robot) {
-    log.toStdout(`done ${results.passedValidation} ${results.sourceChecksum}`);
+    log.toStdout(JSON.stringify({
+      command: 'done',
+      data: {
+        passedValidation: results.passedValidation,
+        sourceChecksum: results.sourceChecksum
+      }
+    }));
   } else {
     if (results.passedValidation) {
       console.log('Your flash is complete!');
@@ -98,7 +106,12 @@ form.run([
 }).catch(function(error) {
 
   if (options.robot) {
-    log.toStderr(error.message);
+    log.toStderr(JSON.stringify({
+      command: 'error',
+      data: {
+        message: error.message
+      }
+    }));
   } else {
     utils.printError(error);
   }

lib/src/child-writer/utils.js

@@ -137,45 +137,3 @@ exports.getTemporaryLogFilePath = function() {
     return logFilePath;
   });
 };
-
-/**
- * @summary Parse an output line from the Etcher CLI
- * @function
- * @public
- *
- * @description
- * This function parses an output line for when the CLI
- * was called with the `--robot` argument.
- *
- * @param {String} line - line
- * @returns {(Object|Undefined)} parsed output
- *
- * @example
- * const data = utils.parseEtcherCLIRobotLine('progress write 50% 0.5s 400');
- */
-exports.parseEtcherCLIRobotLine = function(line) {
-  const data = line.split(' ');
-  const command = _.first(data);
-
-  if (command === 'progress') {
-    return {
-      command: command,
-      data: {
-        type: _.nth(data, 1),
-        percentage: _.parseInt(_.nth(data, 2)),
-        eta: _.parseInt(_.nth(data, 3)),
-        speed: _.parseInt(_.nth(data, 4))
-      }
-    };
-  }
-
-  if (command === 'done') {
-    return {
-      command: command,
-      data: {
-        passedValidation: _.nth(data, 1) === 'true',
-        sourceChecksum: _.nth(data, 2)
-      }
-    };
-  }
-};

lib/src/child-writer/writer-proxy.js

@@ -72,11 +72,7 @@ return isElevated().then(function(elevated) {
     });
 
     tail.on('line', function(line) {
-      const data = utils.parseEtcherCLIRobotLine(line);
-
-      if (data) {
-        process.send(data);
-      }
+      process.send(JSON.parse(line));
     });
   }