fix(CLI): wait for robot output to be flushed before exitting (#616)

When using the `--robot` option, we write to `stdout`/`stderr` using
`WritableStream#write()`. This operation is asynchronous, however we're
not waiting for the data to be flushed before calling `process.exit()`
right after emitting the `done` event.

This causes a rance condition where sometimes `done` is never written to
the log file, and therefore the GUI remains waiting forever.

Change-Type: patch
Changelog-Entry: Fix application stuck at "Finishing".
See: https://github.com/resin-io/etcher/issues/613
See: https://github.com/resin-io/etcher/issues/609
See: https://github.com/resin-io/etcher/issues/573
Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

lib/cli/etcher.js

@@ -91,43 +91,48 @@ form.run([
   });
 }).then((results) => {
 
-  if (options.robot) {
-    log.toStdout(JSON.stringify({
-      command: 'done',
-      data: {
-        passedValidation: results.passedValidation,
-        sourceChecksum: results.sourceChecksum
-      }
-    }));
-  } else {
+  return Bluebird.try(() => {
+    if (options.robot) {
+      return log.toStdout(JSON.stringify({
+        command: 'done',
+        data: {
+          passedValidation: results.passedValidation,
+          sourceChecksum: results.sourceChecksum
+        }
+      }));
+    }
+
     if (results.passedValidation) {
       console.log('Your flash is complete!');
       console.log(`Checksum: ${results.sourceChecksum}`);
     } else {
       console.error('Validation failed!');
     }
-  }
-
-  if (results.passedValidation) {
-    process.exit(EXIT_CODES.SUCCESS);
-  } else {
-    process.exit(EXIT_CODES.VALIDATION_ERROR);
-  }
+  }).then(() => {
+    if (results.passedValidation) {
+      process.exit(EXIT_CODES.SUCCESS);
+    } else {
+      process.exit(EXIT_CODES.VALIDATION_ERROR);
+    }
+  });
 
 }).catch((error) => {
 
-  if (options.robot) {
-    log.toStderr(JSON.stringify({
-      command: 'error',
-      data: {
-        message: error.message,
-        description: error.description,
-        code: error.code
-      }
-    }));
-  } else {
-    utils.printError(error);
-  }
+  return Bluebird.try(() => {
+    if (options.robot) {
+      return log.toStderr(JSON.stringify({
+        command: 'error',
+        data: {
+          message: error.message,
+          description: error.description,
+          code: error.code
+        }
+      }));
+    }
+
+    utils.printError(error);
+  }).then(() => {
+    process.exit(EXIT_CODES.GENERAL_ERROR);
+  });
 
-  process.exit(EXIT_CODES.GENERAL_ERROR);
 }).finally(log.close);

lib/cli/log.js

@@ -16,6 +16,7 @@
 
 'use strict';
 
+const Bluebird = require('bluebird');
 const fs = require('fs');
 const options = require('./cli');
 const logStream = options.log ? fs.createWriteStream(options.log) : null;
@@ -46,12 +47,17 @@ const STDERR_STREAM = logStream || process.stderr;
  * to it, otherwise to `process.stdout`.
  *
  * @param {String} line - line
+ * @returns {Promise}
  *
  * @example
  * log.toStdout('Hello world!');
  */
 exports.toStdout = (line) => {
-  STDOUT_STREAM.write(line + '\n');
+  return new Bluebird((resolve) => {
+    STDOUT_STREAM.write(line + '\n', () => {
+      return resolve();
+    });
+  });
 };
 
 /**
@@ -64,12 +70,17 @@ exports.toStdout = (line) => {
  * to it, otherwise to `process.stderr`.
  *
  * @param {String} line - line
+ * @returns {Promise}
  *
  * @example
  * log.toStderr('Hello world!');
  */
 exports.toStderr = (line) => {
-  STDERR_STREAM.write(line + '\n');
+  return new Bluebird((resolve) => {
+    STDERR_STREAM.write(line + '\n', () => {
+      return resolve();
+    });
+  });
 };
 
 /**
@@ -77,11 +88,19 @@ exports.toStderr = (line) => {
  * @function
  * @public
  *
+ * @returns {Promise}
+ *
  * @example
  * log.close();
  */
 exports.close = () => {
-  if (logStream) {
-    logStream.close();
-  }
+  return new Bluebird((resolve) => {
+    if (!logStream) {
+      return resolve();
+    }
+
+    logStream.close(() => {
+      return resolve();
+    });
+  });
 };