extract writeFileLines into its own function

lib/storage.js

@@ -71,6 +71,34 @@ storage.flushToStorage = (options, callback) => {
   })
 }
 
+/**
+ * Fully write or rewrite the datafile
+ * @param {String} filename
+ * @param {String[]} lines
+ * @param {Function} callback
+ */
+storage.writeFileLines = (filename, lines, callback = () => {}) => {
+  try {
+    const stream = fs.createWriteStream(filename)
+    const readable = Readable.from(lines)
+    readable.on('data', (line) => {
+      try {
+        stream.write(line)
+        stream.write('\n')
+      } catch (err) {
+        callback(err)
+      }
+    })
+    readable.on('end', () => {
+      stream.close(callback)
+    })
+    readable.on('error', callback)
+    stream.on('error', callback)
+  } catch (err) {
+    callback(err)
+  }
+}
+
 /**
  * Fully write or rewrite the datafile, immune to crashes during the write operation (data will not be lost)
  * @param {String} filename
@@ -89,25 +117,7 @@ storage.crashSafeWriteFileLines = (filename, lines, callback = () => {}) => {
       })
     },
     cb => {
-      try {
+      storage.writeFileLines(tempFilename, lines, cb)
-        const stream = fs.createWriteStream(tempFilename)
-        const readable = Readable.from(lines)
-        readable.on('data', (line) => {
-          try {
-            stream.write(line)
-            stream.write('\n')
-          } catch (err) {
-            cb(err)
-          }
-        })
-        readable.on('end', () => {
-          stream.close(cb)
-        })
-        readable.on('error', cb)
-        stream.on('error', cb)
-      } catch (err) {
-        cb(err)
-      }
     },
     async.apply(storage.flushToStorage, tempFilename),
     cb => {