From c9207f7fc24d6ab879561632ba3c08fee07a9cc4 Mon Sep 17 00:00:00 2001
From: Olov Lassus <olov.lassus@gmail.com>
Date: Thu, 5 Mar 2015 01:03:34 +0100
Subject: [PATCH] fs: fix corruption in writeFile and writeFileSync

1. writeFileSync bumps position incorrectly, causing it to drift in
iteration three and onwards.

2. Append mode files will get corrupted in the middle if writeFile or
writeFileSync iterates multiple times, unless running on Linux. position
starts out as null so first write is OK, but then position will refer to
a location inside an existing file, corrupting that data. Linux ignores
position for append mode files so it doesn't happen there.

This commit fixes these two related issues by bumping position correctly
and by always using null as the position argument to write/writeSync for
append mode files.

PR-URL: https://github.com/iojs/io.js/pull/1063
Reviewed-By: Bert Belder <bertbelder@gmail.com>
---
 lib/fs.js | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/lib/fs.js b/lib/fs.js
index 77bcbac61a5eca..472d03cc75414c 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -1099,7 +1099,9 @@ function writeAll(fd, buffer, offset, length, position, callback) {
       } else {
         offset += written;
         length -= written;
-        position += written;
+        if (position !== null) {
+          position += written;
+        }
         writeAll(fd, buffer, offset, length, position, callback);
       }
     }
@@ -1148,13 +1150,17 @@ fs.writeFileSync = function(path, data, options) {
   if (!(data instanceof Buffer)) {
     data = new Buffer('' + data, options.encoding || 'utf8');
   }
-  var written = 0;
+  var offset = 0;
   var length = data.length;
   var position = /a/.test(flag) ? null : 0;
   try {
-    while (written < length) {
-      written += fs.writeSync(fd, data, written, length - written, position);
-      position += written;
+    while (length > 0) {
+      var written = fs.writeSync(fd, data, offset, length, position);
+      offset += written;
+      length -= written;
+      if (position !== null) {
+        position += written;
+      }
     }
   } finally {
     fs.closeSync(fd);