Fix #2822: Incorrect usage of fwrite()

We only used to check (and not always) if the return value of fwrite() is boolean FALSE,
while it is possible that the otherwise returned bytecount is less than the length of
data that we're trying to write. This allowed incomplete writes over network streams
and possibly a few other edge cases.

1 files changed, 10 insertions, 2 deletions

diff --git a/system/helpers/file_helper.php b/system/helpers/file_helper.php
index 4b45a62d0..0587740b1 100644
--- a/system/helpers/file_helper.php
+++ b/system/helpers/file_helper.php
@@ -79,11 +79,19 @@ if ( ! function_exists('write_file'))
 		}
 
 		flock($fp, LOCK_EX);
-		fwrite($fp, $data);
+
+		for ($written = 0, $length = strlen($data); $written < $length; $written += $result)
+		{
+			if (($result = fwrite($fp, substr($data, $written))) === FALSE)
+			{
+				break;
+			}
+		}
+
 		flock($fp, LOCK_UN);
 		fclose($fp);
 
-		return TRUE;
+		return is_int($result);
 	}
 }