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, 31 insertions, 13 deletions

diff --git a/system/core/Output.php b/system/core/Output.php
index 10332f0d8..a7680b3d0 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -542,17 +542,26 @@ class CI_Output {
 			return;
 		}
 
-		$expire = time() + ($this->cache_expiration * 60);
-
-		// Put together our serialized info.
-		$cache_info = serialize(array(
-			'expire'	=> $expire,
-			'headers'	=> $this->headers
-		));
-
 		if (flock($fp, LOCK_EX))
 		{
-			fwrite($fp, $cache_info.'ENDCI--->'.$output);
+			$expire = time() + ($this->cache_expiration * 60);
+
+			// Put together our serialized info.
+			$cache_info = serialize(array(
+				'expire'	=> $expire,
+				'headers'	=> $this->headers
+			));
+
+			$output = $cache_info.'ENDCI--->'.$output;
+
+			for ($written = 0, $length = strlen($output); $written < $length; $written += $result)
+			{
+				if (($result = fwrite($fp, substr($output, $written))) === FALSE)
+				{
+					break;
+				}
+			}
+
 			flock($fp, LOCK_UN);
 		}
 		else
@@ -560,13 +569,22 @@ class CI_Output {
 			log_message('error', 'Unable to secure a file lock for file at: '.$cache_path);
 			return;
 		}
+
 		fclose($fp);
-		@chmod($cache_path, FILE_WRITE_MODE);
 
-		log_message('debug', 'Cache file written: '.$cache_path);
+		if (is_int($result))
+		{
+			@chmod($cache_path, FILE_WRITE_MODE);
+			log_message('debug', 'Cache file written: '.$cache_path);
 
-		// Send HTTP cache-control headers to browser to match file cache settings.
-		$this->set_cache_header($_SERVER['REQUEST_TIME'], $expire);
+			// Send HTTP cache-control headers to browser to match file cache settings.
+			$this->set_cache_header($_SERVER['REQUEST_TIME'], $expire);
+		}
+		else
+		{
+			@unlink($cache_path);
+			log_message('error', 'Unable to write the complete cache content at: '.$cache_path);
+		}
 	}
 
 	// --------------------------------------------------------------------