From e4a147150ed0f7048c99e0bfbe1f3e4170070ced Mon Sep 17 00:00:00 2001
From: Dion Hulse <dd32@git.wordpress.org>
Date: Thu, 1 Oct 2015 07:45:35 +0000
Subject: [PATCH] Rewrite `insert_with_markers()` to use `flock()` when
 available, significant cleanup of the function too.

The call to `flock()` is an exclusive advisory lock, which in my testing only PHP respects (apache continues to read it).
Not all filesystems support locking (remote NFS mounts for example) so this offers minimal benefit to those platforms, but offers much better protection against file corruption on systems which do support it.
The call is blocking, so a second process will wait for the first to complete before writing if supported.

See #31767


git-svn-id: https://develop.svn.wordpress.org/trunk@34740 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/includes/misc.php | 102 +++++++++++++++++++--------------
 1 file changed, 60 insertions(+), 42 deletions(-)

diff --git a/src/wp-admin/includes/misc.php b/src/wp-admin/includes/misc.php
index 0e104e0d38..66867d2732 100644
--- a/src/wp-admin/includes/misc.php
+++ b/src/wp-admin/includes/misc.php
@@ -102,50 +102,68 @@ function extract_from_markers( $filename, $marker ) {
  * @return bool True on write success, false on failure.
  */
 function insert_with_markers( $filename, $marker, $insertion ) {
-	if (!file_exists( $filename ) || is_writeable( $filename ) ) {
-		if (!file_exists( $filename ) ) {
-			$markerdata = '';
-		} else {
-			$markerdata = explode( "\n", implode( '', file( $filename ) ) );
-		}
-
-		if ( !$f = @fopen( $filename, 'w' ) )
-			return false;
-
-		$foundit = false;
-		if ( $markerdata ) {
-			$state = true;
-			foreach ( $markerdata as $n => $markerline ) {
-				if (strpos($markerline, '# BEGIN ' . $marker) !== false)
-					$state = false;
-				if ( $state ) {
-					if ( $n + 1 < count( $markerdata ) )
-						fwrite( $f, "{$markerline}\n" );
-					else
-						fwrite( $f, "{$markerline}" );
-				}
-				if (strpos($markerline, '# END ' . $marker) !== false) {
-					fwrite( $f, "# BEGIN {$marker}\n" );
-					if ( is_array( $insertion ))
-						foreach ( $insertion as $insertline )
-							fwrite( $f, "{$insertline}\n" );
-					fwrite( $f, "# END {$marker}\n" );
-					$state = true;
-					$foundit = true;
-				}
-			}
-		}
-		if (!$foundit) {
-			fwrite( $f, "\n# BEGIN {$marker}\n" );
-			foreach ( $insertion as $insertline )
-				fwrite( $f, "{$insertline}\n" );
-			fwrite( $f, "# END {$marker}\n" );
-		}
-		fclose( $f );
-		return true;
-	} else {
+	if ( ! is_writeable( $filename ) ) {
 		return false;
 	}
+
+	if ( ! is_array( $insertion ) ) {
+		$insertion = array( $insertion );
+	}
+
+	$start_marker = "# BEGIN {$marker}";
+	$end_marker   = "# END {$marker}";
+
+	$fp = fopen( $filename, 'r+' );
+	if ( ! $fp ) {
+		return false;
+	}
+
+	// Attempt to get a lock. If the filesystem supports locking, this will block until the lock is acquired.
+	flock( $fp, LOCK_EX );
+
+	$lines = array();
+	while ( ! feof( $fp ) ) {
+		$lines[] = rtrim( fgets( $fp ), "\r\n" );
+	}
+
+	// Split out the existing file into the preceeding lines, and those that appear after the marker
+	$pre_lines = $post_lines = array();
+	$found_marker = $found_end_marker = false;
+	foreach ( $lines as $line ) {
+		if ( ! $found_marker && false !== strpos( $line, $start_marker ) ) {
+			$found_marker = true;
+			continue;
+		} elseif ( ! $found_end_marker && false !== strpos( $line, $end_marker ) ) {
+			$found_end_marker = true;
+			continue;
+		}
+		if ( ! $found_marker ) {
+			$pre_lines[] = $line;
+		} elseif ( $found_marker && $found_end_marker ) {
+			$post_lines[] = $line;
+		}
+	}
+
+	// Generate the new file data
+	$new_file_data = implode( "\n", array_merge(
+		$pre_lines,
+		array( $start_marker ),
+		$insertion,
+		array( $end_marker ),
+		$post_lines
+	) );
+
+	// Write to the start of the file, and truncate it to that length
+	fseek( $fp, 0 );
+	$bytes = fwrite( $fp, $new_file_data );
+	if ( $bytes ) {
+		ftruncate( $fp, $bytes );
+	}
+
+	flock( $fp, LOCK_UN );
+	fclose( $fp );
+
+	return (bool) $bytes;
 }
 
 /**