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

Built from https://develop.svn.wordpress.org/trunk@34740


git-svn-id: http://core.svn.wordpress.org/trunk@34704 1a063a9b-81f0-0310-95a4-ce76da25c4cd

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 ( ! 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 {
 		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;
 }
 
 /**

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34739';
+$wp_version = '4.4-alpha-34740';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.