Index: file.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/file.inc,v
retrieving revision 1.102
diff -u -p -r1.102 file.inc
--- file.inc	2 Jul 2007 14:41:35 -0000	1.102
+++ file.inc	15 Jul 2007 05:15:40 -0000
@@ -799,10 +799,70 @@ function file_transfer($source, $headers
 
   $source = file_create_path($source);
 
-  // Transfer file in 1024 byte chunks to save memory usage.
   if ($fd = fopen($source, 'rb')) {
-    while (!feof($fd)) {
-      print fread($fd, 1024);
+    // Tell client that we accept byte ranges.
+    drupal_set_header('Accept-Ranges: bytes');
+    // Get file size.
+    $filesize = filesize($source);
+    $end_file = $filesize - 1;
+    $valid = FALSE;
+    $satisfiable = FALSE;
+    // Is this a partial request?
+    if (isset($_SERVER['HTTP_RANGE'])) {
+      preg_match('/^bytes=(\S+)$/i', $_SERVER['HTTP_RANGE'], $ranges);
+      $ranges = explode(',', array_pop($ranges));
+      foreach ($ranges as $key => $range) {
+        if (substr_count($range, '-') == 1) {
+          $valid = TRUE;
+          if (substr($range, 0, 1) == '-') {
+            $satisfiable = TRUE;
+            $ranges[$key] = array('from' => max(0, $end_file + $range), 'to' => $end_file);
+          }
+          else {
+            $range = explode('-', $range);
+            if ($range[0] <= $end_file) {
+              if ($range[1] === '') {
+                $satisfiable = TRUE;
+                $ranges[$key] = array('from' => $range[0], 'to' => $end_file);
+              }
+              elseif ($range[0] <= $range[1]) {
+                $satisfiable = TRUE;
+                $ranges[$key] = array('from' => $range[0], 'to' => min($range[1], $end_file));
+              }
+            }
+          }
+        }
+        if (!$valid || !$satisfiable) {
+          unset($ranges[$key]);
+        }
+      }
+    }
+    if ($satisfiable) {
+      drupal_set_header('HTTP/1.1 206 Partial Content');
+      foreach ($ranges as $range) {
+        // Move file pointer.
+        fseek($fd, $range['from']);
+        drupal_set_header(sprintf('Content-Range: bytes %d-%d/%d', $range['from'], $range['to'], $filesize));
+        $length = $range['to'] + 1 - $range['from'];
+      }
+    }
+    else {
+      if ($valid && !isset($_SERVER['If-Range'])) {
+        drupal_set_header('HTTP/1.1 416 Requested Range Not Satisfiable');
+        drupal_set_header('Content-Range: *');
+      }
+      else {
+        $length = $filesize;
+      }
+    }
+    if (isset($length)) {
+      drupal_set_header('Content-Length: '. $length);
+      // Transfer file in 1024 byte chunks to save memory usage.
+      while ($length > 0) {
+        $read = min(1024, $length);
+        print fread($fd, $read);
+        $length -= $read;
+      }
     }
     fclose($fd);
   }