Git.pm: fix cat_blob crashes on large files

Read and write each 1024 byte buffer, rather than trying to buffer
the entire content of the file.  We are only copying the contents to
a file descriptor and do not use it ourselves.

Previous code would crash on all files > 2 Gib, when the offset
variable became negative (perhaps below the level of perl),
resulting in a crash.  On a 32 bit system, or a system with low
memory it might crash before reaching 2 GiB due to memory
exhaustion.

This code may leave a partial file behind in case of failure, where
the old code would leave a completely empty file.  Neither version
verifies the correctness of the content.  Calling code must take
care of verification and cleanup.

Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/perl/Git.pm b/perl/Git.pm
index 497f420178a73061901393f8c21a9feb17054b6d..cebf8f34c237aaa0df9fbf8a2985e9b3d1377721 100644 (file)
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -890,20 +890,22 @@ sub cat_blob {
        my $size = $1;
 
        my $blob;
-       my $bytesRead = 0;
+       my $bytesLeft = $size;
 
        while (1) {
-               my $bytesLeft = $size - $bytesRead;
                last unless $bytesLeft;
 
                my $bytesToRead = $bytesLeft < 1024 ? $bytesLeft : 1024;
-               my $read = read($in, $blob, $bytesToRead, $bytesRead);
+               my $read = read($in, $blob, $bytesToRead);
                unless (defined($read)) {
                        $self->_close_cat_blob();
                        throw Error::Simple("in pipe went bad");
                }
-
-               $bytesRead += $read;
+               unless (print $fh $blob) {
+                       $self->_close_cat_blob();
+                       throw Error::Simple("couldn't write to passed in filehandle");
+               }
+               $bytesLeft -= $read;
        }
 
        # Skip past the trailing newline.
@@ -918,11 +920,6 @@ sub cat_blob {
                throw Error::Simple("didn't find newline after blob");
        }
 
-       unless (print $fh $blob) {
-               $self->_close_cat_blob();
-               throw Error::Simple("couldn't write to passed in filehandle");
-       }
-
        return $size;
 }