Libguestfs - Jan 2011 - [PATCH] Don't display a progress bar if stderr isn't on a tty

Apart from being a good idea, this works round an apparent bug in either
Term::ProgressBar or Term::ReadKey which seems to result in an attempt to write
an exceptionally long progress bar.

Fixes RHBZ#671083
---
 lib/Sys/VirtV2V/Connection/Source.pm |   30 ++++++++++++++++++++++--------
 1 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/lib/Sys/VirtV2V/Connection/Source.pm
b/lib/Sys/VirtV2V/Connection/Source.pm
index 4f94e20..5216503 100644
--- a/lib/Sys/VirtV2V/Connection/Source.pm
+++ b/lib/Sys/VirtV2V/Connection/Source.pm
@@ -126,9 +126,20 @@ sub _volume_copy
 
     # Copy the contents of the source stream to the destination stream
     my $total = 0;
-    my $progress = new Term::ProgressBar({name => $src->get_name(),
-                                          count => $expected,
-                                          ETA => 'linear' });
+
+    # Initialize a progress bar if STDERR is on a tty
+    my $progress;
+    if (-t STDERR) {
+        $progress = new Term::ProgressBar({name => $src->get_name(),
+                                           count => $expected,
+                                           ETA => 'linear' });
+    } else {
+        print STDERR user_message(__x("Transferring storage volume {name}:
".
+                                      "{size} bytes",
+                                      name => $src->get_name(),
+                                      size => $expected));
+    }
+
     my $next_update = 0;
     for (;;) {
         my $buf = $src_s->read(4 * 1024 * 1024);
@@ -137,12 +148,15 @@ sub _volume_copy
         $total += length($buf);
         $dst_s->write($buf);
 
-        $next_update = $progress->update($total) if ($total >
$next_update);
+        $next_update = $progress->update($total)
+            if (defined($progress) && $total > $next_update);
+    }
+    if (defined($progress)) {
+        # Indicate that we finished regardless of how much data was written
+        $progress->update($expected);
+        # The progress bar doesn't print a newline on completion
+        print STDERR "\n";
     }
-    # Indicate that we finished regardless of how much data was written
-    $progress->update($expected);
-    # The progress bar doesn't print a newline on completion
-    print STDERR "\n";
 
     # This would be closed implicitly, but we want to report read/write errors
     # before checking for a short volume
-- 
1.7.3.5

On Thu, Jan 20, 2011 at 05:22:28PM +0000, Matthew Booth
wrote:
> Apart from being a good idea, this works round an apparent bug in either
> Term::ProgressBar or Term::ReadKey which seems to result in an attempt to
write
> an exceptionally long progress bar.
> 
> Fixes RHBZ#671083
ACK.

I'm a bit surprised that the progress bar is sent to STDERR by default
(the default in Term::ProgressBar).

For reference, similar code is used in guestfish except we check if
stdin is a tty not stderr, and we output to stdout:

http://git.annexia.org/?p=libguestfs.git;a=blob;f=fish/fish.c;h=10f645f5ddea81954b361d2ece62c20f2fd8eea1;hb=HEAD#l490
http://git.annexia.org/?p=libguestfs.git;a=blob;f=fish/progress.c;hb=HEAD

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org