tar: Rewrite the tar plugin in Python.

Thanks: Nir Soffer.

README

@@ -120,22 +120,24 @@ of the test suite:
 
  - libnbd >= 0.9.8
 
-For the Perl, example4 and tar plugins:
+For the Perl and example4 plugins:
 
  - perl interpreter
 
  - perl development libraries
 
- - perl modules ExtUtils::Embed, IO::File and Cwd
+ - perl modules ExtUtils::Embed
 
-For the Python plugin:
+For the Python and tar plugins:
 
  - python interpreter (version 3 only)
 
  - python development libraries
 
  - python unittest to run the test suite
 
+ - python tarfile.py (part of standard library)
+
 For the OCaml plugin:
 
  - OCaml >= 4.02.2

configure.ac

@@ -1203,7 +1203,7 @@ feature "nbd .................................... " \
 feature "ssh .................................... " \
         test "x$HAVE_SSH_TRUE" = "x"
 feature "tar .................................... " \
-        test "x$HAVE_PERL_TRUE" = "x"
+        test "x$HAVE_PYTHON_TRUE" = "x"
 feature "vddk ................................... " \
         test "x$HAVE_VDDK_TRUE" = "x"
 

plugins/tar/Makefile.am

@@ -31,19 +31,18 @@
 
 include $(top_srcdir)/common-rules.mk
 
-source = tar.pl
-
 EXTRA_DIST = \
-	$(source) \
+	nbdkit-tar-plugin.pod \
+	tar.py \
 	$(NULL)
 
-if HAVE_PERL
+if HAVE_PYTHON
 
 plugin_SCRIPTS = nbdkit-tar-plugin
 CLEANFILES += nbdkit-tar-plugin
 
 # We have to do the rewriting here to avoid stupid exec_prefix.
-nbdkit-tar-plugin: $(source)
+nbdkit-tar-plugin: tar.py
 	rm -f $@ $@-t
 	sed 's,\@sbindir\@,${sbindir},g' < $< > $@-t
 	mv $@-t $@
@@ -54,8 +53,8 @@ if HAVE_POD
 man_MANS = nbdkit-tar-plugin.1
 CLEANFILES += $(man_MANS)
 
-nbdkit-tar-plugin.1: $(source)
-	$(PODWRAPPER) --section=1 --name nbdkit-tar-plugin --man $@ \
+nbdkit-tar-plugin.1: nbdkit-tar-plugin.pod
+	$(PODWRAPPER) --section=1 --man $@ \
 	    --html $(top_builddir)/html/$@.html \
 	    $<
 

plugins/tar/tar.pl → plugins/tar/nbdkit-tar-plugin.pod

@@ -1,8 +1,3 @@
-#!@sbindir@/nbdkit perl
-# -*- perl -*-
-
-=pod
-
 =head1 NAME
 
 nbdkit-tar-plugin - read and write files inside tar files without unpacking
@@ -94,11 +89,10 @@ =head1 VERSION
 
 =head1 SEE ALSO
 
-L<https://github.com/libguestfs/nbdkit/blob/master/plugins/tar/tar.pl>,
 L<nbdkit(1)>,
 L<nbdkit-offset-filter(1)>,
 L<nbdkit-plugin(3)>,
-L<nbdkit-perl-plugin(3)>,
+L<nbdkit-python-plugin(3)>,
 L<nbdkit-xz-filter(1)>,
 L<tar(1)>.
 
@@ -111,114 +105,3 @@ =head1 AUTHORS
 =head1 COPYRIGHT
 
 Copyright (C) 2017-2020 Red Hat Inc.
-
-=cut
-
-use strict;
-
-use Cwd qw(abs_path);
-use IO::File;
-
-my $tar;                        # Tar file.
-my $file;                       # File within the tar file.
-my $offset;                     # Offset within tar file.
-my $size;                       # Size of disk image within tar file.
-
-sub config
-{
-    my $k = shift;
-    my $v = shift;
-
-    if ($k eq "tar") {
-        $tar = abs_path ($v);
-    }
-    elsif ($k eq "file") {
-        $file = $v;
-    }
-    else {
-        die "unknown parameter $k";
-    }
-}
-
-# Check all the config parameters were set.
-sub config_complete
-{
-    die "tar or file parameter was not set\n"
-        unless defined $tar && defined $file;
-
-    die "$tar: file not found\n"
-        unless -f $tar;
-}
-
-# Find the extent of the file within the tar file.
-sub get_ready
-{
-    open (my $pipe, "-|", "tar", "--no-auto-compress", "-tRvf", $tar, $file)
-        or die "$tar: could not open or parse tar file, see errors above";
-    while (<$pipe>) {
-        if (/^block\s(\d+):\s\S+\s\S+\s(\d+)/) {
-            # Add one for the tar header, and multiply by the block size.
-            $offset = ($1 + 1) * 512;
-            $size = $2;
-            Nbdkit::debug ("tar: file: $file offset: $offset size: $size")
-        }
-    }
-    close ($pipe);
-
-    die "offset or size could not be parsed.  Probably the tar file is not a tar file or the file does not exist in the tar file.  See any errors above.\n"
-        unless defined $offset && defined $size;
-}
-
-# Accept a connection from a client, create and return the handle
-# which is passed back to other calls.
-sub open
-{
-    my $readonly = shift;
-    my $mode = "<";
-    $mode = "+<" unless $readonly;
-    my $fh = IO::File->new;
-    $fh->open ($tar, $mode) or die "$tar: open: $!";
-    $fh->binmode;
-    my $h = { fh => $fh, readonly => $readonly };
-    return $h;
-}
-
-# Close the connection.
-sub close
-{
-    my $h = shift;
-    my $fh = $h->{fh};
-    $fh->close;
-}
-
-# Return the size.
-sub get_size
-{
-    my $h = shift;
-    return $size;
-}
-
-# Read.
-sub pread
-{
-    my $h = shift;
-    my $fh = $h->{fh};
-    my $count = shift;
-    my $offs = shift;
-    $fh->seek ($offset + $offs, 0) or die "seek: $!";
-    my $r;
-    $fh->read ($r, $count) or die "read: $!";
-    return $r;
-}
-
-# Write.
-sub pwrite
-{
-    my $h = shift;
-    my $fh = $h->{fh};
-    my $buf = shift;
-    my $count = length ($buf);
-    my $offs = shift;
-    $fh->seek ($offset + $offs, 0) or die "seek: $!";
-    print $fh ($buf);
-}

plugins/tar/tar.py

@@ -0,0 +1,104 @@
+#!@sbindir@/nbdkit python
+# -*- python -*-
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+# Note this uses API v1 since we may wish to copy it and use it with
+# older versions of nbdkit.  Also it doesn't use get_ready() for the
+# same reason.
+
+import builtins
+import os.path
+import tarfile
+import nbdkit
+
+tar = None                      # Tar file.
+f = None                        # File within the tar file.
+offset = None                   # Offset of file within the tar file.
+size = None                     # Size of file within the tar file.
+
+def config(k, v):
+    global tar, f
+
+    if k == "tar":
+        tar = os.path.abspath(v)
+    elif k == "file":
+        f = v
+    else:
+        raise RuntimeError("unknown parameter: %s" % key)
+
+# Check all the config parameters were set.
+def config_complete():
+    global tar, f, offset, size
+
+    if tar is None or f is None:
+        raise RuntimeError("tar or file parameter was not set")
+    if not os.path.exists(tar):
+        raise RuntimeError("$s: file not found" % tar)
+
+    # Find the extent of the file within the tar file.
+    for m in tarfile.open(tar, mode='r:'):
+        if m.name == f:
+            offset = m.offset_data
+            size = m.size
+    if offset is None or size is None:
+        raise RuntimeError("offset or size could not be parsed.  Probably the tar file is not a tar file or the file does not exist in the tar file.")
+
+# Accept a connection from a client, create and return the handle
+# which is passed back to other calls.
+def open(readonly):
+    global tar
+    if readonly:
+        mode = 'rb'
+    else:
+        mode = 'r+b'
+    return { 'fh': builtins.open(tar, mode) }
+
+# Close the connection.
+def close(h):
+    h['fh'].close()
+
+# Return the size.
+def get_size(h):
+    global size
+    return size
+
+# Read.
+#
+# Python plugin thread model is always
+# NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS so seeking here is fine.
+def pread(h, count, offs):
+    global offset
+    h['fh'].seek(offset + offs)
+    return h['fh'].read(count)
+
+# Write.
+def pwrite(h, buf, offs):
+    global offset
+    h['fh'].seek(offset + offs)
+    h['fh'].write(buf)

tests/Makefile.am

@@ -828,10 +828,10 @@ test_streaming_SOURCES = test-streaming.c
 test_streaming_CFLAGS = $(WARNINGS_CFLAGS) $(LIBNBD_CFLAGS)
 test_streaming_LDADD = $(LIBNBD_LIBS)
 
-# tar plugin test (written in perl).
-if HAVE_PERL
+# tar plugin test (written in python).
+if HAVE_PYTHON
 TESTS += test-tar.sh
-endif HAVE_PERL
+endif HAVE_PYTHON
 EXTRA_DIST += test-tar.sh
 
 # tmpdisk plugin test.

tests/test-dump-plugin.sh

@@ -43,10 +43,10 @@ do_test ()
 {
     vg=; [ "$NBDKIT_VALGRIND" = "1" ] && vg="-valgrind"
     case "$1$vg" in
-        python-valgrind | ruby-valgrind | tcl-valgrind)
+        python-valgrind | ruby-valgrind | tar-valgrind | tcl-valgrind)
             echo "$0: skipping $1$vg because this language doesn't support valgrind"
             ;;
-        example4* | tar*)
+        example4*)
             # These tests are written in Perl so we have to check that
             # the Perl plugin was compiled.
             if nbdkit perl --version; then run_test $1; fi

tests/test-help-plugin.sh

@@ -43,10 +43,10 @@ do_test ()
 {
     vg=; [ "$NBDKIT_VALGRIND" = "1" ] && vg="-valgrind"
     case "$1$vg" in
-        python-valgrind | ruby-valgrind | tcl-valgrind)
+        python-valgrind | ruby-valgrind | tar-valgrind | tcl-valgrind)
             echo "$0: skipping $1$vg because this language doesn't support valgrind"
             ;;
-        example4* | tar*)
+        example4*)
             # These tests are written in Perl so we have to check that
             # the Perl plugin was compiled.
             if nbdkit perl --version; then run_test $1; fi

tests/test-tar.sh

@@ -34,14 +34,18 @@ source ./functions.sh
 set -e
 set -x
 
+# Python scripts break valgrind.
+if [ "$NBDKIT_VALGRIND" = "1" ]; then
+    echo "$0: skipping Python test under valgrind."
+    exit 77
+fi
+
 requires test -f disk
 requires guestfish --version
-requires tar --version
 
-# The tar plugin requires some Perl modules, this checks if they are
-# installed.
-requires perl -MCwd -e 1
-requires perl -MIO::File -e 1
+# The tar plugin is written in Python and uses the tarfile module.
+requires python --version
+requires python -c 'import tarfile'
 
 sock=`mktemp -u`
 files="tar.pid tar.tar $sock"
@@ -54,7 +58,15 @@ tar cf tar.tar disk
 # Run nbdkit.
 start_nbdkit -P tar.pid -U $sock tar tar=tar.tar file=disk
 
-# Now see if we can open the disk from the tar file.
-guestfish -x --ro --format=raw -a "nbd://?socket=$sock" -m /dev/sda1 <<EOF
+# Now see if we can open, read and write the disk from the tar file.
+guestfish -x --format=raw -a "nbd://?socket=$sock" -m /dev/sda1 <<EOF
+  # Check for existing file.
   cat /hello.txt
+
+  # Write a new file.
+  write /test.txt "hello"
+  cat /test.txt
 EOF
+
+# Check that the tar file isn't corrupt.
+tar tvvf tar.tar