1 files changed, 90 insertions, 0 deletions
diff --git a/t/lib-chunk/corrupt-chunk-file.pl b/t/lib-chunk/corrupt-chunk-file.pl
new file mode 100644
index 0000000..0e11aad
--- /dev/null
+++ b/t/lib-chunk/corrupt-chunk-file.pl
@@ -0,0 +1,90 @@
+#!/usr/bin/perl
+
+my ($chunk, $seek, $bytes) = @ARGV;
+$bytes =~ s/../chr(hex($&))/ge;
+
+binmode STDIN;
+binmode STDOUT;
+
+# A few helpers to read bytes, or read and copy them to the
+# output.
+sub get {
+	my $n = shift;
+	return unless $n;
+	read(STDIN, my $buf, $n)
+		or die "read error or eof: $!\n";
+	return $buf;
+}
+sub copy {
+	my $buf = get(@_);
+	print $buf;
+	return $buf;
+}
+
+# Some platforms' perl builds don't support 64-bit integers, and hence do not
+# allow packing/unpacking quadwords with "Q". The chunk format uses 64-bit file
+# offsets to support files of any size, but in practice our test suite will
+# only use small files. So we can fake it by asking for two 32-bit values and
+# discarding the first (most significant) one, which is equivalent as long as
+# it's just zero.
+sub unpack_quad {
+	my $bytes = shift;
+	my ($n1, $n2) = unpack("NN", $bytes);
+	die "quad value exceeds 32 bits" if $n1;
+	return $n2;
+}
+sub pack_quad {
+	my $n = shift;
+	my $ret = pack("NN", 0, $n);
+	# double check that our original $n did not exceed the 32-bit limit.
+	# This is presumably impossible on a 32-bit system (which would have
+	# truncated much earlier), but would still alert us on a 64-bit build
+	# of a new test that would fail on a 32-bit build (though we'd
+	# presumably see the die() from unpack_quad() in such a case).
+	die "quad round-trip failed" if unpack_quad($ret) != $n;
+	return $ret;
+}
+
+# read until we find table-of-contents entry for chunk;
+# note that we cheat a bit by assuming 4-byte alignment and
+# that no ToC entry will accidentally look like a header.
+#
+# If we don't find the entry, copy() will hit EOF and exit
+# (which should cause the caller to fail the test).
+while (copy(4) ne $chunk) { }
+my $offset = unpack_quad(copy(8));
+
+# In clear mode, our length will change. So figure out
+# the length by comparing to the offset of the next chunk, and
+# then adjust that offset (and all subsequent) ones.
+my $len;
+if ($seek eq "clear") {
+	my $id;
+	do {
+		$id = copy(4);
+		my $next = unpack_quad(get(8));
+		if (!defined $len) {
+			$len = $next - $offset;
+		}
+		print pack_quad($next - $len + length($bytes));
+	} while (unpack("N", $id));
+}
+
+# and now copy up to our existing chunk data
+copy($offset - tell(STDIN));
+if ($seek eq "clear") {
+	# if clearing, skip past existing data
+	get($len);
+} else {
+	# otherwise, copy up to the requested offset,
+	# and skip past the overwritten bytes
+	copy($seek);
+	get(length($bytes));
+}
+
+# now write out the requested bytes, along
+# with any other remaining data
+print $bytes;
+while (read(STDIN, my $buf, 4096)) {
+	print $buf;
+}