2 files changed, 151 insertions, 0 deletions
diff --git a/t/lib-pack.sh b/t/lib-pack.sh
new file mode 100644
index 0000000000..fecd5a0279
--- /dev/null
+++ b/t/lib-pack.sh
@@ -0,0 +1,78 @@
+#!/bin/sh
+#
+# Support routines for hand-crafting weird or malicious packs.
+#
+# You can make a complete pack like:
+#
+#   pack_header 2 >foo.pack &&
+#   pack_obj e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 >>foo.pack &&
+#   pack_obj e68fe8129b546b101aee9510c5328e7f21ca1d18 >>foo.pack &&
+#   pack_trailer foo.pack
+
+# Print the big-endian 4-byte octal representation of $1
+uint32_octal () {
+	n=$1
+	printf '\%o' $(($n / 16777216)); n=$((n % 16777216))
+	printf '\%o' $(($n /    65536)); n=$((n %    65536))
+	printf '\%o' $(($n /      256)); n=$((n %      256))
+	printf '\%o' $(($n           ));
+}
+
+# Print the big-endian 4-byte binary representation of $1
+uint32_binary () {
+	printf "$(uint32_octal "$1")"
+}
+
+# Print a pack header, version 2, for a pack with $1 objects
+pack_header () {
+	printf 'PACK' &&
+	printf '\0\0\0\2' &&
+	uint32_binary "$1"
+}
+
+# Print the pack data for object $1, as a delta against object $2 (or as a full
+# object if $2 is missing or empty). The output is suitable for including
+# directly in the packfile, and represents the entirety of the object entry.
+# Doing this on the fly (especially picking your deltas) is quite tricky, so we
+# have hardcoded some well-known objects. See the case statements below for the
+# complete list.
+pack_obj () {
+	case "$1" in
+	# empty blob
+	e69de29bb2d1d6434b8b29ae775ad8c2e48c5391)
+		case "$2" in
+		'')
+			printf '\060\170\234\003\0\0\0\0\1'
+			return
+			;;
+		esac
+		;;
+
+	# blob containing "\7\76"
+	e68fe8129b546b101aee9510c5328e7f21ca1d18)
+		case "$2" in
+		'')
+			printf '\062\170\234\143\267\3\0\0\116\0\106'
+			return
+			;;
+		esac
+		;;
+	esac
+
+	echo >&2 "BUG: don't know how to print $1${2:+ (from $2)}"
+	return 1
+}
+
+# Compute and append pack trailer to "$1"
+pack_trailer () {
+	test-sha1 -b <"$1" >trailer.tmp &&
+	cat trailer.tmp >>"$1" &&
+	rm -f trailer.tmp
+}
+
+# Remove any existing packs to make sure that
+# whatever we index next will be the pack that we
+# actually use.
+clear_packs () {
+	rm -f .git/objects/pack/*
+}
diff --git a/t/t5308-pack-detect-duplicates.sh b/t/t5308-pack-detect-duplicates.sh
new file mode 100755
index 0000000000..04fe242410
--- /dev/null
+++ b/t/t5308-pack-detect-duplicates.sh
@@ -0,0 +1,73 @@
+#!/bin/sh
+
+test_description='handling of duplicate objects in incoming packfiles'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-pack.sh
+
+# The sha1s we have in our pack. It's important that these have the same
+# starting byte, so that they end up in the same fanout section of the index.
+# That lets us make sure we are exercising the binary search with both sets.
+LO_SHA1=e68fe8129b546b101aee9510c5328e7f21ca1d18
+HI_SHA1=e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
+
+# And here's a "missing sha1" which will produce failed lookups. It must also
+# be in the same fanout section, and should be between the two (so that during
+# our binary search, we are sure to end up looking at one or the other of the
+# duplicate runs).
+MISSING_SHA1='e69d000000000000000000000000000000000000'
+
+# git will never intentionally create packfiles with
+# duplicate objects, so we have to construct them by hand.
+#
+# $1 is the name of the packfile to create
+#
+# $2 is the number of times to duplicate each object
+create_pack () {
+	pack_header "$((2 * $2))" >"$1" &&
+	for i in $(test_seq 1 "$2"); do
+		pack_obj $LO_SHA1 &&
+		pack_obj $HI_SHA1
+	done >>"$1" &&
+	pack_trailer "$1"
+}
+
+# double-check that create_pack actually works
+test_expect_success 'pack with no duplicates' '
+	create_pack no-dups.pack 1 &&
+	git index-pack --stdin <no-dups.pack
+'
+
+test_expect_success 'index-pack will allow duplicate objects by default' '
+	clear_packs &&
+	create_pack dups.pack 100 &&
+	git index-pack --stdin <dups.pack
+'
+
+test_expect_success 'create batch-check test vectors' '
+	cat >input <<-EOF &&
+	$LO_SHA1
+	$HI_SHA1
+	$MISSING_SHA1
+	EOF
+	cat >expect <<-EOF
+	$LO_SHA1 blob 2
+	$HI_SHA1 blob 0
+	$MISSING_SHA1 missing
+	EOF
+'
+
+test_expect_success 'lookup in duplicated pack (binary search)' '
+	git cat-file --batch-check <input >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'lookup in duplicated pack (GIT_USE_LOOKUP)' '
+	(
+		GIT_USE_LOOKUP=1 &&
+		export GIT_USE_LOOKUP &&
+		git cat-file --batch-check <input >actual
+	) &&
+	test_cmp expect actual
+'
+
+test_done