v4, 3 partst0021: avoid grepping for a Perl-specific string at filter output

diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index 1c840348bd..963b66e08c 100755
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -735,7 +735,7 @@ test_expect_success PERL 'process filter should restart after unexpected write f
 		rm -f debug.log &&
 		git checkout --quiet --no-progress . 2>git-stderr.log &&
 
-		grep "smudge write error at" git-stderr.log &&
+		grep "smudge write error" git-stderr.log &&
 		test_i18ngrep "error: external filter" git-stderr.log &&
 
 		cat >expected.log <<-EOF &&

Makefile, pkt-line.c, pkt-line.h, t/helper/test-rot13-filter.c, t/helper/test-tool.c, t/helper/test-tool.h

diff --git a/Makefile b/Makefile
index 2ec9b2dc6b..ae7def7c66 100644
--- a/Makefile
+++ b/Makefile
@@ -772,6 +772,7 @@ TEST_BUILTINS_OBJS += test-read-midx.o
 TEST_BUILTINS_OBJS += test-ref-store.o
 TEST_BUILTINS_OBJS += test-reftable.o
 TEST_BUILTINS_OBJS += test-regex.o
+TEST_BUILTINS_OBJS += test-rot13-filter.o
 TEST_BUILTINS_OBJS += test-repository.o
 TEST_BUILTINS_OBJS += test-revision-walking.o
 TEST_BUILTINS_OBJS += test-run-command.o
diff --git a/pkt-line.c b/pkt-line.c
index 8e43c2def4..ce4e73b683 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -309,7 +309,8 @@ int write_packetized_from_fd_no_flush(int fd_in, int fd_out)
 	return err;
 }
 
-int write_packetized_from_buf_no_flush(const char *src_in, size_t len, int fd_out)
+int write_packetized_from_buf_no_flush_count(const char *src_in, size_t len,
+					     int fd_out, int *packet_counter)
 {
 	int err = 0;
 	size_t bytes_written = 0;
@@ -324,6 +325,8 @@ int write_packetized_from_buf_no_flush(const char *src_in, size_t len, int fd_ou
 			break;
 		err = packet_write_gently(fd_out, src_in + bytes_written, bytes_to_write);
 		bytes_written += bytes_to_write;
+		if (packet_counter)
+			(*packet_counter)++;
 	}
 	return err;
 }
diff --git a/pkt-line.h b/pkt-line.h
index 1f623de60a..79c538b99e 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -32,7 +32,13 @@ void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((f
 int packet_flush_gently(int fd);
 int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 int write_packetized_from_fd_no_flush(int fd_in, int fd_out);
-int write_packetized_from_buf_no_flush(const char *src_in, size_t len, int fd_out);
+int write_packetized_from_buf_no_flush_count(const char *src_in, size_t len,
+					     int fd_out, int *packet_counter);
+static inline int write_packetized_from_buf_no_flush(const char *src_in,
+						     size_t len, int fd_out)
+{
+	return write_packetized_from_buf_no_flush_count(src_in, len, fd_out, NULL);
+}
 
 /*
  * Stdio versions of packet_write functions. When mixing these with fd
diff --git a/t/helper/test-rot13-filter.c b/t/helper/test-rot13-filter.c
new file mode 100644
index 0000000000..f8d564c622
--- /dev/null
+++ b/t/helper/test-rot13-filter.c
@@ -0,0 +1,382 @@
+/*
+ * Example implementation for the Git filter protocol version 2
+ * See Documentation/gitattributes.txt, section "Filter Protocol"
+ *
+ * Usage: test-tool rot13-filter [--always-delay] --log=<path> <capabilities>
+ *
+ * Log path defines a debug log file that the script writes to. The
+ * subsequent arguments define a list of supported protocol capabilities
+ * ("clean", "smudge", etc).
+ *
+ * When --always-delay is given all pathnames with the "can-delay" flag
+ * that don't appear on the list bellow are delayed with a count of 1
+ * (see more below).
+ *
+ * This implementation supports special test cases:
+ * (1) If data with the pathname "clean-write-fail.r" is processed with
+ *     a "clean" operation then the write operation will die.
+ * (2) If data with the pathname "smudge-write-fail.r" is processed with
+ *     a "smudge" operation then the write operation will die.
+ * (3) If data with the pathname "error.r" is processed with any
+ *     operation then the filter signals that it cannot or does not want
+ *     to process the file.
+ * (4) If data with the pathname "abort.r" is processed with any
+ *     operation then the filter signals that it cannot or does not want
+ *     to process the file and any file after that is processed with the
+ *     same command.
+ * (5) If data with a pathname that is a key in the delay hash is
+ *     requested (e.g. "test-delay10.a") then the filter responds with
+ *     a "delay" status and sets the "requested" field in the delay hash.
+ *     The filter will signal the availability of this object after
+ *     "count" (field in delay hash) "list_available_blobs" commands.
+ * (6) If data with the pathname "missing-delay.a" is processed that the
+ *     filter will drop the path from the "list_available_blobs" response.
+ * (7) If data with the pathname "invalid-delay.a" is processed that the
+ *     filter will add the path "unfiltered" which was not delayed before
+ *     to the "list_available_blobs" response.
+ */
+
+#include "test-tool.h"
+#include "pkt-line.h"
+#include "string-list.h"
+#include "strmap.h"
+#include "parse-options.h"
+
+static FILE *logfile;
+static int always_delay, has_clean_cap, has_smudge_cap;
+static struct strmap delay = STRMAP_INIT;
+
+static inline const char *str_or_null(const char *str)
+{
+	return str ? str : "(null)";
+}
+
+static char *rot13(char *str)
+{
+	char *c;
+	for (c = str; *c; c++)
+		if (isalpha(*c))
+			*c += tolower(*c) < 'n' ? 13 : -13;
+	return str;
+}
+
+static char *get_value(char *buf, const char *key)
+{
+	const char *orig_buf = buf;
+	if (!buf ||
+	    !skip_prefix((const char *)buf, key, (const char **)&buf) ||
+	    !skip_prefix((const char *)buf, "=", (const char **)&buf) ||
+	    !*buf)
+		die("expected key '%s', got '%s'", key, str_or_null(orig_buf));
+	return buf;
+}
+
+/*
+ * Read a text packet, expecting that it is in the form "key=value" for
+ * the given key. An EOF does not trigger any error and is reported
+ * back to the caller with NULL. Die if the "key" part of "key=value" does
+ * not match the given key, or the value part is empty.
+ */
+static char *packet_key_val_read(const char *key)
+{
+	char *buf;
+	if (packet_read_line_gently(0, NULL, &buf) < 0)
+		return NULL;
+	return xstrdup(get_value(buf, key));
+}
+
+static inline void assert_remote_capability(struct strset *caps, const char *cap)
+{
+	if (!strset_contains(caps, cap))
+		die("required '%s' capability not available from remote", cap);
+}
+
+static void read_capabilities(struct strset *remote_caps)
+{
+	for (;;) {
+		char *buf = packet_read_line(0, NULL);
+		if (!buf)
+			break;
+		strset_add(remote_caps, get_value(buf, "capability"));
+	}
+
+	assert_remote_capability(remote_caps, "clean");
+	assert_remote_capability(remote_caps, "smudge");
+	assert_remote_capability(remote_caps, "delay");
+}
+
+static void check_and_write_capabilities(struct strset *remote_caps,
+					 const char **caps, int nr_caps)
+{
+	int i;
+	for (i = 0; i < nr_caps; i++) {
+		if (!strset_contains(remote_caps, caps[i]))
+			die("our capability '%s' is not available from remote",
+			    caps[i]);
+		packet_write_fmt(1, "capability=%s\n", caps[i]);
+	}
+	packet_flush(1);
+}
+
+struct delay_entry {
+	int requested, count;
+	char *output;
+};
+
+static void free_delay_entries(void)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *ent;
+
+	strmap_for_each_entry(&delay, &iter, ent) {
+		struct delay_entry *delay_entry = ent->value;
+		free(delay_entry->output);
+		free(delay_entry);
+	}
+	strmap_clear(&delay, 0);
+}
+
+static void add_delay_entry(char *pathname, int count, int requested)
+{
+	struct delay_entry *entry = xcalloc(1, sizeof(*entry));
+	entry->count = count;
+	entry->requested = requested;
+	if (strmap_put(&delay, pathname, entry))
+		BUG("adding the same path twice to delay hash?");
+}
+
+static void reply_list_available_blobs_cmd(void)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *ent;
+	struct string_list_item *str_item;
+	struct string_list paths = STRING_LIST_INIT_NODUP;
+
+	/* flush */
+	if (packet_read_line(0, NULL))
+		die("bad list_available_blobs end");
+
+	strmap_for_each_entry(&delay, &iter, ent) {
+		struct delay_entry *delay_entry = ent->value;
+		if (!delay_entry->requested)
+			continue;
+		delay_entry->count--;
+		if (!strcmp(ent->key, "invalid-delay.a")) {
+			/* Send Git a pathname that was not delayed earlier */
+			packet_write_fmt(1, "pathname=unfiltered");
+		}
+		if (!strcmp(ent->key, "missing-delay.a")) {
+			/* Do not signal Git that this file is available */
+		} else if (!delay_entry->count) {
+			string_list_append(&paths, ent->key);
+			packet_write_fmt(1, "pathname=%s", ent->key);
+		}
+	}
+
+	/* Print paths in sorted order. */
+	string_list_sort(&paths);
+	for_each_string_list_item(str_item, &paths)
+		fprintf(logfile, " %s", str_item->string);
+	string_list_clear(&paths, 0);
+
+	packet_flush(1);
+
+	fprintf(logfile, " [OK]\n");
+	packet_write_fmt(1, "status=success");
+	packet_flush(1);
+}
+
+static void command_loop(void)
+{
+	for (;;) {
+		char *buf, *output;
+		char *pathname;
+		struct delay_entry *entry;
+		struct strbuf input = STRBUF_INIT;
+		char *command = packet_key_val_read("command");
+
+		if (!command) {
+			fprintf(logfile, "STOP\n");
+			break;
+		}
+		fprintf(logfile, "IN: %s", command);
+
+		if (!strcmp(command, "list_available_blobs")) {
+			reply_list_available_blobs_cmd();
+			free(command);
+			continue;
+		}
+
+		pathname = packet_key_val_read("pathname");
+		if (!pathname)
+			die("unexpected EOF while expecting pathname");
+		fprintf(logfile, " %s", pathname);
+
+		/* Read until flush */
+		while ((buf = packet_read_line(0, NULL))) {
+			if (!strcmp(buf, "can-delay=1")) {
+				entry = strmap_get(&delay, pathname);
+				if (entry && !entry->requested)
+					entry->requested = 1;
+				else if (!entry && always_delay)
+					add_delay_entry(pathname, 1, 1);
+			} else if (starts_with(buf, "ref=") ||
+				   starts_with(buf, "treeish=") ||
+				   starts_with(buf, "blob=")) {
+				fprintf(logfile, " %s", buf);
+			} else {
+				/*
+				 * In general, filters need to be graceful about
+				 * new metadata, since it's documented that we
+				 * can pass any key-value pairs, but for tests,
+				 * let's be a little stricter.
+				 */
+				die("Unknown message '%s'", buf);
+			}
+		}
+
+		read_packetized_to_strbuf(0, &input, 0);
+		fprintf(logfile, " %"PRIuMAX" [OK] -- ", (uintmax_t)input.len);
+
+		entry = strmap_get(&delay, pathname);
+		if (entry && entry->output) {
+			output = entry->output;
+		} else if (!strcmp(pathname, "error.r") || !strcmp(pathname, "abort.r")) {
+			output = "";
+		} else if (!strcmp(command, "clean") && has_clean_cap) {
+			output = rot13(input.buf);
+		} else if (!strcmp(command, "smudge") && has_smudge_cap) {
+			output = rot13(input.buf);
+		} else {
+			die("bad command '%s'", command);
+		}
+
+		if (!strcmp(pathname, "error.r")) {
+			fprintf(logfile, "[ERROR]\n");
+			packet_write_fmt(1, "status=error");
+			packet_flush(1);
+		} else if (!strcmp(pathname, "abort.r")) {
+			fprintf(logfile, "[ABORT]\n");
+			packet_write_fmt(1, "status=abort");
+			packet_flush(1);
+		} else if (!strcmp(command, "smudge") &&
+			   (entry = strmap_get(&delay, pathname)) &&
+			   entry->requested == 1) {
+			fprintf(logfile, "[DELAYED]\n");
+			packet_write_fmt(1, "status=delayed");
+			packet_flush(1);
+			entry->requested = 2;
+			if (entry->output != output) {
+				free(entry->output);
+				entry->output = xstrdup(output);
+			}
+		} else {
+			int i, nr_packets = 0;
+			size_t output_len;
+			const char *p;
+			packet_write_fmt(1, "status=success");
+			packet_flush(1);
+
+			if (skip_prefix(pathname, command, &p) &&
+			    !strcmp(p, "-write-fail.r")) {
+				fprintf(logfile, "[WRITE FAIL]\n");
+				die("%s write error", command);
+			}
+
+			output_len = strlen(output);
+			fprintf(logfile, "OUT: %"PRIuMAX" ", (uintmax_t)output_len);
+
+			if (write_packetized_from_buf_no_flush_count(output,
+				output_len, 1, &nr_packets))
+				die("failed to write buffer to stdout");
+			packet_flush(1);
+
+			for (i = 0; i < nr_packets; i++)
+				fprintf(logfile, ".");
+			fprintf(logfile, " [OK]\n");
+
+			packet_flush(1);
+		}
+		free(pathname);
+		strbuf_release(&input);
+		free(command);
+	}
+}
+
+static void packet_initialize(void)
+{
+	char *pkt_buf = packet_read_line(0, NULL);
+
+	if (!pkt_buf || strcmp(pkt_buf, "git-filter-client"))
+		die("bad initialize: '%s'", str_or_null(pkt_buf));
+
+	pkt_buf = packet_read_line(0, NULL);
+	if (!pkt_buf || strcmp(pkt_buf, "version=2"))
+		die("bad version: '%s'", str_or_null(pkt_buf));
+
+	pkt_buf = packet_read_line(0, NULL);
+	if (pkt_buf)
+		die("bad version end: '%s'", pkt_buf);
+
+	packet_write_fmt(1, "git-filter-server");
+	packet_write_fmt(1, "version=2");
+	packet_flush(1);
+}
+
+static const char *rot13_usage[] = {
+	"test-tool rot13-filter [--always-delay] --log=<path> <capabilities>",
+	NULL
+};
+
+int cmd__rot13_filter(int argc, const char **argv)
+{
+	int i, nr_caps;
+	struct strset remote_caps = STRSET_INIT;
+	const char *log_path = NULL;
+
+	struct option options[] = {
+		OPT_BOOL(0, "always-delay", &always_delay,
+			 "delay all paths with the can-delay flag"),
+		OPT_STRING(0, "log", &log_path, "path",
+			   "path to the debug log file"),
+		OPT_END()
+	};
+	nr_caps = parse_options(argc, argv, NULL, options, rot13_usage,
+				PARSE_OPT_STOP_AT_NON_OPTION);
+
+	if (!log_path || !nr_caps)
+		usage_with_options(rot13_usage, options);
+
+	logfile = fopen(log_path, "a");
+	if (!logfile)
+		die_errno("failed to open log file");
+
+	for (i = 0; i < nr_caps; i++) {
+		if (!strcmp(argv[i], "smudge"))
+			has_smudge_cap = 1;
+		if (!strcmp(argv[i], "clean"))
+			has_clean_cap = 1;
+	}
+
+	add_delay_entry("test-delay10.a", 1, 0);
+	add_delay_entry("test-delay11.a", 1, 0);
+	add_delay_entry("test-delay20.a", 2, 0);
+	add_delay_entry("test-delay10.b", 1, 0);
+	add_delay_entry("missing-delay.a", 1, 0);
+	add_delay_entry("invalid-delay.a", 1, 0);
+
+	fprintf(logfile, "START\n");
+	packet_initialize();
+
+	read_capabilities(&remote_caps);
+	check_and_write_capabilities(&remote_caps, argv, nr_caps);
+	fprintf(logfile, "init handshake complete\n");
+	strset_clear(&remote_caps);
+
+	command_loop();
+
+	if (fclose(logfile))
+		die_errno("error closing logfile");
+	free_delay_entries();
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 318fdbab0c..d6a560f832 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -65,6 +65,7 @@ static struct test_cmd cmds[] = {
 	{ "read-midx", cmd__read_midx },
 	{ "ref-store", cmd__ref_store },
 	{ "reftable", cmd__reftable },
+	{ "rot13-filter", cmd__rot13_filter },
 	{ "dump-reftable", cmd__dump_reftable },
 	{ "regex", cmd__regex },
 	{ "repository", cmd__repository },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index bb79927163..21a91b1019 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -54,6 +54,7 @@ int cmd__read_cache(int argc, const char **argv);
 int cmd__read_graph(int argc, const char **argv);
 int cmd__read_midx(int argc, const char **argv);
 int cmd__ref_store(int argc, const char **argv);
+int cmd__rot13_filter(int argc, const char **argv);
 int cmd__reftable(int argc, const char **argv);
 int cmd__regex(int argc, const char **argv);
 int cmd__repository(int argc, const char **argv);

t/t0021-conversion.sh, t/t0021/rot13-filter.pl, t/t2080-parallel-checkout-basics.sh, t/t2082-parallel-checkout-attributes.sh

diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index 963b66e08c..abecd75e4e 100755
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -17,9 +17,6 @@ tr \
   'nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM'
 EOF
 
-write_script rot13-filter.pl "$PERL_PATH" \
-	<"$TEST_DIRECTORY"/t0021/rot13-filter.pl
-
 generate_random_characters () {
 	LEN=$1
 	NAME=$2
@@ -365,8 +362,8 @@ test_expect_success 'diff does not reuse worktree files that need cleaning' '
 	test_line_count = 0 count
 '
 
-test_expect_success PERL 'required process filter should filter data' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'required process filter should filter data' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	test_config_global filter.protocol.required true &&
 	rm -rf repo &&
 	mkdir repo &&
@@ -450,8 +447,8 @@ test_expect_success PERL 'required process filter should filter data' '
 	)
 '
 
-test_expect_success PERL 'required process filter should filter data for various subcommands' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'required process filter should filter data for various subcommands' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	test_config_global filter.protocol.required true &&
 	(
 		cd repo &&
@@ -561,9 +558,9 @@ test_expect_success PERL 'required process filter should filter data for various
 	)
 '
 
-test_expect_success PERL 'required process filter takes precedence' '
+test_expect_success 'required process filter takes precedence' '
 	test_config_global filter.protocol.clean false &&
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean" &&
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean" &&
 	test_config_global filter.protocol.required true &&
 	rm -rf repo &&
 	mkdir repo &&
@@ -587,8 +584,8 @@ test_expect_success PERL 'required process filter takes precedence' '
 	)
 '
 
-test_expect_success PERL 'required process filter should be used only for "clean" operation only' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean" &&
+test_expect_success 'required process filter should be used only for "clean" operation only' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean" &&
 	rm -rf repo &&
 	mkdir repo &&
 	(
@@ -622,8 +619,8 @@ test_expect_success PERL 'required process filter should be used only for "clean
 	)
 '
 
-test_expect_success PERL 'required process filter should process multiple packets' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'required process filter should process multiple packets' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	test_config_global filter.protocol.required true &&
 
 	rm -rf repo &&
@@ -687,8 +684,8 @@ test_expect_success PERL 'required process filter should process multiple packet
 	)
 '
 
-test_expect_success PERL 'required process filter with clean error should fail' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'required process filter with clean error should fail' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	test_config_global filter.protocol.required true &&
 	rm -rf repo &&
 	mkdir repo &&
@@ -706,8 +703,8 @@ test_expect_success PERL 'required process filter with clean error should fail'
 	)
 '
 
-test_expect_success PERL 'process filter should restart after unexpected write failure' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'process filter should restart after unexpected write failure' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	rm -rf repo &&
 	mkdir repo &&
 	(
@@ -761,8 +758,8 @@ test_expect_success PERL 'process filter should restart after unexpected write f
 	)
 '
 
-test_expect_success PERL 'process filter should not be restarted if it signals an error' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'process filter should not be restarted if it signals an error' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	rm -rf repo &&
 	mkdir repo &&
 	(
@@ -804,8 +801,8 @@ test_expect_success PERL 'process filter should not be restarted if it signals a
 	)
 '
 
-test_expect_success PERL 'process filter abort stops processing of all further files' '
-	test_config_global filter.protocol.process "rot13-filter.pl debug.log clean smudge" &&
+test_expect_success 'process filter abort stops processing of all further files' '
+	test_config_global filter.protocol.process "test-tool rot13-filter --log=debug.log clean smudge" &&
 	rm -rf repo &&
 	mkdir repo &&
 	(
@@ -861,10 +858,10 @@ test_expect_success PERL 'invalid process filter must fail (and not hang!)' '
 	)
 '
 
-test_expect_success PERL 'delayed checkout in process filter' '
-	test_config_global filter.a.process "rot13-filter.pl a.log clean smudge delay" &&
+test_expect_success 'delayed checkout in process filter' '
+	test_config_global filter.a.process "test-tool rot13-filter --log=a.log clean smudge delay" &&
 	test_config_global filter.a.required true &&
-	test_config_global filter.b.process "rot13-filter.pl b.log clean smudge delay" &&
+	test_config_global filter.b.process "test-tool rot13-filter --log=b.log clean smudge delay" &&
 	test_config_global filter.b.required true &&
 
 	rm -rf repo &&
@@ -940,8 +937,8 @@ test_expect_success PERL 'delayed checkout in process filter' '
 	)
 '
 
-test_expect_success PERL 'missing file in delayed checkout' '
-	test_config_global filter.bug.process "rot13-filter.pl bug.log clean smudge delay" &&
+test_expect_success 'missing file in delayed checkout' '
+	test_config_global filter.bug.process "test-tool rot13-filter --log=bug.log clean smudge delay" &&
 	test_config_global filter.bug.required true &&
 
 	rm -rf repo &&
@@ -960,8 +957,8 @@ test_expect_success PERL 'missing file in delayed checkout' '
 	grep "error: .missing-delay\.a. was not filtered properly" git-stderr.log
 '
 
-test_expect_success PERL 'invalid file in delayed checkout' '
-	test_config_global filter.bug.process "rot13-filter.pl bug.log clean smudge delay" &&
+test_expect_success 'invalid file in delayed checkout' '
+	test_config_global filter.bug.process "test-tool rot13-filter --log=bug.log clean smudge delay" &&
 	test_config_global filter.bug.required true &&
 
 	rm -rf repo &&
@@ -990,10 +987,10 @@ do
 		mode_prereq='UTF8_NFD_TO_NFC' ;;
 	esac
 
-	test_expect_success PERL,SYMLINKS,$mode_prereq \
+	test_expect_success SYMLINKS,$mode_prereq \
 	"delayed checkout with $mode-collision don't write to the wrong place" '
 		test_config_global filter.delay.process \
-			"\"$TEST_ROOT/rot13-filter.pl\" --always-delay delayed.log clean smudge delay" &&
+			"test-tool rot13-filter --always-delay --log=delayed.log clean smudge delay" &&
 		test_config_global filter.delay.required true &&
 
 		git init $mode-collision &&
@@ -1026,12 +1023,12 @@ do
 	'
 done
 
-test_expect_success PERL,SYMLINKS,CASE_INSENSITIVE_FS \
+test_expect_success SYMLINKS,CASE_INSENSITIVE_FS \
 "delayed checkout with submodule collision don't write to the wrong place" '
 	git init collision-with-submodule &&
 	(
 		cd collision-with-submodule &&
-		git config filter.delay.process "\"$TEST_ROOT/rot13-filter.pl\" --always-delay delayed.log clean smudge delay" &&
+		git config filter.delay.process "test-tool rot13-filter --always-delay --log=delayed.log clean smudge delay" &&
 		git config filter.delay.required true &&
 
 		# We need Git to treat the submodule "a" and the
@@ -1062,11 +1059,11 @@ test_expect_success PERL,SYMLINKS,CASE_INSENSITIVE_FS \
 	)
 '
 
-test_expect_success PERL 'setup for progress tests' '
+test_expect_success 'setup for progress tests' '
 	git init progress &&
 	(
 		cd progress &&
-		git config filter.delay.process "rot13-filter.pl delay-progress.log clean smudge delay" &&
+		git config filter.delay.process "test-tool rot13-filter --log=delay-progress.log clean smudge delay" &&
 		git config filter.delay.required true &&
 
 		echo "*.a filter=delay" >.gitattributes &&
@@ -1132,12 +1129,12 @@ do
 	'
 done
 
-test_expect_success PERL 'delayed checkout correctly reports the number of updated entries' '
+test_expect_success 'delayed checkout correctly reports the number of updated entries' '
 	rm -rf repo &&
 	git init repo &&
 	(
 		cd repo &&
-		git config filter.delay.process "../rot13-filter.pl delayed.log clean smudge delay" &&
+		git config filter.delay.process "test-tool rot13-filter --log=delayed.log clean smudge delay" &&
 		git config filter.delay.required true &&
 
 		echo "*.a filter=delay" >.gitattributes &&
diff --git a/t/t0021/rot13-filter.pl b/t/t0021/rot13-filter.pl
deleted file mode 100644
index 7bb93768f3..0000000000
--- a/t/t0021/rot13-filter.pl
+++ /dev/null
@@ -1,247 +0,0 @@
-#
-# Example implementation for the Git filter protocol version 2
-# See Documentation/gitattributes.txt, section "Filter Protocol"
-#
-# Usage: rot13-filter.pl [--always-delay] <log path> <capabilities>
-#
-# Log path defines a debug log file that the script writes to. The
-# subsequent arguments define a list of supported protocol capabilities
-# ("clean", "smudge", etc).
-#
-# When --always-delay is given all pathnames with the "can-delay" flag
-# that don't appear on the list bellow are delayed with a count of 1
-# (see more below).
-#
-# This implementation supports special test cases:
-# (1) If data with the pathname "clean-write-fail.r" is processed with
-#     a "clean" operation then the write operation will die.
-# (2) If data with the pathname "smudge-write-fail.r" is processed with
-#     a "smudge" operation then the write operation will die.
-# (3) If data with the pathname "error.r" is processed with any
-#     operation then the filter signals that it cannot or does not want
-#     to process the file.
-# (4) If data with the pathname "abort.r" is processed with any
-#     operation then the filter signals that it cannot or does not want
-#     to process the file and any file after that is processed with the
-#     same command.
-# (5) If data with a pathname that is a key in the DELAY hash is
-#     requested (e.g. "test-delay10.a") then the filter responds with
-#     a "delay" status and sets the "requested" field in the DELAY hash.
-#     The filter will signal the availability of this object after
-#     "count" (field in DELAY hash) "list_available_blobs" commands.
-# (6) If data with the pathname "missing-delay.a" is processed that the
-#     filter will drop the path from the "list_available_blobs" response.
-# (7) If data with the pathname "invalid-delay.a" is processed that the
-#     filter will add the path "unfiltered" which was not delayed before
-#     to the "list_available_blobs" response.
-#
-
-use 5.008;
-sub gitperllib {
-	# Git assumes that all path lists are Unix-y colon-separated ones. But
-	# when the Git for Windows executes the test suite, its MSYS2 Bash
-	# calls git.exe, and colon-separated path lists are converted into
-	# Windows-y semicolon-separated lists of *Windows* paths (which
-	# naturally contain a colon after the drive letter, so splitting by
-	# colons simply does not cut it).
-	#
-	# Detect semicolon-separated path list and handle them appropriately.
-
-	if ($ENV{GITPERLLIB} =~ /;/) {
-		return split(/;/, $ENV{GITPERLLIB});
-	}
-	return split(/:/, $ENV{GITPERLLIB});
-}
-use lib (gitperllib());
-use strict;
-use warnings;
-use IO::File;
-use Git::Packet;
-
-my $MAX_PACKET_CONTENT_SIZE = 65516;
-
-my $always_delay = 0;
-if ( $ARGV[0] eq '--always-delay' ) {
-	$always_delay = 1;
-	shift @ARGV;
-}
-
-my $log_file                = shift @ARGV;
-my @capabilities            = @ARGV;
-
-open my $debug, ">>", $log_file or die "cannot open log file: $!";
-
-my %DELAY = (
-	'test-delay10.a' => { "requested" => 0, "count" => 1 },
-	'test-delay11.a' => { "requested" => 0, "count" => 1 },
-	'test-delay20.a' => { "requested" => 0, "count" => 2 },
-	'test-delay10.b' => { "requested" => 0, "count" => 1 },
-	'missing-delay.a' => { "requested" => 0, "count" => 1 },
-	'invalid-delay.a' => { "requested" => 0, "count" => 1 },
-);
-
-sub rot13 {
-	my $str = shift;
-	$str =~ y/A-Za-z/N-ZA-Mn-za-m/;
-	return $str;
-}
-
-print $debug "START\n";
-$debug->flush();
-
-packet_initialize("git-filter", 2);
-
-my %remote_caps = packet_read_and_check_capabilities("clean", "smudge", "delay");
-packet_check_and_write_capabilities(\%remote_caps, @capabilities);
-
-print $debug "init handshake complete\n";
-$debug->flush();
-
-while (1) {
-	my ( $res, $command ) = packet_key_val_read("command");
-	if ( $res == -1 ) {
-		print $debug "STOP\n";
-		exit();
-	}
-	print $debug "IN: $command";
-	$debug->flush();
-
-	if ( $command eq "list_available_blobs" ) {
-		# Flush
-		packet_compare_lists([1, ""], packet_bin_read()) ||
-			die "bad list_available_blobs end";
-
-		foreach my $pathname ( sort keys %DELAY ) {
-			if ( $DELAY{$pathname}{"requested"} >= 1 ) {
-				$DELAY{$pathname}{"count"} = $DELAY{$pathname}{"count"} - 1;
-				if ( $pathname eq "invalid-delay.a" ) {
-					# Send Git a pathname that was not delayed earlier
-					packet_txt_write("pathname=unfiltered");
-				}
-				if ( $pathname eq "missing-delay.a" ) {
-					# Do not signal Git that this file is available
-				} elsif ( $DELAY{$pathname}{"count"} == 0 ) {
-					print $debug " $pathname";
-					packet_txt_write("pathname=$pathname");
-				}
-			}
-		}
-
-		packet_flush();
-
-		print $debug " [OK]\n";
-		$debug->flush();
-		packet_txt_write("status=success");
-		packet_flush();
-	} else {
-		my ( $res, $pathname ) = packet_key_val_read("pathname");
-		if ( $res == -1 ) {
-			die "unexpected EOF while expecting pathname";
-		}
-		print $debug " $pathname";
-		$debug->flush();
-
-		# Read until flush
-		my ( $done, $buffer ) = packet_txt_read();
-		while ( $buffer ne '' ) {
-			if ( $buffer eq "can-delay=1" ) {
-				if ( exists $DELAY{$pathname} and $DELAY{$pathname}{"requested"} == 0 ) {
-					$DELAY{$pathname}{"requested"} = 1;
-				} elsif ( !exists $DELAY{$pathname} and $always_delay ) {
-					$DELAY{$pathname} = { "requested" => 1, "count" => 1 };
-				}
-			} elsif ($buffer =~ /^(ref|treeish|blob)=/) {
-				print $debug " $buffer";
-			} else {
-				# In general, filters need to be graceful about
-				# new metadata, since it's documented that we
-				# can pass any key-value pairs, but for tests,
-				# let's be a little stricter.
-				die "Unknown message '$buffer'";
-			}
-
-			( $done, $buffer ) = packet_txt_read();
-		}
-		if ( $done == -1 ) {
-			die "unexpected EOF after pathname '$pathname'";
-		}
-
-		my $input = "";
-		{
-			binmode(STDIN);
-			my $buffer;
-			my $done = 0;
-			while ( !$done ) {
-				( $done, $buffer ) = packet_bin_read();
-				$input .= $buffer;
-			}
-			if ( $done == -1 ) {
-				die "unexpected EOF while reading input for '$pathname'";
-			}			
-			print $debug " " . length($input) . " [OK] -- ";
-			$debug->flush();
-		}
-
-		my $output;
-		if ( exists $DELAY{$pathname} and exists $DELAY{$pathname}{"output"} ) {
-			$output = $DELAY{$pathname}{"output"}
-		} elsif ( $pathname eq "error.r" or $pathname eq "abort.r" ) {
-			$output = "";
-		} elsif ( $command eq "clean" and grep( /^clean$/, @capabilities ) ) {
-			$output = rot13($input);
-		} elsif ( $command eq "smudge" and grep( /^smudge$/, @capabilities ) ) {
-			$output = rot13($input);
-		} else {
-			die "bad command '$command'";
-		}
-
-		if ( $pathname eq "error.r" ) {
-			print $debug "[ERROR]\n";
-			$debug->flush();
-			packet_txt_write("status=error");
-			packet_flush();
-		} elsif ( $pathname eq "abort.r" ) {
-			print $debug "[ABORT]\n";
-			$debug->flush();
-			packet_txt_write("status=abort");
-			packet_flush();
-		} elsif ( $command eq "smudge" and
-			exists $DELAY{$pathname} and
-			$DELAY{$pathname}{"requested"} == 1 ) {
-			print $debug "[DELAYED]\n";
-			$debug->flush();
-			packet_txt_write("status=delayed");
-			packet_flush();
-			$DELAY{$pathname}{"requested"} = 2;
-			$DELAY{$pathname}{"output"} = $output;
-		} else {
-			packet_txt_write("status=success");
-			packet_flush();
-
-			if ( $pathname eq "${command}-write-fail.r" ) {
-				print $debug "[WRITE FAIL]\n";
-				$debug->flush();
-				die "${command} write error";
-			}
-
-			print $debug "OUT: " . length($output) . " ";
-			$debug->flush();
-
-			while ( length($output) > 0 ) {
-				my $packet = substr( $output, 0, $MAX_PACKET_CONTENT_SIZE );
-				packet_bin_write($packet);
-				# dots represent the number of packets
-				print $debug ".";
-				if ( length($output) > $MAX_PACKET_CONTENT_SIZE ) {
-					$output = substr( $output, $MAX_PACKET_CONTENT_SIZE );
-				} else {
-					$output = "";
-				}
-			}
-			packet_flush();
-			print $debug " [OK]\n";
-			$debug->flush();
-			packet_flush();
-		}
-	}
-}
diff --git a/t/t2080-parallel-checkout-basics.sh b/t/t2080-parallel-checkout-basics.sh
index c683e60007..00ce3033d3 100755
--- a/t/t2080-parallel-checkout-basics.sh
+++ b/t/t2080-parallel-checkout-basics.sh
@@ -230,12 +230,9 @@ test_expect_success SYMLINKS 'parallel checkout checks for symlinks in leading d
 # check the final report including sequential, parallel, and delayed entries
 # all at the same time. So we must have finer control of the parallel checkout
 # variables.
-test_expect_success PERL '"git checkout ." report should not include failed entries' '
-	write_script rot13-filter.pl "$PERL_PATH" \
-		<"$TEST_DIRECTORY"/t0021/rot13-filter.pl &&
-
+test_expect_success '"git checkout ." report should not include failed entries' '
 	test_config_global filter.delay.process \
-		"\"$(pwd)/rot13-filter.pl\" --always-delay delayed.log clean smudge delay" &&
+		"test-tool rot13-filter --always-delay --log=delayed.log clean smudge delay" &&
 	test_config_global filter.delay.required true &&
 	test_config_global filter.cat.clean cat  &&
 	test_config_global filter.cat.smudge cat  &&
diff --git a/t/t2082-parallel-checkout-attributes.sh b/t/t2082-parallel-checkout-attributes.sh
index 2525457961..f3511cd43a 100755
--- a/t/t2082-parallel-checkout-attributes.sh
+++ b/t/t2082-parallel-checkout-attributes.sh
@@ -138,12 +138,9 @@ test_expect_success 'parallel-checkout and external filter' '
 # The delayed queue is independent from the parallel queue, and they should be
 # able to work together in the same checkout process.
 #
-test_expect_success PERL 'parallel-checkout and delayed checkout' '
-	write_script rot13-filter.pl "$PERL_PATH" \
-		<"$TEST_DIRECTORY"/t0021/rot13-filter.pl &&
-
+test_expect_success 'parallel-checkout and delayed checkout' '
 	test_config_global filter.delay.process \
-		"\"$(pwd)/rot13-filter.pl\" --always-delay \"$(pwd)/delayed.log\" clean smudge delay" &&
+		"test-tool rot13-filter --always-delay --log=\"$(pwd)/delayed.log\" clean smudge delay" &&
 	test_config_global filter.delay.required true &&
 
 	echo "abcd" >original &&