t0021: implementation the rot13-filter.pl script in C

This script is currently used by three test files: t0021-conversion.sh,
t2080-parallel-checkout-basics.sh, and
t2082-parallel-checkout-attributes.sh. To avoid the need for the PERL
dependency at these tests, let's convert the script to a C test-tool
command. The following commit will take care of actually modifying the
said tests to use the new C helper and removing the Perl script.

The Perl script flushes the log file handler after each write. As
commented in [1], this seems to be an early design decision that was
later reconsidered, but possibly ended up being left in the code by
accident:

	>> +$debug->flush();
	>
	> Isn't $debug flushed automatically?

	Maybe, but autoflush is not explicitly enabled. I will
	enable it again (I disabled it because of Eric's comment
	but I re-read the comment and he is only talking about
	pipes).

Anyways, this behavior is not really needed for the tests and the
flush() calls make the code slightly larger, so let's avoid them
altogether in the new C version.

[1]: https://lore.kernel.org/git/[email protected]/

Helped-by: Johannes Schindelin <[email protected]>
Signed-off-by: Matheus Tavares <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: matheustavares

Makefile

@@ -764,6 +764,7 @@ 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

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;
 }

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