pkt-line: add packet_write_gently()

packet_write_fmt_gently() uses format_packet() which lets the caller
only send string data via "%s". That means it cannot be used for
arbitrary data that may contain NULs.

Add packet_write_gently() which writes arbitrary data and does not die
in case of an error. The function is used by other pkt-line functions in
a subsequent patch.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pkt-line.c

@@ -171,6 +171,23 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
 	return status;
 }
 
+static int packet_write_gently(const int fd_out, const char *buf, size_t size)
+{
+	static char packet_write_buffer[LARGE_PACKET_MAX];
+	size_t packet_size;
+
+	if (size > sizeof(packet_write_buffer) - 4)
+		return error("packet write failed - data exceeds max packet size");
+
+	packet_trace(buf, size, 1);
+	packet_size = size + 4;
+	set_packet_header(packet_write_buffer, packet_size);
+	memcpy(packet_write_buffer + 4, buf, size);
+	if (write_in_full(fd_out, packet_write_buffer, packet_size) == packet_size)
+		return 0;
+	return error("packet write failed");
+}
+
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...)
 {
 	va_list args;