pkt-line: add packet_write_fmt_gently()

packet_write_fmt() would die in case of a write error even though for
some callers an error would be acceptable. Add packet_write_fmt_gently()
which writes a formatted pkt-line like packet_write_fmt() but does not
die in case of an error. The function is used in a subsequent patch.

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

pkt-line.c

@@ -125,16 +125,42 @@ static void format_packet(struct strbuf *out, const char *fmt, va_list args)
 	packet_trace(out->buf + orig_len + 4, n - 4, 1);
 }
 
+static int packet_write_fmt_1(int fd, int gently,
+			      const char *fmt, va_list args)
+{
+	struct strbuf buf = STRBUF_INIT;
+	ssize_t count;
+
+	format_packet(&buf, fmt, args);
+	count = write_in_full(fd, buf.buf, buf.len);
+	if (count == buf.len)
+		return 0;
+
+	if (!gently) {
+		check_pipe(errno);
+		die_errno("packet write with format failed");
+	}
+	return error("packet write with format failed");
+}
+
 void packet_write_fmt(int fd, const char *fmt, ...)
 {
-	static struct strbuf buf = STRBUF_INIT;
 	va_list args;
 
-	strbuf_reset(&buf);
 	va_start(args, fmt);
-	format_packet(&buf, fmt, args);
+	packet_write_fmt_1(fd, 0, fmt, args);
 	va_end(args);
-	write_or_die(fd, buf.buf, buf.len);
+}
+
+int packet_write_fmt_gently(int fd, const char *fmt, ...)
+{
+	int status;
+	va_list args;
+
+	va_start(args, fmt);
+	status = packet_write_fmt_1(fd, 1, fmt, args);
+	va_end(args);
+	return status;
 }
 
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...)

pkt-line.h

@@ -23,6 +23,7 @@ void packet_flush(int fd);
 void packet_write_fmt(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 void packet_buf_flush(struct strbuf *buf);
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
+int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 
 /*
  * Read a packetized line into the buffer, which must be at least size bytes