[PATCH v2 02/14] pkt-line: promote static buffer in packet_write_gently() to callers

["Jeff Hostetler via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>

Move the static buffer used in `packet_write_gently()` to its callers.
This is a first step to make packet writing more thread-safe.

Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
---
 pkt-line.c | 33 ++++++++++++++++++++++++---------
 pkt-line.h | 10 ++++++++--
 2 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/pkt-line.c b/pkt-line.c
index d633005ef74..14af049cd9c 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -194,26 +194,34 @@ 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)
+/*
+ * Use the provided scratch space to build a combined <hdr><buf> buffer
+ * and write it to the file descriptor (in one write if possible).
+ */
+static int packet_write_gently(const int fd_out, const char *buf, size_t size,
+			       struct packet_scratch_space *scratch)
 {
-	static char packet_write_buffer[LARGE_PACKET_MAX];
 	size_t packet_size;
 
-	if (size > sizeof(packet_write_buffer) - 4)
+	if (size > sizeof(scratch->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) < 0)
+
+	set_packet_header(scratch->buffer, packet_size);
+	memcpy(scratch->buffer + 4, buf, size);
+
+	if (write_in_full(fd_out, scratch->buffer, packet_size) < 0)
 		return error(_("packet write failed"));
 	return 0;
 }
 
 void packet_write(int fd_out, const char *buf, size_t size)
 {
-	if (packet_write_gently(fd_out, buf, size))
+	static struct packet_scratch_space scratch;
+
+	if (packet_write_gently(fd_out, buf, size, &scratch))
 		die_errno(_("packet write failed"));
 }
 
@@ -244,6 +252,12 @@ void packet_buf_write_len(struct strbuf *buf, const char *data, size_t len)
 
 int write_packetized_from_fd(int fd_in, int fd_out)
 {
+	/*
+	 * TODO We could save a memcpy() if we essentially inline
+	 * TODO packet_write_gently() here and change the xread()
+	 * TODO to pass &buf[4].
+	 */
+	static struct packet_scratch_space scratch;
 	static char buf[LARGE_PACKET_DATA_MAX];
 	int err = 0;
 	ssize_t bytes_to_write;
@@ -254,7 +268,7 @@ int write_packetized_from_fd(int fd_in, int fd_out)
 			return COPY_READ_ERROR;
 		if (bytes_to_write == 0)
 			break;
-		err = packet_write_gently(fd_out, buf, bytes_to_write);
+		err = packet_write_gently(fd_out, buf, bytes_to_write, &scratch);
 	}
 	if (!err)
 		err = packet_flush_gently(fd_out);
@@ -263,6 +277,7 @@ int write_packetized_from_fd(int fd_in, int fd_out)
 
 int write_packetized_from_buf(const char *src_in, size_t len, int fd_out)
 {
+	static struct packet_scratch_space scratch;
 	int err = 0;
 	size_t bytes_written = 0;
 	size_t bytes_to_write;
@@ -274,7 +289,7 @@ int write_packetized_from_buf(const char *src_in, size_t len, int fd_out)
 			bytes_to_write = len - bytes_written;
 		if (bytes_to_write == 0)
 			break;
-		err = packet_write_gently(fd_out, src_in + bytes_written, bytes_to_write);
+		err = packet_write_gently(fd_out, src_in + bytes_written, bytes_to_write, &scratch);
 		bytes_written += bytes_to_write;
 	}
 	if (!err)
diff --git a/pkt-line.h b/pkt-line.h
index 8c90daa59ef..4ccd6f88926 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -5,6 +5,13 @@
 #include "strbuf.h"
 #include "sideband.h"
 
+#define LARGE_PACKET_MAX 65520
+#define LARGE_PACKET_DATA_MAX (LARGE_PACKET_MAX - 4)
+
+struct packet_scratch_space {
+	char buffer[LARGE_PACKET_MAX];
+};
+
 /*
  * Write a packetized stream, where each line is preceded by
  * its length (including the header) as a 4-byte hex number.
@@ -213,8 +220,7 @@ enum packet_read_status packet_reader_read(struct packet_reader *reader);
 enum packet_read_status packet_reader_peek(struct packet_reader *reader);
 
 #define DEFAULT_PACKET_MAX 1000
-#define LARGE_PACKET_MAX 65520
-#define LARGE_PACKET_DATA_MAX (LARGE_PACKET_MAX - 4)
+
 extern char packet_buffer[LARGE_PACKET_MAX];
 
 struct packet_writer {
-- 
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