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pkt-line: eliminate the need for static buffer in packet_write_gently()

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Teach `packet_write_gently()` to write the pkt-line header and the actual
buffer in 2 separate calls to `write_in_full()` and avoid the need for a
static buffer, thread-safe scratch space, or an excessively large stack
buffer.

Change `write_packetized_from_fd()` to allocate a temporary buffer rather
than using a static buffer to avoid similar issues here.

These changes are intended to make it easier to use pkt-line routines in
a multi-threaded context with multiple concurrent writers writing to
different streams.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff Hostetler 2021-03-15 21:08:18 +00:00 committed by Junio C Hamano
parent 59ec22464f
commit 7455e05e4e
1 changed files with 20 additions and 8 deletions
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28
pkt-line.c
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@ -196,17 +196,26 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
static int packet_write_gently(const int fd_out, const char *buf, size_t size)
{
static char packet_write_buffer[LARGE_PACKET_MAX];
char header[4];
size_t packet_size;
if (size > sizeof(packet_write_buffer) - 4)
if (size > LARGE_PACKET_DATA_MAX)
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(header, packet_size);
/*
* Write the header and the buffer in 2 parts so that we do
* not need to allocate a buffer or rely on a static buffer.
* This also avoids putting a large buffer on the stack which
* might have multi-threading issues.
*/
if (write_in_full(fd_out, header, 4) < 0 ||
write_in_full(fd_out, buf, size) < 0)
return error(_("packet write failed"));
return 0;
}
@ -244,20 +253,23 @@ 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)
{
static char buf[LARGE_PACKET_DATA_MAX];
char *buf = xmalloc(LARGE_PACKET_DATA_MAX);
int err = 0;
ssize_t bytes_to_write;
while (!err) {
bytes_to_write = xread(fd_in, buf, sizeof(buf));
if (bytes_to_write < 0)
bytes_to_write = xread(fd_in, buf, LARGE_PACKET_DATA_MAX);
if (bytes_to_write < 0) {
free(buf);
return COPY_READ_ERROR;
}
if (bytes_to_write == 0)
break;
err = packet_write_gently(fd_out, buf, bytes_to_write);
}
if (!err)
err = packet_flush_gently(fd_out);
free(buf);
return err;
}