Re: [PATCH] stream_to_pack: xread does not guarantee to read all requested bytes

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 20, 2013, 18:27 UTC
Message-ID: <xmqq8uzw6wuw.fsf@gitster.dls.corp.google.com>
In-Reply-To: <CALWbr2yaQaCte6+Y3GEa8Hxyhq6GPS64aTNzkGo8pdpcd9ZVUg@mail.gmail.com>

Antoine Pelisse <apelisse@gmail.com> writes:

> I was actually wondering when it's better to use xread() over
> read_in_full()?

When the caller wants to do more control over a read that may have to loop. For example, this loop in builtin/index-pack.c::fill()

	do {
		ssize_t ret = xread(input_fd, input_buffer + input_len,
				sizeof(input_buffer) - input_len);
		if (ret <= 0) {
			if (!ret)
				die(_("early EOF"));
			die_errno(_("read error on input"));
		}
		input_len += ret;
		if (from_stdin)
			display_throughput(progress, consumed_bytes + input_len);
	} while (input_len < min);

cannot be replaced blindly with read_in_full() because (1) the caller wants to do the "display_throughput()" part in the loop, and (2) the caller wants to fill at least "min" bytes but can happily accept to read more up to the size of the input_buffer.