On Mon, Nov 02, 2015 at 02:36:26PM -0500, David Turner wrote:
> A HTTP server is permitted to return a non-range response to a HTTP
> range request (and Apache httpd in fact does this in some cases).
> While libcurl knows how to correctly handle this (by skipping bytes
> before and after the requested range), it only turns on this handling
> if it is aware that a range request is being made. By manually
> setting the range header instead of using CURLOPT_RANGE, we were
> hiding the fact that this was a range request from libcurl. This
> could cause corruption.
>
> Signed-off-by: David Turner <[email protected]>
> ---
>
> This version breaks the range option formatting/setting out to a
> helper function, as suggested by Junio and Jeff.
>
> In addition, it clears the range option when curl slots are cleared
> before reuse, also as suggested
Thanks, this looks much nicer to me.
A few minor comments:
> +static void http_opt_request_remainder(CURL *curl, ssize_t lo)
I notice you used ssize_t here. If we are going to deal with large files, I
would think off_t would make more sense (i.e., to allow >2GB on a 32-bit
system).
But much worse than that, the value we are passing typically comes from
ftell(), which only returns a long. So we're truncated anyway in that
case.
I certainly don't think we are making anything _worse_ here; the problem
is in the existing code. But I don't think ssize_t is making anything
better (it's generally the same size as a long anyway). So I think I'd
prefer one of the following:
1. Leave it as "long". At least then we are matching ftell(), which is
clear (and works fine on 64-bit machines).
2. Use off_t here instead. It doesn't fix the problem, but at least
fixes our one component, so it's working towards a better solution
in the long run.
3. Detect and complain when we overflow the long. Hopefully ftell()
returns -1 on a 32-bit system when the file is larger than 2GB, so
this Just Works already, and we don't create a broken output.
4. Fix all of the callers. I suspect this would involve calling
fstat(fileno(fh)) to get a real off_t.
Options (3) and (4) are obviously more work, and I don't necessarily
expect you to do them. But I think I'd prefer (2) to what you have now.
Using off_t has an issue with being unsigned, but...
> +{
> + char buf[128];
> + int len = 0;
> +
> + if (lo >= 0)
> + len += xsnprintf(buf + len, 128 - len, "%"PRIiMAX,
> + (intmax_t)lo);
> + len += xsnprintf(buf + len, 128 - len, "-");
I think we could just drop this "lo >= 0". Now that there is no "hi"
(which I think is fine), there's no reason to call the function at all
if you do not have a limit.
Also, we should prefer "sizeof(buf)" to repeating the "128", as the two
getting out of sync would be disastrous. So altogether something like:
static void http_opt_request_remainder(CURL *curl, off_t pos)
{
char buf[128];
xsnprintf(buf, sizeof(buf), "%"PRIuMAX", (uintmax_t)pos);
curl_easy_setopt(curl, CURLOPT_RANGE, buf);
}
would be enough, I think.
-Peff
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