URLs might end with a slash and follow redirects, or could be a
generated by a script such as /getpkg.php?id=12345. In both cases, we
may have a better filename that we can write to, taken from either
content-disposition header, or the effective URL.
Specific to the first case, we write to a temporary file of the format
'alpmtmp.XXXXXX', where XXXXXX is randomized by mkstemp(3). Since this
is a randomly generated file, we cannot support resuming and the file is
unlinked in the event of an interrupt.
We also run into the possibility of changing out the filename from under
alpm on a -U operation, so callers of _alpm_download can optionally pass
a pointer to a *char to be filled in by curl_download_internal with the
actual filename we wrote to. Any sync operation will pass a NULL pointer
here, as we rely on specific names for packages from a mirror.
Fixes FS#22645.
Signed-off-by: Dave Reisner <d@falconindy.com>
6c9b82e72a