The Golang built-in gzip library is serialized, and fairly slow
at decompressing. It also only decompresses on demand, versus
pipelining decompression.
This change switches to using the pigz external command
for gzip decompression, as opposed to using the built-in
golang one. This code is not vendored, but will be used
if it autodetected as part of the OS.
This also switches to using context, versus a manually
managed channel to manage cancellations, and synchronization.
There is a little bit of weirdness around manually having
to cancel in the error cases.
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
fd35494a25