robots.txt: disallow access to snapshots

My dmesg is filled with the oom killer bringing down processes while the
Bingbot downloads every snapshot for every commit of the Linux kernel in
tar.xz format. Sure, I should be running with memory limits, and now I'm
using cgroups, but a more general solution is to prevent crawlers from
wasting resources like that in the first place.

Suggested-by: Natanael Copa <ncopa@alpinelinux.org>
Suggested-by: Julius Plenz <plenz@cis.fu-berlin.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
cache: document negative ttls and add about ttl

We've long supported negative ttls, for infinite cache, except the
documentation incorrectly showed one of our defaults as being 5 and not
-1. As well, with a negative ttl, we were actually making the HTTP
expired header go backwards. This changes it to go ahead ten years
instead.

Further, we add an cache-about-ttl option to set a different ttl for
about pages, which are now increasingly being filtered through markdown
or just sent statically anyway.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
cache: id means static, even if head is specified too

Pages like /commit?h=wip&id=8a335ce618ba77fbf05148d6f8be17bd48ba4340
were being marked as dynamic, because of h=wip, when it should be
static, because of id=.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
add a note about generating agefile in hook
Use strbuf for reading configuration files

Use struct strbuf from Git instead of fixed-size buffers to remove the
limit on the length of configuration file lines and refactor
read_config_line() to improve readability.

Note that this also fixes a buffer overflow that existed with the
original fixed-size buffer implementation.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>
Makefile: Change default prefix to "/usr/local"

Locally installed packages are usually installed to /usr/local.
Packagers can use `make prefix=/usr` to get back the old behavior.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>
Fix section-from-path > 1

When having found the first path separator occurrence at position i, we
invoked strchr() on the same position i in subsequent iterations
resulting in the same path separator being returned by strchr() over and
over again. Increase the position by one to skip the occurrence that has
just been found and advance to the next separator.

Reported-by: Konstantin Ryabitsev <mricon@kernel.org>
Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>