Used to determine symlink size with stat and value with readlink.
This could technically result in garbage if symlink changed between
calls. Also gets around the broken stat implementation in our
network filesystem (returns size + 1 giving a byte of garbage).
The computation of urlHash didn't take the name into account, so
subsequent fetchurl calls with the same URL but a different name would
resolve to the same cached store path.
The "name" attribute defaults to "source", which we should use for all
similar functions (e.g. fetchTarball and in Hydra) to ensure that we
get a consistent store path regardless of how the tree is fetched.
"source" is not necessarily a correct label, but using an empty name
is problematic: you get an ugly store path ending in a dash, and it's
impossible to have a fixed-output derivation that produces that path
because ".drv" is not a valid store name.
Fixes#904.
You can now include files via the "builders" option, using the syntax
"@<filename>". Having only one option makes it easier to override
builders completely.
For backward compatibility, the default is "@/etc/nix/machines", or
"@<filename>" for each file name in NIX_REMOTE_SYSTEMS.
This makes it slightly more manageable to see at a glance what in a
build's sandbox profile is unique to the build and what is standard. Also
a first step to factoring more of our Darwin logic into scheme functions
that will allow us a bit more flexibility. And of course less of that
nasty codegen in C++! 😀
This speeds up commands like "nix cat-store". For example:
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nar-cache /nix/store/i60yncmq6w9dyv37zd2k454g0fkl3arl-systemd-234/etc/udev/udev.conf
real 0m4.336s
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nar-cache /nix/store/i60yncmq6w9dyv37zd2k454g0fkl3arl-systemd-234/etc/udev/udev.conf
real 0m0.045s
The primary motivation is to allow hydra-server to serve files from S3
binary caches. Previously Hydra had a hack to do "nix-store -r
<path>", but that fetches the entire closure so is prohibitively
expensive.
There is no garbage collection of the NAR cache yet. Also, the entire
NAR is read when accessing a single member file. We could generate the
NAR listing to provide random access.
Note: the NAR cache is indexed by the store path hash, not the content
hash, so NAR caches should not be shared between binary caches, unless
you're sure that all your builds are binary-reproducible.
