Allowing stuff like

  NIX_REMOTE=https://cache.nixos.org nix-store -qR /nix/store/x1p1gl3a4kkz5ci0nfbayjqlqmczp1kq-geeqie-1.1

or

  NIX_REMOTE=https://cache.nixos.org nix-store --export /nix/store/x1p1gl3a4kkz5ci0nfbayjqlqmczp1kq-geeqie-1.1 | nix-store --import

This for instance allows hydra-queue-runner to add the S3 backend
at runtime.

The st_size field of a symlink doesn't have to be correct, e.g. for
/dev/fd symlinks.

This enables an optimisation in hydra-queue-runner, preventing a
download of a NAR it just uploaded to the cache when reading files
like hydra-build-products.

For example,

  $ NIX_REMOTE=file:///my-cache nix ls-store -lR /nix/store/f4kbgl8shhyy76rkk3nbxr0lz8d2ip7q-binutils-2.23.1
  dr-xr-xr-x                    0 ./bin
  -r-xr-xr-x                30748 ./bin/addr2line
  -r-xr-xr-x                66973 ./bin/ar
  ...

Similarly, "nix ls-nar" lists the contents of a NAR file, "nix
cat-nar" extracts a file from a NAR file, and "nix cat-store" extract
a file from a Nix store.

This is primary to allow hydra-queue-runner to extract files like
"nix-support/hydra-build-products" from NARs in binary caches.

Also makes it robust against concurrent deletions.

This eliminates some unnecessary (presumably cached) I/O.

So now you can do

  $ NIX_REMOTE=file:///tmp/binary-cache nix-instantiate '<nixpkgs>' -A hello

and lots of other operations.

So you can now do:

  $ NIX_REMOTE=file:///tmp/binary-cache nix-store -qR /nix/store/...

Throw a specific error for incomplete parse errors.

The latter is supposed to be more efficient.

This is necessary for long-running processes like hydra-queue-runner:
if a nix-daemon worker is killed, we need to stop reusing that
connection.

`nix-repl` will use this for deciding whether to keep waiting for input or
error out right away.

This allows a RemoteStore object to be used safely from multiple
threads concurrently. It will make multiple daemon connections if
necessary.

Note: pool.hh and sync.hh have been copied from the Hydra source tree.

OpenSSL can randomly segfault unless we register a callback function
to do locking.

https://www.openssl.org/docs/manmaster/crypto/threads.html

Otherwise using curl is not safe in multi-threaded applications
because it installs a SIGALRM handler.

The first occurrence of "runtime dependencies" wasn't related to the surrounding narrative.

http://hydra.nixos.org/build/32085949