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BinaryCacheStore: Optionally write a NAR listing

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The store parameter "write-nar-listing=1" will cause BinaryCacheStore
to write a file ‘<store-hash>.ls.xz’ for each ‘<store-hash>.narinfo’
added to the binary cache. This file contains an XZ-compressed JSON
file describing the contents of the NAR, excluding the contents of
regular files.

E.g.

  {
    "version": 1,
    "root": {
      "type": "directory",
      "entries": {
        "lib": {
          "type": "directory",
          "entries": {
            "Mcrt1.o": {
              "type": "regular",
              "size": 1288
            },
            "Scrt1.o": {
              "type": "regular",
              "size": 3920
            },
          }
        }
      }
      ...
    }
  }

(The actual file has no indentation.)

This is intended to speed up the NixOS channels programs index
generator [1], since fetching gazillions of large NARs from
cache.nixos.org is currently a bottleneck for updating the regular
(non-small) channel.

[1] https://github.com/NixOS/nixos-channel-scripts/blob/master/generate-programs-index.cc
This commit is contained in:
Eelco Dolstra 2016-10-21 16:50:28 +02:00
parent 307cc8c33d
commit 542ae5c8f8
10 changed files with 81 additions and 20 deletions
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2
src/libstore/download.cc
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@ -558,7 +558,7 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
Hash hash = hashString(expectedHash ? expectedHash.type : htSHA256, *res.data);
info.path = store->makeFixedOutputPath(false, hash, name);
info.narHash = hashString(htSHA256, *sink.s);
store->addToStore(info, *sink.s, false, true);
store->addToStore(info, sink.s, false, true);
storePath = info.path;
}