lix/src/nix/make-content-addressable.cc
Eelco Dolstra 0abb3ad537 Allow content-addressable paths to have references
This adds a command 'nix make-content-addressable' that rewrites the
specified store paths into content-addressable paths. The advantage of
such paths is that 1) they can be imported without signatures; 2) they
can enable deduplication in cases where derivation changes do not
cause output changes (apart from store path hashes).

For example,

  $ nix make-content-addressable -r nixpkgs.cowsay
  rewrote '/nix/store/g1g31ah55xdia1jdqabv1imf6mcw0nb1-glibc-2.25-49' to '/nix/store/48jfj7bg78a8n4f2nhg269rgw1936vj4-glibc-2.25-49'
  ...
  rewrote '/nix/store/qbi6rzpk0bxjw8lw6azn2mc7ynnn455q-cowsay-3.03+dfsg1-16' to '/nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16'

We can then copy the resulting closure to another store without
signatures:

  $ nix copy --trusted-public-keys '' ---to ~/my-nix /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16

In order to support self-references in content-addressable paths,
these paths are hashed "modulo" self-references, meaning that
self-references are zeroed out during hashing. Somewhat annoyingly,
this means that the NAR hash stored in the Nix database is no longer
necessarily equal to the output of "nix hash-path"; for
content-addressable paths, you need to pass the --modulo flag:

  $ nix path-info --json /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16  | jq -r .[].narHash
  sha256:0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16
  1ggznh07khq0hz6id09pqws3a8q9pn03ya3c03nwck1kwq8rclzs

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16 --modulo iq6g2x4q62xp7y7493bibx0qn5w7xz67
  0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw
2019-10-21 17:47:24 +02:00

83 lines
2.5 KiB
C++

#include "command.hh"
#include "store-api.hh"
#include "references.hh"
using namespace nix;
struct CmdMakeContentAddressable : StorePathsCommand
{
CmdMakeContentAddressable()
{
realiseMode = Build;
}
std::string name() override
{
return "make-content-addressable";
}
std::string description() override
{
return "test";
}
void run(ref<Store> store, Paths storePaths) override
{
auto paths = store->topoSortPaths(PathSet(storePaths.begin(), storePaths.end()));
paths.reverse();
std::map<Path, Path> remappings;
for (auto & path : paths) {
auto oldInfo = store->queryPathInfo(path);
auto oldHashPart = storePathToHash(path);
auto name = storePathToName(path);
StringSink sink;
store->narFromPath(path, sink);
StringMap rewrites;
ValidPathInfo info;
for (auto & ref : oldInfo->references) {
if (ref == path)
info.references.insert("self");
else {
auto replacement = get(remappings, ref, ref);
// FIXME: warn about unremapped paths?
info.references.insert(replacement);
if (replacement != ref)
rewrites[storePathToHash(ref)] = storePathToHash(replacement);
}
}
*sink.s = rewriteStrings(*sink.s, rewrites);
HashModuloSink hashModuloSink(htSHA256, oldHashPart);
hashModuloSink((unsigned char *) sink.s->data(), sink.s->size());
info.narHash = hashModuloSink.finish().first;
info.narSize = sink.s->size();
replaceInSet(info.references, path, std::string("self"));
info.path = store->makeFixedOutputPath(true, info.narHash, name, info.references);
replaceInSet(info.references, std::string("self"), info.path);
info.ca = makeFixedOutputCA(true, info.narHash);
printError("rewrote '%s' to '%s'", path, info.path);
auto source = sinkToSource([&](Sink & nextSink) {
RewritingSink rsink2(oldHashPart, storePathToHash(info.path), nextSink);
rsink2((unsigned char *) sink.s->data(), sink.s->size());
rsink2.flush();
});
store->addToStore(info, *source);
remappings[path] = info.path;
}
}
};
static RegisterCommand r1(make_ref<CmdMakeContentAddressable>());