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Add an optional hash parameter to builtins.fetchGit #3216

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Add an optional hash parameter to builtins.fetchGit #3216

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36 changes: 36 additions & 0 deletions doc/manual/expressions/builtins.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -405,6 +405,20 @@ stdenv.mkDerivation { … }
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>hash</term>
<listitem>
<para>
The <link xlink:href="https://www.w3.org/TR/SRI/">SRI</link> hash
of the output path. Please note that this can only
be used in conjunction with <varname>rev</varname> or <varname>ref</varname>.
</para>
<para>
The hash can be generated by running
<command>nix to-sri --type sha256 $(nix-prefetch-url git://github.com/owner/repo --rev abcdef)</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ref</term>
<listitem>
Expand Down Expand Up @@ -504,6 +518,28 @@ stdenv.mkDerivation { … }
<programlisting>builtins.fetchGit {
url = "ssh://git@github.com/nixos/nix.git";
ref = "master";
}</programlisting>
</example>

<example>
<title>Fetching a given revision from a repo and validate its hash</title>
<para>
<function>builtins.fetchGit</function> can create a content-addressable
path to ensure that nothing changes.
</para>
<programlisting>builtins.fetchGit {
url = "git://github.com/NixOS/nix";
rev = "d1db7fa9528154284de55d37e5186ac06fcbffc9";
hash = "sha256-B5yIPHhEm0eysJKEsO7nqxprh9vcblFxpJG11gXJus1=";
}</programlisting>
</example>

<example>
<title>Fetching a given tag from a repo and validate its hash</title>
<programlisting>builtins.fetchGit {
url = "git://github.com/NixOS/nix";
ref = "refs/tags/2.2.2";
hash = "sha256-wGVMnUCo8Ms0EdXNlTEAvTBnD/CwOwoAlNCGEijOTJc=";
}</programlisting>
</example>
</listitem>
Expand Down
66 changes: 52 additions & 14 deletions src/libexpr/primops/fetchGit.cc
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Expand Up @@ -28,11 +28,28 @@ std::regex revRegex("^[0-9a-fA-F]{40}$");

GitInfo exportGit(ref<Store> store, const std::string & uri,
std::optional<std::string> ref, std::string rev,
const std::string & name)
const std::string & name, std::optional<Hash> hash)
{
if (evalSettings.pureEval && rev == "")
throw Error("in pure evaluation mode, 'fetchGit' requires a Git revision");

std::optional<StorePath> expectedStorePath;
GitInfo gitInfo;
if (hash) {
// Disallow `hash` usage if no rev/ref is given.
if (rev == "" && !ref) {
throw Error("Cannot create a fixed-output derivation for a git repo without a git revision or ref");
}

expectedStorePath = store->makeFixedOutputPath(true, *hash, name);
if (store->isValidPath(*expectedStorePath)) {
gitInfo.storePath = store->printStorePath(*expectedStorePath);
gitInfo.rev = rev;
gitInfo.shortRev = std::string(gitInfo.rev, 0, 7);
return gitInfo;
}
}

if (!ref && rev == "" && hasPrefix(uri, "/") && pathExists(uri + "/.git")) {

bool clean = true;
Expand Down Expand Up @@ -139,7 +156,6 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
}

// FIXME: check whether rev is an ancestor of ref.
GitInfo gitInfo;
gitInfo.rev = rev != "" ? rev : chomp(readFile(localRefFile));
gitInfo.shortRev = std::string(gitInfo.rev, 0, 7);

Expand All @@ -149,20 +165,25 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
Path storeLink = cacheDir + "/" + storeLinkName + ".link";
PathLocks storeLinkLock({storeLink}, fmt("waiting for lock on '%1%'...", storeLink)); // FIXME: broken

try {
auto json = nlohmann::json::parse(readFile(storeLink));
// Only return cached git repo if no hash is set. If a hash exists,
// the proper store path would've been returned earlier, otherwise the hash
// needs to be validated.
if (!hash) {
try {
auto json = nlohmann::json::parse(readFile(storeLink));

assert(json["name"] == name && json["rev"] == gitInfo.rev);
assert(json["name"] == name && json["rev"] == gitInfo.rev);

gitInfo.storePath = json["storePath"];
gitInfo.storePath = json["storePath"];

if (store->isValidPath(store->parseStorePath(gitInfo.storePath))) {
gitInfo.revCount = json["revCount"];
return gitInfo;
}
if (store->isValidPath(store->parseStorePath(gitInfo.storePath))) {
gitInfo.revCount = json["revCount"];
return gitInfo;
}

} catch (SysError & e) {
if (e.errNo != ENOENT) throw;
} catch (SysError & e) {
if (e.errNo != ENOENT) throw;
}
}

auto source = sinkToSource([&](Sink & sink) {
Expand All @@ -176,7 +197,21 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,

unpackTarfile(*source, tmpDir);

gitInfo.storePath = store->printStorePath(store->addToStore(name, tmpDir));
auto storePath = store->addToStore(name, tmpDir);
if (expectedStorePath && storePath != expectedStorePath) {
unsigned int status = resUntrustedPath;
Hash got = hashPath(hash->type, store->toRealPath(store->printStorePath(storePath))).first;
throw Error(
status,
"hash mismatch in git repo (%s, rev %s):\n wanted: %s\n got: %s",
uri,
gitInfo.rev,
hash->to_string(SRI, true),
got.to_string(SRI, true)
);
}

gitInfo.storePath = store->printStorePath(storePath);

gitInfo.revCount = std::stoull(runProgram("git", true, { "-C", cacheDir, "rev-list", "--count", gitInfo.rev }));

Expand All @@ -197,6 +232,7 @@ static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Va
std::string url;
std::optional<std::string> ref;
std::string rev;
std::optional<Hash> hash;
std::string name = "source";
PathSet context;

Expand All @@ -216,6 +252,8 @@ static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Va
rev = state.forceStringNoCtx(*attr.value, *attr.pos);
else if (n == "name")
name = state.forceStringNoCtx(*attr.value, *attr.pos);
else if (n == "hash")
hash = Hash(state.forceStringNoCtx(*attr.value, *attr.pos), htUnknown);
else
throw EvalError("unsupported argument '%s' to 'fetchGit', at %s", attr.name, *attr.pos);
}
Expand All @@ -230,7 +268,7 @@ static void prim_fetchGit(EvalState & state, const Pos & pos, Value * * args, Va
// whitelist. Ah well.
state.checkURI(url);

auto gitInfo = exportGit(state.store, url, ref, rev, name);
auto gitInfo = exportGit(state.store, url, ref, rev, name, hash);

state.mkAttrs(v, 8);
mkString(*state.allocAttr(v, state.sOutPath), gitInfo.storePath, PathSet({gitInfo.storePath}));
Expand Down
6 changes: 6 additions & 0 deletions tests/fetchGit.sh
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Expand Up @@ -88,6 +88,12 @@ path3=$(nix eval --raw "(builtins.fetchGit { url = $repo; ref = \"master\"; }).o
path3=$(nix eval --raw "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; }).outPath")
[[ $path = $path3 ]]

path4=$(nix eval --raw "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; hash = \"sha256-Hr8g6AqANb3xqX28eu1XnjK/3ab8Gv6TJSnkb1LezG8=\"; }).outPath")
[[ $path = $path4 ]]

nix eval --raw "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; hash = \"sha256-B5yIPHhEm0eysJKEsO7nqxprh9vcblFxpJG11gXJus1=\"; }).outPath" || status=$?
[[ "$status" = "102" ]]

# Committing should not affect the store path.
git -C $repo commit -m 'Bla3' -a

Expand Down