Merge pull request #7708 from ShamrockLee/primop-rebasehash

primops: add builtins.convertHash

doc/manual/src/release-notes/rl-next.md

@@ -8,4 +8,6 @@
 
 - Introduce new flake installable syntax `flakeref#.attrPath` where the "." prefix denotes no searching of default attribute prefixes like `packages.<SYSTEM>` or `legacyPackages.<SYSTEM>`.
 
+- Introduce a new built-in function [`builtins.convertHash`](@docroot@/language/builtins.md#builtins-convertHash).
+
 - `builtins.fetchTree` is now marked as stable.

perl/lib/Nix/Store.xs

@@ -78,7 +78,7 @@ SV * queryReferences(char * path)
 SV * queryPathHash(char * path)
     PPCODE:
         try {
-            auto s = store()->queryPathInfo(store()->parseStorePath(path))->narHash.to_string(Base32, true);
+            auto s = store()->queryPathInfo(store()->parseStorePath(path))->narHash.to_string(HashFormat::Base32, true);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -104,7 +104,7 @@ SV * queryPathInfo(char * path, int base32)
                 XPUSHs(&PL_sv_undef);
             else
                 XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(*info->deriver).c_str(), 0)));
-            auto s = info->narHash.to_string(base32 ? Base32 : Base16, true);
+            auto s = info->narHash.to_string(base32 ? HashFormat::Base32 : HashFormat::Base16, true);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
             mXPUSHi(info->registrationTime);
             mXPUSHi(info->narSize);
@@ -206,7 +206,7 @@ SV * hashPath(char * algo, int base32, char * path)
     PPCODE:
         try {
             Hash h = hashPath(parseHashType(algo), path).first;
-            auto s = h.to_string(base32 ? Base32 : Base16, false);
+            auto s = h.to_string(base32 ? HashFormat::Base32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -217,7 +217,7 @@ SV * hashFile(char * algo, int base32, char * path)
     PPCODE:
         try {
             Hash h = hashFile(parseHashType(algo), path);
-            auto s = h.to_string(base32 ? Base32 : Base16, false);
+            auto s = h.to_string(base32 ? HashFormat::Base32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -228,7 +228,7 @@ SV * hashString(char * algo, int base32, char * s)
     PPCODE:
         try {
             Hash h = hashString(parseHashType(algo), s);
-            auto s = h.to_string(base32 ? Base32 : Base16, false);
+            auto s = h.to_string(base32 ? HashFormat::Base32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());
@@ -239,7 +239,7 @@ SV * convertHash(char * algo, char * s, int toBase32)
     PPCODE:
         try {
             auto h = Hash::parseAny(s, parseHashType(algo));
-            auto s = h.to_string(toBase32 ? Base32 : Base16, false);
+            auto s = h.to_string(toBase32 ? HashFormat::Base32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());

src/libexpr/eval-cache.cc

@@ -50,7 +50,7 @@ struct AttrDb
         Path cacheDir = getCacheDir() + "/nix/eval-cache-v5";
         createDirs(cacheDir);
 
-        Path dbPath = cacheDir + "/" + fingerprint.to_string(Base16, false) + ".sqlite";
+        Path dbPath = cacheDir + "/" + fingerprint.to_string(HashFormat::Base16, false) + ".sqlite";
 
         state->db = SQLite(dbPath);
         state->db.isCache();

src/libexpr/primops.cc

@@ -1758,7 +1758,7 @@ static void prim_hashFile(EvalState & state, const PosIdx pos, Value * * args, V
 
     auto path = realisePath(state, pos, *args[1]);
 
-    v.mkString(hashString(*ht, path.readFile()).to_string(Base16, false));
+    v.mkString(hashString(*ht, path.readFile()).to_string(HashFormat::Base16, false));
 }
 
 static RegisterPrimOp primop_hashFile({
@@ -3760,7 +3760,7 @@ static void prim_hashString(EvalState & state, const PosIdx pos, Value * * args,
     NixStringContext context; // discarded
     auto s = state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.hashString");
 
-    v.mkString(hashString(*ht, s).to_string(Base16, false));
+    v.mkString(hashString(*ht, s).to_string(HashFormat::Base16, false));
 }
 
 static RegisterPrimOp primop_hashString({
@@ -3774,6 +3774,101 @@ static RegisterPrimOp primop_hashString({
     .fun = prim_hashString,
 });
 
+static void prim_convertHash(EvalState & state, const PosIdx pos, Value * * args, Value & v)
+{
+    state.forceAttrs(*args[0], pos, "while evaluating the first argument passed to builtins.convertHash");
+    auto &inputAttrs = args[0]->attrs;
+
+    Bindings::iterator iteratorHash = getAttr(state, state.symbols.create("hash"), inputAttrs, "while locating the attribute 'hash'");
+    auto hash = state.forceStringNoCtx(*iteratorHash->value, pos, "while evaluating the attribute 'hash'");
+
+    Bindings::iterator iteratorHashAlgo = inputAttrs->find(state.symbols.create("hashAlgo"));
+    std::optional<HashType> ht = std::nullopt;
+    if (iteratorHashAlgo != inputAttrs->end()) {
+        ht = parseHashType(state.forceStringNoCtx(*iteratorHashAlgo->value, pos, "while evaluating the attribute 'hashAlgo'"));
+    }
+
+    Bindings::iterator iteratorToHashFormat = getAttr(state, state.symbols.create("toHashFormat"), args[0]->attrs, "while locating the attribute 'toHashFormat'");
+    HashFormat hf = parseHashFormat(state.forceStringNoCtx(*iteratorToHashFormat->value, pos, "while evaluating the attribute 'toHashFormat'"));
+
+    v.mkString(Hash::parseAny(hash, ht).to_string(hf, hf == HashFormat::SRI));
+}
+
+static RegisterPrimOp primop_convertHash({
+    .name = "__convertHash",
+    .args = {"args"},
+    .doc = R"(
+      Return the specified representation of a hash string, based on the attributes presented in *args*:
+
+      - `hash`
+
+        The hash to be converted.
+        The hash format is detected automatically.
+
+      - `hashAlgo`
+
+        The algorithm used to create the hash. Must be one of
+        - `"md5"`
+        - `"sha1"`
+        - `"sha256"`
+        - `"sha512"`
+
+        The attribute may be omitted when `hash` is an [SRI hash](https://www.w3.org/TR/SRI/#the-integrity-attribute) or when the hash is prefixed with the hash algorithm name followed by a colon.
+        That `<hashAlgo>:<hashBody>` syntax is supported for backwards compatibility with existing tooling.
+
+      - `toHashFormat`
+
+        The format of the resulting hash. Must be one of
+        - `"base16"`
+        - `"base32"`
+        - `"base64"`
+        - `"sri"`
+
+      The result hash is the *toHashFormat* representation of the hash *hash*.
+
+      > **Example**
+      >
+      >   Convert a SHA256 hash in Base16 to SRI:
+      >
+      > ```nix
+      > builtins.convertHash {
+      >   hash = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
+      >   toHashFormat = "sri";
+      >   hashAlgo = "sha256";
+      > }
+      > ```
+      >
+      >     "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU="
+
+      > **Example**
+      >
+      >   Convert a SHA256 hash in SRI to Base16:
+      >
+      > ```nix
+      > builtins.convertHash {
+      >   hash = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
+      >   toHashFormat = "base16";
+      > }
+      > ```
+      >
+      >     "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+
+      > **Example**
+      >
+      >   Convert a hash in the form `<hashAlgo>:<hashBody>` in Base16 to SRI:
+      >
+      > ```nix
+      > builtins.convertHash {
+      >   hash = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855";
+      >   toHashFormat = "sri";
+      > }
+      > ```
+      >
+      >     "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU="
+    )",
+    .fun = prim_convertHash,
+});
+
 struct RegexCache
 {
     // TODO use C++20 transparent comparison when available

src/libexpr/primops/fetchTree.cc

@@ -31,7 +31,7 @@ void emitTreeAttrs(
 
     auto narHash = input.getNarHash();
     assert(narHash);
-    attrs.alloc("narHash").mkString(narHash->to_string(SRI, true));
+    attrs.alloc("narHash").mkString(narHash->to_string(HashFormat::SRI, true));
 
     if (input.getType() == "git")
         attrs.alloc("submodules").mkBool(
@@ -297,7 +297,7 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
             : hashFile(htSHA256, state.store->toRealPath(storePath));
         if (hash != *expectedHash)
             state.debugThrowLastTrace(EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
-                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true)));
+                *url, expectedHash->to_string(HashFormat::Base32, true), hash.to_string(HashFormat::Base32, true)));
     }
 
     state.allowAndSetStorePathString(storePath, v);

src/libexpr/tests/error_traces.cc

@@ -1084,7 +1084,7 @@ namespace nix {
 
         ASSERT_TRACE1("hashString \"foo\" \"content\"",
                       UsageError,
-                      hintfmt("unknown hash algorithm '%s'", "foo"));
+                      hintfmt("unknown hash algorithm '%s', expect 'md5', 'sha1', 'sha256', or 'sha512'", "foo"));
 
         ASSERT_TRACE2("hashString \"sha256\" {}",
                       TypeError,

src/libfetchers/fetchers.cc

@@ -147,12 +147,12 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
     };
 
     auto narHash = store->queryPathInfo(tree.storePath)->narHash;
-    input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
+    input.attrs.insert_or_assign("narHash", narHash.to_string(HashFormat::SRI, true));
 
     if (auto prevNarHash = getNarHash()) {
         if (narHash != *prevNarHash)
             throw Error((unsigned int) 102, "NAR hash mismatch in input '%s' (%s), expected '%s', got '%s'",
-                to_string(), tree.actualPath, prevNarHash->to_string(SRI, true), narHash.to_string(SRI, true));
+                to_string(), tree.actualPath, prevNarHash->to_string(HashFormat::SRI, true), narHash.to_string(HashFormat::SRI, true));
     }
 
     if (auto prevLastModified = getLastModified()) {

src/libfetchers/git.cc

@@ -46,7 +46,7 @@ bool touchCacheFile(const Path & path, time_t touch_time)
 Path getCachePath(std::string_view key)
 {
     return getCacheDir() + "/nix/gitv3/" +
-        hashString(htSHA256, key).to_string(Base32, false);
+        hashString(htSHA256, key).to_string(HashFormat::Base32, false);
 }
 
 // Returns the name of the HEAD branch.
@@ -417,7 +417,7 @@ struct GitInputScheme : InputScheme
         auto checkHashType = [&](const std::optional<Hash> & hash)
         {
             if (hash.has_value() && !(hash->type == htSHA1 || hash->type == htSHA256))
-                throw Error("Hash '%s' is not supported by Git. Supported types are sha1 and sha256.", hash->to_string(Base16, true));
+                throw Error("Hash '%s' is not supported by Git. Supported types are sha1 and sha256.", hash->to_string(HashFormat::Base16, true));
         };
 
         auto getLockedAttrs = [&]()

src/libfetchers/github.cc

@@ -125,7 +125,7 @@ struct GitArchiveInputScheme : InputScheme
         auto path = owner + "/" + repo;
         assert(!(ref && rev));
         if (ref) path += "/" + *ref;
-        if (rev) path += "/" + rev->to_string(Base16, false);
+        if (rev) path += "/" + rev->to_string(HashFormat::Base16, false);
         return ParsedURL {
             .scheme = type(),
             .path = path,
@@ -296,7 +296,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
             : "https://api.%s/repos/%s/%s/tarball/%s";
 
         const auto url = fmt(urlFmt, host, getOwner(input), getRepo(input),
-            input.getRev()->to_string(Base16, false));
+            input.getRev()->to_string(HashFormat::Base16, false));
 
         return DownloadUrl { url, headers };
     }
@@ -362,7 +362,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         auto url = fmt("https://%s/api/v4/projects/%s%%2F%s/repository/archive.tar.gz?sha=%s",
             host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo"),
-            input.getRev()->to_string(Base16, false));
+            input.getRev()->to_string(HashFormat::Base16, false));
 
         Headers headers = makeHeadersWithAuthTokens(host);
         return DownloadUrl { url, headers };
@@ -449,7 +449,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("git.sr.ht");
         auto url = fmt("https://%s/%s/%s/archive/%s.tar.gz",
             host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo"),
-            input.getRev()->to_string(Base16, false));
+            input.getRev()->to_string(HashFormat::Base16, false));
 
         Headers headers = makeHeadersWithAuthTokens(host);
         return DownloadUrl { url, headers };

src/libfetchers/mercurial.cc

@@ -206,7 +206,7 @@ struct MercurialInputScheme : InputScheme
         auto checkHashType = [&](const std::optional<Hash> & hash)
         {
             if (hash.has_value() && hash->type != htSHA1)
-                throw Error("Hash '%s' is not supported by Mercurial. Only sha1 is supported.", hash->to_string(Base16, true));
+                throw Error("Hash '%s' is not supported by Mercurial. Only sha1 is supported.", hash->to_string(HashFormat::Base16, true));
         };
 
 
@@ -252,7 +252,7 @@ struct MercurialInputScheme : InputScheme
             }
         }
 
-        Path cacheDir = fmt("%s/nix/hg/%s", getCacheDir(), hashString(htSHA256, actualUrl).to_string(Base32, false));
+        Path cacheDir = fmt("%s/nix/hg/%s", getCacheDir(), hashString(htSHA256, actualUrl).to_string(HashFormat::Base32, false));
 
         /* If this is a commit hash that we already have, we don't
            have to pull again. */

src/libfetchers/tarball.cc

@@ -250,7 +250,7 @@ struct CurlInputScheme : InputScheme
         // NAR hashes are preferred over file hashes since tar/zip
         // files don't have a canonical representation.
         if (auto narHash = input.getNarHash())
-            url.query.insert_or_assign("narHash", narHash->to_string(SRI, true));
+            url.query.insert_or_assign("narHash", narHash->to_string(HashFormat::SRI, true));
         return url;
     }
 

src/libstore/binary-cache-store.cc

@@ -164,7 +164,7 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     auto [fileHash, fileSize] = fileHashSink.finish();
     narInfo->fileHash = fileHash;
     narInfo->fileSize = fileSize;
-    narInfo->url = "nar/" + narInfo->fileHash->to_string(Base32, false) + ".nar"
+    narInfo->url = "nar/" + narInfo->fileHash->to_string(HashFormat::Base32, false) + ".nar"
         + (compression == "xz" ? ".xz" :
            compression == "bzip2" ? ".bz2" :
            compression == "zstd" ? ".zst" :

src/libstore/build/local-derivation-goal.cc

@@ -1066,7 +1066,7 @@ void LocalDerivationGoal::initTmpDir() {
                 env[i.first] = i.second;
             } else {
                 auto hash = hashString(htSHA256, i.first);
-                std::string fn = ".attr-" + hash.to_string(Base32, false);
+                std::string fn = ".attr-" + hash.to_string(HashFormat::Base32, false);
                 Path p = tmpDir + "/" + fn;
                 writeFile(p, rewriteStrings(i.second, inputRewrites));
                 chownToBuilder(p);
@@ -2583,8 +2583,8 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
                     delayedException = std::make_exception_ptr(
                         BuildError("hash mismatch in fixed-output derivation '%s':\n  specified: %s\n     got:    %s",
                             worker.store.printStorePath(drvPath),
-                            wanted.to_string(SRI, true),
+                            wanted.to_string(HashFormat::SRI, true),
-                            got.to_string(SRI, true)));
+                            got.to_string(HashFormat::SRI, true)));
                 }
                 if (!newInfo0.references.empty())
                     delayedException = std::make_exception_ptr(

src/libstore/builtins/fetchurl.cc

@@ -65,7 +65,7 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
                 if (!hasSuffix(hashedMirror, "/")) hashedMirror += '/';
                 std::optional<HashType> ht = parseHashTypeOpt(getAttr("outputHashAlgo"));
                 Hash h = newHashAllowEmpty(getAttr("outputHash"), ht);
-                fetch(hashedMirror + printHashType(h.type) + "/" + h.to_string(Base16, false));
+                fetch(hashedMirror + printHashType(h.type) + "/" + h.to_string(HashFormat::Base16, false));
                 return;
             } catch (Error & e) {
                 debug(e.what());

src/libstore/content-address.cc

@@ -60,7 +60,7 @@ std::string ContentAddress::render() const
                 + makeFileIngestionPrefix(method);
         },
     }, method.raw)
-        + this->hash.to_string(Base32, true);
+        + this->hash.to_string(HashFormat::Base32, true);
 }
 
 /**

src/libstore/daemon.cc

@@ -334,7 +334,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         auto hash = store->queryPathInfo(path)->narHash;
         logger->stopWork();
-        to << hash.to_string(Base16, false);
+        to << hash.to_string(HashFormat::Base16, false);
         break;
     }
 

src/libstore/derivations.cc

@@ -542,7 +542,7 @@ std::string Derivation::unparse(const Store & store, bool maskOutputs,
             [&](const DerivationOutput::CAFixed & dof) {
                 s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(dof.path(store, name, i.first)));
                 s += ','; printUnquotedString(s, dof.ca.printMethodAlgo());
-                s += ','; printUnquotedString(s, dof.ca.hash.to_string(Base16, false));
+                s += ','; printUnquotedString(s, dof.ca.hash.to_string(HashFormat::Base16, false));
             },
             [&](const DerivationOutput::CAFloating & dof) {
                 s += ','; printUnquotedString(s, "");
@@ -775,7 +775,7 @@ DrvHash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOut
             auto & dof = std::get<DerivationOutput::CAFixed>(i.second.raw);
             auto hash = hashString(htSHA256, "fixed:out:"
                 + dof.ca.printMethodAlgo() + ":"
-                + dof.ca.hash.to_string(Base16, false) + ":"
+                + dof.ca.hash.to_string(HashFormat::Base16, false) + ":"
                 + store.printStorePath(dof.path(store, drv.name, i.first)));
             outputHashes.insert_or_assign(i.first, std::move(hash));
         }
@@ -820,7 +820,7 @@ DrvHash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOut
             const auto h = get(res.hashes, outputName);
             if (!h)
                 throw Error("no hash for output '%s' of derivation '%s'", outputName, drv.name);
-            inputs2[h->to_string(Base16, false)].value.insert(outputName);
+            inputs2[h->to_string(HashFormat::Base16, false)].value.insert(outputName);
         }
     }
 
@@ -925,7 +925,7 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
             [&](const DerivationOutput::CAFixed & dof) {
                 out << store.printStorePath(dof.path(store, drv.name, i.first))
                     << dof.ca.printMethodAlgo()
-                    << dof.ca.hash.to_string(Base16, false);
+                    << dof.ca.hash.to_string(HashFormat::Base16, false);
             },
             [&](const DerivationOutput::CAFloating & dof) {
                 out << ""
@@ -957,7 +957,7 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
 std::string hashPlaceholder(const OutputNameView outputName)
 {
     // FIXME: memoize?
-    return "/" + hashString(htSHA256, concatStrings("nix-output:", outputName)).to_string(Base32, false);
+    return "/" + hashString(htSHA256, concatStrings("nix-output:", outputName)).to_string(HashFormat::Base32, false);
 }
 
 
@@ -1162,7 +1162,7 @@ nlohmann::json DerivationOutput::toJSON(
         [&](const DerivationOutput::CAFixed & dof) {
             res["path"] = store.printStorePath(dof.path(store, drvName, outputName));
             res["hashAlgo"] = dof.ca.printMethodAlgo();
-            res["hash"] = dof.ca.hash.to_string(Base16, false);
+            res["hash"] = dof.ca.hash.to_string(HashFormat::Base16, false);
             // FIXME print refs?
         },
         [&](const DerivationOutput::CAFloating & dof) {

src/libstore/downstream-placeholder.cc

@@ -5,7 +5,7 @@ namespace nix {
 
 std::string DownstreamPlaceholder::render() const
 {
-    return "/" + hash.to_string(Base32, false);
+    return "/" + hash.to_string(HashFormat::Base32, false);
 }
 
 
@@ -31,7 +31,7 @@ DownstreamPlaceholder DownstreamPlaceholder::unknownDerivation(
     xpSettings.require(Xp::DynamicDerivations);
     auto compressed = compressHash(placeholder.hash, 20);
     auto clearText = "nix-computed-output:"
-        + compressed.to_string(Base32, false)
+        + compressed.to_string(HashFormat::Base32, false)
         + ":" + std::string { outputName };
     return DownstreamPlaceholder {
         hashString(htSHA256, clearText)

src/libstore/export-import.cc

@@ -41,7 +41,7 @@ void Store::exportPath(const StorePath & path, Sink & sink)
     Hash hash = hashSink.currentHash().first;
     if (hash != info->narHash && info->narHash != Hash(info->narHash.type))
         throw Error("hash of path '%s' has changed from '%s' to '%s'!",
-            printStorePath(path), info->narHash.to_string(Base32, true), hash.to_string(Base32, true));
+            printStorePath(path), info->narHash.to_string(HashFormat::Base32, true), hash.to_string(HashFormat::Base32, true));
 
     teeSink
         << exportMagic

src/libstore/gc.cc

@@ -43,7 +43,7 @@ static void makeSymlink(const Path & link, const Path & target)
 
 void LocalStore::addIndirectRoot(const Path & path)
 {
-    std::string hash = hashString(htSHA1, path).to_string(Base32, false);
+    std::string hash = hashString(htSHA1, path).to_string(HashFormat::Base32, false);
     Path realRoot = canonPath(fmt("%1%/%2%/auto/%3%", stateDir, gcRootsDir, hash));
     makeSymlink(realRoot, path);
 }

src/libstore/legacy-ssh-store.cc

@@ -209,7 +209,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
                 << ServeProto::Command::AddToStoreNar
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
-                << info.narHash.to_string(Base16, false);
+                << info.narHash.to_string(HashFormat::Base16, false);
             ServeProto::write(*this, *conn, info.references);
             conn->to
                 << info.registrationTime

src/libstore/local-store.cc

@@ -826,7 +826,7 @@ uint64_t LocalStore::addValidPath(State & state,
 
     state.stmts->RegisterValidPath.use()
         (printStorePath(info.path))
-        (info.narHash.to_string(Base16, true))
+        (info.narHash.to_string(HashFormat::Base16, true))
         (info.registrationTime == 0 ? time(0) : info.registrationTime)
         (info.deriver ? printStorePath(*info.deriver) : "", (bool) info.deriver)
         (info.narSize, info.narSize != 0)
@@ -933,7 +933,7 @@ void LocalStore::updatePathInfo(State & state, const ValidPathInfo & info)
 {
     state.stmts->UpdatePathInfo.use()
         (info.narSize, info.narSize != 0)
-        (info.narHash.to_string(Base16, true))
+        (info.narHash.to_string(HashFormat::Base16, true))
         (info.ultimate ? 1 : 0, info.ultimate)
         (concatStringsSep(" ", info.sigs), !info.sigs.empty())
         (renderContentAddress(info.ca), (bool) info.ca)
@@ -1236,7 +1236,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
             if (hashResult.first != info.narHash)
                 throw Error("hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
-                    printStorePath(info.path), info.narHash.to_string(Base32, true), hashResult.first.to_string(Base32, true));
+                    printStorePath(info.path), info.narHash.to_string(HashFormat::Base32, true), hashResult.first.to_string(HashFormat::Base32, true));
 
             if (hashResult.second != info.narSize)
                 throw Error("size mismatch importing path '%s';\n  specified: %s\n  got:       %s",
@@ -1252,8 +1252,8 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
                 if (specified.hash != actualHash.hash) {
                     throw Error("ca hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
                         printStorePath(info.path),
-                        specified.hash.to_string(Base32, true),
+                        specified.hash.to_string(HashFormat::Base32, true),
-                        actualHash.hash.to_string(Base32, true));
+                        actualHash.hash.to_string(HashFormat::Base32, true));
                 }
             }
 
@@ -1545,7 +1545,7 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
         for (auto & link : readDirectory(linksDir)) {
             printMsg(lvlTalkative, "checking contents of '%s'", link.name);
             Path linkPath = linksDir + "/" + link.name;
-            std::string hash = hashPath(htSHA256, linkPath).first.to_string(Base32, false);
+            std::string hash = hashPath(htSHA256, linkPath).first.to_string(HashFormat::Base32, false);
             if (hash != link.name) {
                 printError("link '%s' was modified! expected hash '%s', got '%s'",
                     linkPath, link.name, hash);
@@ -1578,7 +1578,7 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 
                 if (info->narHash != nullHash && info->narHash != current.first) {
                     printError("path '%s' was modified! expected hash '%s', got '%s'",
-                        printStorePath(i), info->narHash.to_string(Base32, true), current.first.to_string(Base32, true));
+                        printStorePath(i), info->narHash.to_string(HashFormat::Base32, true), current.first.to_string(HashFormat::Base32, true));
                     if (repair) repairPath(i); else errors = true;
                 } else {
 

src/libstore/nar-info-disk-cache.cc

@@ -332,9 +332,9 @@ public:
                     (std::string(info->path.name()))
                     (narInfo ? narInfo->url : "", narInfo != 0)
                     (narInfo ? narInfo->compression : "", narInfo != 0)
-                    (narInfo && narInfo->fileHash ? narInfo->fileHash->to_string(Base32, true) : "", narInfo && narInfo->fileHash)
+                    (narInfo && narInfo->fileHash ? narInfo->fileHash->to_string(HashFormat::Base32, true) : "", narInfo && narInfo->fileHash)
                     (narInfo ? narInfo->fileSize : 0, narInfo != 0 && narInfo->fileSize)
-                    (info->narHash.to_string(Base32, true))
+                    (info->narHash.to_string(HashFormat::Base32, true))
                     (info->narSize)
                     (concatStringsSep(" ", info->shortRefs()))
                     (info->deriver ? std::string(info->deriver->to_string()) : "", (bool) info->deriver)

src/libstore/nar-info.cc

@@ -105,10 +105,10 @@ std::string NarInfo::to_string(const Store & store) const
     assert(compression != "");
     res += "Compression: " + compression + "\n";
     assert(fileHash && fileHash->type == htSHA256);
-    res += "FileHash: " + fileHash->to_string(Base32, true) + "\n";
+    res += "FileHash: " + fileHash->to_string(HashFormat::Base32, true) + "\n";
     res += "FileSize: " + std::to_string(fileSize) + "\n";
     assert(narHash.type == htSHA256);
-    res += "NarHash: " + narHash.to_string(Base32, true) + "\n";
+    res += "NarHash: " + narHash.to_string(HashFormat::Base32, true) + "\n";
     res += "NarSize: " + std::to_string(narSize) + "\n";
 
     res += "References: " + concatStringsSep(" ", shortRefs()) + "\n";

src/libstore/optimise-store.cc

@@ -146,10 +146,10 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
        contents of the symlink (i.e. the result of readlink()), not
        the contents of the target (which may not even exist). */
     Hash hash = hashPath(htSHA256, path).first;
-    debug("'%1%' has hash '%2%'", path, hash.to_string(Base32, true));
+    debug("'%1%' has hash '%2%'", path, hash.to_string(HashFormat::Base32, true));
 
     /* Check if this is a known hash. */
-    Path linkPath = linksDir + "/" + hash.to_string(Base32, false);
+    Path linkPath = linksDir + "/" + hash.to_string(HashFormat::Base32, false);
 
     /* Maybe delete the link, if it has been corrupted. */
     if (pathExists(linkPath)) {

src/libstore/path-info.cc

@@ -12,7 +12,7 @@ std::string ValidPathInfo::fingerprint(const Store & store) const
             store.printStorePath(path));
     return
         "1;" + store.printStorePath(path) + ";"
-        + narHash.to_string(Base32, true) + ";"
+        + narHash.to_string(HashFormat::Base32, true) + ";"
         + std::to_string(narSize) + ";"
         + concatStringsSep(",", store.printStorePathSet(references));
 }
@@ -161,7 +161,7 @@ void ValidPathInfo::write(
     if (includePath)
         sink << store.printStorePath(path);
     sink << (deriver ? store.printStorePath(*deriver) : "")
-         << narHash.to_string(Base16, false);
+         << narHash.to_string(HashFormat::Base16, false);
     WorkerProto::write(store,
         WorkerProto::WriteConn { .to = sink },
         references);

src/libstore/path.cc

@@ -35,7 +35,7 @@ StorePath::StorePath(std::string_view _baseName)
 }
 
 StorePath::StorePath(const Hash & hash, std::string_view _name)
-    : baseName((hash.to_string(Base32, false) + "-").append(std::string(_name)))
+    : baseName((hash.to_string(HashFormat::Base32, false) + "-").append(std::string(_name)))
 {
     checkName(baseName, name());
 }

src/libstore/realisation.hh

@@ -39,7 +39,7 @@ struct DrvOutput {
     std::string to_string() const;
 
     std::string strHash() const
-    { return drvHash.to_string(Base16, true); }
+    { return drvHash.to_string(HashFormat::Base16, true); }
 
     static DrvOutput parse(const std::string &);
 

src/libstore/remote-store.cc

@@ -541,7 +541,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
         conn->to << WorkerProto::Op::AddToStoreNar
                  << printStorePath(info.path)
                  << (info.deriver ? printStorePath(*info.deriver) : "")
-                 << info.narHash.to_string(Base16, false);
+                 << info.narHash.to_string(HashFormat::Base16, false);
         WorkerProto::write(*this, *conn, info.references);
         conn->to << info.registrationTime << info.narSize
                  << info.ultimate << info.sigs << renderContentAddress(info.ca)

src/libstore/store-api.cc

@@ -154,7 +154,7 @@ StorePath Store::makeStorePath(std::string_view type,
 StorePath Store::makeStorePath(std::string_view type,
     const Hash & hash, std::string_view name) const
 {
-    return makeStorePath(type, hash.to_string(Base16, true), name);
+    return makeStorePath(type, hash.to_string(HashFormat::Base16, true), name);
 }
 
 
@@ -192,7 +192,7 @@ StorePath Store::makeFixedOutputPath(std::string_view name, const FixedOutputInf
             hashString(htSHA256,
                 "fixed:out:"
                 + makeFileIngestionPrefix(info.method)
-                + info.hash.to_string(Base16, true) + ":"),
+                + info.hash.to_string(HashFormat::Base16, true) + ":"),
             name);
     }
 }
@@ -884,7 +884,7 @@ std::string Store::makeValidityRegistration(const StorePathSet & paths,
         auto info = queryPathInfo(i);
 
         if (showHash) {
-            s += info->narHash.to_string(Base16, false) + "\n";
+            s += info->narHash.to_string(HashFormat::Base16, false) + "\n";
             s += fmt("%1%\n", info->narSize);
         }
 
@@ -938,7 +938,7 @@ StorePathSet Store::exportReferences(const StorePathSet & storePaths, const Stor
 
 json Store::pathInfoToJSON(const StorePathSet & storePaths,
     bool includeImpureInfo, bool showClosureSize,
-    Base hashBase,
+    HashFormat hashFormat,
     AllowInvalidFlag allowInvalid)
 {
     json::array_t jsonList = json::array();
@@ -951,7 +951,7 @@ json Store::pathInfoToJSON(const StorePathSet & storePaths,
 
             jsonPath["path"] = printStorePath(info->path);
             jsonPath["valid"] = true;
-            jsonPath["narHash"] = info->narHash.to_string(hashBase, true);
+            jsonPath["narHash"] = info->narHash.to_string(hashFormat, true);
             jsonPath["narSize"] = info->narSize;
 
             {
@@ -993,7 +993,7 @@ json Store::pathInfoToJSON(const StorePathSet & storePaths,
                     if (!narInfo->url.empty())
                         jsonPath["url"] = narInfo->url;
                     if (narInfo->fileHash)
-                        jsonPath["downloadHash"] = narInfo->fileHash->to_string(hashBase, true);
+                        jsonPath["downloadHash"] = narInfo->fileHash->to_string(hashFormat, true);
                     if (narInfo->fileSize)
                         jsonPath["downloadSize"] = narInfo->fileSize;
                     if (showClosureSize)

src/libstore/store-api.hh

@@ -676,7 +676,7 @@ public:
      */
     nlohmann::json pathInfoToJSON(const StorePathSet & storePaths,
         bool includeImpureInfo, bool showClosureSize,
-        Base hashBase = Base32,
+        HashFormat hashFormat = HashFormat::Base32,
         AllowInvalidFlag allowInvalid = DisallowInvalid);
 
     /**

src/libutil/hash.cc

@@ -111,26 +111,26 @@ static std::string printHash32(const Hash & hash)
 std::string printHash16or32(const Hash & hash)
 {
     assert(hash.type);
-    return hash.to_string(hash.type == htMD5 ? Base16 : Base32, false);
+    return hash.to_string(hash.type == htMD5 ? HashFormat::Base16 : HashFormat::Base32, false);
 }
 
 
-std::string Hash::to_string(Base base, bool includeType) const
+std::string Hash::to_string(HashFormat hashFormat, bool includeType) const
 {
     std::string s;
-    if (base == SRI || includeType) {
+    if (hashFormat == HashFormat::SRI || includeType) {
         s += printHashType(type);
-        s += base == SRI ? '-' : ':';
+        s += hashFormat == HashFormat::SRI ? '-' : ':';
     }
-    switch (base) {
+    switch (hashFormat) {
-    case Base16:
+    case HashFormat::Base16:
         s += printHash16(*this);
         break;
-    case Base32:
+    case HashFormat::Base32:
         s += printHash32(*this);
         break;
-    case Base64:
+    case HashFormat::Base64:
-    case SRI:
+    case HashFormat::SRI:
         s += base64Encode(std::string_view((const char *) hash, hashSize));
         break;
     }
@@ -267,7 +267,7 @@ Hash newHashAllowEmpty(std::string_view hashStr, std::optional<HashType> ht)
         if (!ht)
             throw BadHash("empty hash requires explicit hash type");
         Hash h(*ht);
-        warn("found empty hash, assuming '%s'", h.to_string(SRI, true));
+        warn("found empty hash, assuming '%s'", h.to_string(HashFormat::SRI, true));
         return h;
     } else
         return Hash::parseAny(hashStr, ht);
@@ -386,13 +386,48 @@ Hash compressHash(const Hash & hash, unsigned int newSize)
 }
 
 
+std::optional<HashFormat> parseHashFormatOpt(std::string_view hashFormatName)
+{
+    if (hashFormatName == "base16") return HashFormat::Base16;
+    if (hashFormatName == "base32") return HashFormat::Base32;
+    if (hashFormatName == "base64") return HashFormat::Base64;
+    if (hashFormatName == "sri") return HashFormat::SRI;
+    return std::nullopt;
+}
+
+HashFormat parseHashFormat(std::string_view hashFormatName)
+{
+    auto opt_f = parseHashFormatOpt(hashFormatName);
+    if (opt_f)
+        return *opt_f;
+    throw UsageError("unknown hash format '%1%', expect 'base16', 'base32', 'base64', or 'sri'", hashFormatName);
+}
+
+std::string_view printHashFormat(HashFormat HashFormat)
+{
+    switch (HashFormat) {
+    case HashFormat::Base64:
+        return "base64";
+    case HashFormat::Base32:
+        return "base32";
+    case HashFormat::Base16:
+        return "base16";
+    case HashFormat::SRI:
+        return "sri";
+    default:
+        // illegal hash base enum value internally, as opposed to external input
+        // which should be validated with nice error message.
+        assert(false);
+    }
+}
+
 std::optional<HashType> parseHashTypeOpt(std::string_view s)
 {
     if (s == "md5") return htMD5;
-    else if (s == "sha1") return htSHA1;
+    if (s == "sha1") return htSHA1;
-    else if (s == "sha256") return htSHA256;
+    if (s == "sha256") return htSHA256;
-    else if (s == "sha512") return htSHA512;
+    if (s == "sha512") return htSHA512;
-    else return std::optional<HashType> {};
+    return std::nullopt;
 }
 
 HashType parseHashType(std::string_view s)
@@ -401,7 +436,7 @@ HashType parseHashType(std::string_view s)
     if (opt_h)
         return *opt_h;
     else
-        throw UsageError("unknown hash algorithm '%1%'", s);
+        throw UsageError("unknown hash algorithm '%1%', expect 'md5', 'sha1', 'sha256', or 'sha512'", s);
 }
 
 std::string_view printHashType(HashType ht)

src/libutil/hash.hh

@@ -23,7 +23,21 @@ extern std::set<std::string> hashTypes;
 
 extern const std::string base32Chars;
 
-enum Base : int { Base64, Base32, Base16, SRI };
+/**
+ * @brief Enumeration representing the hash formats.
+ */
+enum struct HashFormat : int {
+    /// @brief Base 64 encoding.
+    /// @see [IETF RFC 4648, section 4](https://datatracker.ietf.org/doc/html/rfc4648#section-4).
+    Base64,
+    /// @brief Nix-specific base-32 encoding. @see base32Chars
+    Base32,
+    /// @brief Lowercase hexadecimal encoding. @see base16Chars
+    Base16,
+    /// @brief "<hash algo>:<Base 64 hash>", format of the SRI integrity attribute.
+    /// @see W3C recommendation [Subresource Intergrity](https://www.w3.org/TR/SRI/).
+    SRI
+};
 
 
 struct Hash
@@ -114,16 +128,16 @@ public:
      * or base-64. By default, this is prefixed by the hash type
      * (e.g. "sha256:").
      */
-    std::string to_string(Base base, bool includeType) const;
+    std::string to_string(HashFormat hashFormat, bool includeType) const;
 
     std::string gitRev() const
     {
-        return to_string(Base16, false);
+        return to_string(HashFormat::Base16, false);
     }
 
     std::string gitShortRev() const
     {
-        return std::string(to_string(Base16, false), 0, 7);
+        return std::string(to_string(HashFormat::Base16, false), 0, 7);
     }
 
     static Hash dummy;
@@ -167,6 +181,21 @@ HashResult hashPath(HashType ht, const Path & path,
  */
 Hash compressHash(const Hash & hash, unsigned int newSize);
 
+/**
+ * Parse a string representing a hash format.
+ */
+HashFormat parseHashFormat(std::string_view hashFormatName);
+
+/**
+ * std::optional version of parseHashFormat that doesn't throw error.
+ */
+std::optional<HashFormat> parseHashFormatOpt(std::string_view hashFormatName);
+
+/**
+ * The reverse of parseHashFormat.
+ */
+std::string_view printHashFormat(HashFormat hashFormat);
+
 /**
  * Parse a string representing a hash type.
  */

src/libutil/tests/hash.cc

@@ -18,28 +18,28 @@ namespace nix {
         // values taken from: https://tools.ietf.org/html/rfc1321
         auto s1 = "";
         auto hash = hashString(HashType::htMD5, s1);
-        ASSERT_EQ(hash.to_string(Base::Base16, true), "md5:d41d8cd98f00b204e9800998ecf8427e");
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true), "md5:d41d8cd98f00b204e9800998ecf8427e");
     }
 
     TEST(hashString, testKnownMD5Hashes2) {
         // values taken from: https://tools.ietf.org/html/rfc1321
         auto s2 = "abc";
         auto hash = hashString(HashType::htMD5, s2);
-        ASSERT_EQ(hash.to_string(Base::Base16, true), "md5:900150983cd24fb0d6963f7d28e17f72");
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true), "md5:900150983cd24fb0d6963f7d28e17f72");
     }
 
     TEST(hashString, testKnownSHA1Hashes1) {
         // values taken from: https://tools.ietf.org/html/rfc3174
         auto s = "abc";
         auto hash = hashString(HashType::htSHA1, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),"sha1:a9993e364706816aba3e25717850c26c9cd0d89d");
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),"sha1:a9993e364706816aba3e25717850c26c9cd0d89d");
     }
 
     TEST(hashString, testKnownSHA1Hashes2) {
         // values taken from: https://tools.ietf.org/html/rfc3174
         auto s = "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq";
         auto hash = hashString(HashType::htSHA1, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),"sha1:84983e441c3bd26ebaae4aa1f95129e5e54670f1");
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),"sha1:84983e441c3bd26ebaae4aa1f95129e5e54670f1");
     }
 
     TEST(hashString, testKnownSHA256Hashes1) {
@@ -47,7 +47,7 @@ namespace nix {
         auto s = "abc";
 
         auto hash = hashString(HashType::htSHA256, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),
                 "sha256:ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad");
     }
 
@@ -55,7 +55,7 @@ namespace nix {
         // values taken from: https://tools.ietf.org/html/rfc4634
         auto s = "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq";
         auto hash = hashString(HashType::htSHA256, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),
                 "sha256:248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1");
     }
 
@@ -63,7 +63,7 @@ namespace nix {
         // values taken from: https://tools.ietf.org/html/rfc4634
         auto s = "abc";
         auto hash = hashString(HashType::htSHA512, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),
                 "sha512:ddaf35a193617abacc417349ae20413112e6fa4e89a9"
                 "7ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd"
                 "454d4423643ce80e2a9ac94fa54ca49f");
@@ -74,11 +74,26 @@ namespace nix {
         auto s = "abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu";
 
         auto hash = hashString(HashType::htSHA512, s);
-        ASSERT_EQ(hash.to_string(Base::Base16, true),
+        ASSERT_EQ(hash.to_string(HashFormat::Base16, true),
                 "sha512:8e959b75dae313da8cf4f72814fc143f8f7779c6eb9f7fa1"
                 "7299aeadb6889018501d289e4900f7e4331b99dec4b5433a"
                 "c7d329eeb6dd26545e96e55b874be909");
     }
+
+    /* ----------------------------------------------------------------------------
+     * parseHashFormat, parseHashFormatOpt, printHashFormat
+     * --------------------------------------------------------------------------*/
+
+    TEST(hashFormat, testRoundTripPrintParse) {
+        for (const HashFormat hashFormat: { HashFormat::Base64, HashFormat::Base32, HashFormat::Base16, HashFormat::SRI}) {
+            ASSERT_EQ(parseHashFormat(printHashFormat(hashFormat)), hashFormat);
+            ASSERT_EQ(*parseHashFormatOpt(printHashFormat(hashFormat)), hashFormat);
+        }
+    }
+
+    TEST(hashFormat, testParseHashFormatOptException) {
+        ASSERT_EQ(parseHashFormatOpt("sha0042"), std::nullopt);
+    }
 }
 
 namespace rc {

src/nix-store/nix-store.cc

@@ -406,7 +406,7 @@ static void opQuery(Strings opFlags, Strings opArgs)
                     auto info = store->queryPathInfo(j);
                     if (query == qHash) {
                         assert(info->narHash.type == htSHA256);
-                        cout << fmt("%s\n", info->narHash.to_string(Base32, true));
+                        cout << fmt("%s\n", info->narHash.to_string(HashFormat::Base32, true));
                     } else if (query == qSize)
                         cout << fmt("%d\n", info->narSize);
                 }
@@ -769,8 +769,8 @@ static void opVerifyPath(Strings opFlags, Strings opArgs)
         if (current.first != info->narHash) {
             printError("path '%s' was modified! expected hash '%s', got '%s'",
                 store->printStorePath(path),
-                info->narHash.to_string(Base32, true),
+                info->narHash.to_string(HashFormat::Base32, true),
-                current.first.to_string(Base32, true));
+                current.first.to_string(HashFormat::Base32, true));
             status = 1;
         }
     }
@@ -892,7 +892,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                         out << info->narSize // downloadSize
                             << info->narSize;
                         if (GET_PROTOCOL_MINOR(clientVersion) >= 4)
-                            out << info->narHash.to_string(Base32, true)
+                            out << info->narHash.to_string(HashFormat::Base32, true)
                                 << renderContentAddress(info->ca)
                                 << info->sigs;
                     } catch (InvalidPath &) {

src/nix/flake.cc

@@ -179,7 +179,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
             j["url"] = flake.lockedRef.to_string(); // FIXME: rename to lockedUrl
             j["locked"] = fetchers::attrsToJSON(flake.lockedRef.toAttrs());
             if (auto rev = flake.lockedRef.input.getRev())
-                j["revision"] = rev->to_string(Base16, false);
+                j["revision"] = rev->to_string(HashFormat::Base16, false);
             if (auto dirtyRev = fetchers::maybeGetStrAttr(flake.lockedRef.toAttrs(), "dirtyRev"))
                 j["dirtyRevision"] = *dirtyRev;
             if (auto revCount = flake.lockedRef.input.getRevCount())
@@ -206,7 +206,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
             if (auto rev = flake.lockedRef.input.getRev())
                 logger->cout(
                     ANSI_BOLD "Revision:" ANSI_NORMAL "      %s",
-                    rev->to_string(Base16, false));
+                    rev->to_string(HashFormat::Base16, false));
             if (auto dirtyRev = fetchers::maybeGetStrAttr(flake.lockedRef.toAttrs(), "dirtyRev"))
                 logger->cout(
                     ANSI_BOLD "Revision:" ANSI_NORMAL "      %s",
@@ -1345,7 +1345,7 @@ struct CmdFlakePrefetch : FlakeCommand, MixJSON
         if (json) {
             auto res = nlohmann::json::object();
             res["storePath"] = store->printStorePath(tree.storePath);
-            res["hash"] = hash.to_string(SRI, true);
+            res["hash"] = hash.to_string(HashFormat::SRI, true);
             res["original"] = fetchers::attrsToJSON(resolvedRef.toAttrs());
             res["locked"] = fetchers::attrsToJSON(lockedRef.toAttrs());
             logger->cout(res.dump());
@@ -1353,7 +1353,7 @@ struct CmdFlakePrefetch : FlakeCommand, MixJSON
             notice("Downloaded '%s' to '%s' (hash '%s').",
                 lockedRef.to_string(),
                 store->printStorePath(tree.storePath),
-                hash.to_string(SRI, true));
+                hash.to_string(HashFormat::SRI, true));
         }
     }
 };

src/nix/hash.cc

@@ -11,7 +11,7 @@ using namespace nix;
 struct CmdHashBase : Command
 {
     FileIngestionMethod mode;
-    Base base = SRI;
+    HashFormat hashFormat = HashFormat::SRI;
     bool truncate = false;
     HashType ht = htSHA256;
     std::vector<std::string> paths;
@@ -22,25 +22,25 @@ struct CmdHashBase : Command
         addFlag({
             .longName = "sri",
             .description = "Print the hash in SRI format.",
-            .handler = {&base, SRI},
+            .handler = {&hashFormat, HashFormat::SRI},
         });
 
         addFlag({
             .longName = "base64",
             .description = "Print the hash in base-64 format.",
-            .handler = {&base, Base64},
+            .handler = {&hashFormat, HashFormat::Base64},
         });
 
         addFlag({
             .longName = "base32",
             .description = "Print the hash in base-32 (Nix-specific) format.",
-            .handler = {&base, Base32},
+            .handler = {&hashFormat, HashFormat::Base32},
         });
 
         addFlag({
             .longName = "base16",
             .description = "Print the hash in base-16 format.",
-            .handler = {&base, Base16},
+            .handler = {&hashFormat, HashFormat::Base16},
         });
 
         addFlag(Flag::mkHashTypeFlag("type", &ht));
@@ -94,18 +94,18 @@ struct CmdHashBase : Command
 
             Hash h = hashSink->finish().first;
             if (truncate && h.hashSize > 20) h = compressHash(h, 20);
-            logger->cout(h.to_string(base, base == SRI));
+            logger->cout(h.to_string(hashFormat, hashFormat == HashFormat::SRI));
         }
     }
 };
 
 struct CmdToBase : Command
 {
-    Base base;
+    HashFormat hashFormat;
     std::optional<HashType> ht;
     std::vector<std::string> args;
 
-    CmdToBase(Base base) : base(base)
+    CmdToBase(HashFormat hashFormat) : hashFormat(hashFormat)
     {
         addFlag(Flag::mkHashTypeOptFlag("type", &ht));
         expectArgs("strings", &args);
@@ -114,16 +114,16 @@ struct CmdToBase : Command
     std::string description() override
     {
         return fmt("convert a hash to %s representation",
-            base == Base16 ? "base-16" :
+            hashFormat == HashFormat::Base16 ? "base-16" :
-            base == Base32 ? "base-32" :
+            hashFormat == HashFormat::Base32 ? "base-32" :
-            base == Base64 ? "base-64" :
+            hashFormat == HashFormat::Base64 ? "base-64" :
             "SRI");
     }
 
     void run() override
     {
         for (auto s : args)
-            logger->cout(Hash::parseAny(s, ht).to_string(base, base == SRI));
+            logger->cout(Hash::parseAny(s, ht).to_string(hashFormat, hashFormat == HashFormat::SRI));
     }
 };
 
@@ -133,10 +133,10 @@ struct CmdHash : NixMultiCommand
         : MultiCommand({
                 {"file", []() { return make_ref<CmdHashBase>(FileIngestionMethod::Flat);; }},
                 {"path", []() { return make_ref<CmdHashBase>(FileIngestionMethod::Recursive); }},
-                {"to-base16", []() { return make_ref<CmdToBase>(Base16); }},
+                {"to-base16", []() { return make_ref<CmdToBase>(HashFormat::Base16); }},
-                {"to-base32", []() { return make_ref<CmdToBase>(Base32); }},
+                {"to-base32", []() { return make_ref<CmdToBase>(HashFormat::Base32); }},
-                {"to-base64", []() { return make_ref<CmdToBase>(Base64); }},
+                {"to-base64", []() { return make_ref<CmdToBase>(HashFormat::Base64); }},
-                {"to-sri", []() { return make_ref<CmdToBase>(SRI); }},
+                {"to-sri", []() { return make_ref<CmdToBase>(HashFormat::SRI); }},
           })
     { }
 
@@ -162,7 +162,7 @@ static int compatNixHash(int argc, char * * argv)
 {
     std::optional<HashType> ht;
     bool flat = false;
-    Base base = Base16;
+    HashFormat hashFormat = HashFormat::Base16;
     bool truncate = false;
     enum { opHash, opTo } op = opHash;
     std::vector<std::string> ss;
@@ -173,10 +173,10 @@ static int compatNixHash(int argc, char * * argv)
         else if (*arg == "--version")
             printVersion("nix-hash");
         else if (*arg == "--flat") flat = true;
-        else if (*arg == "--base16") base = Base16;
+        else if (*arg == "--base16") hashFormat = HashFormat::Base16;
-        else if (*arg == "--base32") base = Base32;
+        else if (*arg == "--base32") hashFormat = HashFormat::Base32;
-        else if (*arg == "--base64") base = Base64;
+        else if (*arg == "--base64") hashFormat = HashFormat::Base64;
-        else if (*arg == "--sri") base = SRI;
+        else if (*arg == "--sri") hashFormat = HashFormat::SRI;
         else if (*arg == "--truncate") truncate = true;
         else if (*arg == "--type") {
             std::string s = getArg(*arg, arg, end);
@@ -184,19 +184,19 @@ static int compatNixHash(int argc, char * * argv)
         }
         else if (*arg == "--to-base16") {
             op = opTo;
-            base = Base16;
+            hashFormat = HashFormat::Base16;
         }
         else if (*arg == "--to-base32") {
             op = opTo;
-            base = Base32;
+            hashFormat = HashFormat::Base32;
         }
         else if (*arg == "--to-base64") {
             op = opTo;
-            base = Base64;
+            hashFormat = HashFormat::Base64;
         }
         else if (*arg == "--to-sri") {
             op = opTo;
-            base = SRI;
+            hashFormat = HashFormat::SRI;
         }
         else if (*arg != "" && arg->at(0) == '-')
             return false;
@@ -209,14 +209,14 @@ static int compatNixHash(int argc, char * * argv)
         CmdHashBase cmd(flat ? FileIngestionMethod::Flat : FileIngestionMethod::Recursive);
         if (!ht.has_value()) ht = htMD5;
         cmd.ht = ht.value();
-        cmd.base = base;
+        cmd.hashFormat = hashFormat;
         cmd.truncate = truncate;
         cmd.paths = ss;
         cmd.run();
     }
 
     else {
-        CmdToBase cmd(base);
+        CmdToBase cmd(hashFormat);
         cmd.args = ss;
         if (ht.has_value()) cmd.ht = ht;
         cmd.run();

src/nix/path-info.cc

@@ -90,7 +90,7 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
             std::cout << store->pathInfoToJSON(
                 // FIXME: preserve order?
                 StorePathSet(storePaths.begin(), storePaths.end()),
-                true, showClosureSize, SRI, AllowInvalid).dump();
+                true, showClosureSize, HashFormat::SRI, AllowInvalid).dump();
         }
 
         else {

src/nix/prefetch.cc

@@ -310,13 +310,13 @@ struct CmdStorePrefetchFile : StoreCommand, MixJSON
         if (json) {
             auto res = nlohmann::json::object();
             res["storePath"] = store->printStorePath(storePath);
-            res["hash"] = hash.to_string(SRI, true);
+            res["hash"] = hash.to_string(HashFormat::SRI, true);
             logger->cout(res.dump());
         } else {
             notice("Downloaded '%s' to '%s' (hash '%s').",
                 url,
                 store->printStorePath(storePath),
-                hash.to_string(SRI, true));
+                hash.to_string(HashFormat::SRI, true));
         }
     }
 };

src/nix/verify.cc

@@ -108,8 +108,8 @@ struct CmdVerify : StorePathsCommand
                         act2.result(resCorruptedPath, store->printStorePath(info->path));
                         printError("path '%s' was modified! expected hash '%s', got '%s'",
                             store->printStorePath(info->path),
-                            info->narHash.to_string(Base32, true),
+                            info->narHash.to_string(HashFormat::Base32, true),
-                            hash.first.to_string(Base32, true));
+                            hash.first.to_string(HashFormat::Base32, true));
                     }
                 }
 

tests/functional/lang/eval-okay-convertHash.exp

@@ -0,0 +1 @@
+{ hashesBase16 = [ "d41d8cd98f00b204e9800998ecf8427e" "6c69ee7f211c640419d5366cc076ae46" "bb3438fbabd460ea6dbd27d153e2233b" "da39a3ee5e6b4b0d3255bfef95601890afd80709" "cd54e8568c1b37cf1e5badb0779bcbf382212189" "6d12e10b1d331dad210e47fd25d4f260802b7e77" "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855" "900a4469df00ccbfd0c145c6d1e4b7953dd0afafadd7534e3a4019e8d38fc663" "ad0387b3bd8652f730ca46d25f9c170af0fd589f42e7f23f5a9e6412d97d7e56" "cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e" "9d0886f8c6b389398a16257bc79780fab9831c7fc11c8ab07fa732cb7b348feade382f92617c9c5305fefba0af02ab5fd39a587d330997ff5bd0db19f7666653" "21644b72aa259e5a588cd3afbafb1d4310f4889680f6c83b9d531596a5a284f34dbebff409d23bcc86aee6bad10c891606f075c6f4755cb536da27db5693f3a7" ]; hashesBase32 = [ "3y8bwfr609h3lh9ch0izcqq7fl" "26mrvc0v1nslch8r0w45zywsbc" "1v4gi57l97pmnylq6lmgxkhd5v" "143xibwh31h9bvxzalr0sjvbbvpa6ffs" "i4hj30pkrfdpgc5dbcgcydqviibfhm6d" "fxz2p030yba2bza71qhss79k3l5y24kd" "0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73" "0qy6iz9yh6a079757mxdmypx0gcmnzjd3ij5q78bzk00vxll82lh" "0mkygpci4r4yb8zz5rs2kxcgvw0a2yf5zlj6r8qgfll6pnrqf0xd" "0zdl9zrg8r3i9c1g90lgg9ip5ijzv3yhz91i0zzn3r8ap9ws784gkp9dk9j3aglhgf1amqb0pj21mh7h1nxcl18akqvvf7ggqsy30yg" "19ncrpp37dx0nzzjw4k6zaqkb9mzaq2myhgpzh5aff7qqcj5wwdxslg6ixwncm7gyq8l761gwf87fgsh2bwfyr52s53k2dkqvw8c24x" "2kz74snvckxldmmbisz9ikmy031d28cs6xfdbl6rhxx42glpyz4vww4lajrc5akklxwixl0js4g84233pxvmbykiic5m7i5m9r4nr11" ]; hashesBase64 = [ "1B2M2Y8AsgTpgAmY7PhCfg==" "bGnufyEcZAQZ1TZswHauRg==" "uzQ4+6vUYOptvSfRU+IjOw==" "2jmj7l5rSw0yVb/vlWAYkK/YBwk=" "zVToVowbN88eW62wd5vL84IhIYk=" "bRLhCx0zHa0hDkf9JdTyYIArfnc=" "47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=" "kApEad8AzL/QwUXG0eS3lT3Qr6+t11NOOkAZ6NOPxmM=" "rQOHs72GUvcwykbSX5wXCvD9WJ9C5/I/Wp5kEtl9flY=" "z4PhNX7vuL3xVChQ1m2AB9Yg5AULVxXcg/SpIdNs6c5H0NE8XYXysP+DGNKHfuwvY7kxvUdBeoGlODJ6+SfaPg==" "nQiG+MaziTmKFiV7x5eA+rmDHH/BHIqwf6cyy3s0j+reOC+SYXycUwX++6CvAqtf05pYfTMJl/9b0NsZ92ZmUw==" "IWRLcqolnlpYjNOvuvsdQxD0iJaA9sg7nVMVlqWihPNNvr/0CdI7zIau5rrRDIkWBvB1xvR1XLU22ifbVpPzpw==" ]; hashesSRI = [ "md5-1B2M2Y8AsgTpgAmY7PhCfg==" "md5-bGnufyEcZAQZ1TZswHauRg==" "md5-uzQ4+6vUYOptvSfRU+IjOw==" "sha1-2jmj7l5rSw0yVb/vlWAYkK/YBwk=" "sha1-zVToVowbN88eW62wd5vL84IhIYk=" "sha1-bRLhCx0zHa0hDkf9JdTyYIArfnc=" "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=" "sha256-kApEad8AzL/QwUXG0eS3lT3Qr6+t11NOOkAZ6NOPxmM=" "sha256-rQOHs72GUvcwykbSX5wXCvD9WJ9C5/I/Wp5kEtl9flY=" "sha512-z4PhNX7vuL3xVChQ1m2AB9Yg5AULVxXcg/SpIdNs6c5H0NE8XYXysP+DGNKHfuwvY7kxvUdBeoGlODJ6+SfaPg==" "sha512-nQiG+MaziTmKFiV7x5eA+rmDHH/BHIqwf6cyy3s0j+reOC+SYXycUwX++6CvAqtf05pYfTMJl/9b0NsZ92ZmUw==" "sha512-IWRLcqolnlpYjNOvuvsdQxD0iJaA9sg7nVMVlqWihPNNvr/0CdI7zIau5rrRDIkWBvB1xvR1XLU22ifbVpPzpw==" ]; }

tests/functional/lang/eval-okay-convertHash.nix

@@ -0,0 +1,31 @@
+let
+  hashAlgos = [ "md5" "md5" "md5" "sha1" "sha1" "sha1" "sha256" "sha256" "sha256" "sha512" "sha512" "sha512" ];
+  hashesBase16 = import ./eval-okay-hashstring.exp;
+  map2 = f: { fsts, snds }: if fsts == [ ] then [ ] else [ (f (builtins.head fsts) (builtins.head snds)) ] ++ map2 f { fsts = builtins.tail fsts; snds = builtins.tail snds; };
+  map2' = f: fsts: snds: map2 f { inherit fsts snds; };
+  getOutputHashes = hashes: {
+    hashesBase16 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base16";}) hashAlgos hashes;
+    hashesBase32 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base32";}) hashAlgos hashes;
+    hashesBase64 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base64";}) hashAlgos hashes;
+    hashesSRI    = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "sri"   ;}) hashAlgos hashes;
+  };
+  getOutputHashesColon = hashes: {
+    hashesBase16 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base16";}) hashAlgos hashes;
+    hashesBase32 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base32";}) hashAlgos hashes;
+    hashesBase64 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base64";}) hashAlgos hashes;
+    hashesSRI    = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "sri"   ;}) hashAlgos hashes;
+  };
+  outputHashes = getOutputHashes hashesBase16;
+in
+# map2'`
+assert map2' (s1: s2: s1 + s2) [ "a" "b" ] [ "c" "d" ] == [ "ac" "bd" ];
+# hashesBase16
+assert outputHashes.hashesBase16 == hashesBase16;
+# standard SRI hashes
+assert outputHashes.hashesSRI == (map2' (hashAlgo: hashBody: hashAlgo + "-" + hashBody) hashAlgos outputHashes.hashesBase64);
+# without prefix
+assert builtins.all (x: getOutputHashes x == outputHashes) (builtins.attrValues outputHashes);
+# colon-separated.
+# Note that colon prefix must not be applied to the standard SRI. e.g. "sha256:sha256-..." is illegal.
+assert builtins.all (x: getOutputHashesColon x == outputHashes) (with outputHashes; [ hashesBase16 hashesBase32 hashesBase64 ]);
+outputHashes