1 files changed, 180 insertions, 0 deletions
diff --git a/src/buildtool/file_system/git_cas.cpp b/src/buildtool/file_system/git_cas.cpp
new file mode 100644
index 00000000..e77d8d6e
--- /dev/null
+++ b/src/buildtool/file_system/git_cas.cpp
@@ -0,0 +1,180 @@
+#include "src/buildtool/file_system/git_cas.hpp"
+
+#include <sstream>
+
+#include "src/buildtool/file_system/file_system_manager.hpp"
+#include "src/buildtool/logging/logger.hpp"
+#include "src/utils/cpp/hex_string.hpp"
+
+extern "C" {
+#include <git2.h>
+}
+
+namespace {
+
+constexpr auto kOIDRawSize{GIT_OID_RAWSZ};
+constexpr auto kOIDHexSize{GIT_OID_HEXSZ};
+
+[[nodiscard]] auto GitLastError() noexcept -> std::string {
+    git_error const* err{nullptr};
+    if ((err = git_error_last()) != nullptr and err->message != nullptr) {
+        return fmt::format("error code {}: {}", err->klass, err->message);
+    }
+    return "<unknown error>";
+}
+
+[[nodiscard]] auto GitObjectID(std::string const& id,
+                               bool is_hex_id = false) noexcept
+    -> std::optional<git_oid> {
+    if ((is_hex_id and id.size() < kOIDHexSize) or id.size() < kOIDRawSize) {
+        Logger::Log(LogLevel::Error,
+                    "invalid git object id {}",
+                    is_hex_id ? id : ToHexString(id));
+        return std::nullopt;
+    }
+    git_oid oid{};
+    if (is_hex_id and git_oid_fromstr(&oid, id.data()) == 0) {
+        return oid;
+    }
+    if (not is_hex_id and
+        git_oid_fromraw(
+            &oid,
+            reinterpret_cast<unsigned char const*>(id.data())  // NOLINT
+            ) == 0) {
+        return oid;
+    }
+    Logger::Log(LogLevel::Error,
+                "parsing git object id {} failed with:\n{}",
+                is_hex_id ? id : ToHexString(id),
+                GitLastError());
+    return std::nullopt;
+}
+
+[[nodiscard]] auto GitTypeToObjectType(git_object_t const& type) noexcept
+    -> std::optional<ObjectType> {
+    switch (type) {
+        case GIT_OBJECT_BLOB:
+            return ObjectType::File;
+        case GIT_OBJECT_TREE:
+            return ObjectType::Tree;
+        default:
+            Logger::Log(LogLevel::Error,
+                        "unsupported git object type {}",
+                        git_object_type2string(type));
+            return std::nullopt;
+    }
+}
+
+}  // namespace
+
+auto GitCAS::Open(std::filesystem::path const& repo_path) noexcept
+    -> GitCASPtr {
+    try {
+        auto cas = std::make_shared<GitCAS>();
+        if (cas->OpenODB(repo_path)) {
+            return std::static_pointer_cast<GitCAS const>(cas);
+        }
+    } catch (std::exception const& ex) {
+        Logger::Log(LogLevel::Error,
+                    "opening git object database failed with:\n{}",
+                    ex.what());
+    }
+    return nullptr;
+}
+
+GitCAS::GitCAS() noexcept {
+    if (not(initialized_ = (git_libgit2_init() >= 0))) {
+        Logger::Log(LogLevel::Error, "initializing libgit2 failed");
+    }
+}
+GitCAS::~GitCAS() noexcept {
+    if (odb_ != nullptr) {
+        git_odb_free(odb_);
+        odb_ = nullptr;
+    }
+    if (initialized_) {
+        git_libgit2_shutdown();
+    }
+}
+
+auto GitCAS::ReadObject(std::string const& id, bool is_hex_id) const noexcept
+    -> std::optional<std::string> {
+    if (not initialized_) {
+        return std::nullopt;
+    }
+
+    auto oid = GitObjectID(id, is_hex_id);
+    if (not oid) {
+        return std::nullopt;
+    }
+
+    git_odb_object* obj = nullptr;
+    if (git_odb_read(&obj, odb_, &oid.value()) != 0) {
+        Logger::Log(LogLevel::Error,
+                    "reading git object {} from database failed with:\n{}",
+                    is_hex_id ? id : ToHexString(id),
+                    GitLastError());
+        return std::nullopt;
+    }
+
+    std::string data(static_cast<char const*>(git_odb_object_data(obj)),
+                     git_odb_object_size(obj));
+    git_odb_object_free(obj);
+
+    return data;
+}
+
+auto GitCAS::ReadHeader(std::string const& id, bool is_hex_id) const noexcept
+    -> std::optional<std::pair<std::size_t, ObjectType>> {
+    if (not initialized_) {
+        return std::nullopt;
+    }
+
+    auto oid = GitObjectID(id, is_hex_id);
+    if (not oid) {
+        return std::nullopt;
+    }
+
+    std::size_t size{};
+    git_object_t type{};
+    if (git_odb_read_header(&size, &type, odb_, &oid.value()) != 0) {
+        Logger::Log(LogLevel::Error,
+                    "reading git object header {} from database failed "
+                    "with:\n{}",
+                    is_hex_id ? id : ToHexString(id),
+                    GitLastError());
+        return std::nullopt;
+    }
+
+    if (auto obj_type = GitTypeToObjectType(type)) {
+        return std::make_pair(size, *obj_type);
+    }
+
+    return std::nullopt;
+}
+
+auto GitCAS::OpenODB(std::filesystem::path const& repo_path) noexcept -> bool {
+    if (initialized_) {
+        {  // lock as git_repository API has no thread-safety guarantees
+            std::unique_lock lock{repo_mutex_};
+            git_repository* repo = nullptr;
+            if (git_repository_open(&repo, repo_path.c_str()) != 0) {
+                Logger::Log(LogLevel::Error,
+                            "opening git repository {} failed with:\n{}",
+                            repo_path.string(),
+                            GitLastError());
+                return false;
+            }
+            git_repository_odb(&odb_, repo);
+            git_repository_free(repo);
+        }
+        if (odb_ == nullptr) {
+            Logger::Log(LogLevel::Error,
+                        "obtaining git object database {} failed with:\n{}",
+                        repo_path.string(),
+                        GitLastError());
+            return false;
+        }
+    }
+    return initialized_;
+}