bytestream_server: store temporary files under the local-buil-root

The bytestream server implementation (deployed by just execute) now
stores the temporary files under

  $local_build_root/protocol-depenedent/generation-0

so that they can be garbage collected if "just exectue" is terminated
before they are cleaned up.

3 files changed, 16 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ffa17d97..761fe55c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,8 @@ A feature release on top of `1.1.0`, backwards compatible.
   all entries in a Git repository. Previously it was possible for
   entries to be skipped inadvertently in, e.g., imported archives
   if `gitignore` files were present.
+- Temporary files generated by `just execute` are now created inside
+  the local build root.
 
 ## Release `1.1.0` (2023-05-19)
 
diff --git a/src/buildtool/execution_api/execution_service/bytestream_server.cpp b/src/buildtool/execution_api/execution_service/bytestream_server.cpp
index 234c4adc..b450c697 100644
--- a/src/buildtool/execution_api/execution_service/bytestream_server.cpp
+++ b/src/buildtool/execution_api/execution_service/bytestream_server.cpp
@@ -113,7 +113,14 @@ auto BytestreamServiceImpl::Write(
                  *hash,
                  request.write_offset(),
                  request.finish_write());
-    auto tmp_dir = TmpDir::Create("execution-service");
+    auto lock = GarbageCollector::SharedLock();
+    if (!lock) {
+        auto str = fmt::format("Could not acquire SharedLock");
+        logger_.Emit(LogLevel::Error, str);
+        return grpc::Status{grpc::StatusCode::INTERNAL, str};
+    }
+    auto tmp_dir = TmpDir::Create(StorageConfig::GenerationCacheRoot(0) /
+                                  "execution-service");
     if (!tmp_dir) {
         return ::grpc::Status{::grpc::StatusCode::INTERNAL,
                               "could not create TmpDir"};
@@ -129,21 +136,16 @@ auto BytestreamServiceImpl::Write(
         of.write(request.data().data(),
                  static_cast<std::streamsize>(request.data().size()));
     }
-    auto lock = GarbageCollector::SharedLock();
-    if (!lock) {
-        auto str = fmt::format("Could not acquire SharedLock");
-        logger_.Emit(LogLevel::Error, str);
-        return grpc::Status{grpc::StatusCode::INTERNAL, str};
-    }
     if (NativeSupport::IsTree(*hash)) {
-        if (not storage_->CAS().StoreTree(tmp)) {
+        if (not storage_->CAS().StoreTree</*kOwner=*/true>(tmp)) {
             auto str = fmt::format("could not store tree {}", *hash);
             logger_.Emit(LogLevel::Error, str);
             return ::grpc::Status{::grpc::StatusCode::INVALID_ARGUMENT, str};
         }
     }
     else {
-        if (not storage_->CAS().StoreBlob(tmp, /*is_executable=*/false)) {
+        if (not storage_->CAS().StoreBlob</*kOwner=*/true>(
+                tmp, /*is_executable=*/false)) {
             auto str = fmt::format("could not store blob {}", *hash);
             logger_.Emit(LogLevel::Error, str);
             return ::grpc::Status{::grpc::StatusCode::INVALID_ARGUMENT, str};
diff --git a/src/buildtool/storage/local_cas.hpp b/src/buildtool/storage/local_cas.hpp
index af613b1d..4726f8b8 100644
--- a/src/buildtool/storage/local_cas.hpp
+++ b/src/buildtool/storage/local_cas.hpp
@@ -70,11 +70,13 @@ class LocalCAS {
     }
 
     /// \brief Store tree from file path.
+    /// \tparam kOwner          Indicates ownership for optimization (hardlink).
     /// \param file_path    The path of the file to store as tree.
     /// \returns Digest of the stored tree or nullopt otherwise.
+    template <bool kOwner = false>
     [[nodiscard]] auto StoreTree(std::filesystem::path const& file_path)
         const noexcept -> std::optional<bazel_re::Digest> {
-        return cas_tree_.StoreBlobFromFile(file_path);
+        return cas_tree_.StoreBlobFromFile(file_path, kOwner);
     }
 
     /// \brief Store tree from bytes.