3 files changed, 69 insertions, 0 deletions
diff --git a/src/buildtool/crypto/TARGETS b/src/buildtool/crypto/TARGETS
index ab2d6b21..47309f72 100644
--- a/src/buildtool/crypto/TARGETS
+++ b/src/buildtool/crypto/TARGETS
@@ -22,7 +22,12 @@
   { "type": ["@", "rules", "CC", "library"]
   , "name": ["hash_function"]
   , "hdrs": ["hash_function.hpp"]
+  , "srcs": ["hash_function.cpp"]
   , "deps": ["hasher", ["@", "gsl", "", "gsl"]]
+  , "private-deps":
+    [ ["src/buildtool/logging", "logging"]
+    , ["src/buildtool/logging", "log_level"]
+    ]
   , "stage": ["src", "buildtool", "crypto"]
   }
 }
diff --git a/src/buildtool/crypto/hash_function.cpp b/src/buildtool/crypto/hash_function.cpp
new file mode 100644
index 00000000..89bb0cb8
--- /dev/null
+++ b/src/buildtool/crypto/hash_function.cpp
@@ -0,0 +1,56 @@
+// Copyright 2023 Huawei Cloud Computing Technology Co., Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/buildtool/crypto/hash_function.hpp"
+
+#include <fstream>
+#include <string>
+
+#include "src/buildtool/logging/log_level.hpp"
+#include "src/buildtool/logging/logger.hpp"
+
+[[nodiscard]] auto HashFunction::ComputeHashFile(
+    const std::filesystem::path& file_path,
+    bool as_tree) noexcept
+    -> std::optional<std::pair<Hasher::HashDigest, std::uintmax_t>> {
+    static constexpr std::size_t kChunkSize{4048};
+    try {
+        auto hasher = Hasher();
+        auto size = std::filesystem::file_size(file_path);
+        if (HashType() == JustHash::Native) {
+            hasher.Update(
+                (as_tree ? std::string{"tree "} : std::string{"blob "}) +
+                std::to_string(size) + '\0');
+        }
+        std::string chunk{};
+        chunk.resize(kChunkSize);
+        std::ifstream file_reader(file_path.string(), std::ios::binary);
+        if (file_reader.is_open()) {
+            auto chunk_size = gsl::narrow<std::streamsize>(chunk.size());
+            do {
+                file_reader.read(chunk.data(), chunk_size);
+                auto count = file_reader.gcount();
+                hasher.Update(chunk.substr(0, gsl::narrow<std::size_t>(count)));
+            } while (file_reader.good());
+            file_reader.close();
+            return std::make_pair(std::move(hasher).Finalize(), size);
+        }
+    } catch (std::exception const& e) {
+        Logger::Log(LogLevel::Debug,
+                    "Error while trying to hash {}: {}",
+                    file_path.string(),
+                    e.what());
+    }
+    return std::nullopt;
+}
diff --git a/src/buildtool/crypto/hash_function.hpp b/src/buildtool/crypto/hash_function.hpp
index 44341777..fa141ed2 100644
--- a/src/buildtool/crypto/hash_function.hpp
+++ b/src/buildtool/crypto/hash_function.hpp
@@ -16,9 +16,11 @@
 #define INCLUDED_SRC_BUILDTOOL_CRYPTO_HASH_FUNCTION_HPP
 
 #include <cstdint>
+#include <filesystem>
 #include <functional>
 #include <optional>
 #include <string>
+#include <utility>
 
 #include "src/buildtool/crypto/hasher.hpp"
 
@@ -53,6 +55,12 @@ class HashFunction {
         return ComputeTaggedHash(data, kBlobTagCreator);
     }
 
+    /// \brief Compute the blob hash of a file or std::nullopt on IO error.
+    [[nodiscard]] static auto ComputeHashFile(
+        const std::filesystem::path& file_path,
+        bool as_tree) noexcept
+        -> std::optional<std::pair<Hasher::HashDigest, std::uintmax_t>>;
+
     /// \brief Compute a tree hash.
     [[nodiscard]] static auto ComputeTreeHash(std::string const& data) noexcept
         -> Hasher::HashDigest {