Create separate library for DescribeBackend

3 files changed, 105 insertions, 0 deletions

diff --git a/src/buildtool/storage/TARGETS b/src/buildtool/storage/TARGETS
index 2d624afb..705d86c6 100644
--- a/src/buildtool/storage/TARGETS
+++ b/src/buildtool/storage/TARGETS
@@ -103,4 +103,16 @@
   , "stage": ["src", "buildtool", "storage"]
   , "private-deps": [["@", "gsl", "", "gsl"]]
   }
+, "backend_description":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["backend_description"]
+  , "hdrs": ["backend_description.hpp"]
+  , "srcs": ["backend_description.cpp"]
+  , "deps":
+    [ ["src/buildtool/common/remote", "remote_common"]
+    , ["src/utils/cpp", "expected"]
+    ]
+  , "stage": ["src", "buildtool", "storage"]
+  , "private-deps": [["@", "fmt", "", "fmt"], ["@", "json", "", "json"]]
+  }
 }
diff --git a/src/buildtool/storage/backend_description.cpp b/src/buildtool/storage/backend_description.cpp
new file mode 100644
index 00000000..456f79c6
--- /dev/null
+++ b/src/buildtool/storage/backend_description.cpp
@@ -0,0 +1,59 @@
+// Copyright 2024 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/storage/backend_description.hpp"
+
+#include <exception>
+
+#include "fmt/core.h"
+#include "nlohmann/json.hpp"
+
+auto DescribeBackend(std::optional<ServerAddress> const& address,
+                     ExecutionProperties const& properties,
+                     std::vector<DispatchEndpoint> const& dispatch) noexcept
+    -> expected<std::string, std::string> {
+    auto description = nlohmann::json{
+        {"remote_address", address ? address->ToJson() : nlohmann::json{}},
+        {"platform_properties", properties}};
+    if (not dispatch.empty()) {
+        try {
+            // only add the dispatch list, if not empty, so that keys remain
+            // not only more readable, but also backwards compatible with
+            // earlier versions.
+            auto dispatch_list = nlohmann::json::array();
+            for (auto const& [props, endpoint] : dispatch) {
+                auto entry = nlohmann::json::array();
+                entry.push_back(nlohmann::json(props));
+                entry.push_back(endpoint.ToJson());
+                dispatch_list.push_back(entry);
+            }
+            description["endpoint dispatch list"] = dispatch_list;
+        } catch (std::exception const& e) {
+            return unexpected{fmt::format(
+                "Failed to serialize endpoint dispatch list:\n{}", e.what())};
+        }
+    }
+    try {
+        // json::dump with json::error_handler_t::replace will not throw an
+        // exception if invalid UTF-8 sequences are detected in the input.
+        // Instead, it will replace them with the UTF-8 replacement
+        // character, but still it needs to be inside a try-catch clause to
+        // ensure the noexcept modifier of the enclosing function.
+        return description.dump(
+            2, ' ', false, nlohmann::json::error_handler_t::replace);
+    } catch (std::exception const& e) {
+        return unexpected{fmt::format(
+            "Failed to dump backend description to JSON:\n{}", e.what())};
+    }
+}
diff --git a/src/buildtool/storage/backend_description.hpp b/src/buildtool/storage/backend_description.hpp
new file mode 100644
index 00000000..544ee1b9
--- /dev/null
+++ b/src/buildtool/storage/backend_description.hpp
@@ -0,0 +1,34 @@
+// Copyright 2024 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.
+
+#ifndef INCLUDED_SRC_BUILDTOOL_STORAGE_BACKEND_DESCRIPTION_HPP
+#define INCLUDED_SRC_BUILDTOOL_STORAGE_BACKEND_DESCRIPTION_HPP
+
+#include <map>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "src/buildtool/common/remote/remote_common.hpp"
+#include "src/utils/cpp/expected.hpp"
+
+/// \brief String representation of the used execution backend.
+[[nodiscard]] auto DescribeBackend(
+    std::optional<ServerAddress> const& address,
+    ExecutionProperties const& properties,
+    std::vector<DispatchEndpoint> const& dispatch) noexcept
+    -> expected<std::string, std::string>;
+
+#endif  // INCLUDED_SRC_BUILDTOOL_STORAGE_BACKEND_DESCRIPTION_HPP