target service: Replace duplicated code in TC shard computation

...by using the new DescribeBackend method instead. This ensures
that the TC shard computation is indeed consistent between local
and serve endpoint.

2 files changed, 13 insertions, 36 deletions

diff --git a/src/buildtool/serve_api/serve_service/TARGETS b/src/buildtool/serve_api/serve_service/TARGETS
index 40b11f34..6239a0e7 100644
--- a/src/buildtool/serve_api/serve_service/TARGETS
+++ b/src/buildtool/serve_api/serve_service/TARGETS
@@ -118,6 +118,7 @@
     , ["src/buildtool/main", "analyse_context"]
     , ["src/buildtool/common", "config"]
     , ["src/buildtool/serve_api/remote", "serve_api"]
+    , ["src/buildtool/storage", "backend_description"]
     ]
   }
 , "configuration_service":
diff --git a/src/buildtool/serve_api/serve_service/target.cpp b/src/buildtool/serve_api/serve_service/target.cpp
index 6cae3d8b..1e69af63 100644
--- a/src/buildtool/serve_api/serve_service/target.cpp
+++ b/src/buildtool/serve_api/serve_service/target.cpp
@@ -40,6 +40,7 @@
 #include "src/buildtool/progress_reporting/progress.hpp"
 #include "src/buildtool/progress_reporting/progress_reporter.hpp"
 #include "src/buildtool/serve_api/serve_service/target_utils.hpp"
+#include "src/buildtool/storage/backend_description.hpp"
 #include "src/buildtool/storage/garbage_collector.hpp"
 #include "src/buildtool/storage/target_cache_key.hpp"
 #include "src/utils/cpp/verify_hash.hpp"
@@ -138,7 +139,7 @@ auto TargetService::ServeTarget(
 
     // start filling in the backend description
     auto const address = RemoteExecutionConfig::RemoteAddress();
-    // read in the execution properties and add it to the description;
+    // read in the execution properties.
     // Important: we will need to pass these platform properties also to the
     // executor (via the graph_traverser) in order for the build to be properly
     // dispatched to the correct remote-execution endpoint.
@@ -146,11 +147,7 @@ auto TargetService::ServeTarget(
     for (auto const& p : request->execution_properties()) {
         platform_properties[p.name()] = p.value();
     }
-    auto description = nlohmann::json{
-        {"remote_address", address ? address->ToJson() : nlohmann::json{}},
-        {"platform_properties", platform_properties}};
-
-    // read in the dispatch list and add it to the description, if not empty
+    // Read in the dispatch list
     if (auto msg = IsAHash(request->dispatch_info().hash()); msg) {
         logger_->Emit(LogLevel::Error, "{}", *msg);
         return ::grpc::Status{::grpc::StatusCode::INVALID_ARGUMENT, *msg};
@@ -165,40 +162,19 @@ auto TargetService::ServeTarget(
     // keep dispatch list, as it needs to be passed to the executor (via the
     // graph_traverser)
     auto dispatch_list = *res;
-    // parse dispatch list to json and add to description
-    auto dispatch_json = nlohmann::json::array();
-    try {
-        for (auto const& [props, endpoint] : dispatch_list) {
-            auto entry = nlohmann::json::array();
-            entry.push_back(nlohmann::json(props));
-            entry.push_back(endpoint.ToJson());
-            dispatch_json.push_back(entry);
-        }
-    } catch (std::exception const& ex) {
-        logger_->Emit(LogLevel::Info,
-                      "Parsing dispatch list to JSON failed with:\n{}",
-                      ex.what());
-    }
-    if (not dispatch_json.empty()) {
-        description["endpoint dispatch list"] = std::move(dispatch_json);
-    }
 
-    // add backend description to CAS;
-    // we match the sharding strategy from regular just builds, i.e., allowing
-    // fields with invalid UTF-8 characters to be considered for the serialized
-    // JSON description, but using the UTF-8 replacement character to solve any
-    // decoding errors.
-    std::string description_str;
-    try {
-        description_str = description.dump(
-            2, ' ', false, nlohmann::json::error_handler_t::replace);
-    } catch (std::exception const& ex) {
-        // normally shouldn't happen
-        std::string err{"Failed to dump backend JSON description to string"};
+    // get backend description
+    auto description =
+        DescribeBackend(address, platform_properties, dispatch_list);
+    if (not description) {
+        auto err = fmt::format("Failed to create backend description:\n{}",
+                               description.error());
         logger_->Emit(LogLevel::Error, err);
         return ::grpc::Status{::grpc::StatusCode::INTERNAL, err};
     }
-    auto execution_backend_dgst = storage_.CAS().StoreBlob(description_str);
+
+    // add backend description to CAS
+    auto execution_backend_dgst = storage_.CAS().StoreBlob(*description);
     if (not execution_backend_dgst) {
         std::string err{
             "Failed to store execution backend description in local CAS"};