serve service: Respond also with digest in serve repository tree RPCs

...besides the simple Git hash, if syncing was done. This way one
can know what digest to ask for from the remote. The serve client
also needs to now know what hash function the remote expects.

The serve service proto file is updated accordingly.

4 files changed, 32 insertions, 41 deletions

diff --git a/src/other_tools/root_maps/commit_git_map.cpp b/src/other_tools/root_maps/commit_git_map.cpp
index f221f63f..8f96eb82 100644
--- a/src/other_tools/root_maps/commit_git_map.cpp
+++ b/src/other_tools/root_maps/commit_git_map.cpp
@@ -82,13 +82,13 @@ void EnsureRootAsAbsent(
         if (not *has_tree) {
             // try to see if serve endpoint has the information to prepare the
             // root itself
-            auto serve_result =
+            auto const serve_result =
                 serve->RetrieveTreeFromCommit(repo_info.hash,
                                               repo_info.subdir,
                                               /*sync_tree = */ false);
             if (serve_result) {
                 // if serve has set up the tree, it must match what we expect
-                auto const& served_tree_id = *serve_result;
+                auto const& served_tree_id = serve_result->tree;
                 if (tree_id != served_tree_id) {
                     (*logger)(fmt::format("Mismatch in served root tree "
                                           "id:\nexpected {}, but got {}",
@@ -671,7 +671,7 @@ void EnsureCommit(
         if (serve != nullptr) {
             // if root purely absent, request only the subdir tree
             if (repo_info.absent and not fetch_absent) {
-                auto serve_result =
+                auto const serve_result =
                     serve->RetrieveTreeFromCommit(repo_info.hash,
                                                   repo_info.subdir,
                                                   /*sync_tree = */ false);
@@ -683,7 +683,7 @@ void EnsureCommit(
                             {repo_info.ignore_special
                                  ? FileRoot::kGitTreeIgnoreSpecialMarker
                                  : FileRoot::kGitTreeMarker,
-                             *std::move(serve_result)}),
+                             serve_result->tree}),
                         /*is_cache_hit=*/false));
                     return;
                 }
@@ -700,12 +700,13 @@ void EnsureCommit(
             // otherwise, request (and sync) the whole commit tree, to ensure
             // we maintain the id file association
             else {
-                auto serve_result =
+                auto const serve_result =
                     serve->RetrieveTreeFromCommit(repo_info.hash,
                                                   /*subdir = */ ".",
                                                   /*sync_tree = */ true);
                 if (serve_result) {
-                    auto const& root_tree_id = *serve_result;
+                    auto const root_tree_id = serve_result->tree;
+                    auto const remote_digest = serve_result->digest;
                     // verify if we know the tree already in the local Git cache
                     GitOpKey op_key = {.params =
                                            {
@@ -721,6 +722,7 @@ void EnsureCommit(
                         ts,
                         {std::move(op_key)},
                         [root_tree_id,
+                         remote_digest,
                          tree_id_file,
                          repo_info,
                          repo_root,
@@ -875,18 +877,13 @@ void EnsureCommit(
                                 }
                             }
 
-                            // try to get root tree from remote CAS
-                            auto const root_digest =
-                                ArtifactDigestFactory::Create(
-                                    native_storage_config->hash_function
-                                        .GetType(),
-                                    root_tree_id,
-                                    0,
-                                    /*is_tree=*/true);
-                            if (remote_api != nullptr and root_digest and
+                            // try to get root tree from remote CAS; use the
+                            // digest received from serve; whether native or
+                            // compatible, it will either way be imported to Git
+                            if (remote_api != nullptr and remote_digest and
                                 remote_api->RetrieveToCas(
                                     {Artifact::ObjectInfo{
-                                        .digest = *root_digest,
+                                        .digest = *remote_digest,
                                         .type = ObjectType::Tree}},
                                     *local_api)) {
                                 progress->TaskTracker().Stop(repo_info.origin);
@@ -907,7 +904,7 @@ void EnsureCommit(
                                 }
                                 if (not local_api->RetrieveToPaths(
                                         {Artifact::ObjectInfo{
-                                            .digest = *root_digest,
+                                            .digest = *remote_digest,
                                             .type = ObjectType::Tree}},
                                         {tmp_dir->GetPath()})) {
                                     (*logger)(fmt::format(
diff --git a/src/other_tools/root_maps/content_git_map.cpp b/src/other_tools/root_maps/content_git_map.cpp
index ecae60ac..2338c066 100644
--- a/src/other_tools/root_maps/content_git_map.cpp
+++ b/src/other_tools/root_maps/content_git_map.cpp
@@ -71,7 +71,7 @@ void EnsureRootAsAbsent(
             // try to see if serve endpoint has the information to prepare the
             // root itself; this is redundant if root is not already cached
             if (is_cache_hit) {
-                auto serve_result = serve->RetrieveTreeFromArchive(
+                auto const serve_result = serve->RetrieveTreeFromArchive(
                     key.archive.content_hash.Hash(),
                     key.repo_type,
                     key.subdir,
@@ -80,12 +80,11 @@ void EnsureRootAsAbsent(
                 if (serve_result) {
                     // if serve has set up the tree, it must match what we
                     // expect
-                    auto const& served_tree_id = *serve_result;
-                    if (tree_id != served_tree_id) {
+                    if (tree_id != serve_result->tree) {
                         (*logger)(fmt::format("Mismatch in served root tree "
                                               "id:\nexpected {}, but got {}",
                                               tree_id,
-                                              served_tree_id),
+                                              serve_result->tree),
                                   /*fatal=*/true);
                         return;
                     }
@@ -1047,7 +1046,7 @@ auto CreateContentGitMap(
                 // request the resolved subdir tree from the serve endpoint, if
                 // given
                 if (serve != nullptr) {
-                    auto serve_result = serve->RetrieveTreeFromArchive(
+                    auto const serve_result = serve->RetrieveTreeFromArchive(
                         key.archive.content_hash.Hash(),
                         key.repo_type,
                         key.subdir,
@@ -1058,7 +1057,7 @@ auto CreateContentGitMap(
                         progress->TaskTracker().Stop(key.archive.origin);
                         (*setter)(std::pair(
                             nlohmann::json::array(
-                                {FileRoot::kGitTreeMarker, *serve_result}),
+                                {FileRoot::kGitTreeMarker, serve_result->tree}),
                             /*is_cache_hit = */ false));
                         return;
                     }
diff --git a/src/other_tools/root_maps/distdir_git_map.cpp b/src/other_tools/root_maps/distdir_git_map.cpp
index 82c0c623..ef460949 100644
--- a/src/other_tools/root_maps/distdir_git_map.cpp
+++ b/src/other_tools/root_maps/distdir_git_map.cpp
@@ -224,21 +224,20 @@ auto CreateDistdirGitMap(
                             if (not *has_tree) {
                                 // try to see if serve endpoint has the
                                 // information to prepare the root itself
-                                auto serve_result =
+                                auto const serve_result =
                                     serve->RetrieveTreeFromDistdir(
                                         key.content_list,
                                         /*sync_tree=*/false);
                                 if (serve_result) {
                                     // if serve has set up the tree, it must
                                     // match what we expect
-                                    auto const& served_tree_id = *serve_result;
-                                    if (distdir_tree_id != served_tree_id) {
+                                    if (distdir_tree_id != serve_result->tree) {
                                         (*logger)(
                                             fmt::format(
                                                 "Mismatch in served root tree "
                                                 "id:\nexpected {}, but got {}",
                                                 distdir_tree_id,
-                                                served_tree_id),
+                                                serve_result->tree),
                                             /*fatal=*/true);
                                         return;
                                     }
@@ -376,19 +375,18 @@ auto CreateDistdirGitMap(
                     }
                     // try to see if serve endpoint has the information to
                     // prepare the root itself
-                    auto serve_result =
+                    auto const serve_result =
                         serve->RetrieveTreeFromDistdir(key.content_list,
                                                        /*sync_tree=*/false);
                     if (serve_result) {
                         // if serve has set up the tree, it must match what we
                         // expect
-                        auto const& served_tree_id = *serve_result;
-                        if (tree_id != served_tree_id) {
+                        if (tree_id != serve_result->tree) {
                             (*logger)(
                                 fmt::format("Mismatch in served root tree "
                                             "id:\nexpected {}, but got {}",
                                             tree_id,
-                                            served_tree_id),
+                                            serve_result->tree),
                                 /*fatal=*/true);
                             return;
                         }
@@ -520,18 +518,17 @@ auto CreateDistdirGitMap(
             // now ask serve endpoint if it can set up the root; as this is for
             // a present root, a corresponding remote endpoint is needed
             if (serve != nullptr and remote_api != nullptr) {
-                auto serve_result =
+                auto const serve_result =
                     serve->RetrieveTreeFromDistdir(key.content_list,
                                                    /*sync_tree=*/true);
                 if (serve_result) {
                     // if serve has set up the tree, it must match what we
                     // expect
-                    auto const& served_tree_id = *serve_result;
-                    if (tree_id != served_tree_id) {
+                    if (tree_id != serve_result->tree) {
                         (*logger)(fmt::format("Mismatch in served root tree "
                                               "id:\nexpected {}, but got {}",
                                               tree_id,
-                                              served_tree_id),
+                                              serve_result->tree),
                                   /*fatal=*/true);
                         return;
                     }
diff --git a/src/other_tools/root_maps/foreign_file_git_map.cpp b/src/other_tools/root_maps/foreign_file_git_map.cpp
index 8bc09b86..25c77947 100644
--- a/src/other_tools/root_maps/foreign_file_git_map.cpp
+++ b/src/other_tools/root_maps/foreign_file_git_map.cpp
@@ -156,17 +156,15 @@ void HandleAbsentForeignFile(ForeignFileInfo const& key,
                 /*is_cache_hit=*/false));
             return;
         }
-        auto serve_result = serve->RetrieveTreeFromForeignFile(
+        auto const serve_result = serve->RetrieveTreeFromForeignFile(
             key.archive.content_hash.Hash(), key.name, key.executable);
         if (serve_result) {
-            // if serve has set up the tree, it must match what we
-            // expect
-            auto const& served_tree_id = *serve_result;
-            if (tree_id != served_tree_id) {
+            // if serve has set up the tree, it must match what we expect
+            if (tree_id != serve_result->tree) {
                 (*logger)(fmt::format("Mismatch in served root tree "
                                       "id: expected {}, but got {}",
                                       tree_id,
-                                      served_tree_id),
+                                      serve_result->tree),
                           /*fatal=*/true);
                 return;
             }