CasClient: Fall back to single blob upload, if batch uploading made no progress

We already accept short writes in batch uploads, but when no
progress is made, we cannot simply retry, as this might lead to
an infinite loop. Instead, we give up on batching and upload each
blob one by one.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/buildtool/execution_api/remote/bazel/bazel_cas_client.cpp b/src/buildtool/execution_api/remote/bazel/bazel_cas_client.cpp
index aa6b7c9f..aac7f2a5 100644
--- a/src/buildtool/execution_api/remote/bazel/bazel_cas_client.cpp
+++ b/src/buildtool/execution_api/remote/bazel/bazel_cas_client.cpp
@@ -592,6 +592,20 @@ auto BazelCasClient::BatchUpdateBlobs(
                                                 missing_blobs.begin(),
                                                 missing_blobs.end());
     }
+    if (result.empty() and missing > 0) {
+        // The batch upload did not make _any_ progress. So there is no value in
+        // trying that again; instead, we fall back to uploading each blob
+        // sequentially.
+        logger_.Emit(LogLevel::Debug, "Falling back to sequential blob upload");
+        std::size_t count = 0;
+        std::for_each(
+            begin, end, [this, &count, &instance_name](auto const& blob) {
+                if (UpdateSingleBlob(instance_name, *blob)) {
+                    count += 1;
+                }
+            });
+        return count;
+    }
 
     return result.size();
 }