fix(tvix): Chunk the AddTextToStore request r/1736

Rather than sending the entire AddTextToStore request along in a single
message, send it in a stream of chunks using the same metadata-first
approach we've been using for the other store gRPC requests. This fixes
a bug where certain builds could send more data than the maximum gRPC
request size (4194304 bytes, it would appear), resulting in a
RESOURCE_EXHAUSTED error.

The initial chunk size, which is currently constant but should be made
dynamic at some point in the future, has been chosen based on the IPC
bandwidth delay product for tazjin's desktop, rounded up.

Change-Id: I6f0232cdbc98653484816b39855126873fc59a03
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1835
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: kanepyork <rikingcoding@gmail.com>

1 files changed, 27 insertions, 6 deletions

diff --git a/third_party/nix/src/libstore/rpc-store.cc b/third_party/nix/src/libstore/rpc-store.cc
index 92ad4e762bf9..bc1fcc73d818 100644
--- a/third_party/nix/src/libstore/rpc-store.cc
+++ b/third_party/nix/src/libstore/rpc-store.cc
@@ -5,6 +5,7 @@
 #include <memory>
 #include <optional>
 #include <ostream>
+#include <string_view>
 
 #include <absl/status/status.h>
 #include <absl/strings/str_cat.h>
@@ -36,6 +37,11 @@ namespace nix {
 
 namespace store {
 
+// Should be set to the bandwidth delay product between the client and the
+// daemon. The current value, which should eventually be determined dynamically,
+// has currently been set to a developer's deskop computer, rounded up
+constexpr size_t kChunkSize = 1024 * 64;
+
 using google::protobuf::util::TimeUtil;
 using grpc::ClientContext;
 using nix::proto::WorkerService;
@@ -308,14 +314,29 @@ Path RpcStore::addTextToStore(const std::string& name,
         "repairing is not supported when building through the Nix daemon");
   }
   ClientContext ctx;
-  proto::AddTextToStoreRequest request;
-  request.set_name(name);
-  request.set_content(content);
+  proto::StorePath result;
+  auto writer = stub_->AddTextToStore(&ctx, &result);
+
+  proto::AddTextToStoreRequest meta;
+  meta.mutable_meta()->set_name(name);
+  meta.mutable_meta()->set_size(content.size());
   for (const auto& ref : references) {
-    request.add_references(ref);
+    meta.mutable_meta()->add_references(ref);
   }
-  proto::StorePath result;
-  SuccessOrThrow(stub_->AddTextToStore(&ctx, request, &result), __FUNCTION__);
+  writer->Write(meta);
+
+  for (int i = 0; i <= content.size(); i += kChunkSize) {
+    auto len = std::min(kChunkSize, content.size() - i);
+    proto::AddTextToStoreRequest data;
+    data.set_data(content.data() + i, len);
+    if (!writer->Write(data)) {
+      // Finish() below will error
+      break;
+    }
+  }
+
+  writer->WritesDone();
+  SuccessOrThrow(writer->Finish(), __FUNCTION__);
   return result.path();
 }