fix(Datastore): Create a plaintext transport channel when using the Emulator

[mw-ship-it]

Problem Statement

When using the java-datastore SDK with GrpcTransportOptions and connecting to a local Datastore Emulator (e.g., via the DATASTORE_EMULATOR_HOST environment variable), the client consistently throws an UNAUTHENTICATED: Request is missing required authentication credential error.

The Root Cause

In GrpcDatastoreRpc.java, the SDK constructor detects the emulator correctly and creates an unauthenticated, plaintext gRPC channel specifically tailored for local development via getClientContextForEmulator(datastoreOptions).

However, right after generating this specialized context, the SDK uses a builder (DatastoreStubSettings.newBuilder) that unconditionally overwrites the transport channel provider with a default production-oriented channel provider in order to set channel pooling limits.

Because the emulator's custom local channel gets overwritten by this production channel configuration, the SDK ultimately discards the emulator settings and attempts to connect securely to the actual production endpoint (datastore.googleapis.com), but without any credentials (since it knows it's an emulator). Production immediately rejects the call.

The Fix

The fix converts the monolithic DatastoreStubSettings builder chain into a sequential one, and conditionally applies the custom channel pooling provider only if the environment is not an emulator:

      DatastoreStubSettings.Builder datastoreStubSettingsBuilder =
          DatastoreStubSettings.newBuilder(clientContext)
              .applyToAllUnaryMethods(retrySettingSetter(datastoreOptions));

      if (!isEmulator(datastoreOptions)) {
        datastoreStubSettingsBuilder.setTransportChannelProvider(
           // ... Production connection pool settings
        );
      }

Why this is a safe fix without side effects

1. Zero Impact on Production Traffic: The fix relies exclusively on the existing, battle-tested isEmulator() method. If the SDK is pointed at production, !isEmulator returns true, and the code path executes the exact same transport channel override as before. Production throughput, connection pooling, and auth behavior remain 100% untouched.

2. Restores Original Intent: For emulator traffic, the channel provider override is gracefully skipped. This allows the custom, unauthenticated local gRPC channel created specifically for the emulator in getClientContextForEmulator() to survive and be used by the GrpcDatastoreStub.

3. Architecturally Safe: It introduces no new dependencies, requires no new variables or complex state management, and makes no changes to the public API surface. It simply resolves an unintentional clobbering of configuration variables at object instantiation time.

[gemini-code-assist]

Code Review

This pull request updates the GrpcDatastoreRpc class to conditionally configure the gRPC connection pool, ensuring it is only set when not running in an emulator environment. Additionally, the DatastoreStubSettings.Builder has been renamed for clarity. The review feedback recommends removing the descriptive comment for the connection pool configuration to align with repository standards regarding stale or misplaced comments.

[gemini-code-assist]

The comment describing the connection pool configuration is misplaced and refers to a specific implementation context. In accordance with repository rules, comments that refer to stale or misplaced implementations should be removed rather than updated or moved to a different block.

      DatastoreStubSettings.Builder datastoreStubSettingsBuilder =
          DatastoreStubSettings.newBuilder(clientContext)
              .applyToAllUnaryMethods(retrySettingSetter(datastoreOptions));
      if (!isEmulator(datastoreOptions)) {

References

1. Remove comments that refer to stale implementations instead of updating them.