chore: add grpc-server API for SpannerLib

Adds a gRPC server that exposes the API of SpannerLib. This allows clients
to connect to run SpannerLib as a child process and connect to it using
gRPC.

Author: olavloite

.github/workflows/spanner-lib-tests.yml

@@ -48,19 +48,27 @@ jobs:
       - name: Build shared library
         working-directory: spannerlib/shared
         run: go build -o spannerlib.so -buildmode=c-shared shared_lib.go
+      - name: Build gRPC server
+        working-directory: spannerlib/grpc-server
+        run: |
+          go build -o grpc_server server.go
+          chmod +x grpc_server
       - name: Copy to Java wrapper
         working-directory: spannerlib
         run: |
           echo "$RUNNER_OS"
           if [ "$RUNNER_OS" == "Windows" ]; then
             mkdir -p wrappers/spannerlib-java/src/main/resources/win32-x86-64
             cp shared/spannerlib.so wrappers/spannerlib-java/src/main/resources/win32-x86-64/spanner.dll
+            cp grpc-server/grpc_server wrappers/spannerlib-java/src/main/resources/win32-x86-64/grpc_server
           elif [ "$RUNNER_OS" == "macOS" ]; then
             mkdir -p wrappers/spannerlib-java/src/main/resources/darwin-aarch64
             cp shared/spannerlib.so wrappers/spannerlib-java/src/main/resources/darwin-aarch64/libspanner.dylib
+            cp grpc-server/grpc_server wrappers/spannerlib-java/src/main/resources/darwin-aarch64/grpc_server
           else
             mkdir -p wrappers/spannerlib-java/src/main/resources/linux-x86-64
             cp shared/spannerlib.so wrappers/spannerlib-java/src/main/resources/linux-x86-64/libspanner.so
+            cp grpc-server/grpc_server wrappers/spannerlib-java/src/main/resources/linux-x86-64/grpc_server
           fi
         shell: bash
       - name: ls spannerlib.so

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "spannerlib/grpc-server/googleapis"]
+	path = spannerlib/grpc-server/googleapis
+	url = git@github.com:googleapis/googleapis.git

spannerlib/api/rows.go

@@ -165,6 +165,9 @@ func (rows *rows) Next(ctx context.Context) (*structpb.ListValue, error) {
 		return nil, spanner.ToSpannerError(status.Error(codes.FailedPrecondition, "cannot read more data after returning stats"))
 	}
 	ok := rows.backend.Next()
+	if !ok && rows.backend.Err() != nil {
+		return nil, rows.backend.Err()
+	}
 	if !ok {
 		rows.done = true
 		// No more rows. Read stats and return nil.

spannerlib/go.mod

@@ -7,9 +7,11 @@ toolchain go1.25.1
 replace github.com/googleapis/go-sql-spanner => ..
 
 require (
+	cloud.google.com/go/longrunning v0.6.7
 	cloud.google.com/go/spanner v1.85.1
 	github.com/google/go-cmp v0.7.0
 	github.com/googleapis/go-sql-spanner v1.18.0
+	google.golang.org/genproto/googleapis/api v0.0.0-20250818200422-3122310a409c
 	google.golang.org/grpc v1.75.1
 	google.golang.org/protobuf v1.36.9
 )
@@ -21,7 +23,6 @@ require (
 	cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
 	cloud.google.com/go/compute/metadata v0.8.0 // indirect
 	cloud.google.com/go/iam v1.5.2 // indirect
-	cloud.google.com/go/longrunning v0.6.7 // indirect
 	cloud.google.com/go/monitoring v1.24.2 // indirect
 	github.com/GoogleCloudPlatform/grpc-gcp-go/grpcgcp v1.5.3 // indirect
 	github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.29.0 // indirect
@@ -62,6 +63,5 @@ require (
 	golang.org/x/time v0.12.0 // indirect
 	google.golang.org/api v0.249.0 // indirect
 	google.golang.org/genproto v0.0.0-20250804133106-a7a43d27e69b // indirect
-	google.golang.org/genproto/googleapis/api v0.0.0-20250818200422-3122310a409c // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20250908214217-97024824d090 // indirect
 )

spannerlib/grpc-server/build-java-darwin-aarch64.sh

@@ -0,0 +1,3 @@
+go build -o grpc_server server.go
+chmod +x grpc_server
+cp grpc_server ../wrappers/spannerlib-java/src/main/resources/darwin-aarch64/grpc_server

spannerlib/grpc-server/build-protos.sh

@@ -0,0 +1,18 @@
+PATH="${PATH}:${HOME}/go/bin"
+rm -rf googleapis/google/spannerlib
+cp -r google/spannerlib googleapis/google
+cd googleapis || exit 1
+protoc \
+  --go_out=../ \
+  --go_opt=paths=source_relative \
+  --go-grpc_out=../ \
+  --go-grpc_opt=paths=source_relative \
+  google/spannerlib/v1/spannerlib.proto
+protoc \
+  --java_out=../../wrappers/spannerlib-java/src/main/java/ \
+  --plugin=protoc-gen-java-grpc=/Users/loite/protoc-gen-grpc-java-1.75.0-osx-aarch_64.exe \
+  --java-grpc_out=../../wrappers/spannerlib-java/src/main/java/ \
+  --java-grpc_opt=paths=source_relative \
+  google/spannerlib/v1/spannerlib.proto
+cd .. || exit 1
+rm -rf googleapis/google/spannerlib