Ensure .proto file name is globally unique

[ejweber]

In service of longhorn/longhorn#5595.

Longhorn-manager has a BackingImageManagerService client, and thus imports backing-image-manager. After upgrading the Kubernetes dependency of longhorn-manager to v1.27.1, I came across this error when executing longhorn-manager:

panic: proto: file "rpc.proto" is already registered
See https://protobuf.dev/reference/go/faq#namespace-conflict


goroutine 1 [running]:
google.golang.org/protobuf/reflect/protoregistry.glob..func1({0x3ba6860?, 0xc000111bc0?}, {0x3ba6860?, 0xc000111bc0})
        /go/pkg/mod/google.golang.org/protobuf@v1.30.0/reflect/protoregistry/registry.go:56 +0x266
google.golang.org/protobuf/reflect/protoregistry.(*Files).RegisterFile(0xc0001aa8a0, {0x3bdf0d8?, 0xc000452540?})
        /go/pkg/mod/google.golang.org/protobuf@v1.30.0/reflect/protoregistry/registry.go:130 +0x502
google.golang.org/protobuf/internal/filedesc.Builder.Build({{0x0, 0x0}, {0xc000803c00, 0xa8d, 0xc00}, 0x0, 0xd, 0x0, 0x1, {0x3bade58, ...}, ...})
        /go/pkg/mod/google.golang.org/protobuf@v1.30.0/internal/filedesc/build.go:112 +0x26b
github.com/golang/protobuf/proto.RegisterFile({0x36688d9, 0x9}, {0x4f8be80, 0x34d, 0x34d})
        /go/pkg/mod/github.com/golang/protobuf@v1.5.3/proto/registry.go:48 +0x187
github.com/longhorn/backing-image-manager/pkg/rpc.init.1()
        /go/pkg/mod/github.com/longhorn/backing-image-manager@v0.0.0-20220609065820-a08f7f47442f/pkg/rpc/rpc.pb.go:680 +0x50
FAIL    github.com/longhorn/longhorn-manager/controller 0.106s

After reading the referenced web page and doing some additional digging, I came across golang/protobuf#1122. For reasons debated in that issue, the name that feeds into the proto.RegisterFile function in any .pb.go file must be globally unique in a Go program. Unfortunately, the Kubernetes version update introduced a new transitive dependency on go.etcd.io/etcd/api/v3, which also has an rpc.proto file that conflicts with backing-image-manager's rpc.proto file. Since we can't easily change that one, it makes sense to more fully specify ours.

The entire purpose of this PR is to change this:
proto.RegisterFile("rpc.proto", fileDescriptor_77a6da22d6a3feb1),
to this:
proto.RegisterFile("github.com/longhorn/backing-image-manager/pkg/rpc/rpc.proto", fileDescriptor_cdf73a3350f27fd7).

Sadly, protoc makes this a bit annoying to do, resulting in the file copying I did in generate_grpc.sh.

[PhanLe1010]

Quick question. Is it ok to combine the import path like:

protoc -I "${TMP_DIR_BASE}" "proto/vendor/protobuf/src/" "${TMP_DIR}/rpc.proto" --go_out=plugins=grpc:"${TMP_DIR_BASE}"

[PhanLe1010]

Looks like no

[ejweber]

I spoke with @PhanLe1010 offline and we are agreed. I tried to find a good primary source for protoc (not protoc-gen-go) flags, but struggled. The protoc --help output provides the following direction:

  -IPATH, --proto_path=PATH   Specify the directory in which to search for
                              imports.  May be specified multiple times;
                              directories will be searched in order.  If not
                              given, the current working directory is used.
                              If not found in any of the these directories,
                              the --descriptor_set_in descriptors will be
                              checked for required proto file.

[PhanLe1010]

LGTM. Thanks for the PR

[innobead]

LGTM.

Suggest applying the same way to other repos if needed.

cc @longhorn/dev