chenBright commented on issue #3287:
URL: https://github.com/apache/brpc/issues/3287#issuecomment-4552550621
Thanks for the heads-up and the offer to help with the migration. After
surveying the codebase, here's the planned proposal.
**Scope**
39 .proto files in the repo enable cc_generic_services (7 in brpc's own
builtin services, 23 in examples, 7 in tests, 1 in tools). We plan to migrate
all of
them to a brpc-owned protoc plugin before xx_generic_services becomes a
no-op.
**Plan**
1. New protoc-gen-brpc C++ plugin, modeled after the existing
protoc-gen-mcpack plugin we already ship (src/mcpack2pb/generator.cpp). Single
binary, standard PluginMain entry point.
2. Inject into the stock *.pb.h / *.pb.cc via OpenForInsert
(namespace_scope for declarations, global_scope for definitions). This keeps
#include "foo.pb.h" working unchanged — zero source-code changes
for users. Since the plugin is only active on protobuf versions where
cc_generic_services is already a no-op, there's no risk of duplicate-symbol
collisions with the legacy stubs.
3. Generated output is source-compatible with what cc_generic_services
produces today: same class names, same namespaces, same virtual signatures,
same _Stub(RpcChannel*) constructor. We're aiming for
source-level compatibility only — old/new outputs never coexist in the
same binary, so byte-level ABI alignment isn't required.
4. No dependency on protobuf private symbols. Instead of
internal::AssignDescriptors + descriptor_table_xxx +
file_level_service_descriptors_xxx, we resolve descriptors via the public
DescriptorPool::generated_pool()->FindServiceByName(...) API, cached at
module-init time into file-scope pointers — runtime cost is a single load, no
call_once check on the hot path.
5. Misuse detection — to catch users who forget to remove option
cc_generic_services from their .proto or forget to wire the plugin into their
build:
- Compile-time: generated classes embed a BrpcGeneratedTag typedef;
Server::AddService does a static_assert on it.
- Runtime: each generated service registers its full name in a global
set at static init; AddServiceInternal rejects services not produced by the
plugin, with an actionable error message.
- Hand-written google::protobuf::Service subclasses (we have one —
BaiduMasterService) can declare the tag manually or go through an
AddServiceUnchecked escape hatch.
@haberman I would be grateful for any feedback or suggestions you may have
on my proposal.
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