protobuf

Example: protobuf

Demonstrates using protoc-gen-slogschema with a Connect-RPC / gRPC service.

The plugin generates a MarshalSLog() []slog.Attr method directly on each protoc-gen-go message type. This means:

• One struct for both wire transport and logging — no separate logging struct, no field mapping
• Annotations in the .proto file control logging behaviour at the source of truth
• *User implements slogschema.SLogMarshaler automatically — pass it straight to ToAttrs

Files

File	Origin	Description
user.proto	Hand-written	Proto definition with slogschema annotations
user.pb.go	protoc-gen-go (simulated)	Standard Go message types and getters
user.slogschema.pb.go	protoc-gen-slogschema (simulated)	Generated MarshalSLog() methods
main.go	Hand-written	Usage example

In a real project user.pb.go and user_slogschema.pb.go are both generated — you only maintain user.proto.

Run

go run github.com/silvercory/slog-schema/example/protobuf

Output

level=INFO  msg="user loaded"               id=sha256:... email=sha256:... name="Bob Smith" phone=sha256:... role=editor created_at=2024-03-15T09:00:00Z address.street="10 Downing St" address.city=London address.country_code=GB notify_email=alerts@example.com roles.0=read roles.1=write
level=ERROR msg="user suspended"            id=sha256:... email=sha256:... name="Bob Smith" phone=sha256:... role=suspended ...
level=INFO  msg="notification method changed" ... notify_sms=+447700900001 ...
level=INFO  msg="user updated"              ... (address absent)

Notice:

• password_hash never appears — skip: true in the proto means it is absent from MarshalSLog entirely
• id, email, phone are hashed on every line
• display_name is logged as name (custom key via name: "name" annotation)
• notify_email / notify_sms — only the set oneof variant appears; it switches on the third line
• address disappears on the last line (omitempty + nil pointer)

Annotations used in user.proto

message User {
  uint64 id           = 1 [(slogschema.v1.field) = {hashed: true, omitempty: true}];
  string email        = 2 [(slogschema.v1.field) = {hashed: true}];
  string display_name = 3 [(slogschema.v1.field) = {name: "name"}];
  string phone        = 4 [(slogschema.v1.field) = {hashed: true, omitempty: true}];
  string role         = 5;
  string password_hash = 6 [(slogschema.v1.field) = {skip: true}];
  ...
}

Generating in a real project

Install the plugin and run protoc alongside your existing generators:

go install github.com/silvercory/slog-schema/cmd/protoc-gen-slogschema@latest

protoc \
  --go_out=. \
  --go-grpc_out=. \
  --slogschema_out=. \
  --proto_path=. \
  api/user.proto

With buf:

# buf.gen.yaml
plugins:
  - plugin: go
    out: gen
  - plugin: connect-go
    out: gen
  - plugin: slogschema
    out: gen