pb2zap

Migrate a Go codebase off Protocol Buffers and onto ZAP — zero-copy wire, no Marshal/Unmarshal, no gRPC.

pb2zap is a go/ast codemod. It is syntactic — it does not type-check — so it runs on a tree mid-migration that does not yet compile.

go install github.com/zap-proto/pb2zap/cmd/pb2zap@latest
pb2zap -map rules.txt -w ./...

rules.txt is one rule per line — pbImportPath wireImportPath wirePkgName:

github.com/acme/app/pb/mount_pb  github.com/acme/app/wire/mount  mountwire
github.com/acme/app/pb/filer_pb  github.com/acme/app/wire/filer  filerwire

What it rewrites

The one transform that is unambiguous from syntax alone — construction:

&mount_pb.ConfigureRequest{CollectionCapacity: n}
// becomes
mountwire.NewConfigureRequest(mountwire.ConfigureRequestInput{CollectionCapacity: n})

It adds the wire import, drops the pb import once nothing else references it, and reports (never guesses) the pb selectors it leaves — the field reads that need accessors and the writes that immutable ZAP cannot express.

What it deliberately does not do

pb→ZAP is not a 1:1 transform; it is a data-flow split. A *pb.Msg is one type used to both build (set fields) and read (get fields). ZAP splits that into three — Input (build) → []byte (transport) → View (read). A value that is constructed, threaded through several functions, mutated, then read has no single ZAP type; it has to be restructured into build-once / read-many. pb2zap does the safe mechanical piece and points a human at the rest, rather than emit code that compiles by accident.

Library

out, changed, pbLeft, err := pb2zap.Rewrite("file.go", src, rules)

Pure function, golang.org/x/tools only. See the migration guide.