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A Protocol Buffers compiler that generates optimized marshaling & unmarshaling Go code for ProtoBuf APIv2


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vtprotobuf, the Vitess Protocol Buffers compiler

This repository provides the protoc-gen-go-vtproto plug-in for protoc, which is used by Vitess to generate optimized marshall & unmarshal code.

The code generated by this compiler is based on the optimized code generated by gogo/protobuf, although this package is not a fork of the original gogo compiler, as it has been implemented to support the new ProtoBuf APIv2 packages.

Available features

vtprotobuf is implemented as a helper plug-in that must be run alongside the upstream protoc-gen-go generator, as it generates fully-compatible auxiliary code to speed up (de)serialization of Protocol Buffer messages.

The following features can be generated:

  • size: generates a func (p *YourProto) SizeVT() int helper that behaves identically to calling proto.Size(p) on the message, except the size calculation is fully unrolled and does not use reflection. This helper function can be used directly, and it'll also be used by the marshal codegen to ensure the destination buffer is properly sized before ProtoBuf objects are marshalled to it.

  • equal: generates the following helper methods

    • func (this *YourProto) EqualVT(that *YourProto) bool: this function behaves almost identically to calling proto.Equal(this, that) on messages, except the equality calculation is fully unrolled and does not use reflection. This helper function can be used directly.

    • func (this *YourProto) EqualMessageVT(thatMsg proto.Message) bool: this function behaves like the above this.EqualVT(that), but allows comparing against arbitrary proto messages. If thatMsg is not of type *YourProto, false is returned. The uniform signature provided by this method allows accessing this method via type assertions even if the message type is not known at compile time. This allows implementing a generic func EqualVT(proto.Message, proto.Message) bool without reflection.

  • marshal: generates the following helper methods

    • func (p *YourProto) MarshalVT() ([]byte, error): this function behaves identically to calling proto.Marshal(p), except the actual marshalling has been fully unrolled and does not use reflection or allocate memory. This function simply allocates a properly sized buffer by calling SizeVT on the message and then uses MarshalToSizedBufferVT to marshal to it.

    • func (p *YourProto) MarshalToVT(data []byte) (int, error): this function can be used to marshal a message to an existing buffer. The buffer must be large enough to hold the marshalled message, otherwise this function will panic. It returns the number of bytes marshalled. This function is useful e.g. when using memory pooling to re-use serialization buffers.

    • func (p *YourProto) MarshalToSizedBufferVT(data []byte) (int, error): this function behaves like MarshalTo but expects that the input buffer has the exact size required to hold the message, otherwise it will panic.

  • marshal_strict: generates the following helper methods

    • func (p *YourProto) MarshalVTStrict() ([]byte, error): this function behaves like MarshalVT, except fields are marshalled in a strict order by field's numbers they were declared in .proto file.

    • func (p *YourProto) MarshalToVTStrict(data []byte) (int, error): this function behaves like MarshalToVT, except fields are marshalled in a strict order by field's numbers they were declared in .proto file.

    • func (p *YourProto) MarshalToSizedBufferVTStrict(data []byte) (int, error): this function behaves like MarshalToSizedBufferVT, except fields are marshalled in a strict order by field's numbers they were declared in .proto file.

  • unmarshal: generates a func (p *YourProto) UnmarshalVT(data []byte) that behaves similarly to calling proto.Unmarshal(data, p) on the message, except the unmarshalling is performed by unrolled codegen without using reflection and allocating as little memory as possible. If the receiver p is not fully zeroed-out, the unmarshal call will actually behave like proto.Merge(data, p). This is because the proto.Unmarshal in the ProtoBuf API is implemented by resetting the destination message and then calling proto.Merge on it. To ensure proper Unmarshal semantics, ensure you've called proto.Reset on your message before calling UnmarshalVT, or that your message has been newly allocated.

  • unmarshal_unsafe generates a func (p *YourProto) UnmarshalVTUnsafe(data []byte) that behaves like UnmarshalVT, except it unsafely casts slices of data to bytes and string fields instead of copying them to newly allocated arrays, so that it performs less allocations. Data received from the wire has to be left untouched for the lifetime of the message. Otherwise, the message's bytes and string fields can be corrupted.

  • pool: generates the following helper methods

    • func (p *YourProto) ResetVT(): this function behaves similarly to proto.Reset(p), except it keeps as much memory as possible available on the message, so that further calls to UnmarshalVT on the same message will need to allocate less memory. This an API meant to be used with memory pools and does not need to be used directly.

    • func (p *YourProto) ReturnToVTPool(): this function returns message p to a local memory pool so it can be reused later. It clears the object properly with ResetVT before storing it on the pool. This method should only be used on messages that were obtained from a memory pool by calling YourProtoFromVTPool. Using p after calling this method will lead to undefined behavior.

    • func YourProtoFromVTPool() *YourProto: this function returns a YourProto message from a local memory pool, or allocates a new one if the pool is currently empty. The returned message is always empty and ready to be used (e.g. by calling UnmarshalVT on it). Once the message has been processed, it must be returned to the memory pool by calling ReturnToVTPool() on it. Returning the message to the pool is not mandatory (it does not leak memory), but if you don't return it, that defeats the whole point of memory pooling.

  • clone: generates the following helper methods

    • func (p *YourProto) CloneVT() *YourProto: this function behaves similarly to calling proto.Clone(p) on the message, except the cloning is performed by unrolled codegen without using reflection. If the receiver p is nil a typed nil is returned.

    • func (p *YourProto) CloneMessageVT() proto.Message: this function behaves like the above p.CloneVT(), but provides a uniform signature in order to be accessible via type assertions even if the type is not known at compile time. This allows implementing a generic func CloneVT(proto.Message) without reflection. If the receiver p is nil, a typed nil pointer of the message type will be returned inside a proto.Message interface.


  1. Install protoc-gen-go-vtproto:

    go install
  2. Ensure your project is already using the ProtoBuf v2 API (i.e. The vtprotobuf compiler is not compatible with APIv1 generated code.

  3. Update your protoc generator to use the new plug-in. Example from Vitess:

    for name in $(PROTO_SRC_NAMES); do \
        $(VTROOT)/bin/protoc \
        --go_out=. --plugin protoc-gen-go="${GOBIN}/protoc-gen-go" \
        --go-grpc_out=. --plugin protoc-gen-go-grpc="${GOBIN}/protoc-gen-go-grpc" \
        --go-vtproto_out=. --plugin protoc-gen-go-vtproto="${GOBIN}/protoc-gen-go-vtproto" \
        --go-vtproto_opt=features=marshal+unmarshal+size \
        proto/$${name}.proto; \

    Note that the vtproto compiler runs like an auxiliary plug-in to the protoc-gen-go in APIv2, just like the new GRPC compiler plug-in, protoc-gen-go-grpc. You need to run it alongside the upstream generator, not as a replacement.

  4. (Optional) Pass the features that you want to generate as --go-vtproto_opt. If no features are given, all the codegen steps will be performed.

  5. (Optional) If you have enabled the pool option, you need to manually specify which ProtoBuf objects will be pooled.

    • You can tag messages explicitly in the .proto files with option (vtproto.mempool):
    syntax = "proto3";
    package app;
    option go_package = "app";
    import "";
    message SampleMessage {
        option (vtproto.mempool) = true; // Enable memory pooling
        string name = 1;
        optional string project_id = 2;
        // ...
    • Alternatively, you can enumerate the pooled objects with --go-vtproto_opt=pool=<import>.<message> flags passed via the CLI:
        $(VTROOT)/bin/protoc ... \
            --go-vtproto_opt=features=marshal+unmarshal+size+pool \
  6. (Optional) if you want to selectively compile the generate vtprotobuf files, the --vtproto_opt=buildTag=<tag> can be used.

    When using this option, the generated code will only be compiled in if a build tag is provided.

    It is recommended, but not required, to use vtprotobuf as the build tag if this is desired, especially if your project is imported by others. This will reduce the number of build tags a user will need to configure if they are importing multiple libraries following this pattern.

    When using this option, it is strongly recommended to make your code compile with and without the build tag. This can be done with type assertions before using vtprotobuf generated methods. The grpc.Codec{} object (discussed below) shows an example.

  7. Compile the .proto files in your project. You should see _vtproto.pb.go files next to the .pb.go and _grpc.pb.go files that were already being generated.

  8. (Optional) Switch your RPC framework to use the optimized helpers (see following sections)

vtprotobuf package and well-known types

Your generated _vtproto.pb.go files will have a dependency on this Go package to access some helper functions as well as the optimized code for ProtoBuf well-known types. vtprotobuf will detect these types embedded in your own Messages and generate optimized code to marshal and unmarshal them.

Using the optimized code with RPC frameworks

The protoc-gen-go-vtproto compiler does not overwrite any of the default marshalling or unmarshalling code for your ProtoBuf objects. Instead, it generates helper methods that can be called explicitly to opt-in to faster (de)serialization.

vtprotobuf with GRPC

To use vtprotobuf with the new versions of GRPC, you need to register the codec provided by the package.

package servenv

import (
	_ ""

func init() {

Note that we perform a blank import _ "" of the default proto coded that ships with GRPC to ensure it's being replaced by us afterwards. The provided Codec will serialize & deserialize all ProtoBuf messages using the optimized codegen.

Mixing ProtoBuf implementations with GRPC

If you're running a complex GRPC service, you may need to support serializing ProtoBuf messages from different sources, including from external packages that will not have optimized vtprotobuf marshalling code. This is perfectly doable by implementing a custom codec in your own project that serializes messages based on their type. The Vitess project implements a custom codec to support ProtoBuf messages from Vitess itself and those generated by the etcd API -- you can use it as a reference.


Twirp does not support customizing the Marshalling/Unmarshalling codec by default. In order to support vtprotobuf, you'll need to perform a search & replace on the generated Twirp files after running protoc. Here's an example:

for twirp in $${dir}/*.twirp.go; \
do \
  echo 'Updating' $${twirp}; \
  sed -i '' -e 's/respBytes, err := proto.Marshal(respContent)/respBytes, err := respContent.MarshalVT()/g' $${twirp}; \
  sed -i '' -e 's/if err = proto.Unmarshal(buf, reqContent); err != nil {/if err = reqContent.UnmarshalVT(buf); err != nil {/g' $${twirp}; \
done; \


To use vtprotobuf as a DRPC encoding, simply pass as the protolib flag in your protoc-gen-go-drpc invocation.


protoc --go_out=. --go-vtproto_out=. --go-drpc_out=.


To use vtprotobuf with Connect, first implement a custom codec in your own project that serializes messages based on their type (see Mixing ProtoBuf implementations with GRPC). This is required because Connect internally serializes some types such as Status that don't have vtprotobuf helpers. Then pass in connect.WithCodec(mygrpc.Codec{}) as a connect option to the client and handler constructors.

package main

import (


func main() {
	mux := http.NewServeMux()
		connect.WithCodec(mygrpc.Codec{}), // Add connect option to handler.
	// handler serving ...

	client := pingv1connect.NewPingServiceClient(
		connect.WithCodec(mygrpc.Codec{}), // Add connect option to client.
	/// client code here ...

Integrating with buf

vtprotobuf generation can be easily automated if your project's Protocol Buffers are managed with buf.

Simply install protoc-gen-go-vtproto (see Usage section) and add it as a plug-in to your buf.gen.yaml configuration:

version: v1
  enabled: true
  # ...
  - plugin:
    out: ./
    opt: paths=source_relative
  - plugin: go-vtproto
    out: ./
    opt: paths=source_relative

Running buf generate will now also include the vtprotobuf optimized helpers.