protoreflect

README

Protocol Buffer and gRPC Reflection

This repo provides reflection APIs for protocol buffers (also known as "protobufs" for short) and gRPC. The core of reflection in protobufs is the descriptor. A descriptor is itself a protobuf message that describes a .proto source file or any element therein. So a collection of descriptors can describe an entire schema of protobuf types, including RPC services.

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⚠️ Note

This repo was originally built to work with the "V1" API of the Protobuf runtime for Go: github.com/golang/protobuf.

Since the creation of this repo, a new runtime for Go has been release, a "V2" of the API in google.golang.org/protobuf. This new API now includes support for functionality that this repo implements:

• Descriptors: This repo provides github.com/jhump/protoreflect/desc. The new API now provides alternative types in google.golang.org/protobuf/reflect/protoreflect. It also provides ways to access descriptors for statically linked types in google.golang.org/protobuf/reflect/protoregistry and the ability to convert between these descriptor types and their "poorer cousins", descriptor protos, in google.golang.org/protobuf/reflect/protodesc
• Dynamic Messages: This repo provides github.com/jhump/protoreflect/dynamic. The new API now provides an alternative in google.golang.org/protobuf/types/dynamicpb.
• Binary Wire Format: This repo provides github.com/jhump/protoreflect/codec. The new API now provides an alternative in google.golang.org/protobuf/encoding/protowire.

Most protobuf users have likely upgraded to that newer runtime and thus encounter some friction using this repo. It is now recommended to use the above packages in the V2 Protobuf API instead of using the corresponding packages in this repo. But that still leaves a lot of functionality in this repo, such as the desc/builder, desc/protoparse, desc/protoprint, dynamic/grpcdynamic, dynamic/msgregistry, and grpcreflect packages herein. And all of these packages build on the core desc.Descriptor types in this repo. As of v1.15.0, you can convert between this repo's desc.Descriptor types and the V2 API's protoreflect.Descriptor types using Wrap functions in the desc package and Unwrap methods on the desc.Descriptor types. That allows easier interop between these remaining useful packages and new V2 API descriptor implementations.

If you have code that uses the dynamic package in this repo and are trying to interop with V2 APIs, in some cases you can use the proto.MessageV2 converter function (defined in the V1 proto package in github.com/golang/protobuf/proto). This wrapper does not provide 100% complete interop, so in some cases you may have to port your code over to the V2 API's dynamicpb package. (Sorry!)

Later this year, we expect to cut a v2 of this whole repo. A lot of what's in this repo is no longer necessary, but some features still are. The v2 will drop functionality now provided by the V2 Protobuf API. The remaining packages will be updated to make direct use of the V2 Protobuf API and have no more references to the old V1 API. One exception is that a v2 of this repo will not include a new version of the desc/protoparse package in this repo -- that is already available in a brand new module named protocompile.

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Descriptors: The Language Model of Protocol Buffers

import "github.com/jhump/protoreflect/desc"

The desc package herein introduces a Descriptor interface and implementations of it that correspond to each of the descriptor types. These new types are effectively smart wrappers around the generated protobuf types that make them much more useful and easier to use.

You can construct descriptors from file descriptor sets (which can be generated by protoc), and you can also load descriptors for messages and services that are linked into the current binary. "What does it mean for messages and services to be linked in?" you may ask. It means your binary imports a package that was generated by protoc. When you generate Go code from your .proto sources, the resulting package has descriptor information embedded in it. The desc package allows you to easily extract those embedded descriptors.

Descriptors can also be acquired directly from .proto source files (using the protoparse sub-package) or by programmatically constructing them (using the builder sub-package).

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import "github.com/jhump/protoreflect/desc/protoparse"

The protoparse package allows for parsing of .proto source files into rich descriptors. Without this package, you must invoke protoc to either generate a file descriptor set file or to generate Go code (which has descriptor information embedded in it). This package allows reading the source directly without having to invoke protoc.

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import "github.com/jhump/protoreflect/desc/protoprint"

The protoprint package allows for printing of descriptors to .proto source files. This is effectively the inverse of the protoparse package. Combined with the builder package, this is a useful tool for programmatically generating protocol buffer sources.

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import "github.com/jhump/protoreflect/desc/builder"

The builder package allows for programmatic construction of rich descriptors. Descriptors can be constructed programmatically by creating trees of descriptor protos and using the desc package to link those into rich descriptors. But constructing a valid tree of descriptor protos is far from trivial.

So this package provides generous API to greatly simplify that task. It also allows for converting rich descriptors into builders, which means you can programmatically modify/tweak existing descriptors.

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Dynamic Messages and Stubs

import "github.com/jhump/protoreflect/dynamic"

The dynamic package provides a dynamic message implementation. It implements proto.Message but is backed by a message descriptor and a map of fields->values, instead of a generated struct. This is useful for acting generically with protocol buffer messages, without having to generate and link in Go code for every kind of message. This is particularly useful for general-purpose tools that need to operate on arbitrary protocol buffer schemas. This is made possible by having the tools load descriptors at runtime.

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import "github.com/jhump/protoreflect/dynamic/grpcdynamic"

There is also sub-package named grpcdynamic, which provides a dynamic stub implementation. The stub can be used to issue RPC methods using method descriptors instead of generated client interfaces.

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gRPC Server Reflection

import "github.com/jhump/protoreflect/grpcreflect"

The grpcreflect package provides an easy-to-use client for the gRPC reflection service, making it much easier to query for and work with the schemas of remote services.

It also provides some helper methods for querying for rich service descriptors for the services registered in a gRPC server.

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