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
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
Descriptors: The Language Model of Protocol Buffers
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
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
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
or by programmatically constructing them (using 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
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.
builder package allows for programmatic construction of rich descriptors. Descriptors can
be constructed programmatically by creating trees of descriptor protos and using the
to link those into rich descriptors. But constructing a valid tree of descriptor protos is far from
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.
Dynamic Messages and Stubs
dynamic package provides a dynamic message implementation. It implements
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.
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.
gRPC Server Reflection
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.