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08e0030032
The impl package currently supports wrapping legacy v1 enums and messages so that they implement the v2 reflective APIs. This functionality is necessary for v1 and v2 to interoperate. However, the existence of this functionality presents several problems: * A significant portion of the complexity in impl is for legacy wrapping. * This complexity is linked into a Go binary even if all the other messages in the binary natively support v2 reflection. * It presents a cyclic dependency when trying to generate descriptor proto. Suppose you are generating descriptor.proto. The generated code would want to depend on the impl package because impl is the runtime implementation for protobuf messages. However, impl currently depends depends on descriptor in order to wrap legacy enum and messages since it needs the ability to dynamically create new protobuf descriptor types. In the case of descriptor.proto, it would presumably be generated with native reflection support, so the legacy wrapping logic is unneccessary. To break the dependency of impl on descriptor, we move the legacy support logic to a different package and instead add hooks in impl so that legacy support could be dynamically registered at runtime. This is dependency injection. Change-Id: I01a582908ed5629993f6699e9bf2f4bee93857a4 Reviewed-on: https://go-review.googlesource.com/c/151877 Reviewed-by: Herbie Ong <herbie@google.com>
81 lines
2.6 KiB
Go
81 lines
2.6 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package legacy
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import (
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"bytes"
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"compress/gzip"
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"io/ioutil"
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"sync"
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// TODO: Avoid reliance on old API. However, there is currently a
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// chicken and egg problem where we need the descriptor protos to implement
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// the new API.
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protoV1 "github.com/golang/protobuf/proto"
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descriptorV1 "github.com/golang/protobuf/protoc-gen-go/descriptor"
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pref "github.com/golang/protobuf/v2/reflect/protoreflect"
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)
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// Every enum and message type generated by protoc-gen-go since commit 2fc053c5
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// on February 25th, 2016 has had a method to get the raw descriptor.
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// Types that were not generated by protoc-gen-go or were generated prior
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// to that version are not supported.
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//
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// The []byte returned is the encoded form of a FileDescriptorProto message
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// compressed using GZIP. The []int is the path from the top-level file
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// to the specific message or enum declaration.
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type (
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legacyEnum interface {
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EnumDescriptor() ([]byte, []int)
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}
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legacyMessage interface {
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Descriptor() ([]byte, []int)
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}
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)
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var fileDescCache sync.Map // map[*byte]*descriptorV1.FileDescriptorProto
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// legacyLoadFileDesc unmarshals b as a compressed FileDescriptorProto message.
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//
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// This assumes that b is immutable and that b does not refer to part of a
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// concatenated series of GZIP files (which would require shenanigans that
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// rely on the concatenation properties of both protobufs and GZIP).
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// File descriptors generated by protoc-gen-go do not rely on that property.
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func legacyLoadFileDesc(b []byte) *descriptorV1.FileDescriptorProto {
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// Fast-path: check whether we already have a cached file descriptor.
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if v, ok := fileDescCache.Load(&b[0]); ok {
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return v.(*descriptorV1.FileDescriptorProto)
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}
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// Slow-path: decompress and unmarshal the file descriptor proto.
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m := new(descriptorV1.FileDescriptorProto)
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zr, err := gzip.NewReader(bytes.NewReader(b))
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if err != nil {
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panic(err)
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}
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b, err = ioutil.ReadAll(zr)
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if err != nil {
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panic(err)
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}
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// TODO: What about extensions?
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// The protoV1 API does not eagerly unmarshal extensions.
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if err := protoV1.Unmarshal(b, m); err != nil {
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panic(err)
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}
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fileDescCache.Store(&b[0], m)
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return m
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}
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// parentFileDescriptor returns the parent protoreflect.FileDescriptor for the
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// provide descriptor. It returns nil if there is no parent.
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func parentFileDescriptor(d pref.Descriptor) pref.FileDescriptor {
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for ok := true; ok; d, ok = d.Parent() {
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if fd, _ := d.(pref.FileDescriptor); fd != nil {
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return fd
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}
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}
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return nil
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}
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