github.com-golang-protobuf_-_2019-11-26_23-02-00

github.com-golang-protobuf_-_2019-11-26_23-02-00

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Go support for Google’s protocol buffers

Go support for Protocol Buffers – Google’s data interchange format

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Google’s data interchange format.Copyright 2010 The Go Authors.https://github.com/golang/protobuf

This package and the code it generates requires at least Go 1.9.

This software implements Go bindings for protocol buffers. Forinformation about protocol buffers themselves, see https://developers.google.com/protocol-buffers/

Installation

To use this software, you must:- Install the standard C++ implementation of protocol buffers from https://developers.google.com/protocol-buffers/- Of course, install the Go compiler and tools from https://golang.org/ See https://golang.org/doc/install for details or, if you are using gccgo, follow the instructions at https://golang.org/doc/install/gccgo- Grab the code from the repository and install the proto package. The simplest way is to run go get -u github.com/golang/protobuf/protoc-gen-go. The compiler plugin, protoc-gen-go, will be installed in $GOPATH/bin unless $GOBIN is set. It must be in your $PATH for the protocol compiler, protoc, to find it.- If you need a particular version of protoc-gen-go (e.g., to match your proto package version), one option is shell GIT_TAG="v1.2.0" # change as needed go get -d -u github.com/golang/protobuf/protoc-gen-go git -C "$(go env GOPATH)"/src/github.com/golang/protobuf checkout $GIT_TAG go install github.com/golang/protobuf/protoc-gen-go

This software has two parts: a ‘protocol compiler plugin’ thatgenerates Go source files that, once compiled, can access and manageprotocol buffers; and a library that implements run-time support forencoding (marshaling), decoding (unmarshaling), and accessing protocolbuffers.

There is support for gRPC in Go using protocol buffers.See the note at the bottom of this file for details.

There are no insertion points in the plugin.

Using protocol buffers with Go

Once the software is installed, there are two steps to using it.First you must compile the protocol buffer definitions and then importthem, with the support library, into your program.

To compile the protocol buffer definition, run protoc with the –go_outparameter set to the directory you want to output the Go code to.

protoc --go_out=. *.proto

The generated files will be suffixed .pb.go. See the Test code belowfor an example using such a file.

Packages and input paths

The protocol buffer language has a concept of “packages” which does notcorrespond well to the Go notion of packages. In generated Go code,each source .proto file is associated with a single Go package. Thename and import path for this package is specified with the go_packageproto option:

option go_package = "github.com/golang/protobuf/ptypes/any";

The protocol buffer compiler will attempt to derive a package name andimport path if a go_package option is not present, but it isbest to always specify one explicitly.

There is a one-to-one relationship between source .proto files andgenerated .pb.go files, but any number of .pb.go files may becontained in the same Go package.

The output name of a generated file is produced by replacing the.proto suffix with .pb.go (e.g., foo.proto produces foo.pb.go).However, the output directory is selected in one of two ways. Letus say we have inputs/x.proto with a go_package option ofgithub.com/golang/protobuf/p. The corresponding output file maybe:

  • Relative to the import path:

shell protoc --go_out=. inputs/x.proto # writes ./github.com/golang/protobuf/p/x.pb.go

(This can work well with --go_out=$GOPATH.)

  • Relative to the input file:

“`shellprotoc –goout=paths=sourcerelative:. inputs/x.proto

generate ./inputs/x.pb.go

“`

Generated code

The package comment for the proto library contains text describingthe interface provided in Go for protocol buffers. Here is an editedversion.

The proto package converts data structures to and from thewire format of protocol buffers. It works in concert with theGo source code generated for .proto files by the protocol compiler.

A summary of the properties of the protocol buffer interfacefor a protocol buffer variable v:

  • Names are turned from camel_case to CamelCase for export.
  • There are no methods on v to set fields; just treatthem as structure fields.
  • There are getters that return a field’s value if set,and return the field’s default value if unset.The getters work even if the receiver is a nil message.
  • The zero value for a struct is its correct initialization state.All desired fields must be set before marshaling.
  • A Reset() method will restore a protobuf struct to its zero state.
  • Non-repeated fields are pointers to the values; nil means unset.That is, optional or required field int32 f becomes F *int32.
  • Repeated fields are slices.
  • Helper functions are available to aid the setting of fields.Helpers for getting values are superseded by theGetFoo methods and their use is deprecated. msg.Foo = proto.String(“hello”) // set field
  • Constants are defined to hold the default values of all fields thathave them. They have the form DefaultStructNameFieldName.Because the getter methods handle defaulted values,direct use of these constants should be rare.
  • Enums are given type names and maps from names to values.Enum values are prefixed with the enum’s type name. Enum types havea String method, and a Enum method to assist in message construction.
  • Nested groups and enums have type names prefixed with the name ofthe surrounding message type.
  • Extensions are given descriptor names that start with E_,followed by an underscore-delimited list of the nested messagesthat contain it (if any) followed by the CamelCased name of theextension field itself. HasExtension, ClearExtension, GetExtensionand SetExtension are functions for manipulating extensions.
  • Oneof field sets are given a single field in their message,with distinguished wrapper types for each possible field value.
  • Marshal and Unmarshal are functions to encode and decode the wire format.

When the .proto file specifies syntax="proto3", there are some differences:

  • Non-repeated fields of non-message type are values instead of pointers.
  • Enum types do not get an Enum method.

Consider file test.proto, containing

“`proto syntax = “proto2”; package example;

enum FOO { X = 17; };message Test {  required string label = 1;  optional int32 type = 2 [default=77];  repeated int64 reps = 3;}

“`

To create and play with a Test object from the example package,

“`go package main

import (    "log"    "github.com/golang/protobuf/proto"    "path/to/example")func main() {    test := &example.Test{        Label: proto.String("hello"),        Type:  proto.Int32(17),        Reps:  []int64{1, 2, 3},    }    data, err := proto.Marshal(test)    if err != nil {        log.Fatal("marshaling error: ", err)    }    newTest := &example.Test{}    err = proto.Unmarshal(data, newTest)    if err != nil {        log.Fatal("unmarshaling error: ", err)    }    // Now test and newTest contain the same data.    if test.GetLabel() != newTest.GetLabel() {        log.Fatalf("data mismatch %q != %q", test.GetLabel(), newTest.GetLabel())    }    // etc.}

“`

Parameters

To pass extra parameters to the plugin, use a comma-separatedparameter list separated from the output directory by a colon:

protoc --go_out=plugins=grpc,import_path=mypackage:. *.proto
  • paths=(import | source_relative) – specifies how the paths ofgenerated files are structured. See the “Packages and imports paths”section above. The default is import.
  • plugins=plugin1+plugin2 – specifies the list of sub-plugins toload. The only plugin in this repo is grpc.
  • Mfoo/bar.proto=quux/shme – declares that foo/bar.proto isassociated with Go package quux/shme. This is subject to theimport_prefix parameter.

The following parameters are deprecated and should not be used:

  • import_prefix=xxx – a prefix that is added onto the beginning ofall imports.
  • import_path=foo/bar – used as the package if no input filesdeclare go_package. If it contains slashes, everything up to therightmost slash is ignored.

gRPC Support

If a proto file specifies RPC services, protoc-gen-go can be instructed togenerate code compatible with gRPC (http://www.grpc.io/). To do this, passthe plugins parameter to protoc-gen-go; the usual way is to insert it intothe –go_out argument to protoc:

protoc --go_out=plugins=grpc:. *.proto

Compatibility

The library and the generated code are expected to be stable over time.However, we reserve the right to make breaking changes without notice for thefollowing reasons:

  • Security. A security issue in the specification or implementation may come tolight whose resolution requires breaking compatibility. We reserve the rightto address such security issues.
  • Unspecified behavior. There are some aspects of the Protocol Buffersspecification that are undefined. Programs that depend on such unspecifiedbehavior may break in future releases.
  • Specification errors or changes. If it becomes necessary to address aninconsistency, incompleteness, or change in the Protocol Buffersspecification, resolving the issue could affect the meaning or legality ofexisting programs. We reserve the right to address such issues, includingupdating the implementations.
  • Bugs. If the library has a bug that violates the specification, a programthat depends on the buggy behavior may break if the bug is fixed. We reservethe right to fix such bugs.
  • Adding methods or fields to generated structs. These may conflict with fieldnames that already exist in a schema, causing applications to break. When thecode generator encounters a field in the schema that would collide with agenerated field or method name, the code generator will append an underscoreto the generated field or method name.
  • Adding, removing, or changing methods or fields in generated structs thatstart with XXX. These parts of the generated code are exported out ofnecessity, but should not be considered part of the public API.
  • Adding, removing, or changing unexported symbols in generated code.

Any breaking changes outside of these will be announced 6 months in advance toprotobuf@googlegroups.com.

You should, whenever possible, use generated code created by the protoc-gen-gotool built at the same commit as the proto package. The proto packagedeclares package-level constants in the form ProtoPackageIsVersionX.Application code and generated code may depend on one of these constants toensure that compilation will fail if the available version of the proto libraryis too old. Whenever we make a change to the generated code that requires newerlibrary support, in the same commit we will increment the version number of thegenerated code and declare a new package-level constant whose name incorporatesthe latest version number. Removing a compatibility constant is considered abreaking change and would be subject to the announcement policy stated above.

The protoc-gen-go/generator package exposes a plugin interface,which is used by the gRPC code generation. This interface is notsupported and is subject to incompatible changes without notice.

To restore the repository download the bundle

wget https://archive.org/download/github.com-golang-protobuf_-_2019-11-26_23-02-00/golang-protobuf_-_2019-11-26_23-02-00.bundle

and run:

 git clone golang-protobuf_-_2019-11-26_23-02-00.bundle 

Source: https://github.com/golang/protobuf
Uploader: golang
Upload date: 2019-11-26