Go使用proto3的踩坑实战记录

开发环境：windows10，golang1.18.2，goland2022.2

最近在写项目时，一些数据类的结构以protobuf文件给定。因此，需要将这些protobuf文件转换为golang代码。

首先，在下载解析protobuf的包的时候就碰到了第一个问题...

go get -u github.com/golang/protobuf/protoc-gen-go

在我用上述命令后，终端提示该包已弃用

go: module github.com/golang/protobuf is deprecated: Use the "google.golang.org/protobuf" module instead.

随后直接用给出的新地址替换，这一次终端没有给出任何提示，但在GOPATH的bin目录下并没有出现想要的protoc-gen-go.exe文件。

故再次使用go install

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest 

成功安装上述可执行文件。

再次尝试解析.proto文件，报错：

'protoc-gen-go' 不是内部或外部命令，也不是可运行的程序或批处理文件。

又是因为没有将GOPATH\bin目录添加至环境变量中。。添加后测试终端输入：

$:protoc
Usage: D:\Application\protoc-21.7-win64\bin\protoc.exe [OPTION] PROTO_FILES
Parse PROTO_FILES and generate output based on the options given:
  -IPATH, --proto_path=PATH   Specify the directory in which to search for
                              imports.  May be specified multiple times;
                              directories will be searched in order.  If not
                              given, the current working directory is used.
                              If not found in any of the these directories,
                              the --descriptor_set_in descriptors will be
                              checked for required proto file.
  --version                   Show version info and exit.
  -h, --help                  Show this text and exit.
  --encode=MESSAGE_TYPE       Read a text-format message of the given type
                              from standard input and write it in binary
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their imports.
  --deterministic_output      When using --encode, ensure map fields are
                              deterministically ordered. Note that this order
                              is not canonical, and changes across builds or
                              releases of protoc.
  --decode=MESSAGE_TYPE       Read a binary message of the given type from
                              standard input and write it in text format
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their imports.
  --decode_raw                Read an arbitrary protocol message from
                              standard input and write the raw tag/value
                              pairs in text format to standard output.  No
                              PROTO_FILES should be given when using this
                              flag.
  --descriptor_set_in=FILES   Specifies a delimited list of FILES
                              each containing a FileDescriptorSet (a
                              protocol buffer defined in descriptor.proto).
                              The FileDescriptor for each of the PROTO_FILES
                              provided will be loaded from these
                              FileDescriptorSets. If a FileDescriptor
                              appears multiple times, the first occurrence
                              will be used.
  -oFILE,                     Writes a FileDescriptorSet (a protocol buffer,
    --descriptor_set_out=FILE defined in descriptor.proto) containing all of
                              the input files to FILE.
  --include_imports           When using --descriptor_set_out, also include
                              all dependencies of the input files in the
                              set, so that the set is self-contained.
  --include_source_info       When using --descriptor_set_out, do not strip
                              SourceCodeInfo from the FileDescriptorProto.
                              This results in vastly larger descriptors that
                              include information about the original
                              location of each decl in the source file as
                              well as surrounding comments.
  --dependency_out=FILE       Write a dependency output file in the format
                              expected by make. This writes the transitive
                              set of input file paths to FILE
  --error_format=FORMAT       Set the format in which to print errors.
                              FORMAT may be 'gcc' (the default) or 'msvs'
                              (Microsoft Visual Studio format).
  --fatal_warnings            Make warnings be fatal (similar to -Werr in
                              gcc). This flag will make protoc return
                              with a non-zero exit code if any warnings
                              are generated.
  --print_free_field_numbers  Print the free field numbers of the messages
                              defined in the given proto files. Groups share
                              the same field number space with the parent
                              message. Extension ranges are counted as
                              occupied fields numbers.
  --plugin=EXECUTABLE         Specifies a plugin executable to use.
                              Normally, protoc searches the PATH for
                              plugins, but you may specify additional
                              executables not in the path using this flag.
                              Additionally, EXECUTABLE may be of the form
                              NAME=PATH, in which case the given plugin name
                              is mapped to the given executable even if
                              the executable's own name differs.
  --cpp_out=OUT_DIR           Generate C++ header and source.
  --csharp_out=OUT_DIR        Generate C# source file.
  --java_out=OUT_DIR          Generate Java source file.
  --kotlin_out=OUT_DIR        Generate Kotlin file.
  --objc_out=OUT_DIR          Generate Objective-C header and source.
  --php_out=OUT_DIR           Generate PHP source file.
  --pyi_out=OUT_DIR           Generate python pyi stub.
  --python_out=OUT_DIR        Generate Python source file.
  @<filename>                 Read options and filenames from file. If a
                              this argument file is searched. Content of
                              the file will be expanded in the position of
                              @<filename> as in the argument list. Note
                              that shell expansion is not applied to the
                              content of the file (i.e., you cannot use
                              quotes, wildcards, escapes, commands, etc.).
                              Each line corresponds to a single argument,
                              even if it contains spaces.

已经成功完成proto工具的安装。

紧接着，再一次尝试——

提示无法确定生成go文件的路径

protoc --go_out=. test.proto
报错信息：
protoc-gen-go: unable to determine Go import path for "test.proto"

Please specify either:
        • a "go_package" option in the .proto source file, or
        • a "M" argument on the command line.

test.proto文件

如下：

syntax="proto3"; //版本号
package main;  //包名

enum ClassName{   //枚举
  class1=0;  //标号 必须从 0开始
  class2=1;
  class3=2;
}
message Student{ //消息，对应于Go的结构体
  string name=1; //1:标号，唯一 即可（相当于数据库中的Id，不一定要从1 ，2的顺序依次排列。）
  int32 age=2;  //必须指定整型的范围，如int32，int64
  string address=3;
  ClassName cn=4;
}
message Students{
  repeated Student person=1;  // repeated 修饰，相当于Go中切片
  string school=2;
}

• protoc-gen-go v1.27.1
• protoc v3.12.3

原因是protoc-gen-go版本过高，对源proto文件需要添加包名。

还有一种解决办法就是把protoc-gen-go版本退回到1.3.2及以下也可以解决。

最终！！根据报错信息在文件中第二行后添加：（指定生成go文件的路径）

option go_package="/main"; //解决报错:unable to determine Go import path

总算成功在该目录下生成了test.pb.go文件！！！

总结

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