protoc 命令的获得

源码在 https://github.com/google/protobuf ， 如果不想自己编译获得最新版本，则可以下载官方编译好的各个平台的，下载地址：https://github.com/google/protobuf/releases ，注意不是带语言后缀的文件，那是源码，如下图：

下载后的解压缩包含的内容如下（以mac下为例）

我们通过 which 命令可以查到 protoc 的安装目录， 覆盖它即可。

$ which protoc
/usr/local/bin/protoc

This package contains a precompiled Win32 binary version of the protocol buffer
compiler (protoc).  This binary is intended for Windows users who want to
use Protocol Buffers in Java or Python but do not want to compile protoc
themselves.  To install, simply place this binary somewhere in your PATH.

This binary was built using MinGW, but the output is the same regardless of
the C++ compiler used.

You will still need to download the source code package in order to obtain the
Java or Python runtime libraries.  Get it from:
  https://github.com/google/protobuf/releases/

命令参数

$ protoc -help
Usage: protoc [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.
  --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.
  --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.
  -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).
  --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.
  --javanano_out=OUT_DIR      Generate Java Nano source file.
  --js_out=OUT_DIR            Generate JavaScript source.
  --objc_out=OUT_DIR          Generate Objective C header and source.
  --python_out=OUT_DIR        Generate Python source file.
  --ruby_out=OUT_DIR          Generate Ruby source file.

例子

Java 文件生成

$ protoc --java_out=./java/ ./proto/helloworld.proto

protoc 的命令格式为 protoc [OPTION] PROTO_FILES   （最后是待编译的 proto文件）

--java_out 为输出java代码的目录，这里指定的是 ./java/ 目录。

随后我们指定了proto文件的位置 ./proto/helloworld.proto 。

执行上述命令，我们就 ./java/ 目录下就产生了对应的 java文件。

go 文件生成

下面这几种方式生成都可以：

$ protoc --go_out=./go/ ./proto/helloworld.proto

跟上面Java的生成完全一样，只不过这次是让生成 go 的代码。

$ protoc --go_out=./go/ -I proto ./proto/helloworld.proto

这次多了一个参数 -I ， -I=IMPORT_PATH  can be used as a short form of--proto_path.

-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.

IMPORT_PATH specifies a directory in which to look for .proto files when resolvingimport directives. If omitted, the current directory is used. Multiple import directories can be specified by passing the--proto_path option multiple times; they will be searched in order.

简单来说，就是如果多个proto文件之间有互相依赖，生成某个proto文件时，需要import其他几个proto文件，这时候就要用-I来指定搜索目录。

如果没有指定 –I 参数，则在当前目录进行搜索。

上面两种方法产生的目录如下图， –I 参数起作用了后，生成目录少了一级：

javanano 文件生成

$ protoc --javanano_out=ignore_services=true:./javanano/ -I proto ./proto/garlic.proto

由于 javanano 是给 android 用的，没有服务器端代码，所以多了--javanano_out=ignore_services=true:DST_DIR 这个设置，其他完全一样。

参考： https://github.com/grpc/grpc-common/issues/156

更复杂的可以参考：

Android protobuf nano documentation
http://stackoverflow.com/questions/22247951/android-protobuf-nano-documentation

https://developers.google.com/protocol-buffers/docs/proto3#generating

为了更方便的使用gRPC，包括protoc的命令，针对不同语言有下面额外的方法：

http://www.grpc.io/posts/installation

参考资料：

https://github.com/google/protobuf/tree/master/javanano

https://github.com/google/protobuf