Using openembedded SDK to build protobuf-c

brook@vista:~/protobuf$ git clone git://github.com/google/protobuf.git
Cloning into 'protobuf'...
...

brook@vista:~/protobuf/protobuf$ git checkout 3.6.x
Branch 3.6.x set up to track remote branch 3.6.x from origin.
...

brook@vista:~/protobuf/protobuf$ . /opt/oecore-x86_64/environment-setup-cortexa7-neon-vfpv4-oe-linux-gnueabi


brook@vista:~/protobuf/protobuf$ vim configure.ac 
 export CFLAGS
 export CXXFLAGS
### remove below line ###
AC_CONFIG_SUBDIRS([third_party/googletest])

brook@vista:~/home6t/protobuf/protobuf$ ./autogen.sh
+ mkdir -p third_party/googletest/m4
+ autoreconf -f -i -Wall,no-obsolete
...

brook@vista:~/protobuf/protobuf$ ./configure ${CONFIGURE_FLAGS} --prefix=/home/brook/protobuf/
configure: loading site script /opt/oecore-x86_64/site-config-cortexa7-neon-vfpv4-oe-linux-gnueabi
checking whether to enable maintainer-specific portions of Makefiles... yes
checking build system type... x86_64-pc-linux-gnu
...

brook@vista:~/protobuf/protobuf$ make all -j 8
make  all-recursive
Making install in .
make[1]: Entering directory '/home/brook/protobuf/protobuf'
...

brook@vista:~/protobuf/protobuf$ make install
Making install in .
make[1]: Entering directory '/home/brook/protobuf/protobuf'
...


change "/home/brook/protobuf/lib/libprotoc.la"
from
# Libraries that this one depends upon.
dependency_libs=' =/home6t/brook/protobuf/lib/libprotobuf.la =/usr/lib/libstdc++.la'

to
# Libraries that this one depends upon.
dependency_libs=''


brook@vista:~$ mkdir protobuf-c
brook@vista:~$ cd protobuf-c
brook@vista:~/protobuf-c$ git clone git://github.com/protobuf-c/protobuf-c.git
Cloning into 'protobuf-c'...
remote: Enumerating objects: 59, done.
remote: Counting objects: 100% (59/59), done.
...

brook@vista:~/protobuf-c/protobuf-c$ ./autogen.sh
autoreconf: Entering directory `.'
autoreconf: configure.ac: not using Gettext
...

brook@vista:~/protobuf-c/protobuf-c$ PROTOC=/usr/bin/protoc-c protobuf_CFLAGS="-I/home/brook/protobuf/include" protobuf_LIBS="-L/home/brook/protobuf/lib" ./configure ${CONFIGURE_FLAGS} --prefix=/home/brook/protobuf-c
configure: loading site script /opt/oecore-x86_64/site-config-cortexa7-neon-vfpv4-oe-linux-gnueabi
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
...

brook@vista:~/protobuf-c/protobuf-c$ make -j 8
make  all-am
make[1]: Entering directory '/home/brook/protobuf-c/protobuf-c'
  CC       protobuf-c/protobuf-c.lo
...

Protocol Buffers - for C++

Protocol buffers基本上我把他想成是一個資料庫應用的延伸, 這話該如何說呢? 基本上他就是透過名為proto的meta file, 用以描述資料形態與內容(做encode/decode).

How does the Protocol Buffers work?

先定義你的message結構, 如

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;

  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }

  message PhoneNumber {
    required string number = 1;
    optional PhoneType type = 2 [default = HOME];
  }

  repeated PhoneNumber phone = 4;
}

再用protoc將該檔案轉成code, 目前支援(C++, Java and Python), 如下例子, 將brook.proto轉成C++(brook.pb.cc與brook.pb.h).

brook@vista:~/protobuf/CPP$ protoc --cpp_out=. brook.proto
brook@vista:~/protobuf/CPP$ ls
brook.pb.cc  brook.pb.h  brook.proto

這些code會包含存取每一個欄位的API(如下由doxygen產生的圖), 如email()與set_email(), 用以serialize/parse資料,

接著我們就可以用這些API寫一段code, 做serialize/parse資料

#include <iostream>
#include <fstream>
#include "brook.pb.h"
using namespace std;

static void _Serialize(void)
{
        Person person;
        person.set_name("John Doe");
        person.set_id(1234);
        person.set_email("jdoe@example.com");
        fstream output("myfile", ios::out | ios::binary);
        person.SerializeToOstream(&output);
}

static void _Parse(void)
{
        Person person;
        fstream input("myfile", ios::in | ios::binary);
        person.ParseFromIstream(&input);
        cout << "Name: " << person.name() << endl;
        cout << "E-mail: " << person.email() << endl;
}

int main(int argc, char *argv[])
{
        _Serialize();
        _Parse();
        return 0;
}

brook@vista:~/protobuf/CPP$ g++ main.c brook.pb.cc -lprotobuf
brook@vista:~/protobuf/CPP$ ./a.out
Name: John Doe
E-mail: jdoe@example.com

參考資料:
• protocol buffer簡介, https://developers.google.com/protocol-buffers/docs/overview