protobuf使用

TheLudGamer

1. 概述


Protocol Buffers(又名protobuf) 是一种语言中立、平台中立的可扩展机制，用于序列化结构化的数据
它就像JSON，只是它更小、更快
只需定义一次数据如何被结构化，然后就可以使用特殊生成的源代码，轻松地从各种数据流和使用各种语言写入和读取结构化数据
2. 好处


protobuf适配多种语言，可以很方便的序列化结构化的数据，最常被用于定义通信协议(与gRPC一起)和数据存储
使用protobuf的一些优点：

紧凑的数据存储快速解析可在许多编程语言中使用通过自动生成的类来优化功能

3. 示例(Python)


我们创建一个非常简单的“地址簿”应用程序，它可以在文件之间读取和写入人们的联系信息
通讯簿中的每个人都有一个姓名、一个 ID、一个电子邮件地址和一个联系电话号码
3.1 定义协议格式


创建addressbook.proto
syntax = "proto2";package tutorial;message Person {  optional string name = 1;  optional int32 id = 2;  optional string email = 3;  enum PhoneType {    MOBILE = 0;    HOME = 1;    WORK = 2;  }  message PhoneNumber {    optional string number = 1;    optional PhoneType type = 2 [default = HOME];  }  repeated PhoneNumber phones = 4;}message AddressBook {  repeated Person people = 1;}
proto文件以包声明开始，这有助于防止不同项目之间的命名冲突
每个元素上的"= 1"，" = 2" 标记标识字段在二进制编码中使用的唯一“标记”

每个字段必须使用下列修饰符之一进行注释:

optional: 字段可以设置，也可以不设置。如果未设置可选字段值，则使用默认值。对于简单类型，您可以指定自己的默认值，就像我们在示例中对电话号码类型所做的那样。否则，将使用系统默认值: 数值类型为零，字符串为空字符串，布尔为 falserepeated: 字段可以重复任意次数(包括零次)required: 必须提供字段的值，否则消息将被视为“未初始化”。序列化未初始化的消息将引发异常。解析未初始化的消息将失败。除此之外，必填字段的行为与可选字段完全相同

3.2 编译Protocol Buffers


a) 安装编译器
b) 运行
$ protoc --python_out=./ addressbook.proto
因为需要 Python 类，所以可以使用 --python_out
这将在指定的目标目录中生成 addressbook_pb2.py
3.3 写数据

#! /usr/bin/pythonimport addressbook_pb2import sys# This function fills in a Person message based on user input.def PromptForAddress(person):  person.id = int(raw_input("Enter person ID number: "))  person.name = raw_input("Enter name: ")  email = raw_input("Enter email address (blank for none): ")  if email != "":    person.email = email  while True:    number = raw_input("Enter a phone number (or leave blank to finish): ")    if number == "":      break    phone_number = person.phones.add()    phone_number.number = number    type = raw_input("Is this a mobile, home, or work phone? ")    if type == "mobile":      phone_number.type = addressbook_pb2.Person.MOBILE    elif type == "home":      phone_number.type = addressbook_pb2.Person.HOME    elif type == "work":      phone_number.type = addressbook_pb2.Person.WORK    else:      print "Unknown phone type; leaving as default value."# Main procedure:  Reads the entire address book from a file,#   adds one person based on user input, then writes it back out to the same#   file.if len(sys.argv) != 2:  print "Usage:", sys.argv[0], "ADDRESS_BOOK_FILE"  sys.exit(-1)address_book = addressbook_pb2.AddressBook()# Read the existing address book.try:  f = open(sys.argv[1], "rb")  address_book.ParseFromString(f.read())  f.close()except IOError:  print sys.argv[1] + ": Could not open file.  Creating a new one."# Add an address.PromptForAddress(address_book.people.add())# Write the new address book back to disk.f = open(sys.argv[1], "wb")f.write(address_book.SerializeToString())f.close()3.4 读数据

#! /usr/bin/pythonimport addressbook_pb2import sys# Iterates though all people in the AddressBook and prints info about them.def ListPeople(address_book):  for person in address_book.people:    print "Person ID:", person.id    print "  Name:", person.name    if person.HasField('email'):      print "  E-mail address:", person.email    for phone_number in person.phones:      if phone_number.type == addressbook_pb2.Person.PhoneType.MOBILE:        print "  Mobile phone #: ",      elif phone_number.type == addressbook_pb2.Person.PhoneType.HOME:        print "  Home phone #: ",      elif phone_number.type == addressbook_pb2.Person.PhoneType.WORK:        print "  Work phone #: ",      print phone_number.number# Main procedure:  Reads the entire address book from a file and prints all#   the information inside.if len(sys.argv) != 2:  print "Usage:", sys.argv[0], "ADDRESS_BOOK_FILE"  sys.exit(-1)address_book = addressbook_pb2.AddressBook()# Read the existing address book.f = open(sys.argv[1], "rb")address_book.ParseFromString(f.read())f.close()ListPeople(address_book)