1. 概述

Protocol Buffers(又名protobuf) 是一種語(yǔ)言中立、平臺(tái)中立的可擴(kuò)展機(jī)制，用于序列化結(jié)構(gòu)化的數(shù)據(jù)
它就像JSON，只是它更小、更快
只需定義一次數(shù)據(jù)如何被結(jié)構(gòu)化，然后就可以使用特殊生成的源代碼，輕松地從各種數(shù)據(jù)流和使用各種語(yǔ)言寫(xiě)入和讀取結(jié)構(gòu)化數(shù)據(jù)

2. 好處

protobuf適配多種語(yǔ)言，可以很方便的序列化結(jié)構(gòu)化的數(shù)據(jù)，最常被用于定義通信協(xié)議(與gRPC一起)和數(shù)據(jù)存儲(chǔ)
使用protobuf的一些優(yōu)點(diǎn)：

• 緊湊的數(shù)據(jù)存儲(chǔ)
• 快速解析
• 可在許多編程語(yǔ)言中使用
• 通過(guò)自動(dòng)生成的類(lèi)來(lái)優(yōu)化功能

3. 示例(Python)

我們創(chuàng)建一個(gè)非常簡(jiǎn)單的“地址簿”應(yīng)用程序，它可以在文件之間讀取和寫(xiě)入人們的聯(lián)系信息
通訊簿中的每個(gè)人都有一個(gè)姓名、一個(gè) ID、一個(gè)電子郵件地址和一個(gè)聯(lián)系電話(huà)號(hào)碼

3.1 定義協(xié)議格式

創(chuàng)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文件以包聲明開(kāi)始，這有助于防止不同項(xiàng)目之間的命名沖突
每個(gè)元素上的"= 1"，" = 2" 標(biāo)記標(biāo)識(shí)字段在二進(jìn)制編碼中使用的唯一“標(biāo)記”

每個(gè)字段必須使用下列修飾符之一進(jìn)行注釋:

• optional: 字段可以設(shè)置，也可以不設(shè)置。如果未設(shè)置可選字段值，則使用默認(rèn)值。對(duì)于簡(jiǎn)單類(lèi)型，您可以指定自己的默認(rèn)值，就像我們?cè)谑纠袑?duì)電話(huà)號(hào)碼類(lèi)型所做的那樣。否則，將使用系統(tǒng)默認(rèn)值: 數(shù)值類(lèi)型為零，字符串為空字符串，布爾為 false
• repeated: 字段可以重復(fù)任意次數(shù)(包括零次)
• required: 必須提供字段的值，否則消息將被視為“未初始化”。序列化未初始化的消息將引發(fā)異常。解析未初始化的消息將失敗。除此之外，必填字段的行為與可選字段完全相同

3.2 編譯Protocol Buffers

a) 安裝編譯器
b) 運(yùn)行

$ protoc --python_out=./ addressbook.proto

因?yàn)樾枰?Python 類(lèi)，所以可以使用 --python_out
這將在指定的目標(biāo)目錄中生成 addressbook_pb2.py

3.3 寫(xiě)數(shù)據(jù)

#! /usr/bin/python

import addressbook_pb2
import 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 讀數(shù)據(jù)

#! /usr/bin/python

import addressbook_pb2
import 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)