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 false -
repeated: 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/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 读数据
#! /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)
