背景
谷歌出品，必出精品 https://developers.google.com/protocol-buffers
Protocol buffers are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data – think XML, but smaller, faster, and simpler.
Protocol buffers 是 谷歌的 语言无关，平台无关，可扩展的数据序列化协议-如同XML，但是 更小 巧 更快速 更简单。
说白了 就是定义了一种数据格式，就像 xml json string 之类的，一旦定义了要处理的数据格式之后，就可以利用 Protocol buffers 的代码生成工具生成相关的代码。
Protocol buffers 很适合做数据存储或 RPC 数据交换格式。可用于通讯协议、数据存储等领域的语言无关、平台无关、可扩展的序列化结构数据格式
Why not just use XML?
Protocol buffers have many advantages over XML for serializing structured data. Protocol buffers:
- are simpler
- are 3 to 10 times smaller
- are 20 to 100 times faster
- are less ambiguous
- generate data access classes that are easier to use programmatically
For example, let's say you want to model a person with a name and an email. In XML, you need to do:
<person>
<name>John Doe</name>
<email>jdoe@example.com</email>
</person>
while the corresponding protocol buffer message (in protocol buffer text format) is:
# Textual representation of a protocol buffer.
# This is *not* the binary format used on the wire.
person {
name: "John Doe"
email: "jdoe@example.com"
}
When this message is encoded to the protocol buffer binary format (the text format above is just a convenient human-readable representation for debugging and editing), it would probably be 28 bytes long and take around 100-200 nanoseconds to parse. The XML version is at least 69 bytes if you remove whitespace, and would take around 5,000-10,000 nanoseconds to parse.
Base 128 Varints
To understand your simple protocol buffer encoding, you first need to understand varints. Varints are a method of serializing integers using one or more bytes. Smaller numbers take a smaller number of bytes.
Each byte in a varint, except the last byte, has the most significant bit (msb) set – this indicates that there are further bytes to come. The lower 7 bits of each byte are used to store the two's complement representation of the number in groups of 7 bits, least significant group first.
更多关于protocol buffer 编码解码 可以参考如下：
https://developers.google.com/protocol-buffers/docs/encoding?hl=zh-CN
