.proto文件有两种语法标准：proto2和proto3，我们以proto3为例，其语法格式如下：
message <message_name> {
<filed_rule> <filed_type> <filed_name> = <field_number>
规则 类型 名称 编号
}
- message_name: 同一个pkg内，必须唯一
- filed_rule: 可以没有, 常用的有repeated, oneof
- filed_type: 数据类型, protobuf定义的数据类型, 生产代码的会映射成对应语言的数据类型
- filed_name: 字段名称, 同一个message 内必须唯一
- field_number: 字段的编号, 序列化成二进制数据时的字段编号
2.1.1、字段规则
2.1.2、字段类型
基础类型
参考官方文档（Language Guide (proto3) | Protocol Buffers | Google Developers），我这里只保留了我常用编程语言的字段类型
| .proto Type |
Notes |
C++ Type |
Python Type[3] |
C# Type |
| double |
|
double |
float |
double |
| float |
|
float |
float |
float |
| int32 |
Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint32 instead. |
int32 |
int |
int |
| int64 |
Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint64 instead. |
int64 |
int/long[4] |
long |
| uint32 |
Uses variable-length encoding. |
uint32 |
int/long[4] |
uint |
| uint64 |
Uses variable-length encoding. |
uint64 |
int/long[4] |
ulong |
| sint32 |
Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int32s. |
int32 |
int |
int |
| sint64 |
Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int64s. |
int64 |
int/long[4] |
long |
| fixed32 |
Always four bytes. More efficient than uint32 if values are often greater than 228. |
uint32 |
int/long[4] |
uint |
| fixed64 |
Always eight bytes. More efficient than uint64 if values are often greater than 256. |
uint64 |
int/long[4] |
ulong |
| sfixed32 |
Always four bytes. |
int32 |
int |
int |
| sfixed64 |
Always eight bytes. |
int64 |
int/long[4] |
long |
| bool |
|
bool |
bool |
bool |
| string |
A string must always contain UTF-8 encoded or 7-bit ASCII text, and cannot be longer than 232. |
string |
str/unicode[5] |
string |
| bytes |
May contain any arbitrary sequence of bytes no longer than 232. |
string |
str (Python 2)
bytes (Python 3) |
ByteString |
枚举类型
语法如下：
enum <enum_name> {
<element_name> = <element_number>
}
- enum_name: 枚举名称
- element_name: pkg内全局唯一, 很重要
- element_number: 必须从0开始, 0表示类型的默认值, 32-bit integer
如下示例，Corpus就是我们定义的一个枚举类型。
message SearchRequest {
string query = 1;
int32 page_number = 2;
int32 result_per_page = 3;
enum Corpus {
UNIVERSAL = 0;
WEB = 1;
IMAGES = 2;
LOCAL = 3;
NEWS = 4;
PRODUCTS = 5;
VIDEO = 6;
}
Corpus corpus = 4;
}
如果需要将不同的枚举常量映射到相同的值。将allow_alias选项设置为true即可。（最好不要这么使用）
message MyMessage1 {
enum EnumAllowingAlias {
option allow_alias = true;
UNKNOWN = 0;
STARTED = 1;
RUNNING = 1;
}
}
message MyMessage2 {
enum EnumNotAllowingAlias {
UNKNOWN = 0;
STARTED = 1;
// RUNNING = 1; // Uncommenting this line will cause a compile error inside Google and a warning message outside.
}
}
2.1.3、字段编号
2.1.4、综合示例
