Rust Protobuf 对比分析(prost vs rust-protobuf)

prost

优势：

• generates simple, idiomatic and readable Rust types
• 保留 proto 中的注释
• 可以在已有的 Rust types 中增加 attributes 来转换为 Message
• 使用 bytes::{Buf, BufMut} 来抽象而不是 std::io::{Read, Write}
• 可以识别 package 自动转换为 Rust module

不支持 reflection

generated code

prost 可以根据 .proto 文件生成 rust 代码

Packages

package foo.bar → foo::bar module

Messages

message ←> Rust struct

message Foo {
}

// <->

#[derive(Clone, Debug, PartialEq, Message)]
pub struct Foo {
}

Fields

protobuf message fields 对应 Rust struct pub fields

Scalar Values

protobuf type	rust type
double	f64
float	f32
int32,sint32,sfixed32	i32
int64,sint64,sfixed64	i64
uint32, fixed32	u32
uint64, fixed64	u64
bool	bool
string	String
bytes	Vec

Enumerations

.proto 枚举对应 Rust 的 i32

enum PhoneType {
  MOBILE = 0;
  HOME = 1;
  WORK = 2;
}

pub enum PhoneType {
  Mobile = 0,
  Home = 1,
  Work = 2,
}

// PhoneType::Mobile as i32 可行
// #[derive(::prost::Enumeration)] 会给 `PhoneType` 增加方法
impl PhoneType {
  pub fn is_valid(value: i32) -> bool
  pub fn from_i32(value: i32) -> Option<PhoneType>
}

Field Modifiers

.proto Version	modifier	Rust Type
proto2	optional	Option
proto2	required	T
proto3	default	T
proto2/proto3	repeated	Vec

Map Fields

Rust HashMap

Message Fields

proto3 默认会生成 Option<T>

message 会 Box 避免无限 size 的 struct

Oneof Fileds

Oneof 会转换成 enum

message Foo {
  oneof widget {
    int32 quux = 1;
    string bar = 2;
  }
}

pub struct Foo {
  pub widget: Option<foo::Widget>,
}
pub mod foo {
  pub enum Widget {
    Quux(i32),
    Bar(String),
  }
}

Services

prost-build 支持自定义处理 service 定义，根据项目需要生成 trait

Example

syntax = "proto3";
package tutorial;
 
message Person {
  string name = 1;
  int32 id = 2; // unique id number for this person
  string email = 3;
 
  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }
 
  message PhoneNumber {
    string number = 1;
    PhoneNumber type = 2;
  }
  repeated PhoneNumber phones = 4;
}
 
// our address book file is just one of these
message AddressBook {
  repeated Person people = 1;
}

生成的代码

#[derive(Clone, PartialEq, ::prost::Message)]
pub struct Person {
    #[prost(string, tag="1")]
    pub name: ::prost::alloc::string::String,
    /// unique id number for this person
    #[prost(int32, tag="2")]
    pub id: i32,
    #[prost(string, tag="3")]
    pub email: ::prost::alloc::string::String,
    #[prost(message, repeated, tag="4")]
    pub phones: ::prost::alloc::vec::Vec<person::PhoneNumber>,
}
/// Nested message and enum types in `Person`.
pub mod person {
    #[derive(Clone, PartialEq, ::prost::Message)]
    pub struct PhoneNumber {
        #[prost(string, tag="1")]
        pub number: ::prost::alloc::string::String,
        #[prost(message, optional, boxed, tag="2")]
        pub r#type: ::core::option::Option<::prost::alloc::boxed::Box<PhoneNumber>>,
    }
    #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, ::prost::Enumeration)]
    #[repr(i32)]
    pub enum PhoneType {
        Mobile = 0,
        Home = 1,
        Work = 2,
    }
}
/// our address book file is just one of these
#[derive(Clone, PartialEq, ::prost::Message)]
pub struct AddressBook {
    #[prost(message, repeated, tag="1")]
    pub people: ::prost::alloc::vec::Vec<Person>,
}
 

序列化已经存在的类型

Prost 会根据声明的顺序自动推断 struct 中 field 的 tag，加上合适的 derive and field annotation 就能实现序列化/反序列化已有的类型

use prost;
use prost::{Enumeration, Message};
 
#[derive(Clone, PartialEq, Message)]
struct Person {
    #[prost(string, tag = "1")]
    pub id: String, // tag=1
    // NOTE: Old "name" field has been removed
    // pub name: String, // tag=2 (Removed)
    #[prost(string, tag = "6")]
    pub given_name: String, // tag=6
    #[prost(string)]
    pub family_name: String, // tag=7
    #[prost(string)]
    pub formatted_name: String, // tag=8
    #[prost(uint32, tag = "3")]
    pub age: u32, // tag=3
    #[prost(uint32)]
    pub height: u32, // tag=4
    #[prost(enumeration = "Gender")]
    pub gender: i32, // tag=5
    // NOTE: Skip to less commonly occurring fields
    #[prost(string, tag = "16")]
    pub name_prefix: String, // tag=16  (eg. mr/mrs/ms)
    #[prost(string)]
    pub name_suffix: String, // tag=17  (eg. jr/esq)
    #[prost(string)]
    pub maiden_name: String, // tag=18
}
 
#[derive(Clone, Copy, Debug, PartialEq, Eq, Enumeration)]
pub enum Gender {
    Unknown = 0,
    Female = 1,
    Male = 2,
}

rust-protobuf

doc rust codegen doc

优势：

• 生成的代码有运行时库 ？（prost 可以 no_std 支持），支持 reflection
• 更像 cpp protobuf 版本的生成文件（不好说是优势还是劣势）

劣势：

• 文档较少，比如类型之间的对应关系

对比

生成的代码行数 rust-protobuf 是 prost 的十倍， prost 生成的 .rs 几乎与 .proto 行数一致

---

PS. cargo build script doc cargo build 在编译之前会先编译 build.rs 文件并执行，The script may communicate with Cargo by printing specially formatted commands prefixed with cargo: to stdout，比如 println!("cargo:rerun-if-changed={}", file_name);，默认 package 文件任何一个变更都会重新执行

// build.rs
use anyhow::Result;
 
#[rustfmt::skip]
const PROTOBUF_FILES: &[(&str, &str)] = &[
    ("a", "a.proto"),
    ("b", "b.proto"),
    ("c", "c.proto"),
];
 
fn main() -> Result<()> {
    for (dir, file) in PROTOBUF_FILES {
        let file_path = format!("{}/{}", dir, file);
        println!("cargo:rerun-if-changed={}", file_path);
        // prost
        prost_build::Config::new()
            .out_dir(dir)
            .compile_protos(&[&file_path], &[dir])?;
 
        // rust-protobuf
        protobuf_codegen_pure::Codegen::new()
            .out_dir("src/protos")
            .input(&file_path)
            .include(dir)
            .run()
            .expect("Codegen failed");
    }
 
    Ok(())
}