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A pure Rust library to serialize/deserialize protobuf files.



This library intends to provide a simple yet fast (minimal allocations) protobuf parser implementation.

It provides both:

  • pb-rs, a code generation tool:
    • each .proto file will generate a minimal rust module (one function to read, one to write, and one to compute the size of the messages)

    • each message will generate a rust struct where:

      Proto Rust
      bytes Cow<'a, [u8]>
      string Cow<'a, str>
      other scalars rust primitive
      repeated Vec
      repeated, packed, fixed size Cow<'a, [M]>
      optional Option
      message struct
      enum enum
      map HashMap
      oneof Name OneOfName enum
      nested m1 mod_m1 module
      package a.b mod_a::mod_b modules
      import file_a.proto use super::file_a::*
    • no need to use google protoc tool to generate the modules

  • quick-protobuf, a protobuf file parser:
    • this is the crate that you will typically refer to in your library. The generated modules will assume it has been imported.
    • it acts like an event parser, the logic to convert it into struct is handled by pb-rs

Example: protobuf_example project

    1. Install pb-rs binary to convert your proto file into a quick-protobuf compatible source code
cargo install pb-rs
pb-rs /path/to/your/protobuf/file.proto
# will generate a 
# /path/to/your/protobuf/
    1. Add a dependency to quick-protobuf
# Cargo.toml
quick-protobuf = "0.8.0"
    1. Have fun
extern crate quick_protobuf;

mod foo_bar; // (see 1.)

use quick_protobuf::Reader;

// We will suppose here that Foo and Bar are two messages defined in the .proto file
// and converted into rust structs
// FooBar is the root message defined like this:
// message FooBar {
//     repeated Foo foos = 1;
//     repeated Bar bars = 2;
// }
// FooBar is a message generated from a proto file
// in parcicular it contains a `from_reader` function
use foo_bar::FooBar;
use quick_protobuf::{MessageRead, BytesReader};

fn main() {
    // bytes is a buffer on the data we want to deserialize
    // typically bytes is read from a `Read`:
    // r.read_to_end(&mut bytes).expect("cannot read bytes");
    let mut bytes: Vec<u8>;
    # bytes = vec![];

    // we can build a bytes reader directly out of the bytes
    let mut reader = BytesReader::from_bytes(&bytes);

    // now using the generated module decoding is as easy as:
    let foobar = FooBar::from_reader(&mut reader, &bytes).expect("Cannot read FooBar");

    // if instead the buffer contains a length delimited stream of message we could use:
    // while !r.is_eof() {
    //     let foobar: FooBar = r.read_message(&bytes).expect(...);
    //     ...
    // }
    println!("Found {} foos and {} bars", foobar.foos.len(), foobar.bars.len());

Examples directory

You can find basic examples in the examples directory.

Message <-> struct

The best way to check for all kinds of generated code is to look for the codegen_example data:

Proto definition

enum FooEnum {
    FIRST_VALUE = 1;
message BarMessage {
    required int32 b_required_int32 = 1;

message FooMessage {
    optional int32 f_int32 = 1;
    optional int64 f_int64 = 2;
    optional uint32 f_uint32 = 3;
    optional uint64 f_uint64 = 4;
    optional sint32 f_sint32 = 5;
    optional sint64 f_sint64 = 6;
    optional bool f_bool = 7;
    optional FooEnum f_FooEnum = 8;
    optional fixed64 f_fixed64 = 9;
    optional sfixed64 f_sfixed64 = 10;
    optional fixed32 f_fixed32 = 11;
    optional sfixed32 f_sfixed32 = 12;
    optional double f_double = 13;
    optional float f_float = 14;
    optional bytes f_bytes = 15;
    optional string f_string = 16;
    optional FooMessage f_self_message = 17;
    optional BarMessage f_bar_message = 18;
    repeated int32 f_repeated_int32 = 19;
    repeated int32 f_repeated_packed_int32 = 20 [ packed = true ];

Generated structs

#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum FooEnum {
    FIRST_VALUE = 1,

#[derive(Debug, Default, PartialEq, Clone)]
pub struct BarMessage {                                 // all fields are owned: no lifetime parameter
    pub b_required_int32: i32,

#[derive(Debug, Default, PartialEq, Clone)]
pub struct FooMessage<'a> {                             // has borrowed fields: lifetime parameter
    pub f_int32: Option<i32>,
    pub f_int64: Option<i64>,
    pub f_uint32: Option<u32>,
    pub f_uint64: Option<u64>,
    pub f_sint32: Option<i32>,
    pub f_sint64: Option<i64>,
    pub f_bool: Option<bool>,
    pub f_FooEnum: Option<FooEnum>,
    pub f_fixed64: Option<u64>,
    pub f_sfixed64: Option<i64>,
    pub f_fixed32: Option<u32>,
    pub f_sfixed32: Option<i32>,
    pub f_double: Option<f64>,
    pub f_float: Option<f32>,
    pub f_bytes: Option<Cow<'a, [u8]>>,                 // bytes  -> Cow<[u8]>
    pub f_string: Option<Cow<'a, str>>                  // string -> Cow<str>
    pub f_self_message: Option<Box<FooMessage<'a>>>,    // reference cycle -> Boxed message
    pub f_bar_message: Option<BarMessage>,
    pub f_repeated_int32: Vec<i32>,                     // repeated: Vec
    pub f_repeated_packed_int32: Vec<i32>,              // repeated packed: Vec

Leverage rust module system

Nested Messages

message A {
    message B {
        // ...

As rust does not allow a struct and a module to share the same name, we use mod_Name for the nested messages.

pub struct A {

pub mod mod_A {
    pub struct B {
        // ...


package a.b;

Here we could have used the same name, but for consistency with nested messages, modules are prefixed with mod_ as well.

pub mod mod_a {
    pub mod mod_b {
        // ...

Why not rust-protobuf

This library is an alternative to the widely used rust-protobuf.

Pros / Cons

  • Pros

    • Much faster, in particular when working with string, bytes and repeated packed fixed size fields (no extra allocation)
    • No need to install protoc on your machine
    • No trait objects: faster/simpler parser
    • Very simple generated modules (~10x smaller) so you can easily understand what is happening
  • Cons

    • Less popular
      • most rust-protobuf tests have been migrated here (see v2 and v3)
      • quick-protobuf is being used by many people now and is very reliable
      • some missing functionalities
    • Not a drop-in replacement of rust-protobuf
      • everything being explicit you have to handle more things yourself (e.g. Option unwrapping, Cow management)


Have a look at the different generated modules for the same .proto file:


See perftest, an adaptation of rust protobuf's perftest. Depending on your scenario each crate has its merit. quick-protobuf is particularly good at reading large bytes.


Any help is welcome! (Pull requests of course, bug reports, missing functionality etc...)