proto-rs

A .proto file parser for Rust, supporting proto2, proto3, and editions syntax.

This is a Rust port of github.com/emicklei/proto — a Go library for parsing Protocol Buffer definition files.

Features

• Full proto2 and proto3 syntax support
• Edition syntax support
• Complete AST with position tracking
• Visitor pattern for AST traversal
• Walk function for recursive element filtering
• Zero external dependencies
• Comment preservation (inline, leading, C-style, C++ style)

Usage

Add to your Cargo.toml:

[dependencies]
proto-parser = "0.2"

Or use the development version from GitHub:

[dependencies]
proto-parser = { git = "https://github.com/lasorda/proto-rs" }

Parse a .proto file

use proto_parser::{Parser, Element};

let src = r#"
syntax = "proto3";
package example;

message Person {
    string name = 1;
    int32 age = 2;
    repeated string tags = 3;
}
"#;

let mut parser = Parser::new(src);
let proto = parser.parse().unwrap();

for element in &proto.elements {
    match element {
        Element::Message(m) => println!("Message: {}", m.name),
        Element::Package(p) => println!("Package: {}", p.name),
        _ => {}
    }
}

Use the Visitor pattern

use proto_parser::{Visitor, Message, NormalField};

struct FieldCounter {
    count: usize,
}

impl Visitor for FieldCounter {
    fn visit_normal_field(&mut self, _f: &NormalField) {
        self.count += 1;
    }
}

Walk the AST

use proto_parser::{Parser, Element, visitor};
use std::cell::RefCell;
use std::rc::Rc;

let mut parser = Parser::new(r#"syntax = "proto3"; message Foo { string name = 1; }"#);
let proto = parser.parse().unwrap();

let messages = Rc::new(RefCell::new(Vec::new()));
let msgs = messages.clone();
let mut handlers: Vec<visitor::Handler> = vec![Box::new(move |e| {
    if let Element::Message(m) = e {
        msgs.borrow_mut().push(m.name.clone());
    }
})];
visitor::walk(&proto, &mut handlers);
// messages now contains ["Foo"]

Supported AST Types

Type	Description
Syntax	syntax = "proto3";
Edition	edition = "2023";
Import	import "other.proto";
Package	package foo.bar;
ProtoOption	option java_package = "com.example";
Message	Message definitions (also used for extend)
Enum / EnumField	Enum definitions and values
NormalField	Regular fields (including repeated, optional, required)
MapField	map<K, V> fields
Oneof / OneofField	Oneof definitions
Service / Rpc	Service and RPC definitions
Reserved	Reserved field numbers/names
Extensions	Extension ranges (proto2)
Group	Group fields (proto2)
Comment	Line (//) and block (/* */) comments

Go → Rust Design Mapping

Go	Rust
Visitee interface + []Visitee	Element enum + Vec<Element>
Parent Visitee	Omitted — use walk stack
error return	Result<T, ProtoError>
text/scanner.Scanner	Custom Scanner struct
Embedded *Field	FieldCommon as named field
NoopVisitor struct	Trait default methods
WithMessage(func) handlers	Box<dyn FnMut(&Element)>

License

MIT — same as the original Go library.