prost-protovalidate

Validation for Protocol Buffer messages using buf.validate rules, built for prost and prost-reflect — with an optional compile-time validation path via prost-protovalidate-build for schemas without CEL.

By default, dynamically inspects prost-reflect message descriptors, compiles buf.validate constraint annotations (including CEL expressions), and evaluates them against concrete message instances at runtime. For schemas without CEL, prost-protovalidate-build generates impl Validate at compile time so validation runs through monomorphized direct field access — the fastest path at runtime: no reflection, no CEL interpreter on the hot path.

Quick Start

[dependencies]
prost = "0.14"
prost-protovalidate = "0.3"

Annotate your .proto files with buf.validate rules:

syntax = "proto3";

import "buf/validate/validate.proto";

message CreateUserRequest {
  string name = 1 [(buf.validate.field).string.min_len = 1];
  int32 age = 2 [(buf.validate.field).int32.gte = 18];
}

Validate in Rust:

use prost_protovalidate::validate;

let request = CreateUserRequest {
    name: "Alice".to_string(),
    age: 25,
};

match validate(&request) {
    Ok(()) => println!("Validation passed!"),
    Err(e) => println!("Validation failed: {e}"),
}

For repeated validations, construct a Validator once to cache compiled rules:

use prost_protovalidate::Validator;

let validator = Validator::new();
validator.validate(&request)?;

Features

• Compile-time validation via prost-protovalidate-build (fastest at runtime) — companion crate prost-protovalidate-build emits impl Validate at compile time for messages with standard-only rules. Monomorphized direct field access, no prost-reflect transcoding, no CEL interpreter on the hot path. Disable the cel feature to also drop cel, chrono, paste, and transitive thiserror 1.x from your dependency tree. Messages that need CEL fall back to the runtime Validator automatically (with a cargo:warning= diagnostic, never silently skipped).
• Dynamic field inspection via prost-reflect descriptors — no static code generation needed for validators.
• CEL evaluation — compiles and evaluates Common Expression Language expressions for cross-field and complex constraints.
• Aggregated violations — collects all constraint failures instead of short-circuiting on the first error.
• Evaluation caching — Validator caches compiled AST/CEL rules, avoiding re-parsing on every call.

Compatibility

License

MIT OR Apache-2.0