prost-protovalidate

Runtime validation for Protocol Buffer messages using buf.validate rules, built for prost and prost-reflect — with an optional zero-cost generated path via prost-protovalidate-build for schemas that don't need CEL at runtime.

Dynamically inspects prost-reflect message descriptors, compiles buf.validate constraint annotations (including CEL expressions), and evaluates them against concrete message instances. For CEL-free schemas, prost-protovalidate-build emits impl Validate at build time so validation runs through direct field access — 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

• Zero-cost generated validators (no CEL on the hot path) — companion crate prost-protovalidate-build emits impl Validate at build time for messages with standard-only rules. No prost-reflect transcoding, no CEL interpreter, direct field access. 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