`Validated<T>` and 422

Validated<T> is a Vespera extractor wrapper that runs garde validation before your handler is called. Invalid requests are rejected with 422 Unprocessable Entity and a canonical JSON error envelope — no per-handler error mapping, no boilerplate.

Basic Usage

Add garde to your dependencies:

[dependencies]
vespera = "0.1"
garde = { version = "0.20", features = ["derive"] }

Annotate your request type with garde constraints and derive Validate:

use vespera::{Validated, Schema, axum::Json};
use garde::Validate;
 
#[derive(serde::Deserialize, Schema, Validate)]
pub struct CreateUser {
    #[garde(length(min = 3, max = 32))]
    pub username: String,
    #[garde(email)]
    pub email: String,
    #[garde(range(min = 18, max = 120))]
    pub age: u8,
}
 
#[vespera::route(post, tags = ["users"])]
pub async fn create_user(
    Validated(Json(req)): Validated<Json<CreateUser>>,
) -> Json<&'static str> {
    // `req` has already passed garde validation — no manual checks needed.
    Json("ok")
}

422 Response Envelope

When validation fails, Vespera returns HTTP 422 Unprocessable Entity with this JSON body:

{
  "errors": [
    { "path": "username", "message": "length is lower than 3" },
    { "path": "email",    "message": "not a valid email" }
  ]
}

The envelope is identical regardless of which extractor failed — your API clients only need to handle one error shape.

Supported Extractors

Validated<T> works with every common Axum extractor:

Extractor	Validates
`Validated<Json<T>>`	JSON request body
`Validated<Form<T>>`	URL-encoded form body
`Validated<Query<T>>`	URL query parameters
`Validated<Path<T>>`	Path parameters

JNI Hoisting

Under JNI, the same 422 body is hoisted into the binary wire header as "validation_errors": [...]. Java decoders can read validation errors directly from the header without parsing the response body — no special-casing needed on the Java side.

{
  "v": 1,
  "status": 422,
  "headers": { "content-type": "application/json" },
  "validation_errors": [
    { "path": "username", "message": "length is lower than 3" }
  ]
}

Common garde Constraints

#[derive(Deserialize, Schema, Validate)]
pub struct UpdateProfile {
    #[garde(length(min = 1, max = 100))]
    pub display_name: String,
 
    #[garde(url)]
    pub website: Option<String>,
 
    #[garde(length(min = 8))]
    pub password: String,
 
    #[garde(range(min = 0.0, max = 5.0))]
    pub rating: f64,
 
    #[garde(inner(length(min = 1)))]
    pub tags: Vec<String>,
}

See the garde documentation for the full list of available constraints.

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