Derive Macros

Volter provides two derive macros — FromRequestParts and FromRequest — that automatically implement the corresponding extractor traits for your types.

FromRequestParts

Derive to parse query parameters into a struct:

#![allow(unused)]
fn main() {
use serde::Deserialize;
use volter::*;

#[derive(Deserialize, FromRequestParts)]
struct SearchParams {
    q: String,
    page: Option<u32>,
}
}

This generates a FromRequestParts implementation that deserializes the URL query string via serde_urlencoded::from_str — the same parsing used by Query<T>.

Usage in Handlers

#![allow(unused)]
fn main() {
async fn search(params: SearchParams) -> String {
    format!("Searching for '{}'", params.q)
}
}

Without the derive, you would write:

#![allow(unused)]
fn main() {
async fn search(Query(params): Query<SearchParams>) -> String { ... }
}

Requirements

• The type must implement serde::DeserializeOwned (typically via #[derive(serde::Deserialize)])
• The type must be Send + 'static

FromRequest

Derive to parse JSON request bodies into a struct:

#![allow(unused)]
fn main() {
use serde::Deserialize;
use volter::*;

#[derive(Deserialize, FromRequest)]
struct CreateUser {
    name: String,
    email: String,
}
}

This generates a FromRequest implementation that clones the state, then delegates to Json<Self>::from_request.

Usage in Handlers

#![allow(unused)]
fn main() {
async fn create_user(user: CreateUser) -> Result<String, JsonRejection> {
    Ok(format!("Created {}", user.name))
}
}

Requirements

• The type must implement serde::DeserializeOwned
• The type must be Send + 'static
• The state type S must implement Clone + Send + 'static (the generated code clones the state to pass across the .await boundary)

Rejection Types

Both rejection types implement IntoResponse, so you can return them directly from handlers.

Limitations

• Structs only (enums are not supported)
• No field-level attributes or custom validation
• No support for #[from_request(via = ...)] or other configuration attributes