Cargo.toml

[package]
name = "so-actix-web-reqwest"
version = "0.1.0"
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
actix-web = "2.0"
reqwest = "0.10"
serde = "1.0"

main.rs

use actix_web::{post, web, Error, HttpResponse};
use serde::Deserialize;
use std::fmt;

#[derive(Debug, Deserialize)]
pub struct MyError;

impl fmt::Display for MyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Error")
    }
}

pub struct Conn;
struct DbPool;

impl DbPool {
    fn get(&self) -> Result<Conn, Error> {
        Ok(Conn)
    }
}

mod forms {
    use serde::Deserialize;
    #[derive(Deserialize)]
    pub struct BackendForm {
        pub name: String,
        pub url: String,
    }
}

mod actions {
    use super::{Conn, MyError as Error};
    use serde::Serialize;

    #[derive(Serialize)]
    pub struct Backend;

    pub fn create_backend(
        _name: &str,
        _url: &str,
        _version: &str,
        _conn: &Conn,
    ) -> Result<Backend, Error> {
        Ok(Backend)
    }
}
fn main() {}

#[post("/backends")]
async fn add_backend(
    pool: web::Data<DbPool>,
    form: web::Json<forms::BackendForm>,
) -> Result<HttpResponse, Error> {
    // 所有権エラーが出るので `format!` を使って結合する
    let version = reqwest::get(&format!("{}/version", form.url))
        .await
        // map_errを使ってError型に変換可能な値に変換する。
        // ここでは安直にInternalServerErrorを使う。
        // もっと詳細にエラーを出したければ自分で定義した型を使うとよい。
        .map_err(|e| {
            eprintln!("{}", e);
            HttpResponse::InternalServerError().finish()
        })?
        .text()
        .await
        // 同上
        .map_err(|e| {
            eprintln!("{}", e);
            HttpResponse::InternalServerError().finish()
        })?;

    let conn = pool.get().expect("cant get db pool");
    let backend =
        web::block(move || actions::create_backend(&form.name, &form.url, &version, &conn))
            .await
            .map_err(|e| {
                eprintln!("{}", e);
                HttpResponse::InternalServerError().finish()
            })?;

    Ok(HttpResponse::Ok().json(backend))
}