Rust Feature Flags

3. Evaluate flags

use reqwest::Client;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

#[derive(Serialize)]
struct FlagRequest {
    flag_key: String,
    context: HashMap<String, String>,
}

#[derive(Deserialize)]
struct FlagResponse {
    value: bool,
}

async fn get_flag(
    client: &Client,
    sdk_key: &str,
    flag_key: &str,
    context: HashMap<String, String>,
) -> bool {
    let resp = client
        .post("https://flagbit.anethoth.com/api/v1/evaluate")
        .header("X-SDK-Key", sdk_key)
        .json(&FlagRequest {
            flag_key: flag_key.to_string(),
            context,
        })
        .send()
        .await;

    match resp {
        Ok(r) => r.json::<FlagResponse>().await.map(|f| f.value).unwrap_or(false),
        Err(_) => false,
    }
}

// Axum handler with feature flags
use axum::{extract::State, response::Json, routing::get, Router};

async fn search_handler(State(state): State<AppState>) -> Json<SearchResult> {
    let mut ctx = HashMap::new();
    ctx.insert("user_id".into(), "123".into());

    if get_flag(&state.http_client, &state.sdk_key, "new-search", ctx).await {
        Json(new_search_engine().await)
    } else {
        Json(legacy_search().await)
    }
}

// Actix-Web middleware
use actix_web::{web, HttpResponse, middleware};

async fn beta_page(data: web::Data<AppState>) -> HttpResponse {
    let enabled = get_flag(&data.client, &data.sdk_key, "beta-page", HashMap::new()).await;
    if enabled {
        HttpResponse::Ok().body("Welcome to the beta!")
    } else {
        HttpResponse::NotFound().finish()
    }
}