You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: server.rs
    path of file: ./repos/grafbase/cli/crates/cli/tests/graphql-directive
    
    the code of the file until where you have to start completion: use std::time::Duration;

use async_graphql::{EmptyMutation, EmptySubscription, Interface, Object, Schema, SimpleObject, Union, ID};
use async_graphql_axum::{GraphQLRequest, GraphQLResponse};
use axum::{http::HeaderMap, routing::post, Router};

async fn graphql_handler(headers: HeaderMap, req: GraphQLRequest) -> GraphQLResponse {
    let headers = headers
        
    
async fn graphql_handler(headers: HeaderMap, req: GraphQLRequest) -> GraphQLResponse {
    let headers = headers
        .into_iter()
        .map(|(name, value)| {
            (
                name.map(|name| name.to_string()).unwrap_or_default(),
                String::from_utf8_lossy(value.as_bytes()).to_string(),
            )
        })
        .collect();
    let schema = Schema::build(Query { headers }, EmptyMutation, EmptySubscription).finish();

    schema.execute(req.into_inner()).await.into()
}