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: ext.rs
    path of file: ./repos/grafbase/engine/crates/engine/src/context
    
    the code of the file until where you have to start completion: use std::any::{Any, TypeId};

use engine_value::{ConstValue as Value, Value as InputValue}; // WHY?
use graph_entities::QueryResponse;
use http::{
    header::{AsHeaderName, IntoHeaderName},
    HeaderValue,
};
use postgres_connector_types::database_definition::DatabaseDefinition;

use crate::{
    deferred::DeferredWorkloadSender,
    parser::types:
    
    ///     async fn greet(&self, ctx: &Context<'_>) -> String {
    ///
    ///         // Headers can be inserted using the `http` constants
    ///         let was_in_headers = ctx.insert_http_header(ACCESS_CONTROL_ALLOW_ORIGIN, "*");
    ///         assert_eq!(was_in_headers, None);
    ///
    ///         // They can also be inserted using &str
    ///         let was_in_headers = ctx.insert_http_header("Custom-Header", "1234");
    ///         assert_eq!(was_in_headers, None);
    ///
    ///         // If multiple headers with the same key are `inserted` then the most recent
    ///         // one overwrites the previous. If you want multiple headers for the same key, use
    ///         // `append_http_header` for subsequent headers
    ///         let was_in_headers = ctx.insert_http_header("Custom-Header", "Hello World");
    ///         assert_eq!(was_in_headers, Some(HeaderValue::from_static("1234")));
    ///
    ///         String::from("Hello world")
    ///     }