HTTP server

Langoost has a built-in HTTP server. Call http.serve(port, handler) and each incoming request runs your handler in its own isolated VM — a private stack and output buffer per request, so concurrent requests never share mutable state.

A minimal server

The handler receives up to four arguments — method, path, query, body — and returns a string:

import http
import strings
import json

fn handle(method: string, path: string, query: string, body: string): string {
    if path == "/health" {
        return "{\"status\": \"ok\"}"
    }

    if path == "/echo" && method == "POST" {
        return body
    }

    if path == "/greet" {
        let name = "World"
        if strings.contains(query, "name=") {
            let parts = strings.splitN(query, "name=", 2)
            name = parts[1]
        }
        let data: json = {message: "Hello"}
        return json.setString(data, "message", "Hello, " + name + "!")
    }

    return "404 Not Found"
}

http.serve(8080, handle)

Response format

• Plain string → HTTP 200 with that body.
• Status prefix → start the string with a 3-digit code and a space to set the status: "404 Not Found", "500 Internal Server Error", "201 " + json.stringify(resource).
• Content-Type is detected automatically: responses starting with { or [ are sent as application/json; everything else as text/plain; charset=utf-8.

Isolation & shared state

Because each request runs in its own VM, there is no shared mutable state by default — which is what makes requests safe to run concurrently. When you do need to share data across requests, use the global key-value store in runtime.core:

import runtime

runtime.core.share("visits", "0")
let n = toInt(runtime.core.fetch("visits"))
runtime.core.share("visits", toString(n + 1))

HTTP client

The same http module is also a client for talking to other services:

import http

let body = http.get("https://api.example.com/users")

let resp = http.request("GET", "https://api.example.com/me", "", [
    "Authorization: Bearer my-token",
    "Accept: application/json"
])

See the concurrency guide for background work and the thread module.