Cookbook: "Start a Web Server" with dream and cohttp (#3166)

Author: dinakajoy

data/cookbook/start-a-web-server-hello-world/00-cohttp-server.ml

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+---
+packages:
+- name: "cohttp-lwt-unix"
+  tested_version: "5.3.0"
+  used_libraries:
+  - cohttp-lwt-unix
+- name: "lwt"
+  tested_version: "5.7.0"
+  used_libraries:
+  - lwt
+  - lwt.infix
+discussion: |
+  This example shows how to use `cohttp-lwt-unix` to start an HTTP server in OCaml using `Lwt`
+---
+(* The server:
+  - Handles any incoming request on port 8080
+  - Responds with a static `Hello world` message
+  - Uses Server.respond_string to return a simple text response
+  `Lwt (Lwt.Infix)` is used for chaining asynchronous computations *)
+open Lwt.Infix
+open Cohttp_lwt_unix
+
+let () =
+  let callback _conn _req body =
+    Cohttp_lwt.Body.drain_body body >>= fun () -> 
+    Server.respond_string ~status:`OK ~body:"Hello world" ()
+  in
+  let server = Server.make ~callback () in
+  let port = 8080 in
+  let mode = `TCP (`Port port) in
+  Format.printf "listening on http://localhost:%d\n%!" port;
+  Server.create ~mode server |> Lwt_main.run

data/cookbook/start-a-web-server-hello-world/01-dream-server.ml

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+---
+packages:
+- name: "dream"
+  tested_version: "1.0.0~alpha8"
+  used_libraries:
+  - dream
+discussion: |
+  This example uses Dream, a simple and type-safe web framework for OCaml.
+---
+(* The server:
+  - Handles any incoming request on port 8080
+  - Logs requests
+  - Responds with a static `Hello world` message
+  - Returns 404 error for other routes *)
+
+let () =
+  Dream.run
+  @@ Dream.logger
+  @@ Dream.router [
+    Dream.get "/" (fun _ -> Dream.html "Hello World!");
+    Dream.any "/" (fun _ -> Dream.empty `Not_Found);
+  ]