Http Server in Scheme

Here’s the translation of the HTTP Server example from Go to Scheme, formatted in Markdown for Hugo:

(import (rnrs)
        (web server)
        (web request)
        (web response))

;; A fundamental concept in web servers is handlers. In Scheme, we can
;; represent handlers as procedures that take a request and return a response.

(define (hello request)
  (response
   200 '((Content-Type . "text/plain"))
   "hello\n"))

(define (headers request)
  (response
   200 '((Content-Type . "text/plain"))
   (string-append
    (apply string-append
           (map (lambda (header)
                  (string-append (car header) ": " (cdr header) "\n"))
                (request-headers request))))))

;; We define our main procedure to set up and start the server
(define (main)
  (run-server
   (lambda (request)
     (case (request-path request)
       (("/hello") (hello request))
       (("/headers") (headers request))
       (else (response 404 '() "Not Found"))))
   8090))

;; Run the server
(main)

This Scheme code creates a simple HTTP server using a hypothetical web server library. Here’s an explanation of the code:

1. We import necessary libraries for running a web server and handling HTTP requests and responses.

2. We define two handler procedures: hello and headers.

   • The hello procedure simply returns a response with the text “hello\n”.
   • The headers procedure reads all the HTTP request headers and echoes them into the response body.

3. In the main procedure, we set up the server:

   • We use a hypothetical run-server procedure to start the server.
   • We pass a lambda function as the request handler. This function checks the request path and routes it to the appropriate handler.
   • We set the server to listen on port 8090.

4. Finally, we call the main procedure to start the server.

To run the server:

$ scheme http-server.scm &

To access the /hello route:

$ curl localhost:8090/hello
hello

Note that the exact implementation details may vary depending on the specific Scheme implementation and web server library being used. This example provides a general idea of how you might structure an HTTP server in Scheme, following the concepts from the original example.