package tiny_httpd

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Minimal HTTP server using threads


Dune Dependency








Minimal HTTP server using good old threads, with stream abstractions, simple routing, URL encoding/decoding, static asset serving, and optional compression with camlzip. It also supports server-sent events (w3c)

Free from all forms of ppx, async monads, etc. 🙃

Note: it can be useful to add the jemalloc opam package for long running server, as it does a good job at controlling memory usage.

The basic echo server from src/examples/

module S = Tiny_httpd

let () =
  let server = S.create () in
  (* say hello *)
  S.add_route_handler ~meth:`GET server
    S.Route.(exact "hello" @/ string @/ return)
    (fun name _req -> S.Response.make_string (Ok ("hello " ^name ^"!\n")));
  (* echo request *)
  S.add_route_handler server
    S.Route.(exact "echo" @/ return)
    (fun req -> S.Response.make_string (Ok (Format.asprintf "echo:@ %a@." S.Request.pp req)));
  Printf.printf "listening on http://%s:%d\n%!" (S.addr server) (S.port server);
  match server with
  | Ok () -> ()
  | Error e -> raise e
$ dune exec src/examples/echo.exe &
listening on

# the path "hello/name" greets you.
$ curl -X GET http://localhost:8080/hello/quadrarotaphile
hello quadrarotaphile!

# the path "echo" just prints the request.
$ curl -X GET http://localhost:8080/echo --data "howdy y'all" 
 headers=Host: localhost:8080
         User-Agent: curl/7.66.0
         Accept: */*
         Content-Length: 10
         Content-Type: application/x-www-form-urlencoded;
 path="/echo"; body="howdy y'all"}


Similar to python -m http.server, a simple program http_of_dir is provided. It serves files from the current directory.

$ http_of_dir . -p 8080 &
$ curl -X GET http://localhost:8080
<html list of current dir>

Static assets and files

The program http_of_dir relies on the module Tiny_httpd_dir, which can serve directories, as well as virtual file systems.

In 'examples/dune', we produce an OCaml module using the program tiny-httpd-vfs-pack. This module contains a VFS (virtual file system) which can be served as if it were an actual directory.

The dune rule:

  (deps (source_tree files) (:out test_output.txt.expected))
  (enabled_if (= %{system} "linux"))
  (action (run ../src/bin/vfs_pack.exe -o %{targets}

The code to serve the VFS from is as follows:

  Tiny_httpd_dir.add_vfs server
    ~config:(Tiny_httpd_dir.config ~download:true
               ~dir_behavior:Tiny_httpd_dir.Index_or_lists ())
    ~vfs:Vfs.vfs ~prefix:"vfs";

it allows downloading the files, and listing directories. If a directory contains index.html then this will be served instead of listing the content.

Steaming response body

Tiny_httpd provides multiple ways of returning a body in a response. The response body type is:

type body =
  [ `String of string
  | `Stream of byte_stream
  | `Writer of Tiny_httpd_io.Writer.t
  | `Void ]

The simplest way is to return, say, `String "hello". The response will have a set content-length header and its body is just the string. Some responses don't have a body at all, which is where `Void is useful.

The `Stream _ case is more advanced and really only intended for experts.

The `Writer w is new, and is intended as an easy way to write the body in a streaming fashion. See 'examples/' to see a full example. Typically the idea is to create the body with Tiny_httpd_io.Writer.make ~write () where write will be called with an output channel (the connection to the client), and can write whatever it wants to this channel. Once the write function returns the body has been fully sent and the next request can be processed.

Socket activation

Since version 0.10, socket activation is supported indirectly, by allowing a socket to be explicitly passed in to the create function:

module S = Tiny_httpd

let not_found _ _ = ~code:404 "Not Found\n"

let () =
  (* Module [Daemon] is from the [ocaml-systemd] package *)
  let server = match Daemon.listen_fds () with
    (* If no socket passed in, assume server was started explicitly i.e. without
       socket activation *)
    | [] -> S.create ()

    (* If a socket passed in e.g. by systemd, listen on that *)
    | sock :: _ -> S.create ~sock ()
  S.add_route_handler server S.Route.rest_of_path not_found;
  Printf.printf "Listening on http://%s:%d\n%!" (S.addr server) (S.port server);
  match server with
  | Ok () -> ()
  | Error e -> raise e

On Linux, this requires the ocaml-systemd package:

opam install ocaml-systemd

Tip: in the dune file, the package name should be systemd.

In case you're not familiar with socket activation, Lennart Poettering's blog post explains it well.


Why not? If you just want a super basic local server (perhaps for exposing data from a local demon, like Cups or Syncthing do), no need for a ton of dependencies or high scalability libraries.

Use cases might include:

  • serve content directly from a static blog generator;

  • provide a web UI to some tool (like CUPS and syncthing do);

  • implement a basic monitoring page for a service;

  • provide a simple json API for a service, on top of http;

  • use http_of_dir to serve odoc-generated docs or some assets directory.





Dependencies (7)

  1. ocaml >= "4.08"
  2. iostream >= "0.2"
  3. hmap
  4. result
  5. base-threads
  6. seq
  7. dune >= "2.9"

Dev Dependencies (5)

  1. qcheck-core >= "0.9" & with-test
  2. ptime with-test
  3. conf-libcurl with-test
  4. logs with-test
  5. odoc with-doc




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