One-command reverse-proxy mode (ocsigenserver --reverse-proxy URL)

CHANGES

@@ -3,6 +3,9 @@
    "ocsigenserver --serve ./public --port 8000 --directory-listing") now
    serves a directory of static files without any configuration file or
    pre-created log directory. The Staticmod extension is loaded on demand.
+ * One-command reverse proxy: "ocsigenserver --reverse-proxy URL" forwards
+   every request to the base URL given, with no configuration file. The
+   Revproxy extension is loaded on demand.
  * Logging: when no <logdir> (and no <syslog>) is given in the configuration
    file, logs now go to the standard output and standard error instead of to
    files, so that no log directory is required.

doc/index.mld

@@ -34,9 +34,15 @@ terminal. A few options are available:
 {v
 ocsigenserver --serve ./public --port 8000 --directory-listing
 v}
+You can also start a reverse proxy that forwards every request to another
+server, again without any configuration file:
+{v
+ocsigenserver --reverse-proxy http://localhost:9000 --port 8080
+v}
+
 This is the simplest way to get started. For anything more elaborate (several
-hosts, extensions, reverse proxy, etc.) use a configuration file or the library
-API, as described below.
+hosts, extensions, fine-grained reverse proxy rules, etc.) use a configuration
+file or the library API, as described below.
 
 {1 Using Ocsigen Server as an executable}
 

doc/launching.mld

@@ -11,6 +11,10 @@ following options:
          file (logs go to the terminal). DIR can also be given as a plain
          positional argument: "ocsigenserver ./public".
 
+  --reverse-proxy URL
+         Forward every request to the base URL given (for example
+         http://localhost:9000), without a configuration file.
+
   -P, --port
          Port to listen on in serve mode (default 8080).
 

src/extensions/revproxy.ml

@@ -192,3 +192,14 @@ let () =
     ()
 
 let run ~redirection () _ _ _ = gen redirection
+
+(* Publish a "forward everything to TARGET" function so that the one-command
+   reverse-proxy mode can use it after loading this extension dynamically,
+   without a static dependency. *)
+let () =
+  Ocsigen.Server.register_reverse_proxy_server (fun ~target ->
+    let target = Ocsigen_base.Lib.Url.remove_end_slash target in
+    run
+      ~redirection:
+        (create_redirection ~full_url:false ~regexp:"(.*)" (target ^ "/\\1"))
+      ())

src/ocsigenserver.ml

@@ -1,4 +1,6 @@
-let usage = "usage: ocsigenserver [-c configfile | [--serve] DIR [options]]"
+let usage =
+  "usage: ocsigenserver [-c configfile | [--serve] DIR | --reverse-proxy URL [options]]"
+
 let section = Logs.Src.create "ocsigen:main"
 
 (* Report command-line errors through Logs. A stderr reporter is installed
@@ -19,6 +21,7 @@ let fatal fmt =
 let serve_dir = ref None
 let serve_port = ref None
 let directory_listing = ref false
+let reverse_proxy = ref None
 let config_given = ref false
 
 let set_serve_dir d =
@@ -35,6 +38,8 @@ let () =
   let alt_msg =
     "Alternate config file (default " ^ Ocsigen.Config.get_config_file () ^ ")"
   and serve_msg = "Serve the static files of DIR without a configuration file"
+  and proxy_msg =
+    "Forward every request to the base URL given, without a configuration file"
   and port_msg = "Port to listen on in serve mode (default 8080)"
   and listing_msg = "List directory contents in serve mode (when no index file)"
   and silent_msg = "Silent mode (error messages in errors.log only)"
@@ -49,6 +54,9 @@ let () =
       [ "-c", Arg.String set_configfile, alt_msg
       ; "--config", Arg.String set_configfile, alt_msg
       ; "--serve", Arg.String set_serve_dir, serve_msg
+      ; ( "--reverse-proxy"
+        , Arg.String (fun u -> reverse_proxy := Some u)
+        , proxy_msg )
       ; "-P", Arg.Int (fun p -> serve_port := Some p), port_msg
       ; "--port", Arg.Int (fun p -> serve_port := Some p), port_msg
       ; "--directory-listing", Arg.Set directory_listing, listing_msg
@@ -86,14 +94,23 @@ let check_serve_dir dir =
   | exception Sys_error _ -> fatal "no such directory: %s" dir
 
 let () =
-  match !serve_dir with
-  | Some dir ->
+  match !serve_dir, !reverse_proxy with
+  | Some _, Some _ -> fatal "--serve and --reverse-proxy cannot be combined"
+  | Some dir, None ->
       if !config_given
       then fatal "-c/--config cannot be combined with serve mode";
       let dir = check_serve_dir dir in
       Ocsigen.Server.serve ~dir ?port:!serve_port
         ~directory_listing:!directory_listing ()
-  | None ->
+  | None, Some target ->
+      if !config_given
+      then fatal "-c/--config cannot be combined with --reverse-proxy";
+      if !directory_listing
+      then fatal "--directory-listing is only valid when serving a directory";
+      Ocsigen.Server.reverse_proxy ~target ?port:!serve_port ()
+  | None, None ->
       if !serve_port <> None || !directory_listing
-      then fatal "--port and --directory-listing require a directory to serve";
+      then
+        fatal
+          "--port and --directory-listing require a directory to serve or --reverse-proxy";
       Ocsigen.Server.exec (Ocsigen.Parseconfig.parse_config ())

src/server/Ocsigen/server.ml

@@ -475,39 +475,55 @@ let start
     Extensions.start_initialisation ();
     Extensions.set_hosts instructions)
 
-(* Registry through which the Staticmod extension, once loaded, publishes its
-   static-file serving function. This lets the one-command serve mode use the
-   extension without statically linking it (which would clash with the
-   configuration-file path, where the extension is loaded dynamically). *)
+(* Registries through which the Staticmod and Revproxy extensions, once loaded,
+   publish their serving functions. This lets the one-command serve mode use
+   them without statically linking them (which would clash with the
+   configuration-file path, where the extensions are loaded dynamically). *)
 let static_server : (dir:string -> instruction) option ref = ref None
 let register_static_server f = static_server := Some f
+let reverse_proxy_server : (target:string -> instruction) option ref = ref None
+let register_reverse_proxy_server f = reverse_proxy_server := Some f
 
-let serve ?(port = 8080) ?(directory_listing = false) ~dir () =
-  (* One-command serve mode: no configuration file and no log directory are
-     required. Logs go to stderr and the command pipe is placed in a temporary
-     location so that the usual control commands remain available. *)
+(* Common setup of the one-command modes: no configuration file and no log
+   directory are required. Logs go to stderr and the command pipe is placed in a
+   temporary location so that the usual control commands remain available. *)
+let one_command_setup () =
   Config.set_log_to_stderr true;
   Config.set_command_pipe
     (Filename.concat
        (Filename.get_temp_dir_name ())
-       (Printf.sprintf "ocsigenserver-%d.cmd" (Unix.getpid ())));
-  (* Load the Staticmod extension on demand. It registers its serving function
-     through [register_static_server]. *)
+       (Printf.sprintf "ocsigenserver-%d.cmd" (Unix.getpid ())))
+
+(* Load the extension [package] on demand and return the serving function it
+   published in [registry]. *)
+let load_one_command_extension package registry =
   (try
      Ocsigen_base.Loader.loadfiles
        (fun () -> ())
        (fun () -> ())
        false
-       (Ocsigen_base.Loader.findfiles "ocsigenserver.ext.staticmod")
+       (Ocsigen_base.Loader.findfiles package)
    with e ->
      let msg, errno = errmsg e in
      Messages.errlog msg; exit errno);
-  match !static_server with
+  match !registry with
+  | Some f -> f
   | None ->
-      Messages.errlog
-        "The Staticmod extension did not register its serving function";
+      Messages.errlog (package ^ " did not register its serving function");
       exit 1
-  | Some static ->
-      start
-        ~ports:[`All, port]
-        [host ~list_directory_content:directory_listing [static ~dir]]
+
+let serve ?(port = 8080) ?(directory_listing = false) ~dir () =
+  one_command_setup ();
+  let static =
+    load_one_command_extension "ocsigenserver.ext.staticmod" static_server
+  in
+  start
+    ~ports:[`All, port]
+    [host ~list_directory_content:directory_listing [static ~dir]]
+
+let reverse_proxy ?(port = 8080) ~target () =
+  one_command_setup ();
+  let proxy =
+    load_one_command_extension "ocsigenserver.ext.revproxy" reverse_proxy_server
+  in
+  start ~ports:[`All, port] [host [proxy ~target]]

src/server/Ocsigen/server.mli

@@ -37,6 +37,13 @@ val serve : ?port:int -> ?directory_listing:bool -> dir:string -> unit -> unit
     into the program. [port] defaults to 8080. When [directory_listing] is
     [true], directories without an index file are listed. Never returns. *)
 
+val reverse_proxy : ?port:int -> target:string -> unit -> unit
+(** [reverse_proxy ~target ()] starts a server that forwards every request to
+    the [target] base URL (for example [http://localhost:9000]), with no
+    configuration file and no log directory required. This backs
+    [ocsigenserver --reverse-proxy URL]. The Revproxy extension is loaded
+    dynamically on demand. [port] defaults to 8080. Never returns. *)
+
 val start :
    ?ports:(Config.Socket_type.t * int) list
   -> ?ssl_ports:(Config.Socket_type.t * int) list
@@ -94,6 +101,11 @@ val register_static_server : (dir:string -> instruction) -> unit
     static-file serving function, so that {!serve} can use it without a static
     dependency on the extension. *)
 
+val register_reverse_proxy_server : (target:string -> instruction) -> unit
+(** Called by the Revproxy extension when it is loaded to publish its
+    request-forwarding function, so that {!reverse_proxy} can use it without a
+    static dependency on the extension. *)
+
 val host :
    ?regexp:string
   -> ?port:int

test/reverse-proxy.t/run.t

@@ -0,0 +1,28 @@
+Forward every request to another server with a single command, with no
+configuration file.
+
+Start an upstream server that serves a directory:
+
+  $ mkdir upstream
+  $ printf 'hello from upstream' > upstream/hello.txt
+  $ ocsigenserver --serve upstream --port 8071 >upstream.log 2>&1 &
+  $ UPSTREAM_PID=$!
+  $ trap 'kill $UPSTREAM_PID $PROXY_PID 2>/dev/null' EXIT
+
+Wait for the upstream to answer:
+
+  $ curl -s --retry 20 --retry-delay 1 --retry-connrefused \
+  >   http://127.0.0.1:8071/hello.txt
+  hello from upstream (no-eol)
+
+Start a reverse proxy in front of it:
+
+  $ ocsigenserver --reverse-proxy http://127.0.0.1:8071 --port 8072 \
+  >   >proxy.log 2>&1 &
+  $ PROXY_PID=$!
+
+A request to the proxy is forwarded to the upstream and its answer is relayed:
+
+  $ curl -s --retry 20 --retry-delay 1 --retry-connrefused \
+  >   http://127.0.0.1:8072/hello.txt
+  hello from upstream (no-eol)