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|
open Lwt.Syntax
open Lwt.Infix
open Js_of_ocaml
open Markup
let jss = Js.string
let sjs = Js.to_string
type t = async parser * ((signal, sync) stream option -> unit)
(* sic. XEP-0156: "host-meta files MUST be fetched only over HTTPS". I don't make the rules. *)
let well_known_of (domain : string) = "https://" ^ domain ^ "/.well-known/host-meta"
let stanza_open ?from domain : (signal, sync) stream =
(** [open_stanza domain] is an <open /> stanza for [domain].
If [from] is specified, the <open /> stanza has the from parameter.
*)
let open Markup in
let stanza =
let attributes =
let open Option in
[(("", "xmlns"), "urn:ietf:params:xml:ns:xmpp-framing");
(("", "to"), domain)]
@ (map (fun jid -> (("", "from"), jid)) from |> to_list)
@ [(("", "version"), "1.0")]
in
[`Start_element
(("urn:ietf:params:xml:ns:xmpp-framing", "open"),
attributes);
`End_element]
in stanza |> of_list
let stanza_close = string {|<close xmlns="urn:ietf:params:xml:ns:xmpp-framing" />|} |> parse_xml |> signals
exception MalformedStanza of Markup.location * Markup.Error.t
let ws_endpoint (domain : string) =
(** [ws_endpoint domain] is a promise containing the XMPP websocket endpoint associated with [domain], by using the
domain's Web-host Metadata.
This function uses XMLHttpRequest, so while it should work fine in the browser, in environments that don't provide
this constructor (Node.js), there should be some sort of polyfill.
Lastly, if [domain] doesn't provide a well-formed Web-host Metadata file, the function throws an exception. *)
let open Markup in
(* This ugly function extracts the href element from a Link tag's attributes if it's a websocket. *)
let link_websocket = function
| ((_, "rel"), "urn:xmpp:alt-connections:websocket") :: ((_, "href"), href) :: _
| ((_, "href"), href) :: ((_, "rel"), "urn:xmpp:alt-connections:websocket") :: _
-> Some href
| _ -> None
in let parse_xrd xrd =
string xrd
|> parse_xml
|> signals
|> tree ~element:(fun (_, name) attributes children ->
match name with
| "Link" -> link_websocket attributes
| "XRD" -> List.find_map (fun x -> x) children
| _ -> None
)
|> Option.join
in let+ host_meta = Js_of_ocaml_lwt.XmlHttpRequest.perform_raw_url (well_known_of domain)
in match parse_xrd host_meta.content with
| Some x -> x
| None -> failwith (domain ^ "doesn't advertise a WebSocket endpoint via Web-host Metadata.")
let ws_stream (url : string) =
(** [ws_stream url] returns a framed Lwt stream (and its push function) communicating with the websocket located at
[url] using the XMPP protocol.Lwt
Valid XMPP WebSocket subprotocol frames must be sent to the stream, because it directly exposes the websocket
under.
Pushing [None] closes the websocket.
If the websocket is closed server-side, it's still up to the caller to close the stream. *)
let open Lwt_stream in
let handle ws incoming () =
let+ _ = iter (fun msg -> ws##send (jss msg)) incoming
in (ws##close)
in let stream, message = create () (* websocket -> user *)
and incoming, push = create () (* user -> websocket *)
in let (ws : WebSockets.webSocket Js.t) = new%js WebSockets.webSocket_withProtocol (jss url) (jss "xmpp")
in ws##.onmessage :=
Dom.handler (fun x -> Some (sjs x##.data) |> message; Js._false);
ws##.onopen :=
Dom.handler (fun _ -> Lwt.async @@ handle ws incoming; Js._false);
ws##.onclose :=
Dom.handler (fun _ -> message None; Js._true);
stream, push
let connect domain =
(** [connect domain] is an Lwt stream (and its push function) communicating with the XMPP server running at [domain]
via the Websocket subprotocol.
This function is a complex wrapper around ws_stream, that accepts Markup.ml signals and sends framed XML stanzas
to the underlying socket, with exactly one stanza per frame, according to RFC 7935.
In essence, it (tries to) expose an identical interface to the original XMPP streamed protocol.
Here's an ASCII rendered flow of the data through the various streams.
/ -> push -> mu_stream -> to_frames -> ws_push -> \
function user websocket
\ <--- stream <--- markup_lwt <--- ws_stream <--- / *)
let open Lwt_stream in
let+ ws_stream, ws_push = ws_endpoint domain >|= ws_stream in
let mu_stream, mu_push = create () in
let open Markup_lwt in
(* When sending a malformed stanza (one that Markup.ml doesn't like), a MalformedStanza exception is raised. *)
let report loc err =
raise (MalformedStanza (loc, err))
in
(* Consumes a stream of Markup.ml signals into a series of frames sent to the WebSocket. *)
let to_frames fragments =
let stanzas =
let open Markup in
(* Convert a stream of strings to a stream of characters. *)
(* XML declarations are not to be transmitted to the underlying WebSocket,
per IETF recommendation. https://datatracker.ietf.org/doc/html/rfc7395#section-3.3.3 *)
content fragments
|> transform
(* Parse well-formed signals. As soon as we have enough elements to send a well-formed stanza, we send it to
the underlying WebSocket. *)
(fun (depth, signals) s ->
let depth = match s with
| `Start_element _ -> depth + 1
| `End_element -> depth - 1
| _ -> depth
in if depth = 0
then [List.rev (s :: signals) |> of_list |> write_xml |> to_string], Some (0, [])
else [], Some (depth, s :: signals))
(0, [])
|> Markup_lwt.to_lwt_stream
in let+ _ = Lwt_stream.iter (fun x -> ws_push (Some x)) stanzas in ws_push None
in Lwt.async @@ (fun () -> Markup_lwt.(mu_stream |> lwt_stream |> iter to_frames));
ws_stream |> lwt_stream |> strings_to_bytes |> parse_xml ~report, mu_push
|
