support "JOIN 0" command

lib/server/connection.ml

@@ -329,7 +329,6 @@ let join t user chan =
 let on_msg_join t name =
   let* me = require_registered t in
   (* TODO: keys parameter *)
-  (* TODO: "0" parameter means part from all channels *)
   let* chan =
     try
       match name_type name with
@@ -392,6 +391,14 @@ let on_msg_part t name reason =
   with Not_found ->
     Error (notonchannel name)
 
+let on_msg_join_0 t =
+  (* "JOIN 0" actually means part from all joined channels *)
+  let* me = require_registered t in
+  List.iter
+    (leave t me ~why:(`part None))
+    (User.channels me);
+  Ok ()
+
 
 (* welcome and quit *)
 
@@ -523,6 +530,7 @@ let dispatch t = function
   | "PRIVMSG", ([_] | _ :: "" :: _) -> Error notexttosend
   | "PRIVMSG", tgt :: msg :: _ -> on_msg_privmsg t tgt msg
   | "JOIN", tgt :: _ when tgt <> "" -> on_msg_join t tgt
+  | "JOIN 0", _ -> (* hack; see split_command_params *) on_msg_join_0 t
   | "NAMES", tgt :: _ when tgt <> "" -> on_msg_names t tgt
   | "TOPIC", tgt :: args when tgt <> "" -> on_msg_topic t tgt args
   | "PART", tgt :: reason when tgt <> "" -> on_msg_part t tgt reason
@@ -534,7 +542,16 @@ let dispatch t = function
 
 let split_command_params cmd params =
   match cmd, params with
-  | ("PRIVMSG" | "JOIN" | "NAMES" | "PART"), tgts :: rest
+  | "JOIN", "0" :: _ ->
+    ["JOIN 0", []]
+
+  | "JOIN", tgts :: rest
+    when String.contains tgts ',' ->
+    (* TODO: split <keys> argument as well *)
+    String.split_on_char ',' tgts |>
+    List.map (fun tgt -> "JOIN", tgt :: rest)
+
+  | ("PRIVMSG" | "NAMES" | "PART"), tgts :: rest
     when String.contains tgts ',' ->
     (* TODO: "JOIN" should be handled specially *)
     String.split_on_char ',' tgts |>