implement message queue for WebChannels (#703)

* implement message queue for WebChannels

* Removed println debug

---------

Co-authored-by: Adrian Salceanu <[email protected]>

src/WebChannels.jl

@@ -8,6 +8,10 @@ import Genie, Genie.Renderer
 
 const ClientId = UInt # web socket hash
 const ChannelName = String
+const MESSAGE_QUEUE = Dict{UInt, Tuple{
+  Channel{Tuple{String, Channel{Nothing}}},
+  Task}
+}()
 
 struct ChannelNotFoundException <: Exception
   name::ChannelName
@@ -105,10 +109,14 @@ end
 Unsubscribes a web socket client `ws` from `channel`.
 """
 function unsubscribe(ws::HTTP.WebSockets.WebSocket, channel::ChannelName) :: ChannelClientsCollection
-  haskey(CLIENTS, id(ws)) && deleteat!(CLIENTS[id(ws)].channels, CLIENTS[id(ws)].channels .== channel)
-  pop_subscription(id(ws), channel)
+  client = id(ws)
+
+  haskey(CLIENTS, client) && deleteat!(CLIENTS[client].channels, CLIENTS[client].channels .== channel)
+  pop_subscription(client, channel)
+  delete_queue!(MESSAGE_QUEUE, client)
 
-  @debug "Unsubscribed: $(id(ws)) ($(Dates.now()))"
+
+  @debug "Unsubscribed: $(client) ($(Dates.now()))"
   CLIENTS
 end
 function unsubscribe(channel_client::ChannelClient, channel::ChannelName) :: ChannelClientsCollection
@@ -285,16 +293,52 @@ end
 """
 Writes `msg` to web socket for `client`.
 """
+function message(client::ClientId, msg::String)
+  ws = Genie.WebChannels.CLIENTS[client].client
+  # setup a reply channel
+  myfuture = Channel{Nothing}(1)
+
+  # retrieve the message queue or set it up if not present
+  q, _ = get!(MESSAGE_QUEUE, client) do
+      queue = Channel{Tuple{String, Channel{Nothing}}}(10)
+      handler = @async while true
+          message, future = take!(queue)
+          try
+              Sockets.send(ws, message)
+          finally
+              put!(future, nothing)
+          end
+      end
+      queue, handler
+  end
+
+  put!(q, (msg, myfuture))
+
+  take!(myfuture) # Wait until the message is processed
+end
+function message(client::ChannelClient, msg::String) :: Int
+  message(client.client, msg)
+end
 function message(ws::HTTP.WebSockets.WebSocket, msg::String) :: Int
+  message(id(ws), msg)
+end
+
+function message_unsafe(ws::HTTP.WebSockets.WebSocket, msg::String) :: Int
   Sockets.send(ws, msg)
 end
-function message(client::ClientId, msg::String) :: Int
-  message(CLIENTS[client].client, msg)
+function message_unsafe(client::ClientId, msg::String) :: Int
+  message_unsafe(CLIENTS[client].client, msg)
 end
-function message(client::ChannelClient, msg::String) :: Int
-  message(client.client, msg)
+function message_unsafe(client::ChannelClient, msg::String) :: Int
+  message_unsafe(client.client, msg)
 end
 
+function delete_queue!(d::Dict, client::UInt)
+  queue, handler = pop!(MESSAGE_QUEUE, client, (nothing, nothing))
+  if queue !== nothing
+    @async Base.throwto(handler, InterruptException())
+  end
+end
 
 """
 Encodes `msg` in Base64 and tags it with `Genie.config.webchannels_base64_marker`.