Phoenix.socket - How to support wildcard topic

deepukjayan

Is it possible to listen wildcard topic in a channel

# my_socket.ex
  use Phoenix.Socket

  ## Channels
  channel "*", AbcWeb.MyChannel  #something of this sort?

15 comments

/phoenix #socket

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2019-11-18 19:36:42 UTC

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sb8244

Author of Real-Time Phoenix

Welcome to the forum!

Yes this is definitely supported by Phoenix Socket/Channel and is the same format you use. You do need to ensure that the wildcard is at the end of the string. So "users:*" is supported but "users:*:widgets" is not supported. Here’s a toy example of how you might do this.

socket.ex

  channel "wild:*", HelloSocketsWeb.WildcardChannel

wildcard_channel.ex

  def join("wild:" <> numbers, _payload, socket) do
    if numbers_correct?(numbers) do
      {:ok, socket}
    else
      {:error, %{}}
    end
  end

Post #1

bobics

Also, from the official docs:

The star character * acts as a wildcard matcher, so in the following example route, requests for room:lobby and room:123 would both be dispatched to the RoomChannel .
channel "room:*", HelloWeb.RoomChannel

Post #2

deepukjayan

In the above cases

"topic:*"

only wildcard subtopic is supported right?
Is it possible to not consider the topic at all? All the socket connection at an endpoint handled by MyChannel without considering what topic/subtopic.

Post #3

kokolegorille

It would be like having only one channel… Which could be equivalent to any:* if You use only this topic.

The first part of topic acts like the routing part.

What usecase do You want to solve?

Post #4

sb8244

Author of Real-Time Phoenix

You can do "*". I think it’s useful to think of this in terms of Elixir pattern matching. You can write a string pattern match like:

my_string = "test:1"
# my_string == "test:1"

"test:" <> number = "test:1"
# number == "1"

Either approach works. You can not do id <> ":test" = "1:test" in Elixir—the compiler will throw an error. Channels uses pattern matching and follows these same rules.

Post #5

deepukjayan

I have an IOT device that would open a socket connection and start sending data. I really dont have control over how this device send data.

I even have a feeling that Phoenix.Socket is not the right solution for this use case. Is there a different way to allow IOT devices to establish socket connection with elixir applications and let them start pushing data?

Post #6

benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

Yeah Phoenix Sockets are not the right answer here, even if you have a wildcard topic there is still a protocol channel clients are expected to follow. It sounds like you want to do a custom raw websocket connection. I found Phx_raws - Raw websocket on top of Phoenix not sure if it’s still up to date though.

Post #7

deepukjayan

Thanks, let me look into it. I also found GitHub - meh/elixir-socket: Socket wrapping for Elixir. · GitHub

Post #8

sb8244

Author of Real-Time Phoenix

I would suggest trying to stick to cowboy as the WebSocket server if possible. It’s super stable and you’ll get more support for it if you run into issues (because Phoenix uses it). Ben’s link to phx_raws looks promising.

Post #9