# `Issho.Channel`
[🔗](https://github.com/hattoriai/issho/blob/v0.1.0/lib/issho/channel.ex#L1)

The channel a browser joins a room on: one per room per tab, on one
socket for the whole page.

    defmodule MyAppWeb.IsshoChannel do
      use Issho.Channel, instance: MyApp.Issho
    end

    defmodule MyAppWeb.IsshoSocket do
      use Phoenix.Socket
      channel "issho:*", MyAppWeb.IsshoChannel
      def connect(_params, socket, _info), do: {:ok, socket}
      def id(_socket), do: nil
    end

    # In the endpoint:
    socket "/issho/socket", MyAppWeb.IsshoSocket, websocket: [max_frame_size: 1_000_000]

The topic is `"issho:" <> room`, and the join carries a token signed by
your LiveView (`Issho.Token.sign/4`). The token says who the actor is
and what it may do; the policy (`Issho.Policy`) is asked on join, on
every message from the browser, and before each change to a document
goes out to it.

## Messages

From the browser, each with a reply:

  * `"open"`, `%{"doc" => id, "pending" => [transaction ids]}`: opens a
    document of the room; replies its snapshot, and which pending
    transactions (an offline queue's) were already accepted;
  * `"tx"`, `%{"doc" => id, "tx" => transaction}`: commits a transaction
    (`Issho.Transaction`); replies its revision;
  * `"aware"`, a state or `nil`: the session's awareness
    (`Issho.Awareness`);
  * `"content"`, `%{"doc" => id, "epoch" => e, "revision" => r}`: checks
    a revision exists, for a form that publishes it.

To the browser: `"presence_state"` once, `"presence_diff"`, `"tx"` (a
transaction accepted in an open document), `"aware"` (a frame of the
others' states) and, when the session ends, `"bye"` with its reason.

---

*Consult [api-reference.md](api-reference.md) for complete listing*