この記事は、Elixir その2 Advent Calendar 2020 2日目です。
前日は[87, 101, 32, 97, 114, 101, 32, 116, 104, 101, 32, 65, 108, 99, 104, 101, 109, 105, 115, 116, 115, 44, 32, 109, 121, 32, 102, 114, 105, 101, 110, 100, 115, 33]でした。

2020/11/22 追記

Phoenix LiveView uploadsと題して、 https://dev.to/ にも英語で書いてみました

はじめに

Here's a little sneak peek of Phoenix LiveView uploads を動かしたいです
2020/11/21現在、動作することを確認しました！！！
- Phoenix LiveView 0.15 is out with the new uploads feature! I'm super excited to see what folks build with this. We put together a 30 minute deep dive that takes you step-by-step thru adding uploads to an app, including direct to S3 support
~~2020/10/24現在、絶賛レビュー中です~~
- Add live uploads #1184
- 上記のプルリクは、2020/11/6にマージされています
が、2020/11/7現在、私はまだアップロード動作を確認できていません
- といいますのもまだまだ更新は続いているようで、たとえばDo not recover forms on first join #1211というプルリクが続いたりしています
試してみたことの記録を残しておきます
先のプルリクエストは絶賛レビュー中で日々コミットが増えている状況ですので、また明日試すと結果は変わっているかもしれません
mix deps.update --allで最新の更新内容が取り込めます

履歴

2020/11/21
- Phoenix LiveView 0.15.0でuploadsは対応されました
2020/11/7
- 486c4accf6f792d777fe61427e86d69a4025f369まで試しています
- 結果はPhoenix.LiveView.UploadChannel.handle_in/3の同じところでエラーがでています
- cd deps/phoenix_live_view/assets/ && npm install && node node_modules/webpack/bin/webpack.js --mode developmentしています
- いまはこうしておかないと、deps/phoenix_live_view/assets/js/phoenix_live_view.jsの変更が自身のアプリにとりこまれないからです
- 正式リリース時には不要な手順になるとおもいます
2020/10/24
- f2aa53eb21cbe47042f764f6c7e0d26a01d9ee66まで試しています
- (FunctionClauseError) no function clause matching in Phoenix.LiveView.UploadChannel.handle_in/3

Add live uploads #1184にコメントして取り込んでいただいたもの

GitHubのsuggestionで修正案を書いてみました(勝手にレビューに参加しています)
なんとか動かそうとドキュメントを読んでいて気づいた誤りにsuggestionをしてみましたというところです
Update lib/phoenix_live_view/helpers.ex
Update lib/phoenix_live_view.ex
Update guides/server/uploads.md

0. インストール

Installationに従って進めてください

1. プロジェクト作成

$ mix phx.new demo
$ cd demo
$ mix setup

2. Phoenix LiveViewは`0.15.0`

mix.exs

--- a/mix.exs
+++ b/mix.exs
@@ -37,7 +37,7 @@ defmodule Demo.MixProject do
       {:phoenix_ecto, "~> 4.1"},
       {:ecto_sql, "~> 3.4"},
       {:postgrex, ">= 0.0.0"},
-      {:phoenix_live_view, "~> 0.14.6"},
+      {:phoenix_live_view, "~> 0.15.0"},
       {:floki, ">= 0.27.0", only: :test},
       {:phoenix_html, "~> 2.11"},
       {:phoenix_live_reload, "~> 1.2", only: :dev},

オプションの詳しいところが気になる方は、mix help depsでご確認ください

$ mix deps.get

3. Uploadsを利用する

guides/server/uploads.mdを参考にしています

lib/demo_web/router.ex

@@ -18,6 +18,7 @@ defmodule DemoWeb.Router do
     pipe_through :browser

     live "/", PageLive, :index
+    live "/upload", UploadLive, :index
   end

lib/demo_web/live/upload_live.ex

defmodule DemoWeb.UploadLive do
  use DemoWeb, :live_view

  @impl true
  def mount(_params, _session, socket) do
    {:ok,
     socket
     |> assign(:uploaded_files, [])
     |> allow_upload(:avatar, accept: :any, max_entries: 3)}
  end

  def handle_event("validate", params, socket) do
    {:noreply, socket}
  end

  @impl true
  def handle_event("save", params, socket) do
    uploaded_files =
      consume_uploaded_entries(socket, :avatar, fn %{path: path}, _entry ->
        dest = Path.join("priv/static/uploads", Path.basename(path))
        File.cp!(path, dest)
        Routes.static_path(socket, "/uploads/#{Path.basename(dest)}")
      end)

    {:noreply, update(socket, :uploaded_files, &(&1 ++ uploaded_files))}
  end
end

lib/demo_web/live/upload_live.html.leex

<h1>Uploads</h1>


<%= for {_ref, err} <- @uploads.avatar.errors do %>
  <p class="alert"><%= Phoenix.Naming.humanize(err) %></p>
<% end %>

<%= for entry <- @uploads.avatar.entries do %>
  <%= entry.client_name %> - <%= entry.progress %>%
  <%= live_img_preview entry, width: 75 %>
<% end %>

<form phx-submit="save" phx-change="validate">
  <%= live_file_input @uploads.avatar %>
  <button type="submit">Upload</button>
</form>

/uploadにアクセスすると以下のような感じで表示されます

試しにファイルを一つ選択してみます

UPLOADボタンを押す！
こんなエラーがでました

[error] GenServer #PID<0.629.0> terminating
** (File.CopyError) could not copy from "/var/folders/q6/5rpg5x9n6rx6357m9vztp_w00000gp/T//plug-1605/live_view_upload-1605895070-182994678098385-1" to "priv/static/uploads/live_view_upload-1605895070-182994678098385-1": no such file or directory
    (elixir 1.10.4) lib/file.ex:814: File.cp!/3
    (demo 0.1.0) lib/demo_web/live/upload_live.ex:21: anonymous fn/3 in DemoWeb.UploadLive.handle_event/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload_channel.ex:85: Phoenix.LiveView.UploadChannel.handle_call/3
    (phoenix 1.5.7) lib/phoenix/channel/server.ex:269: Phoenix.Channel.Server.handle_call/3
    (stdlib 3.13) gen_server.erl:706: :gen_server.try_handle_call/4
    (stdlib 3.13) gen_server.erl:735: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message (from #PID<0.628.0>): {:consume, %Phoenix.LiveView.UploadEntry{cancelled?: false, client_last_modified: nil, client_name: "photo.png", client_size: 14517, client_type: "image/png", done?: true, preflighted?: true, progress: 100, ref: "0", upload_config: :avatar, upload_ref: "phx-FklJDbRnhJBw6wNh", uuid: "1093de58-ca7a-4466-b20d-accf0f470745", valid?: true}, #Function<0.15802900/2 in DemoWeb.UploadLive.handle_event/3>}
State: %Phoenix.Socket{assigns: %{chunk_timeout: 10000, chunk_timer: nil, done?: true, handle: #PID<0.630.0>, live_view_pid: #PID<0.628.0>, max_file_size: 14517, path: "/var/folders/q6/5rpg5x9n6rx6357m9vztp_w00000gp/T//plug-1605/live_view_upload-1605895070-182994678098385-1", uploaded_size: 14517}, channel: Phoenix.LiveView.UploadChannel, channel_pid: #PID<0.629.0>, endpoint: DemoWeb.Endpoint, handler: Phoenix.LiveView.Socket, id: nil, join_ref: "9", joined: true, private: %{connect_info: %{session: %{"_csrf_token" => "yw03HO6sYtcwV-OPt41fHesj"}}, log_handle_in: false, log_join: :info}, pubsub_server: Demo.PubSub, ref: nil, serializer: Phoenix.Socket.V2.JSONSerializer, topic: "lvu:0", transport: :websocket, transport_pid: #PID<0.623.0>}
Client #PID<0.628.0> is alive

    (stdlib 3.13) gen.erl:208: :gen.do_call/4
    (elixir 1.10.4) lib/gen_server.ex:1020: GenServer.call/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload_channel.ex:14: Phoenix.LiveView.UploadChannel.consume/3
    (elixir 1.10.4) lib/enum.ex:1396: Enum."-map/2-lists^map/1-0-"/2
    (demo 0.1.0) lib/demo_web/live/upload_live.ex:19: DemoWeb.UploadLive.handle_event/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:338: anonymous fn/3 in Phoenix.LiveView.Channel.view_handle_event/3
    (telemetry 0.4.2) /Users/yamauchi/Documents/13_Elixir/phoenix_projects/demo/deps/telemetry/src/telemetry.erl:262: :telemetry.span/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:203: Phoenix.LiveView.Channel.handle_info/2
    (stdlib 3.13) gen_server.erl:680: :gen_server.try_dispatch/4
    (stdlib 3.13) gen_server.erl:756: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
[error] GenServer #PID<0.628.0> terminating
** (stop) exited in: GenServer.call(#PID<0.629.0>, {:consume, %Phoenix.LiveView.UploadEntry{cancelled?: false, client_last_modified: nil, client_name: "photo.png", client_size: 14517, client_type: "image/png", done?: true, preflighted?: true, progress: 100, ref: "0", upload_config: :avatar, upload_ref: "phx-FklJDbRnhJBw6wNh", uuid: "1093de58-ca7a-4466-b20d-accf0f470745", valid?: true}, #Function<0.15802900/2 in DemoWeb.UploadLive.handle_event/3>}, 5000)
    ** (EXIT) an exception was raised:
        ** (File.CopyError) could not copy from "/var/folders/q6/5rpg5x9n6rx6357m9vztp_w00000gp/T//plug-1605/live_view_upload-1605895070-182994678098385-1" to "priv/static/uploads/live_view_upload-1605895070-182994678098385-1": no such file or directory
            (elixir 1.10.4) lib/file.ex:814: File.cp!/3
            (demo 0.1.0) lib/demo_web/live/upload_live.ex:21: anonymous fn/3 in DemoWeb.UploadLive.handle_event/3
            (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload_channel.ex:85: Phoenix.LiveView.UploadChannel.handle_call/3
            (phoenix 1.5.7) lib/phoenix/channel/server.ex:269: Phoenix.Channel.Server.handle_call/3
            (stdlib 3.13) gen_server.erl:706: :gen_server.try_handle_call/4
            (stdlib 3.13) gen_server.erl:735: :gen_server.handle_msg/6
            (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
    (elixir 1.10.4) lib/gen_server.ex:1023: GenServer.call/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload_channel.ex:14: Phoenix.LiveView.UploadChannel.consume/3
    (elixir 1.10.4) lib/enum.ex:1396: Enum."-map/2-lists^map/1-0-"/2
    (demo 0.1.0) lib/demo_web/live/upload_live.ex:19: DemoWeb.UploadLive.handle_event/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:338: anonymous fn/3 in Phoenix.LiveView.Channel.view_handle_event/3
    (telemetry 0.4.2) /Users/yamauchi/Documents/13_Elixir/phoenix_projects/demo/deps/telemetry/src/telemetry.erl:262: :telemetry.span/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:203: Phoenix.LiveView.Channel.handle_info/2
    (stdlib 3.13) gen_server.erl:680: :gen_server.try_dispatch/4
    (stdlib 3.13) gen_server.erl:756: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: %Phoenix.Socket.Message{event: "event", join_ref: "4", payload: %{"event" => "save", "type" => "form", "value" => ""}, ref: "12", topic: "lv:phx-FklJDajpq0ivUgrD"}
State: %{components: {%{}, %{}, 1}, join_ref: "4", serializer: Phoenix.Socket.V2.JSONSerializer, socket: #Phoenix.LiveView.Socket<assigns: %{flash: %{}, live_action: :index, uploaded_files: [], uploads: %{__phoenix_refs_to_names__: %{"phx-FklJDbRnhJBw6wNh" => :avatar}, avatar: #Phoenix.LiveView.UploadConfig<accept: :any, ...>}}, changed: %{}, endpoint: DemoWeb.Endpoint, id: "phx-FklJDajpq0ivUgrD", parent_pid: nil, root_pid: #PID<0.628.0>, router: DemoWeb.Router, view: DemoWeb.UploadLive, ...>, topic: "lv:phx-FklJDajpq0ivUgrD", transport_pid: #PID<0.623.0>, upload_names: %{avatar: {"phx-FklJDbRnhJBw6wNh", nil}}, upload_pids: %{#PID<0.629.0> => {"phx-FklJDbRnhJBw6wNh", "0", nil}}}
[error] GenServer #PID<0.631.0> terminating
** (stop) exited in: GenServer.call(#PID<0.628.0>, {:phoenix, :register_entry_upload, %{channel_pid: #PID<0.631.0>, cid: nil, entry_ref: "0", ref: "phx-FklJDbRnhJBw6wNh"}}, 5000)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
    (elixir 1.10.4) lib/gen_server.ex:1023: GenServer.call/3
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload_channel.ex:28: Phoenix.LiveView.UploadChannel.join/3
    (phoenix 1.5.7) lib/phoenix/channel/server.ex:376: Phoenix.Channel.Server.channel_join/4
    (phoenix 1.5.7) lib/phoenix/channel/server.ex:298: Phoenix.Channel.Server.handle_info/2
    (stdlib 3.13) gen_server.erl:680: :gen_server.try_dispatch/4
    (stdlib 3.13) gen_server.erl:756: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: {Phoenix.Channel, %{"token" => "SFMyNTY.g2gDaAJhBHQAAAADZAADY2lkZAADbmlsZAADcGlkWGQADW5vbm9kZUBub2hvc3QAAAJ0AAAAAAAAAABkAANyZWZoAm0AAAAUcGh4LUZrbEpEYlJuaEpCdzZ3TmhtAAAAATBuBgAyI87mdQFiAAFRgA.BLOubQZKWUBTDL0TroHDprRup-O21gKvFnUzrDj9AEo"}, {#PID<0.623.0>, #Reference<0.2303790502.3383492609.21550>}, %Phoenix.Socket{assigns: %{}, channel: Phoenix.LiveView.UploadChannel, channel_pid: nil, endpoint: DemoWeb.Endpoint, handler: Phoenix.LiveView.Socket, id: nil, join_ref: "13", joined: false, private: %{connect_info: %{session: %{"_csrf_token" => "yw03HO6sYtcwV-OPt41fHesj"}}}, pubsub_server: Demo.PubSub, ref: nil, serializer: Phoenix.Socket.V2.JSONSerializer, topic: "lvu:0", transport: :websocket, transport_pid: #PID<0.623.0>}}
State: #Reference<0.2303790502.3383492609.21552>
[error] exited in: GenServer.call(#PID<0.628.0>, {:phoenix, :register_entry_upload, %{channel_pid: #PID<0.631.0>, cid: nil, entry_ref: "0", ref: "phx-FklJDbRnhJBw6wNh"}}, 5000)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
[error] GenServer #PID<0.632.0> terminating
** (KeyError) key "phx-FklJDbRnhJBw6wNh" not found in: %{"phx-FklJDyZBcshtwQPB" => :avatar}
    :erlang.map_get("phx-FklJDbRnhJBw6wNh", %{"phx-FklJDyZBcshtwQPB" => :avatar})
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload.ex:166: Phoenix.LiveView.Upload.get_upload_by_ref!/2
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/upload.ex:107: Phoenix.LiveView.Upload.update_progress/4
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:139: anonymous fn/4 in Phoenix.LiveView.Channel.handle_info/2
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:992: Phoenix.LiveView.Channel.write_socket/4
    (phoenix_live_view 0.15.0) lib/phoenix_live_view/channel.ex:137: Phoenix.LiveView.Channel.handle_info/2
    (stdlib 3.13) gen_server.erl:680: :gen_server.try_dispatch/4
    (stdlib 3.13) gen_server.erl:756: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: %Phoenix.Socket.Message{event: "progress", join_ref: "16", payload: %{"entry_ref" => "0", "event" => nil, "progress" => %{"error" => "failed"}, "ref" => "phx-FklJDbRnhJBw6wNh"}, ref: "17", topic: "lv:phx-FklJDajpq0ivUgrD"}
State: %{components: {%{}, %{}, 1}, join_ref: "16", serializer: Phoenix.Socket.V2.JSONSerializer, socket: #Phoenix.LiveView.Socket<assigns: %{flash: %{}, live_action: :index, uploaded_files: [], uploads: %{__phoenix_refs_to_names__: %{"phx-FklJDyZBcshtwQPB" => :avatar}, avatar: #Phoenix.LiveView.UploadConfig<accept: :any, ...>}}, changed: %{}, endpoint: DemoWeb.Endpoint, id: "phx-FklJDajpq0ivUgrD", parent_pid: nil, root_pid: #PID<0.632.0>, router: DemoWeb.Router, view: DemoWeb.UploadLive, ...>, topic: "lv:phx-FklJDajpq0ivUgrD", transport_pid: #PID<0.623.0>, upload_names: %{}, upload_pids: %{}}

フォルダがないと言っているようにみえたので、priv/static/uploadsフォルダをこさえてみました
それから気を取り直してもう一度やってみました
おっ！　今度はエラーがでなくなりました
priv/static/uploadsを覗くとファイルができています！！！
- Phoenix LiveView Uploads Deep Diveの動画でもmkdirしているのを確認しました
openコマンドで開いてみると画像が表示されることを確認しました

Wrapping Up

絶賛レビュー中なので待てということかもしれませんが、プルリクエストの対象ブランチが更新されたら取り込んでみて動作確認してみようとおもいます
~~LiveView uploadsできたよ！　という方はぜひコメントをください！~~
Phoenix LiveView Uploads Deep Diveで動画で説明されているのでぜひ見てみてください(~~私はまだみていない~~ |> みた！ )
Enjoy Elixir !!!

LiveView uploadsを動かす 🎉🎉🎉(Elixir/Phoenix)

2020/11/22 追記

はじめに

履歴

Add live uploads #1184にコメントして取り込んでいただいたもの

0. インストール

1. プロジェクト作成

2. Phoenix LiveViewは0.15.0

3. Uploadsを利用する

Wrapping Up

2. Phoenix LiveViewは`0.15.0`