Fix Web Push notification delivery

Finch does not automatically append header content-type: octet-stream for binary payloads.

changelog.d/web_push.fix

@@ -0,0 +1 @@
+Fix web push notifications not successfully delivering

lib/pleroma/http/web_push.ex

@@ -6,7 +6,11 @@ defmodule Pleroma.HTTP.WebPush do
   @moduledoc false
 
   def post(url, payload, headers, options \\ []) do
-    list_headers = Map.to_list(headers)
+    list_headers =
+      headers
+      |> Map.to_list()
+      |> Kernel.++([{"content-type", "octet-stream"}])
+
     Pleroma.HTTP.post(url, payload, list_headers, options)
   end
 end

test/pleroma/http/web_push_test.exs

@@ -0,0 +1,45 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.HTTP.WebPushTest do
+  use ExUnit.Case
+
+  import Tesla.Mock
+  alias Pleroma.HTTP
+
+  @push_url "https://some-push-server/"
+
+  setup do
+    mock(fn
+      %{
+        method: :post,
+        url: @push_url,
+        headers: headers
+      } ->
+        if {"content-type", "octet-stream"} in headers do
+          %Tesla.Env{
+            status: 200
+          }
+        else
+          %Tesla.Env{
+            status: 403
+          }
+        end
+    end)
+
+    :ok
+  end
+
+  test "post" do
+    response =
+      HTTP.WebPush.post(
+        @push_url,
+        "encrypted payload",
+        %{"authorization" => "WebPush"},
+        []
+      )
+
+    assert {:ok, %{status: 200}} = response
+  end
+end