feat: truncates long subjects

complete message still present in the email body

lib/tower/email/message.ex

@@ -1,14 +1,20 @@
 defmodule Tower.Email.Message do
+  @subject_max_length 120
+
   def new(kind, reason, stacktrace \\ nil) do
     Swoosh.Email.new(
       to: Application.fetch_env!(:tower_email, :to),
       from: Application.get_env(:tower_email, :from, {"Undefined From", "[email protected]"}),
-      subject: "[#{app_name()}][#{environment()}] #{kind}: #{reason}",
+      subject: truncate(subject(kind, reason), @subject_max_length),
       html_body: html_body(kind, reason, stacktrace),
       text_body: text_body(kind, reason, stacktrace)
     )
   end
 
+  defp subject(kind, reason) do
+    "[#{app_name()}][#{environment()}] #{kind}: #{reason}"
+  end
+
   defp app_name do
     Application.fetch_env!(:tower_email, :otp_app)
   end
@@ -17,6 +23,15 @@ defmodule Tower.Email.Message do
     Application.fetch_env!(:tower_email, :environment)
   end
 
+  defp truncate(text, max_length) do
+    if String.length(text) <= max_length do
+      text
+    else
+      suffix = "..."
+      "#{String.slice(text, 0, max_length - String.length(suffix))}#{suffix}"
+    end
+  end
+
   require EEx
 
   EEx.function_from_string(

test/tower_email_test.exs

@@ -30,6 +30,34 @@ defmodule TowerEmailTest do
     )
   end
 
+  @tag capture_log: true
+  test "reports long match error" do
+    in_unlinked_process(fn ->
+      %{eleven: "eleven"} = %{
+        one: "one",
+        two: "two",
+        three: "three",
+        four: "four",
+        five: "five",
+        six: "six",
+        seven: "seven",
+        eight: "eight",
+        nine: "nine",
+        ten: "ten"
+      }
+    end)
+
+    # TODO: Support waiting on assert_email_sent with a timeout
+    # Swoosh.TestAssertions.assert_email_sent(subject: "ArithmeticError: bad argument in arithmetic expression")
+    assert_receive(
+      {
+        :email,
+        %{subject: ~s([tower_email][test] MatchError: no match of right hand side value: %{one: "one", two: "two", three: "three", four: "f...)}
+      },
+      1_000
+    )
+  end
+
   defp in_unlinked_process(fun) when is_function(fun, 0) do
     {:ok, pid} = Task.Supervisor.start_link()