From d5b0e5c612bfa6c7fca8460c42648f568ba71a1e Mon Sep 17 00:00:00 2001
From: David Holdeman <dave@holdemanenterprises.com>
Date: Fri, 8 Nov 2024 17:23:39 +0800
Subject: [PATCH 1/2] test wrapping period

test paths where encoding is not needed

test line beginning with period
---
 test/mail/encoders/quoted_printable_test.exs | 36 ++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/test/mail/encoders/quoted_printable_test.exs b/test/mail/encoders/quoted_printable_test.exs
index 71f4087..d96d97c 100644
--- a/test/mail/encoders/quoted_printable_test.exs
+++ b/test/mail/encoders/quoted_printable_test.exs
@@ -146,6 +146,42 @@ defmodule Mail.Encoders.QuotedPrintableTest do
     assert Mail.Encoders.QuotedPrintable.encode(message) == encoding
   end
 
+  test "encodes line beginning with a period" do
+    message = ".xxx"
+
+    encoding =
+      "=2Exxx"
+
+    assert Mail.Encoders.QuotedPrintable.encode(message) == encoding
+  end
+
+  test "encodes 75 chars ending with a period" do
+    message = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx."
+
+    encoding =
+      "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx."
+
+    assert Mail.Encoders.QuotedPrintable.encode(message) == encoding
+  end
+
+  test "encodes 76 chars ending with a period" do
+    message = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx."
+
+    encoding =
+      "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx=\r\n=2E"
+
+    assert Mail.Encoders.QuotedPrintable.encode(message) == encoding
+  end
+
+  test "encodes 77 chars ending with a period" do
+    message = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx."
+
+    encoding =
+      "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx=\r\nx."
+
+    assert Mail.Encoders.QuotedPrintable.encode(message) == encoding
+  end
+
   test "decodes empty string" do
     assert Mail.Encoders.QuotedPrintable.decode("") == ""
   end

From db25a142331a641a6904c0dcd68554f65b9a4e19 Mon Sep 17 00:00:00 2001
From: David Holdeman <dave@holdemanenterprises.com>
Date: Fri, 8 Nov 2024 17:51:06 +0800
Subject: [PATCH 2/2] encode period

---
 lib/mail/encoders/quoted_printable.ex | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/mail/encoders/quoted_printable.ex b/lib/mail/encoders/quoted_printable.ex
index 1e5863e..a0ed783 100644
--- a/lib/mail/encoders/quoted_printable.ex
+++ b/lib/mail/encoders/quoted_printable.ex
@@ -8,7 +8,7 @@ defmodule Mail.Encoders.QuotedPrintable do
 
   @new_line "=\r\n"
   @max_length 76
-  @reserved_chars [?=, ??, ?_]
+  @reserved_chars [?=, ??, ?_, ?.]
 
   @doc """
   Encodes a string into a quoted-printable encoded string.
@@ -55,6 +55,21 @@ defmodule Mail.Encoders.QuotedPrintable do
     end
   end
 
+  # Encode ASCII period character
+  def encode(<<char, tail::binary>>, max_length, acc, line_length) when char in [?.] do
+    escaped = "=" <> Base.encode16(<<char>>)
+    line_length = line_length + byte_size(<<char>>)
+
+    case line_length do
+      1 ->
+        encode(tail, max_length, acc <> escaped, byte_size(escaped))
+      x when x < max_length ->
+        encode(tail, max_length, acc <> <<char>>, line_length)
+      _ ->
+        encode(tail, max_length, acc <> @new_line <> escaped, byte_size(escaped))
+    end
+  end
+
   # Encode all other characters.
   def encode(<<char, tail::binary>>, max_length, acc, line_length) do
     escaped = "=" <> Base.encode16(<<char>>)