Add tests for embedding files and readers

Introduced unit tests to verify the embedding of files and readers in messages, including tests specific to Unix file handling scenarios. These tests ensure correct handling of embed errors and proper cleanup of temporary files.

msg_test.go

@@ -4832,6 +4832,46 @@ func TestMsg_EmbedFile(t *testing.T) {
 	})
 }
 
+func TestMsg_EmbedReader(t *testing.T) {
+	t.Run("EmbedReader with file", func(t *testing.T) {
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		file, err := os.Open("testdata/embed.txt")
+		if err != nil {
+			t.Fatalf("failed to open file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := file.Close(); err != nil {
+				t.Errorf("failed to close file: %s", err)
+			}
+		})
+		if err = message.EmbedReader("embed.txt", file); err != nil {
+			t.Fatalf("failed to embed reader: %s", err)
+		}
+		embeds := message.GetEmbeds()
+		if len(embeds) != 1 {
+			t.Fatalf("failed to retrieve embeds list")
+		}
+		if embeds[0] == nil {
+			t.Fatal("expected embed to be not nil")
+		}
+		if embeds[0].Name != "embed.txt" {
+			t.Errorf("expected embed name to be %s, got: %s", "embed.txt", embeds[0].Name)
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = embeds[0].Writer(messageBuf)
+		if err != nil {
+			t.Errorf("writer func failed: %s", err)
+		}
+		got := strings.TrimSpace(messageBuf.String())
+		if !strings.EqualFold(got, "This is a test embed") {
+			t.Errorf("expected message body to be %s, got: %s", "This is a test embed", got)
+		}
+	})
+}
+
 /*
 // TestNewMsgWithMiddleware tests WithMiddleware
 

msg_unix_test.go

@@ -177,6 +177,144 @@ func TestMsg_AttachReadSeeker_unixOnly(t *testing.T) {
 	})
 }
 
+func TestMsg_EmbedFile_unixOnly(t *testing.T) {
+	t.Run("EmbedFile with fileFromFS fails on open", func(t *testing.T) {
+		if os.Getenv("PERFORM_UNIX_OPEN_WRITE_TESTS") != "true" {
+			t.Skipf("PERFORM_UNIX_OPEN_WRITE_TESTS variable is not set. Skipping unix open/write tests")
+		}
+
+		tempFile, err := os.CreateTemp("testdata/tmp", "embedfile-open-write-test.*.txt")
+		if err != nil {
+			t.Fatalf("failed to create temp file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := os.Remove(tempFile.Name()); err != nil {
+				t.Errorf("failed to remove temp file: %s", err)
+			}
+		})
+		if err = os.Chmod(tempFile.Name(), 0o000); err != nil {
+			t.Fatalf("failed to chmod temp file: %s", err)
+		}
+
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		message.EmbedFile(tempFile.Name())
+		embeds := message.GetEmbeds()
+		if len(embeds) != 1 {
+			t.Fatalf("failed to get embeds, expected 1, got: %d", len(embeds))
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = embeds[0].Writer(messageBuf)
+		if err == nil {
+			t.Error("writer func expected to fail, but didn't")
+		}
+		if !errors.Is(err, os.ErrPermission) {
+			t.Errorf("expected error to be %s, got: %s", os.ErrPermission, err)
+		}
+	})
+	t.Run("EmbedFile with fileFromFS fails on copy", func(t *testing.T) {
+		tempfile, err := os.CreateTemp("testdata/tmp", "embedfile-close-early.*.txt")
+		if err != nil {
+			t.Fatalf("failed to create temp file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := os.Remove(tempfile.Name()); err != nil {
+				t.Errorf("failed to remove temp file: %s", err)
+			}
+		})
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		message.EmbedFile("testdata/embed.txt")
+		emebeds := message.GetEmbeds()
+		if len(emebeds) != 1 {
+			t.Fatalf("failed to get emebeds, expected 1, got: %d", len(emebeds))
+		}
+		messageBuf, err := os.Open(tempfile.Name())
+		if err != nil {
+			t.Fatalf("failed to open temp file: %s", err)
+		}
+		// We close early to cause an error during io.Copy
+		if err = messageBuf.Close(); err != nil {
+			t.Fatalf("failed to close temp file: %s", err)
+		}
+		_, err = emebeds[0].Writer(messageBuf)
+		if err == nil {
+			t.Error("writer func expected to fail, but didn't")
+		}
+	})
+}
+
+func TestMsg_EmbedReader_unixOnly(t *testing.T) {
+	t.Run("EmbedReader with fileFromReader fails on copy", func(t *testing.T) {
+		tempfile, err := os.CreateTemp("", "embedfile-close-early.*.txt")
+		if err != nil {
+			t.Fatalf("failed to create temp file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := os.Remove(tempfile.Name()); err != nil {
+				t.Errorf("failed to remove temp file: %s", err)
+			}
+		})
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		file, err := os.Open("testdata/embed.txt")
+		if err != nil {
+			t.Fatalf("failed to open file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := file.Close(); err != nil {
+				t.Errorf("failed to close file: %s", err)
+			}
+		})
+		if err = message.EmbedReader("embed.txt", file); err != nil {
+			t.Fatalf("failed to embed reader: %s", err)
+		}
+		embeds := message.GetEmbeds()
+		if len(embeds) != 1 {
+			t.Fatalf("failed to get embeds, expected 1, got: %d", len(embeds))
+		}
+		messageBuf, err := os.Open(tempfile.Name())
+		if err != nil {
+			t.Fatalf("failed to open temp file: %s", err)
+		}
+		// We close early to cause an error during io.Copy
+		if err = messageBuf.Close(); err != nil {
+			t.Fatalf("failed to close temp file: %s", err)
+		}
+		_, err = embeds[0].Writer(messageBuf)
+		if err == nil {
+			t.Error("writer func expected to fail, but didn't")
+		}
+	})
+	t.Run("EmbedReader with fileFromReader on closed reader", func(t *testing.T) {
+		tempfile, err := os.CreateTemp("", "embedfile-close-early.*.txt")
+		if err != nil {
+			t.Fatalf("failed to create temp file: %s", err)
+		}
+		if err = tempfile.Close(); err != nil {
+			t.Fatalf("failed to close temp file: %s", err)
+		}
+		t.Cleanup(func() {
+			if err := os.Remove(tempfile.Name()); err != nil {
+				t.Errorf("failed to remove temp file: %s", err)
+			}
+		})
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		if err = message.EmbedReader("embed.txt", tempfile); err == nil {
+			t.Fatalf("expected error, got nil")
+		}
+	})
+}
+
 // TestMsg_WriteToSendmailWithContext tests the WriteToSendmailWithContext() method of the Msg
 func TestMsg_WriteToSendmailWithContext(t *testing.T) {
 	if os.Getenv("TEST_SENDMAIL") != "true" {