Add tests for Msg attachment handling

Introduce new unit tests for verifying the `AttachReader` method and enhancing error handling in attachment functions. These tests cover scenarios for success, file permissions, and early file closure errors.

msg_nowin_test.go

@@ -8,12 +8,83 @@
 package mail
 
 import (
+	"bytes"
 	"context"
+	"errors"
 	"os"
 	"testing"
 	"time"
 )
 
+func TestMsg_AttachFile_unixOnly(t *testing.T) {
+	t.Run("AttachFile with fileFromFS fails on open", func(t *testing.T) {
+		tempfile, err := os.CreateTemp("", "attachfile-unable-to-open.*.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(), 0000); err != nil {
+			t.Fatalf("failed to chmod temp file to 0000: %s", err)
+		}
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		message.AttachFile(tempfile.Name())
+		attachments := message.GetAttachments()
+		if len(attachments) != 1 {
+			t.Fatalf("failed to get attachments, expected 1, got: %d", len(attachments))
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = attachments[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("AttachFile with fileFromFS fails on copy", func(t *testing.T) {
+		tempfile, err := os.CreateTemp("", "attachfile-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.AttachFile("testdata/attachment.txt")
+		attachments := message.GetAttachments()
+		if len(attachments) != 1 {
+			t.Fatalf("failed to get attachments, expected 1, got: %d", len(attachments))
+		}
+		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 = attachments[0].Writer(messageBuf)
+		if err == nil {
+			t.Error("writer func expected to fail, but didn't")
+		}
+		if !errors.Is(err, os.ErrClosed) {
+			t.Errorf("expected error to be %s, got: %s", os.ErrClosed, err)
+		}
+	})
+}
+
 // TestMsg_WriteToSendmailWithContext tests the WriteToSendmailWithContext() method of the Msg
 func TestMsg_WriteToSendmailWithContext(t *testing.T) {
 	if os.Getenv("TEST_SENDMAIL") != "true" {

msg_test.go

@@ -12,6 +12,7 @@ import (
 	ht "html/template"
 	"io"
 	"net"
+	"os"
 	"reflect"
 	"strings"
 	"testing"
@@ -4491,6 +4492,15 @@ func TestMsg_AttachFile(t *testing.T) {
 		if attachments[0].Name != "attachment.txt" {
 			t.Errorf("expected attachment name to be %s, got: %s", "attachment.txt", attachments[0].Name)
 		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err := attachments[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 attachment") {
+			t.Errorf("expected message body to be %s, got: %s", "This is a test attachment", got)
+		}
 	})
 	t.Run("AttachFile with non-existant file", func(t *testing.T) {
 		message := NewMsg()
@@ -4508,6 +4518,63 @@ func TestMsg_AttachFile(t *testing.T) {
 	})
 }
 
+func TestMsg_AttachReader(t *testing.T) {
+	t.Run("AttachReader with file", func(t *testing.T) {
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		file, err := os.Open("testdata/attachment.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.AttachReader("attachment.txt", file); err != nil {
+			t.Fatalf("failed to attach reader: %s", err)
+		}
+		attachments := message.GetAttachments()
+		if len(attachments) != 1 {
+			t.Fatalf("failed to retrieve attachments list")
+		}
+		if attachments[0] == nil {
+			t.Fatal("expected attachment to be not nil")
+		}
+		if attachments[0].Name != "attachment.txt" {
+			t.Errorf("expected attachment name to be %s, got: %s", "attachment.txt", attachments[0].Name)
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = attachments[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 attachment") {
+			t.Errorf("expected message body to be %s, got: %s", "This is a test attachment", got)
+		}
+	})
+	/*
+		t.Run("AttachReader with non-existant file", func(t *testing.T) {
+			message := NewMsg()
+			if message == nil {
+				t.Fatal("message is nil")
+			}
+			message.AttachReader("testdata/non-existant-file.txt")
+			attachments := message.GetAttachments()
+			if len(attachments) != 0 {
+				t.Fatalf("failed to retrieve attachments list")
+			}
+		})
+		t.Run("AttachReader with options", func(t *testing.T) {
+			t.Log("all options have already been tested in file_test.go")
+		})
+
+	*/
+}
+
 /*
 // TestNewMsgWithMiddleware tests WithMiddleware