Attachment issues

[Karitham]

Description

Multiple calls to WriteTo lose files (and embeds).

To Reproduce

Call WriteTo multiple times.

for example, msg.WriteFile and then client.Send(msg)

Expected behaviour

Attachments are written with every call to WriteTo

Screenshots

No response

Attempted Fixes

I haven't attempted any fix yet, but expect that breaking the io.Reader interface to an io.ReadSeeker would be the simplest fix to that issue.

Another way to avoid breaking compatibility would be to call the fileOptions on every call to write, and set the writer in a closure, like this.

		msg.AttachFile(a.Name, func(f *mail.File) {
			buf := bytes.NewBuffer(a.Content)
			f.Writer = func(w io.Writer) (int64, error) {
				return buf.WriteTo(w)
			}
			f.Name = a.Name
			f.Header.Set(string(mail.HeaderContentType), a.ContentType)
		})

If the options are called on WriteTo, subsequent calls to WriteTo get a new writer, or the user can try to seek if that's better.

Additional context

No response

[wneessen]

Hi @Karitham,

thanks for the report but I can't reproduce the behaviour you are experiencing.

I've quickly used this test code:

package main

import (
	"fmt"
	"os"

	"github.com/wneessen/go-mail"
)

func main() {
	m := mail.NewMsg()
	m.Subject("Subject")
	_ = m.To("[email protected]")
	_ = m.From("[email protected]")
	m.SetBodyString(mail.TypeTextPlain, "Content")
	m.AttachFile("main.go")
	m.EmbedFile("main.go")

	fmt.Println("First try:")
	_, _ = m.WriteTo(os.Stdout)
	fmt.Println("Second try:")
	_, _ = m.WriteTo(os.Stdout)
	fmt.Println("Third try:")
	_ = m.WriteToFile("tempfile.out")

	fmt.Println("Send mail:")
	tu := os.Getenv("TEST_USER")
	tp := os.Getenv("TEST_PASS")
	c, err := mail.NewClient(os.Getenv("TEST_HOST"), mail.WithTLSPolicy(mail.TLSMandatory),
		mail.WithSMTPAuth(mail.SMTPAuthPlain), mail.WithUsername(tu),
		mail.WithPassword(tp), mail.WithPort(587))
	if err != nil {
		fmt.Printf("failed to create new client: %s\n", err)
		os.Exit(1)
	}
	if err := c.DialAndSend(m); err != nil {
		fmt.Printf("failed to dial: %s\n", err)
		os.Exit(1)
	}
}

And both the embed and the attached files are present in all 4 outputs (meaning, the two msg.WriteTo() to os.Stdout, the msg.WriteToFile() and the final sending via a mail server to an actual mail account.

Is it possible that you are using an old version of go-mail. I remembers that we had an issue with consecutive writes in a previous version. If you are not using the latest version, can you please retry with v0.3.8, please? In case you are using the latest version, would you be able to provide a proof of concept code snippet that shows the issue in action? Maybe also provide some environment details like OS/Go version, so I can try to reproduce?

[Karitham]

version info

github.com/wneessen/go-mail v0.3.8 h1:ja5D/o/RVwrtRIYFlrO7GmtcjDNeMakGQuwQRZYv0JM=
github.com/wneessen/go-mail v0.3.8/go.mod h1:m25lkU2GYQnlVr6tdwK533/UXxo57V0kLOjaFYmub0E=

reproduction

func main() {
	m := mail.NewMsg()
	m.AttachReader("hi", bytes.NewBuffer([]byte("oh hi mark!")))

	o1 := bytes.Buffer{}
	m.WriteTo(&o1)

	o2 := bytes.Buffer{}
	m.WriteTo(&o2)

	fmt.Println(len(o1.String()), len(o2.String()))
	fmt.Println("----")
	fmt.Println(o1.String())
	fmt.Println("----")
	fmt.Println(o2.String())
}

Output

406 388
----
Date: Tue, 31 Jan 2023 08:51:28 +0100
MIME-Version: 1.0
Message-ID: <114365750.248008344750.QOChqrQRdM1XBKAFa@nixos>
User-Agent: go-mail v0.3.8 // https://github.com/wneessen/go-mail
X-Mailer: go-mail v0.3.8 // https://github.com/wneessen/go-mail
Content-Type: application/octet-stream; name="hi"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="hi"

b2ggaGkgbWFyayE=

----
Date: Tue, 31 Jan 2023 08:51:28 +0100
MIME-Version: 1.0
Message-ID: <114365750.248008344750.QOChqrQRdM1XBKAFa@nixos>
User-Agent: go-mail v0.3.8 // https://github.com/wneessen/go-mail
X-Mailer: go-mail v0.3.8 // https://github.com/wneessen/go-mail
Content-Type: application/octet-stream; name="hi"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="hi"

more description of the issue

Using raw files works because it's implemented as

return &File{
		Name:   filepath.Base(n),
		Header: make(map[string][]string),
		Writer: func(w io.Writer) (int64, error) {
			h, err := os.Open(n)
			if err != nil {
				return 0, err
			}
			nb, err := io.Copy(w, h)
			if err != nil {
				_ = h.Close()
				return nb, fmt.Errorf("failed to copy file to io.Writer: %w", err)
			}
			return nb, h.Close()
		},
	}

which opens the file every time and copies.

AttachReader doesn't have that option.

Also sorry about trying to mess around with AttachFile, it was simply wrong use.
This also brings up another issue: AttachFile should probably fail properly and return an error if Stating the file fails.

[wneessen]

Thanks, again. This helps. I'll have a deeper look soon.

[wneessen]

This has been fixed with PR #111. To not break the current implementation that requires an io.Reader the data is read into memory and then buffered in a io.ReadSeeker. Additionally, there we now have Msg.AttachReadSeeker() and Msg.EmbedReadSeeker() which require an io.ReadSeeker interface to be provided as argument, which should be more efficient since the reading into memory is skipped and left to the io.Seeker.

We are just in the mids of finishing some features, so you can expect a new release containing this fix soon. In the meantime you can work with main.