compose: refactor attachment handling

Refactor the attachment handling process in the composer. The composer
can currently only handle attachments that are stored as files (or pgp
keys). This patch removes this limitation so that any message part can
be handled as an attachment. With this we can treat files, pgp keys and
message parts on an equal footing and it will enable us also to easily
forward attachments.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Tim Culverhouse <tim@timculverhouse.com>

1 files changed, 136 insertions, 0 deletions

diff --git a/lib/attachment.go b/lib/attachment.go
new file mode 100644
index 0000000..d7cbf3f
--- /dev/null
+++ b/lib/attachment.go
@@ -0,0 +1,136 @@
+package lib
+
+import (
+	"bufio"
+	"io"
+	"mime"
+	"net/http"
+	"os"
+	"path/filepath"
+
+	"github.com/emersion/go-message/mail"
+	"github.com/pkg/errors"
+)
+
+type Part struct {
+	MimeType string
+	Params   map[string]string
+	Body     io.Reader
+}
+
+func NewPart(mimetype string, params map[string]string, body io.Reader) *Part {
+	return &Part{
+		MimeType: mimetype,
+		Params:   params,
+		Body:     body,
+	}
+}
+
+type Attachment interface {
+	Name() string
+	WriteTo(w *mail.Writer) error
+}
+
+type FileAttachment struct {
+	path string
+}
+
+func NewFileAttachment(path string) *FileAttachment {
+	return &FileAttachment{
+		path,
+	}
+}
+
+func (fa *FileAttachment) Name() string {
+	return fa.path
+}
+
+func (fa *FileAttachment) WriteTo(w *mail.Writer) error {
+	f, err := os.Open(fa.path)
+	if err != nil {
+		return errors.Wrap(err, "os.Open")
+	}
+	defer f.Close()
+
+	reader := bufio.NewReader(f)
+
+	// if we have an extension, prefer that instead of trying to sniff the header.
+	// That's generally more accurate than sniffing as lots of things are zip files
+	// under the hood, e.g. most office file types
+	ext := filepath.Ext(fa.path)
+	var mimeString string
+	if mimeString = mime.TypeByExtension(ext); mimeString != "" {
+		// found it in the DB
+	} else {
+		// Sniff the mime type instead
+		// http.DetectContentType only cares about the first 512 bytes
+		head, err := reader.Peek(512)
+		if err != nil && err != io.EOF {
+			return errors.Wrap(err, "Peek")
+		}
+		mimeString = http.DetectContentType(head)
+	}
+
+	// mimeString can contain type and params (like text encoding),
+	// so we need to break them apart before passing them to the headers
+	mimeType, params, err := mime.ParseMediaType(mimeString)
+	if err != nil {
+		return errors.Wrap(err, "ParseMediaType")
+	}
+	filename := filepath.Base(fa.path)
+	params["name"] = filename
+
+	// set header fields
+	ah := mail.AttachmentHeader{}
+	ah.SetContentType(mimeType, params)
+	// setting the filename auto sets the content disposition
+	ah.SetFilename(filename)
+
+	aw, err := w.CreateAttachment(ah)
+	if err != nil {
+		return errors.Wrap(err, "CreateAttachment")
+	}
+	defer aw.Close()
+
+	if _, err := reader.WriteTo(aw); err != nil {
+		return errors.Wrap(err, "reader.WriteTo")
+	}
+
+	return nil
+}
+
+type PartAttachment struct {
+	part *Part
+	name string
+}
+
+func NewPartAttachment(part *Part, name string) *PartAttachment {
+	return &PartAttachment{
+		part,
+		name,
+	}
+}
+
+func (pa *PartAttachment) Name() string {
+	return pa.name
+}
+
+func (pa *PartAttachment) WriteTo(w *mail.Writer) error {
+	// set header fields
+	ah := mail.AttachmentHeader{}
+	ah.SetContentType(pa.part.MimeType, pa.part.Params)
+
+	// setting the filename auto sets the content disposition
+	ah.SetFilename(pa.Name())
+
+	aw, err := w.CreateAttachment(ah)
+	if err != nil {
+		return errors.Wrap(err, "CreateAttachment")
+	}
+	defer aw.Close()
+
+	if _, err := io.Copy(aw, pa.part.Body); err != nil {
+		return errors.Wrap(err, "io.Copy")
+	}
+	return nil
+}