Adding PGPType to Msg as preparation to support PGP/MIME in go-mail-middleware

encoding.go

@@ -141,6 +141,8 @@ const (
 	TypeTextPlain      ContentType = "text/plain"
 	TypeTextHTML       ContentType = "text/html"
 	TypeAppOctetStream ContentType = "application/octet-stream"
+	TypePGPSignature   ContentType = "application/pgp-signature"
+	TypePGPEncrypted   ContentType = "application/pgp-encrypted"
 )
 
 // List of MIMETypes

file.go

@@ -14,8 +14,11 @@ type FileOption func(*File)
 
 // File is an attachment or embedded file of the Msg
 type File struct {
-	Name   string
+	ContentType ContentType
+	Desc        string
+	Enc         Encoding
 	Header      textproto.MIMEHeader
+	Name        string
 	Writer      func(w io.Writer) (int64, error)
 }
 
@@ -26,11 +29,45 @@ func WithFileName(n string) FileOption {
 	}
 }
 
+// WithFileDescription sets an optional file description of the File that will be
+// added as Content-Description part
+func WithFileDescription(d string) FileOption {
+	return func(f *File) {
+		f.Desc = d
+	}
+}
+
+// WithFileEncoding sets the encoding of the File. By default we should always use
+// Base64 encoding but there might be exceptions, where this might come handy.
+// Please note that quoted-printable should never be used for attachments/embeds. If this
+// is provided as argument, the function will automatically override back to Base64
+func WithFileEncoding(e Encoding) FileOption {
+	return func(f *File) {
+		if e == EncodingQP {
+			return
+		}
+		f.Enc = e
+	}
+}
+
+// WithFileContentType sets the content type of the File.
+// By default go-mail will try to guess the file type and its corresponding
+// content type and fall back to application/octet-stream if the file type
+// could not be guessed. In some cases, however, it might be needed to force
+// this to a specific type. For such situations this override method can
+// be used
+func WithFileContentType(t ContentType) FileOption {
+	return func(f *File) {
+		f.ContentType = t
+	}
+}
+
 // setHeader sets header fields to a File
 func (f *File) setHeader(h Header, v string) {
 	f.Header.Set(string(h), v)
 }
 
+// getHeader return header fields of a File
 func (f *File) getHeader(h Header) (string, bool) {
 	v := f.Header.Get(string(h))
 	return v, v != ""

header.go

@@ -15,6 +15,9 @@ type Importance int
 
 // List of common generic header field names
 const (
+	// HeaderContentDescription is the "Content-Description" header
+	HeaderContentDescription Header = "Content-Description"
+
 	// HeaderContentDisposition is the "Content-Disposition" header
 	HeaderContentDisposition Header = "Content-Disposition"
 

msg.go

@@ -41,6 +41,18 @@ const (
 	errParseMailAddr = "failed to parse mail address %q: %w"
 )
 
+const (
+	// NoPGP indicates that a message should not be treated as PGP encrypted
+	// or signed and is the default value for a message
+	NoPGP PGPType = iota
+	// PGPEncrypt indicates that a message should be treated as PGP encrypted
+	// This works closely together with the corresponding go-mail-middleware
+	PGPEncrypt
+	// PGPSignature indicates that a message should be treated as PGP signed
+	// This works closely together with the corresponding go-mail-middleware
+	PGPSignature
+)
+
 // MiddlewareType is the type description of the Middleware and needs to be returned
 // in the Middleware interface by the Type method
 type MiddlewareType string
@@ -51,6 +63,10 @@ type Middleware interface {
 	Type() MiddlewareType
 }
 
+// PGPType is a type alias for a int representing a type of PGP encryption
+// or signature
+type PGPType int
+
 // Msg is the mail message struct
 type Msg struct {
 	// addrHeader is a slice of strings that the different mail AddrHeader fields
@@ -77,10 +93,8 @@ type Msg struct {
 	// genHeader is a slice of strings that the different generic mail Header fields
 	genHeader map[Header][]string
 
-	// preformHeader is a slice of strings that the different generic mail Header fields
-	// of which content is already preformated and will not be affected by the automatic line
-	// breaks
-	preformHeader map[Header]string
+	// middlewares is the list of middlewares to apply to the Msg before sending in FIFO order
+	middlewares []Middleware
 
 	// mimever represents the MIME version
 	mimever MIMEVersion
@@ -88,8 +102,14 @@ type Msg struct {
 	// parts represent the different parts of the Msg
 	parts []*Part
 
-	// middlewares is the list of middlewares to apply to the Msg before sending in FIFO order
-	middlewares []Middleware
+	// preformHeader is a slice of strings that the different generic mail Header fields
+	// of which content is already preformated and will not be affected by the automatic line
+	// breaks
+	preformHeader map[Header]string
+
+	// pgptype indicates that a message has a PGPType assigned and therefore will generate
+	// different Content-Type settings in the msgWriter
+	pgptype PGPType
 
 	// sendError holds the SendError in case a Msg could not be delivered during the Client.Send operation
 	sendError error
@@ -161,6 +181,13 @@ func WithMiddleware(mw Middleware) MsgOption {
 	}
 }
 
+// WithPGPType overrides the default PGPType of the message
+func WithPGPType(t PGPType) MsgOption {
+	return func(m *Msg) {
+		m.pgptype = t
+	}
+}
+
 // SetCharset sets the encoding charset of the Msg
 func (m *Msg) SetCharset(c Charset) {
 	m.charset = c
@@ -182,6 +209,11 @@ func (m *Msg) SetMIMEVersion(mv MIMEVersion) {
 	m.mimever = mv
 }
 
+// SetPGPType sets the PGPType of the Msg
+func (m *Msg) SetPGPType(t PGPType) {
+	m.pgptype = t
+}
+
 // Encoding returns the currently set encoding of the Msg
 func (m *Msg) Encoding() string {
 	return m.encoding.String()
@@ -1005,17 +1037,22 @@ func (m *Msg) hasAlt() bool {
 			c++
 		}
 	}
-	return c > 1
+	return c > 1 && m.pgptype == 0
 }
 
 // hasMixed returns true if the Msg has mixed parts
 func (m *Msg) hasMixed() bool {
-	return (len(m.parts) > 0 && len(m.attachments) > 0) || len(m.attachments) > 1
+	return m.pgptype == 0 && ((len(m.parts) > 0 && len(m.attachments) > 0) || len(m.attachments) > 1)
 }
 
 // hasRelated returns true if the Msg has related parts
 func (m *Msg) hasRelated() bool {
-	return (len(m.parts) > 0 && len(m.embeds) > 0) || len(m.embeds) > 1
+	return m.pgptype == 0 && ((len(m.parts) > 0 && len(m.embeds) > 0) || len(m.embeds) > 1)
+}
+
+// hasPGPType returns true if the Msg should be treated as PGP encoded message
+func (m *Msg) hasPGPType() bool {
+	return m.pgptype > 0
 }
 
 // newPart returns a new Part for the Msg

msgwriter.go

@@ -100,12 +100,26 @@ func (mw *msgWriter) writeMsg(m *Msg) {
 		mw.startMP(MIMEAlternative, m.boundary)
 		mw.writeString(DoubleNewLine)
 	}
+	if m.hasPGPType() {
+		switch m.pgptype {
+		case PGPEncrypt:
+			mw.startMP(`encrypted; protocol="application/pgp-encrypted"`, m.boundary)
+		case PGPSignature:
+			mw.startMP(`signed; protocol="application/pgp-signature";`, m.boundary)
+		}
+		mw.writeString(DoubleNewLine)
+		mw.startMP("mixed", m.boundary)
+	}
 
 	for _, p := range m.parts {
 		if !p.del {
 			mw.writePart(p, m.charset)
 		}
 	}
+
+	if m.hasPGPType() {
+		mw.stopMP()
+	}
 	if m.hasAlt() {
 		mw.stopMP()
 	}
@@ -172,17 +186,30 @@ func (mw *msgWriter) stopMP() {
 // addFiles adds the attachments/embeds file content to the mail body
 func (mw *msgWriter) addFiles(fl []*File, a bool) {
 	for _, f := range fl {
+		e := EncodingB64
 		if _, ok := f.getHeader(HeaderContentType); !ok {
 			mt := mime.TypeByExtension(filepath.Ext(f.Name))
 			if mt == "" {
 				mt = "application/octet-stream"
 			}
+			if f.ContentType != "" {
+				mt = string(f.ContentType)
+			}
 			f.setHeader(HeaderContentType, fmt.Sprintf(`%s; name="%s"`, mt,
 				mw.en.Encode(mw.c.String(), f.Name)))
 		}
 
 		if _, ok := f.getHeader(HeaderContentTransferEnc); !ok {
-			f.setHeader(HeaderContentTransferEnc, string(EncodingB64))
+			if f.Enc != "" {
+				e = f.Enc
+			}
+			f.setHeader(HeaderContentTransferEnc, string(e))
+		}
+
+		if f.Desc != "" {
+			if _, ok := f.getHeader(HeaderContentDescription); !ok {
+				f.setHeader(HeaderContentDescription, f.Desc)
+			}
 		}
 
 		if _, ok := f.getHeader(HeaderContentDisposition); !ok {
@@ -208,7 +235,7 @@ func (mw *msgWriter) addFiles(fl []*File, a bool) {
 		if mw.d > 0 {
 			mw.newPart(f.Header)
 		}
-		mw.writeBody(f.Writer, EncodingB64)
+		mw.writeBody(f.Writer, e)
 	}
 }
 
@@ -228,6 +255,9 @@ func (mw *msgWriter) writePart(p *Part, cs Charset) {
 	}
 	if mw.d > 0 {
 		mh := textproto.MIMEHeader{}
+		if p.desc != "" {
+			mh.Add(string(HeaderContentDescription), p.desc)
+		}
 		mh.Add(string(HeaderContentType), ct)
 		mh.Add(string(HeaderContentTransferEnc), cte)
 		mw.newPart(mh)

part.go

@@ -15,6 +15,7 @@ type PartOption func(*Part)
 // Part is a part of the Msg
 type Part struct {
 	ctype ContentType
+	desc  string
 	enc   Encoding
 	del   bool
 	w     func(io.Writer) (int64, error)
@@ -44,6 +45,11 @@ func (p *Part) GetWriteFunc() func(io.Writer) (int64, error) {
 	return p.w
 }
 
+// GetDescription returns the currently set Content-Description of the Part
+func (p *Part) GetDescription() string {
+	return p.desc
+}
+
 // SetContent overrides the content of the Part with the given string
 func (p *Part) SetContent(c string) {
 	buf := bytes.NewBufferString(c)
@@ -60,6 +66,11 @@ func (p *Part) SetEncoding(e Encoding) {
 	p.enc = e
 }
 
+// SetDescription overrides the Content-Description of the Part
+func (p *Part) SetDescription(d string) {
+	p.desc = d
+}
+
 // SetWriteFunc overrides the WriteFunc of the Part
 func (p *Part) SetWriteFunc(w func(io.Writer) (int64, error)) {
 	p.w = w
@@ -77,3 +88,10 @@ func WithPartEncoding(e Encoding) PartOption {
 		p.enc = e
 	}
 }
+
+// WithPartContentDescription overrides the default Part Content-Description
+func WithPartContentDescription(d string) PartOption {
+	return func(p *Part) {
+		p.desc = d
+	}
+}