Provide more ways for middleware to interact with mail parts

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

@@ -14,9 +14,12 @@ type FileOption func(*File)
 
 // File is an attachment or embedded file of the Msg
 type File struct {
-	Name   string
-	Header textproto.MIMEHeader
-	Writer func(w io.Writer) (int64, error)
+	ContentType ContentType
+	Desc        string
+	Enc         Encoding
+	Header      textproto.MIMEHeader
+	Name        string
+	Writer      func(w io.Writer) (int64, error)
 }
 
 // WithFileName sets the filename of the File
@@ -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 != ""

file_test.go

@@ -30,3 +30,84 @@ func TestFile_SetGetHeader(t *testing.T) {
 		t.Errorf("getHeader returned wrong value. Expected: %s, got: %s", "", fi)
 	}
 }
+
+// TestFile_WithFileDescription tests the WithFileDescription option
+func TestFile_WithFileDescription(t *testing.T) {
+	tests := []struct {
+		name string
+		desc string
+	}{
+		{"File description: test", "test"},
+		{"File description: empty", ""},
+	}
+	for _, tt := range tests {
+		m := NewMsg()
+		t.Run(tt.name, func(t *testing.T) {
+			m.AttachFile("file.go", WithFileDescription(tt.desc))
+			al := m.GetAttachments()
+			if len(al) <= 0 {
+				t.Errorf("AttachFile() failed. Attachment list is empty")
+			}
+			a := al[0]
+			if a.Desc != tt.desc {
+				t.Errorf("WithFileDescription() failed. Expected: %s, got: %s", tt.desc, a.Desc)
+			}
+		})
+	}
+}
+
+// TestFile_WithFileEncoding tests the WithFileEncoding option
+func TestFile_WithFileEncoding(t *testing.T) {
+	tests := []struct {
+		name string
+		enc  Encoding
+		want Encoding
+	}{
+		{"File encoding: 8bit raw", NoEncoding, NoEncoding},
+		{"File encoding: Base64", EncodingB64, EncodingB64},
+		{"File encoding: quoted-printable (not allowed)", EncodingQP, ""},
+	}
+	for _, tt := range tests {
+		m := NewMsg()
+		t.Run(tt.name, func(t *testing.T) {
+			m.AttachFile("file.go", WithFileEncoding(tt.enc))
+			al := m.GetAttachments()
+			if len(al) <= 0 {
+				t.Errorf("AttachFile() failed. Attachment list is empty")
+			}
+			a := al[0]
+			if a.Enc != tt.want {
+				t.Errorf("WithFileEncoding() failed. Expected: %s, got: %s", tt.enc, a.Enc)
+			}
+		})
+	}
+}
+
+// TestFile_WithFileContentType tests the WithFileContentType option
+func TestFile_WithFileContentType(t *testing.T) {
+	tests := []struct {
+		name string
+		ct   ContentType
+		want string
+	}{
+		{"File content-type: text/plain", TypeTextPlain, "text/plain"},
+		{"File content-type: html/html", TypeTextHTML, "text/html"},
+		{"File content-type: application/octet-stream", TypeAppOctetStream, "application/octet-stream"},
+		{"File content-type: application/pgp-encrypted", TypePGPEncrypted, "application/pgp-encrypted"},
+		{"File content-type: application/pgp-signature", TypePGPSignature, "application/pgp-signature"},
+	}
+	for _, tt := range tests {
+		m := NewMsg()
+		t.Run(tt.name, func(t *testing.T) {
+			m.AttachFile("file.go", WithFileContentType(tt.ct))
+			al := m.GetAttachments()
+			if len(al) <= 0 {
+				t.Errorf("AttachFile() failed. Attachment list is empty")
+			}
+			a := al[0]
+			if a.ContentType != ContentType(tt.want) {
+				t.Errorf("WithFileContentType() failed. Expected: %s, got: %s", tt.want, a.ContentType)
+			}
+		})
+	}
+}

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
@@ -77,19 +93,23 @@ 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
 
 	// 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()
@@ -774,10 +806,10 @@ func (m *Msg) EmbedFile(n string, o ...FileOption) {
 
 // EmbedReader adds an embedded File from an io.Reader to the Msg
 //
-// CAVEAT: For AttachReader to work it has to read all data of the io.Reader
+// CAVEAT: For EmbedReader to work it has to read all data of the io.Reader
 // into memory first, so it can seek through it. Using larger amounts of
 // data on the io.Reader should be avoided. For such, it is recommeded to
-// either use AttachFile or AttachReadSeeker instead
+// either use EmbedFile or EmbedReadSeeker instead
 func (m *Msg) EmbedReader(n string, r io.Reader, o ...FileOption) {
 	f := fileFromReader(n, r)
 	m.embeds = m.appendFile(m.embeds, f, o...)
@@ -1027,17 +1059,22 @@ 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

msg_test.go

@@ -179,6 +179,36 @@ func TestNewMsgWithBoundary(t *testing.T) {
 	}
 }
 
+// TestNewMsg_WithPGPType tests WithPGPType option
+func TestNewMsg_WithPGPType(t *testing.T) {
+	tests := []struct {
+		name string
+		pt   PGPType
+		hpt  bool
+	}{
+		{"Not a PGP encoded message", NoPGP, false},
+		{"PGP encrypted message", PGPEncrypt, true},
+		{"PGP signed message", PGPSignature, true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := NewMsg(WithPGPType(tt.pt))
+			if m.pgptype != tt.pt {
+				t.Errorf("WithPGPType() failed. Expected: %d, got: %d", tt.pt, m.pgptype)
+			}
+			m.pgptype = 99
+			m.SetPGPType(tt.pt)
+			if m.pgptype != tt.pt {
+				t.Errorf("SetPGPType() failed. Expected: %d, got: %d", tt.pt, m.pgptype)
+			}
+			if m.hasPGPType() != tt.hpt {
+				t.Errorf("hasPGPType() failed. Expected %t, got: %t", tt.hpt, m.hasPGPType())
+			}
+		})
+	}
+}
+
 type uppercaseMiddleware struct{}
 
 func (mw uppercaseMiddleware) Handle(m *Msg) *Msg {