Made File struct more flexible

The File can now be streamed to the SMTP server directly without
being buffered into memory first.

Fixes #4

message.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"io/ioutil"
 	"mime"
+	"os"
 	"path/filepath"
 	"sync"
 	"time"
@@ -220,38 +221,40 @@ func (msg *Message) AddAlternativeWriter(contentType string, f func(io.Writer) e
 
 // A File represents a file that can be attached or embedded in an email.
 type File struct {
-	Name      string
+	// Name represents the base name of the file. If the file is attached to the
-	MimeType  string
+	// message it is the name of the attachment.
-	Content   []byte
+	Name string
-	ContentID string
+	// Header represents the MIME header of the message part that contains the
+	// file content.
+	Header map[string][]string
+	// Copier is a function run when the message is sent. It should copy the
+	// content of the file to w.
+	Copier func(w io.Writer) error
 }
 
-// OpenFile opens a file on disk to create a gomail.File.
+// NewFile creates a File from the given filename.
-func OpenFile(filename string) (*File, error) {
+func NewFile(filename string) *File {
-	content, err := readFile(filename)
-	if err != nil {
-		return nil, err
-	}
-
-	f := CreateFile(filepath.Base(filename), content)
-
-	return f, nil
-}
-
-// CreateFile creates a gomail.File from the given name and content.
-func CreateFile(name string, content []byte) *File {
-	mimeType := mime.TypeByExtension(filepath.Ext(name))
-	if mimeType == "" {
-		mimeType = "application/octet-stream"
-	}
-
 	return &File{
-		Name:     name,
+		Name:   filepath.Base(filename),
-		MimeType: mimeType,
+		Header: make(map[string][]string),
-		Content:  content,
+		Copier: func(w io.Writer) error {
+			h, err := os.Open(filename)
+			if err != nil {
+				return err
+			}
+			if _, err := io.Copy(w, h); err != nil {
+				h.Close()
+				return err
+			}
+			return h.Close()
+		},
 	}
 }
 
+func (f *File) setHeader(field string, value ...string) {
+	f.Header[field] = value
+}
+
 // Attach attaches the files to the email.
 func (msg *Message) Attach(f ...*File) {
 	if msg.attachments == nil {

message_test.go

@@ -198,11 +198,7 @@ func TestAttachmentOnly(t *testing.T) {
 	msg := NewMessage()
 	msg.SetHeader("From", "from@example.com")
 	msg.SetHeader("To", "to@example.com")
-	f, err := OpenFile("/tmp/test.pdf")
+	msg.Attach(testFile("/tmp/test.pdf"))
-	if err != nil {
-		panic(err)
-	}
-	msg.Attach(f)
 
 	want := &message{
 		from: "from@example.com",
@@ -224,7 +220,7 @@ func TestAttachment(t *testing.T) {
 	msg.SetHeader("From", "from@example.com")
 	msg.SetHeader("To", "to@example.com")
 	msg.SetBody("text/plain", "Test")
-	msg.Attach(CreateFile("test.pdf", []byte("Content")))
+	msg.Attach(testFile("/tmp/test.pdf"))
 
 	want := &message{
 		from: "from@example.com",
@@ -243,7 +239,7 @@ func TestAttachment(t *testing.T) {
 			"Content-Disposition: attachment; filename=\"test.pdf\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.pdf")) + "\r\n" +
 			"--_BOUNDARY_1_--\r\n",
 	}
 
@@ -254,8 +250,8 @@ func TestAttachmentsOnly(t *testing.T) {
 	msg := NewMessage()
 	msg.SetHeader("From", "from@example.com")
 	msg.SetHeader("To", "to@example.com")
-	msg.Attach(CreateFile("test.pdf", []byte("Content 1")))
+	msg.Attach(testFile("/tmp/test.pdf"))
-	msg.Attach(CreateFile("test.zip", []byte("Content 2")))
+	msg.Attach(testFile("/tmp/test.zip"))
 
 	want := &message{
 		from: "from@example.com",
@@ -269,13 +265,13 @@ func TestAttachmentsOnly(t *testing.T) {
 			"Content-Disposition: attachment; filename=\"test.pdf\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 1")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.pdf")) + "\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: application/zip; name=\"test.zip\"\r\n" +
 			"Content-Disposition: attachment; filename=\"test.zip\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 2")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.zip")) + "\r\n" +
 			"--_BOUNDARY_1_--\r\n",
 	}
 
@@ -287,8 +283,8 @@ func TestAttachments(t *testing.T) {
 	msg.SetHeader("From", "from@example.com")
 	msg.SetHeader("To", "to@example.com")
 	msg.SetBody("text/plain", "Test")
-	msg.Attach(CreateFile("test.pdf", []byte("Content 1")))
+	msg.Attach(testFile("/tmp/test.pdf"))
-	msg.Attach(CreateFile("test.zip", []byte("Content 2")))
+	msg.Attach(testFile("/tmp/test.zip"))
 
 	want := &message{
 		from: "from@example.com",
@@ -307,13 +303,13 @@ func TestAttachments(t *testing.T) {
 			"Content-Disposition: attachment; filename=\"test.pdf\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 1")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.pdf")) + "\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: application/zip; name=\"test.zip\"\r\n" +
 			"Content-Disposition: attachment; filename=\"test.zip\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 2")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.zip")) + "\r\n" +
 			"--_BOUNDARY_1_--\r\n",
 	}
 
@@ -324,10 +320,10 @@ func TestEmbedded(t *testing.T) {
 	msg := NewMessage()
 	msg.SetHeader("From", "from@example.com")
 	msg.SetHeader("To", "to@example.com")
-	f := CreateFile("image1.jpg", []byte("Content 1"))
+	f := testFile("image1.jpg")
-	f.ContentID = "test-content-id"
+	f.Header["Content-ID"] = []string{"<test-content-id>"}
 	msg.Embed(f)
-	msg.Embed(CreateFile("image2.jpg", []byte("Content 2")))
+	msg.Embed(testFile("image2.jpg"))
 	msg.SetBody("text/plain", "Test")
 
 	want := &message{
@@ -348,14 +344,14 @@ func TestEmbedded(t *testing.T) {
 			"Content-ID: <test-content-id>\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 1")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of image1.jpg")) + "\r\n" +
 			"--_BOUNDARY_1_\r\n" +
 			"Content-Type: image/jpeg; name=\"image2.jpg\"\r\n" +
 			"Content-Disposition: inline; filename=\"image2.jpg\"\r\n" +
 			"Content-ID: <image2.jpg>\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 2")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of image2.jpg")) + "\r\n" +
 			"--_BOUNDARY_1_--\r\n",
 	}
 
@@ -368,8 +364,8 @@ func TestFullMessage(t *testing.T) {
 	msg.SetHeader("To", "to@example.com")
 	msg.SetBody("text/plain", "¡Hola, señor!")
 	msg.AddAlternative("text/html", "¡<b>Hola</b>, <i>señor</i>!</h1>")
-	msg.Attach(CreateFile("test.pdf", []byte("Content 1")))
+	msg.Attach(testFile("test.pdf"))
-	msg.Embed(CreateFile("image.jpg", []byte("Content 2")))
+	msg.Embed(testFile("image.jpg"))
 
 	want := &message{
 		from: "from@example.com",
@@ -402,7 +398,7 @@ func TestFullMessage(t *testing.T) {
 			"Content-ID: <image.jpg>\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 2")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of image.jpg")) + "\r\n" +
 			"--_BOUNDARY_2_--\r\n" +
 			"\r\n" +
 			"--_BOUNDARY_1_\r\n" +
@@ -410,7 +406,7 @@ func TestFullMessage(t *testing.T) {
 			"Content-Disposition: attachment; filename=\"test.pdf\"\r\n" +
 			"Content-Transfer-Encoding: base64\r\n" +
 			"\r\n" +
-			base64.StdEncoding.EncodeToString([]byte("Content 1")) + "\r\n" +
+			base64.StdEncoding.EncodeToString([]byte("Content of test.pdf")) + "\r\n" +
 			"--_BOUNDARY_1_--\r\n",
 	}
 
@@ -582,6 +578,15 @@ func getBoundaries(t *testing.T, count int, msg string) []string {
 
 var boundaryRegExp = regexp.MustCompile("boundary=(\\w+)")
 
+func testFile(name string) *File {
+	f := NewFile(name)
+	f.Copier = func(w io.Writer) error {
+		_, err := w.Write([]byte("Content of " + filepath.Base(f.Name)))
+		return err
+	}
+	return f
+}
+
 func BenchmarkFull(b *testing.B) {
 	emptyFunc := func(from string, to []string, msg io.WriterTo) error {
 		return nil
@@ -598,8 +603,8 @@ func BenchmarkFull(b *testing.B) {
 		})
 		msg.SetBody("text/plain", "¡Hola, señor!")
 		msg.AddAlternative("text/html", "<p>¡Hola, señor!</p>")
-		msg.Attach(CreateFile("benchmark.txt", []byte("Benchmark")))
+		msg.Attach(testFile("benchmark.txt"))
-		msg.Embed(CreateFile("benchmark.jpg", []byte("Benchmark")))
+		msg.Embed(testFile("benchmark.jpg"))
 
 		if err := Send(SendFunc(emptyFunc), msg); err != nil {
 			panic(err)

writeto.go

@@ -4,8 +4,10 @@ import (
 	"encoding/base64"
 	"errors"
 	"io"
+	"mime"
 	"mime/multipart"
 	"mime/quotedprintable"
+	"path/filepath"
 	"time"
 )
 
@@ -109,24 +111,35 @@ func (w *messageWriter) closeMultipart() {
 
 func (w *messageWriter) addFiles(files []*File, isAttachment bool) {
 	for _, f := range files {
-		h := make(map[string][]string)
+		if _, ok := f.Header["Content-Type"]; !ok {
-		h["Content-Type"] = []string{f.MimeType + "; name=\"" + f.Name + "\""}
+			mediaType := mime.TypeByExtension(filepath.Ext(f.Name))
-		h["Content-Transfer-Encoding"] = []string{string(Base64)}
+			if mediaType == "" {
-		if isAttachment {
+				mediaType = "application/octet-stream"
-			h["Content-Disposition"] = []string{"attachment; filename=\"" + f.Name + "\""}
+			}
-		} else {
+			f.setHeader("Content-Type", mediaType+`; name="`+f.Name+`"`)
-			h["Content-Disposition"] = []string{"inline; filename=\"" + f.Name + "\""}
+		}
-			if f.ContentID != "" {
+
-				h["Content-ID"] = []string{"<" + f.ContentID + ">"}
+		if _, ok := f.Header["Content-Transfer-Encoding"]; !ok {
+			f.setHeader("Content-Transfer-Encoding", string(Base64))
+		}
+
+		if _, ok := f.Header["Content-Disposition"]; !ok {
+			var disp string
+			if isAttachment {
+				disp = "attachment"
 			} else {
-				h["Content-ID"] = []string{"<" + f.Name + ">"}
+				disp = "inline"
+			}
+			f.setHeader("Content-Disposition", disp+`; filename="`+f.Name+`"`)
+		}
+
+		if !isAttachment {
+			if _, ok := f.Header["Content-ID"]; !ok {
+				f.setHeader("Content-ID", "<"+f.Name+">")
 			}
 		}
-		w.writeHeaders(h)
+		w.writeHeaders(f.Header)
-		w.writeBody(func(w io.Writer) error {
+		w.writeBody(f.Copier, Base64)
-			_, err := w.Write(f.Content)
-			return err
-		}, Base64)
 	}
 }