Add context support

message.go

@@ -2,6 +2,7 @@ package gomail
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"os"
 	"path/filepath"
@@ -19,6 +20,7 @@ type Message struct {
 	hEncoder    mimeEncoder
 	buf         bytes.Buffer
 	boundary    string
+	ctx         context.Context
 }
 
 type header map[string][]string
@@ -36,6 +38,7 @@ func NewMessage(settings ...MessageSetting) *Message {
 		header:   make(header),
 		charset:  "UTF-8",
 		encoding: QuotedPrintable,
+		ctx:      context.Background(),
 	}
 
 	m.applySettings(settings)
@@ -60,6 +63,19 @@ func (m *Message) Reset() {
 	m.embedded = nil
 }
 
+// Context returns the message's internal context. The context is either set
+// using SetContext or it's defaulted to Background.
+func (m *Message) Context() context.Context {
+	return m.ctx
+}
+
+// WithContext copies the message and makes it use a different context.
+func (m *Message) WithContext(ctx context.Context) *Message {
+	m2 := *m
+	m2.ctx = ctx
+	return &m2
+}
+
 func (m *Message) applySettings(settings []MessageSetting) {
 	for _, s := range settings {
 		s(m)
@@ -84,6 +100,15 @@ func SetEncoding(enc Encoding) MessageSetting {
 	}
 }
 
+// SetContext is a message setting to set the context of the email. The context
+// determines cancellation and timeout for sending the message over the SMTP
+// connection.
+func SetContext(ctx context.Context) MessageSetting {
+	return func(m *Message) {
+		m.ctx = ctx
+	}
+}
+
 // Encoding represents a MIME encoding scheme like quoted-printable or base64.
 type Encoding string
 

smtp.go

@@ -1,6 +1,7 @@
 package gomail
 
 import (
+	"context"
 	"crypto/tls"
 	"fmt"
 	"io"
@@ -26,6 +27,9 @@ type Dialer struct {
 	Auth smtp.Auth
 	// Port represents the port of the SMTP server.
 	Port int
+	// NetDialer is the net.Dialer instance to use. For legacy purposes, if
+	// NetDialTimeout is not net.DialTimeout, then this field is not used.
+	NetDialer net.Dialer
 	// TLSConfig represents the TLS configuration used for the TLS (when the
 	// STARTTLS extension is used) or SSL connection.
 	TLSConfig *tls.Config
@@ -74,12 +78,30 @@ func NewPlainDialer(host string, port int, username, password string) *Dialer {
 // NetDialTimeout specifies the DialTimeout function to establish a connection
 // to the SMTP server. This can be used to override dialing in the case that a
 // proxy or other special behavior is needed.
-var NetDialTimeout = net.DialTimeout
+//
+// Deprecated: use (*Dialer).NetDialer instead. If NetDialTimeout is nil, then
+// (*Dialer).NetDialer is used.
+var NetDialTimeout func(network, address string, timeout time.Duration) (net.Conn, error) = nil
 
 // Dial dials and authenticates to an SMTP server. The returned SendCloser
 // should be closed when done using it.
 func (d *Dialer) Dial() (SendCloser, error) {
-	conn, err := NetDialTimeout("tcp", addr(d.Host, d.Port), d.Timeout)
+	return d.DialCtx(context.Background())
+}
+
+// DialCtx is Dial with context support.
+func (d *Dialer) DialCtx(ctx context.Context) (SendCloser, error) {
+	var conn net.Conn
+	var err error
+
+	if NetDialTimeout == nil {
+		ctx, cancel := context.WithTimeout(ctx, d.Timeout)
+		defer cancel()
+
+		conn, err = d.NetDialer.DialContext(ctx, "tcp", addr(d.Host, d.Port))
+	} else {
+		conn, err = NetDialTimeout("tcp", addr(d.Host, d.Port), d.Timeout)
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -93,6 +115,19 @@ func (d *Dialer) Dial() (SendCloser, error) {
 		return nil, err
 	}
 
+	done := make(chan struct{})
+	defer close(done)
+
+	go func() {
+		select {
+		case <-ctx.Done():
+			// Parent context expired. Immediately terminate and return.
+			c.Close()
+		case <-done:
+			// ok
+		}
+	}()
+
 	if d.Timeout > 0 {
 		conn.SetDeadline(time.Now().Add(d.Timeout))
 	}
@@ -201,12 +236,21 @@ func addr(host string, port int) string {
 // DialAndSend opens a connection to the SMTP server, sends the given emails and
 // closes the connection.
 func (d *Dialer) DialAndSend(m ...*Message) error {
-	s, err := d.Dial()
+	return d.DialAndSendCtx(context.Background(), m...)
+}
+
+// DialAndSendCtx is DialAndSend with context support.
+func (d *Dialer) DialAndSendCtx(ctx context.Context, m ...*Message) error {
+	s, err := d.DialCtx(ctx)
 	if err != nil {
 		return err
 	}
 	defer s.Close()
 
+	for i := range m {
+		m[i] = m[i].WithContext(ctx)
+	}
+
 	return Send(s, m...)
 }
 
@@ -228,7 +272,29 @@ func (c *smtpSender) retryError(err error) bool {
 	return err == io.EOF
 }
 
+type messageContexter interface {
+	Context() context.Context
+}
+
+var _ messageContexter = (*Message)(nil)
+
 func (c *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
+	if ctxer, ok := msg.(messageContexter); ok {
+		if ctx := ctxer.Context(); ctx != context.Background() {
+			done := make(chan struct{})
+			defer close(done)
+
+			go func() {
+				select {
+				case <-ctx.Done():
+					c.conn.Close()
+				case <-done:
+					// ok
+				}
+			}()
+		}
+	}
+
 	if c.d.Timeout > 0 {
 		c.conn.SetDeadline(time.Now().Add(c.d.Timeout))
 	}