Add utility function for generating Message-Id

go.mod

@@ -4,5 +4,6 @@ go 1.12
 
 require (
 	github.com/emersion/go-textwrapper v0.0.0-20160606182133-d0e65e56babe
+	github.com/martinlindhe/base36 v0.0.0-20190418230009-7c6542dfbb41
 	golang.org/x/text v0.3.2
 )

mail/mail.go

@@ -7,3 +7,34 @@
 //
 // RFC 5322 defines the Internet Message Format.
 package mail
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"crypto/rand"
+	"os"
+	"time"
+
+	"github.com/martinlindhe/base36"
+)
+
+// Generates an RFC 2822-compliant Message-Id based on the informational draft
+// "Recommendations for generating Message IDs", for lack of a better
+// authoritative source.
+func GenerateMessageID() string {
+	var (
+		now   bytes.Buffer
+		nonce []byte = make([]byte, 8)
+	)
+	binary.Write(&now, binary.BigEndian, time.Now().UnixNano())
+	rand.Read(nonce)
+	hostname, err := os.Hostname()
+	if err != nil {
+		hostname = "localhost"
+	}
+	return fmt.Sprintf("<%s.%s@%s>",
+		base36.EncodeBytes(now.Bytes()),
+		base36.EncodeBytes(nonce),
+		hostname)
+}

mail/mail_test.go

@@ -1,5 +1,12 @@
 package mail_test
 
+import (
+	"regexp"
+	"testing"
+
+	"github.com/emersion/go-message/mail"
+)
+
 const mailString = "Subject: Your Name\r\n" +
 	"Content-Type: multipart/mixed; boundary=message-boundary\r\n" +
 	"\r\n" +
@@ -33,3 +40,11 @@ const nestedMailString = "Subject: Fwd: Your Name\r\n" +
 	"\r\n" +
 	mailString +
 	"--outer-message-boundary--\r\n"
+
+func TestGenerateMessageID(t *testing.T) {
+	msgId := mail.GenerateMessageID()
+	regex := regexp.MustCompile(`^<.*@.*>$`)
+	if !regex.MatchString(msgId) {
+		t.Error("Generated message ID does not meet RFC requirement")
+	}
+}

textproto/header.go

@@ -8,6 +8,8 @@ import (
 	"net/textproto"
 	"regexp"
 	"strings"
+
+	"log"
 )
 
 type headerField struct {
@@ -260,6 +262,7 @@ func (h *Header) FieldsByKey(k string) HeaderFields {
 func readLineSlice(r *bufio.Reader, line []byte) ([]byte, error) {
 	for {
 		l, more, err := r.ReadLine()
+		log.Println("LINE", string(l), more)
 		if err != nil {
 			return nil, err
 		}
@@ -326,6 +329,7 @@ func hasContinuationLine(r *bufio.Reader) bool {
 func readContinuedLineSlice(r *bufio.Reader) ([]byte, error) {
 	// Read the first line.
 	line, err := readLineSlice(r, nil)
+	log.Println("HEY", string(line), err)
 	if err != nil {
 		return nil, err
 	}
@@ -338,6 +342,7 @@ func readContinuedLineSlice(r *bufio.Reader) ([]byte, error) {
 
 	// Read continuation lines.
 	for hasContinuationLine(r) {
+		log.Println("CONTINUATION")
 		line, err = readLineSlice(r, line)
 		if err != nil {
 			break // bufio will keep err until next read.