Parse To lines in the message itself. Fixes #3

cmd/cmd.go

@@ -1,18 +1,21 @@
 package cmd
 
 import (
+	"bytes"
 	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
 	"net/smtp"
 	"os"
 	"os/user"
+	"regexp"
 	"strings"
 
 	"github.com/ogier/pflag"
 )
 
+// Go runs the MailHog sendmail replacement.
 func Go() {
 	smtpAddr := "localhost:1025"
 
@@ -55,17 +58,28 @@ func Go() {
 		recip = pflag.Args()
 	}
 
-	if len(recip) == 0 {
-		fmt.Fprintln(os.Stderr, "missing recipient")
-		os.Exit(10)
-	}
-
 	body, err := ioutil.ReadAll(os.Stdin)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "error reading stdin")
 		os.Exit(11)
 	}
 
+	if len(recip) == 0 {
+		// We only need to parse the message to get a recipient if none where
+		// provided on the command line.
+		re := regexp.MustCompile("(?im)^To: (.*)\r\n$")
+		n := bytes.IndexByte(body, 0)
+		bodyStr := string(body[:n])
+		includedRecip := re.FindAllString(bodyStr, -1)
+		if includedRecip == nil {
+			fmt.Fprintln(os.Stderr, "missing recipient")
+			os.Exit(10)
+		}
+		newRecip := make([]string, len(recip), len(recip)+len(includedRecip)+1)
+		copy(newRecip, recip)
+		recip = append(newRecip, includedRecip...)
+	}
+
 	err = smtp.SendMail(smtpAddr, nil, fromAddr, recip, body)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, "error sending mail")