test: let the fake SMTP server hand back the DATA it received

mail/sender_test.go

@@ -21,6 +21,15 @@ import (
 // line(s) to write back. Anything not listed gets a plain 250 OK.
 func fakeSMTP(t *testing.T, script map[string]string) string {
 	t.Helper()
+	port, _ := fakeSMTPData(t, script)
+	return port
+}
+
+// fakeSMTPData is fakeSMTP that also hands back the raw DATA the client sent,
+// once the body's terminating dot arrives.
+func fakeSMTPData(t *testing.T, script map[string]string) (string, <-chan []byte) {
+	t.Helper()
+	got := make(chan []byte, 1)
 	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatal(err)
@@ -41,15 +50,21 @@ func fakeSMTP(t *testing.T, script map[string]string) string {
 		}
 		writeLine("220 fake.example ESMTP")
 		inData := false
+		var data bytes.Buffer
 		for {
 			line, err := r.ReadString('\n')
 			if err != nil {
 				return
 			}
+			raw := line
 			line = strings.TrimRight(line, "\r\n")
 			if inData {
+				if line != "." {
+					data.WriteString(raw)
+				}
 				if line == "." {
 					inData = false
+					got <- data.Bytes()
 					if reply, ok := script["DATA_BODY"]; ok {
 						if reply == "CLOSE" {
 							return
@@ -102,7 +117,7 @@ func fakeSMTP(t *testing.T, script map[string]string) string {
 
 	host, port, _ := net.SplitHostPort(ln.Addr().String())
 	_ = host
-	return port
+	return port, got
 }
 
 func testMsg() message {