From 8d7e00e408df4d92c37caabbfd68cdc75ebd2dfb Mon Sep 17 00:00:00 2001
From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Sat, 23 Jan 2021 23:15:58 +0000
Subject: [PATCH] TFO: cleanup the TCP pure ack of SMTP banner

---
 src/src/smtp_out.c        | 12 ++++++++++--
 src/src/transports/smtp.c | 12 +++++++++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/src/smtp_out.c b/src/src/smtp_out.c
index b1a25f70a..2a392e50f 100644
--- a/src/src/smtp_out.c
+++ b/src/src/smtp_out.c
@@ -349,14 +349,22 @@ else
     save_errno = errno;
   else if (early_data && !fastopen_blob && early_data->data && early_data->len)
     {
+    /* We had some early-data to send, but couldn't do TFO */
     HDEBUG(D_transport|D_acl|D_v)
       debug_printf("sending %ld nonTFO early-data\n", (long)early_data->len);
 
+#ifdef TCP_QUICKACK_notdef
+    (void) setsockopt(sock, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
+#endif
     if (send(sock, early_data->data, early_data->len, 0) < 0)
       save_errno = errno;
     }
-#ifdef TCP_QUICKACK
-    (void) setsockopt(sock, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
+#ifdef TCP_QUICKACK_notdef
+  /* Under TFO (with openssl & pipe-conn; testcase 4069, as of
+  5.10.8-100.fc32.x86_64) this seems to be inop.
+  Perhaps overwritten when we (client) go -> ESTABLISHED on seeing the 3rd-ACK?
+  For that case, added at smtp_reap_banner(). */
+  (void) setsockopt(sock, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
 #endif
   }
 
diff --git a/src/src/transports/smtp.c b/src/src/transports/smtp.c
index 0a6bfde18..30669d351 100644
--- a/src/src/transports/smtp.c
+++ b/src/src/transports/smtp.c
@@ -712,7 +712,17 @@ return count;
 static BOOL
 smtp_reap_banner(smtp_context * sx)
 {
-BOOL good_response = smtp_read_response(sx, sx->buffer, sizeof(sx->buffer),
+BOOL good_response;
+#if defined(__linux__) && defined(TCP_QUICKACK)
+  {	/* Hack to get QUICKACK disabled; has to be right after 3whs, and has to on->off */
+  int sock = sx->cctx.sock;
+  struct pollfd p = {.fd = sock, .events = POLLOUT};
+  int rc = poll(&p, 1, 1000);
+  (void) setsockopt(sock, IPPROTO_TCP, TCP_QUICKACK, US &on, sizeof(on));
+  (void) setsockopt(sock, IPPROTO_TCP, TCP_QUICKACK, US &off, sizeof(off));
+  }
+#endif
+good_response = smtp_read_response(sx, sx->buffer, sizeof(sx->buffer),
   '2', (SOB sx->conn_args.ob)->command_timeout);
 #ifdef EXPERIMENTAL_DSN_INFO
 sx->smtp_greeting = string_copy(sx->buffer);
-- 
2.30.2