From a4eeaac87ca38a21a7515d5512599846ed9fdc0b Mon Sep 17 00:00:00 2001
From: Brendan McDonnell <35789100+bmcdonnell@users.noreply.github.com>
Date: Tue, 2 Jul 2024 17:47:14 -0400
Subject: [PATCH] When SO_LINGER is enabled w/ linger time = 0, do hard
 disconnect regardless of whether there's any pending or unacked data

References:
 - Wright & Stevens, "TCP/IP Illustrated, Volume 2"
   - 30.4. tcp_disconnect Function
     - Figure 30.12. tcp_disconnect function: initiate TCP disconnect.
	 - "Hard disconnect" section
 - UNIX Network Programming / Volume 1, Third Edition: The Sockets Networking API
   (aka "UNP")
   - 7.5 Generic Socket Options
     - "SO_LINGER Socket Option" section
---
 src/api/api_msg.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 8092be96..f0e0b5c8 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -981,14 +981,14 @@ lwip_netconn_do_close_internal(struct netconn *conn  WRITE_DELAYED_PARAM)
 #if LWIP_SO_LINGER
     /* check linger possibilities before calling tcp_close */
     err = ERR_OK;
-    /* linger enabled/required at all? (i.e. is there untransmitted data left?) */
-    if ((conn->linger >= 0) && (conn->pcb.tcp->unsent || conn->pcb.tcp->unacked)) {
+    /* linger enabled? */
+    if (conn->linger >= 0) {
       if ((conn->linger == 0)) {
-        /* data left but linger prevents waiting */
+        /* 0-timeout linger prevents waiting */
         tcp_abort(tpcb);
         tpcb = NULL;
-      } else if (conn->linger > 0) {
-        /* data left and linger says we should wait */
+      } else if (conn->pcb.tcp->unsent || conn->pcb.tcp->unacked) {
+        /* data left and nonzero linger says we should wait */
         if (netconn_is_nonblocking(conn)) {
           /* data left on a nonblocking netconn -> cannot linger */
           err = ERR_WOULDBLOCK;