From fa0f7ee6dba3ba14a6fc1172e04a161f514d94b0 Mon Sep 17 00:00:00 2001
From: Dirk Engling <erdgeist@erdgeist.org>
Date: Tue, 27 Oct 2026 03:05:43 +0100
Subject: Revive http keep alive to save tcp connection setup costs

---
 opentracker.c | 17 ++++++++++++-----
 ot_http.c     | 26 ++++++++++++++++++--------
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/opentracker.c b/opentracker.c
index 21eeb42..11da486 100644
--- a/opentracker.c
+++ b/opentracker.c
@@ -177,12 +177,13 @@ static void handle_read(const int64_t sock, struct ot_workstruct *ws) {
 }
 
 static void handle_write(const int64_t sock) {
-  struct http_data *cookie = fdstate_cookie(sock);
-  int               chunked = 0;
+  struct http_data *cookie     = fdstate_cookie(sock);
+  int               chunked    = 0;
+  int               keep_alive = 0;
 
   if (cookie) {
-    if (cookie->flag & STRUCT_HTTP_FLAG_CHUNKED_IN_TRANSFER)
-      chunked = 1;
+    chunked    = (cookie->flag & STRUCT_HTTP_FLAG_CHUNKED_IN_TRANSFER) != 0;
+    keep_alive = (cookie->flag & STRUCT_HTTP_FLAG_KEEPALIVE) != 0;
 
     if (cookie->batch) {
       if (batch_send(sock, cookie->batch) == BATCH_FAILED) {
@@ -197,7 +198,13 @@ static void handle_write(const int64_t sock) {
   /* In a chunked transfer, wait for the next piece once everything queued has gone out */
   if (chunked)
     http_interest_drop(sock, cookie, EVENT_OUT);
-  else
+  else if (keep_alive) {
+    /* The reply is out and the client asked to keep the connection, so stop
+       waiting to write and go back to waiting for the next request */
+    http_interest_drop(sock, cookie, EVENT_OUT);
+    http_interest_add(sock, cookie, EVENT_IN);
+    fdstate_set_expiry(sock, g_now_seconds + OT_CLIENT_TIMEOUT);
+  } else
     handle_dead(sock);
 }
 
diff --git a/ot_http.c b/ot_http.c
index 36819c7..14952b5 100644
--- a/ot_http.c
+++ b/ot_http.c
@@ -727,6 +727,24 @@ ssize_t http_handle_request(const int64_t sock, struct ot_workstruct *ws) {
   /* Tell subroutines where to put reply data */
   ws->reply = ws->outbuf + SUCCESS_HTTP_HEADER_LENGTH;
 
+  /* Find out if the client wants to keep this connection alive, before any
+     subroutine gets to answer: an error reply finishes with the connection
+     on its way out, and ws outlives the connection it was serving */
+  ws->keep_alive = 0;
+#ifdef WANT_KEEPALIVE
+  if ((write_ptr = http_header(ws->request, ws->header_size, "connection")) && (*write_ptr == 'K' || *write_ptr == 'k'))
+    ws->keep_alive = 1;
+#endif
+  {
+    struct http_data *connection = fdstate_cookie(sock);
+    if (connection) {
+      if (ws->keep_alive)
+        connection->flag |= STRUCT_HTTP_FLAG_KEEPALIVE;
+      else
+        connection->flag &= ~STRUCT_HTTP_FLAG_KEEPALIVE;
+    }
+  }
+
   /* This one implicitely tests strlen < 5, too -- remember, it is \n terminated */
   if (memcmp(read_ptr, "GET /", 5))
     HTTPERROR_400;
@@ -763,14 +781,6 @@ ssize_t http_handle_request(const int64_t sock, struct ot_workstruct *ws) {
   else
     HTTPERROR_404;
 
-  /* Find out if the client wants to keep this connection alive */
-  ws->keep_alive = 0;
-#ifdef WANT_KEEPALIVE
-  read_ptr = http_header(ws->request, ws->header_size, "connection");
-  if (read_ptr && (*read_ptr == 'K' || *read_ptr == 'k'))
-    ws->keep_alive = 1;
-#endif
-
   /* If routines handled sending themselves, just return */
   if (ws->reply_size == -2)
     return 0;
-- 
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