upkeep: add a connection upkeep API: curl_easy_conn_upkeep()

Add functionality so that protocols can do custom keepalive on their
connections, when an external API function is called.

Add docs for the new options in 7.62.0

Closes #1641

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/http2.c b/lib/http2.c
index d76919300..c74974ef4 100644
--- a/lib/http2.c
+++ b/lib/http2.c
@@ -233,12 +233,43 @@ static unsigned int http2_conncheck(struct connectdata *check,
                                     unsigned int checks_to_perform)
 {
   unsigned int ret_val = CONNRESULT_NONE;
+  struct http_conn *c = &check->proto.httpc;
+  int rc;
+  bool send_frames = false;
 
   if(checks_to_perform & CONNCHECK_ISDEAD) {
     if(http2_connisdead(check))
       ret_val |= CONNRESULT_DEAD;
   }
 
+  if(checks_to_perform & CONNCHECK_KEEPALIVE) {
+    struct curltime now = Curl_now();
+    time_t elapsed = Curl_timediff(now, check->keepalive);
+
+    if(elapsed > check->upkeep_interval_ms) {
+      /* Perform an HTTP/2 PING */
+      rc = nghttp2_submit_ping(c->h2, 0, ZERO_NULL);
+      if(!rc) {
+        /* Successfully added a PING frame to the session. Need to flag this
+           so the frame is sent. */
+        send_frames = true;
+      }
+      else {
+       failf(check->data, "nghttp2_submit_ping() failed: %s(%d)",
+             nghttp2_strerror(rc), rc);
+      }
+
+      check->keepalive = now;
+    }
+  }
+
+  if(send_frames) {
+    rc = nghttp2_session_send(c->h2);
+    if(rc)
+      failf(check->data, "nghttp2_session_send() failed: %s(%d)",
+            nghttp2_strerror(rc), rc);
+  }
+
   return ret_val;
 }