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, 9 insertions, 0 deletions

diff --git a/lib/urldata.h b/lib/urldata.h
index d3a174d24..85712ba20 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -729,6 +729,7 @@ struct Curl_handler {
 
 #define CONNCHECK_NONE 0                 /* No checks */
 #define CONNCHECK_ISDEAD (1<<0)          /* Check if the connection is dead. */
+#define CONNCHECK_KEEPALIVE (1<<1)       /* Perform any keepalive function. */
 
 #define CONNRESULT_NONE 0                /* No extra information. */
 #define CONNRESULT_DEAD (1<<0)           /* The connection is dead. */
@@ -905,6 +906,13 @@ struct connectdata {
 
   long ip_version; /* copied from the Curl_easy at creation time */
 
+  /* Protocols can use a custom keepalive mechanism to keep connections alive.
+     This allows those protocols to track the last time the keepalive mechanism
+     was used on this connection. */
+  struct curltime keepalive;
+
+  long upkeep_interval_ms;      /* Time between calls for connection upkeep. */
+
   /**** curl_get() phase fields */
 
   curl_socket_t sockfd;   /* socket to read from or CURL_SOCKET_BAD */
@@ -1704,6 +1712,7 @@ struct UserDefined {
                                                   before resolver start */
   void *resolver_start_client; /* pointer to pass to resolver start callback */
   bool disallow_username_in_url; /* disallow username in url */
+  long upkeep_interval_ms;      /* Time between calls for connection upkeep. */
   bool doh; /* DNS-over-HTTPS enabled */
   bool doh_get; /* use GET for DoH requests, instead of POST */
   multidone_func fmultidone;