CURLOPT_MAXAGE_CONN: set the maximum allowed age for conn reuse

... and disconnect too old ones instead of trying to reuse.

Default max age is set to 118 seconds.

Ref: #3722
Closes #3782

lib/conncache.c

@@ -434,6 +434,7 @@ bool Curl_conncache_return_conn(struct connectdata *conn)
   struct connectdata *conn_candidate = NULL;
 
   conn->data = NULL; /* no owner anymore */
+  conn->lastused = Curl_now(); /* it was used up until now */
   if(maxconnects > 0 &&
      Curl_conncache_size(data) > maxconnects) {
     infof(data, "Connection cache is full, closing the oldest one.\n");
@@ -479,7 +480,7 @@ Curl_conncache_extract_bundle(struct Curl_easy *data,
 
     if(!CONN_INUSE(conn) && !conn->data) {
       /* Set higher score for the age passed since the connection was used */
-      score = Curl_timediff(now, conn->now);
+      score = Curl_timediff(now, conn->lastused);
 
       if(score > highscore) {
         highscore = score;
@@ -537,7 +538,7 @@ Curl_conncache_extract_oldest(struct Curl_easy *data)
 
       if(!CONN_INUSE(conn) && !conn->data) {
         /* Set higher score for the age passed since the connection was used */
-        score = Curl_timediff(now, conn->now);
+        score = Curl_timediff(now, conn->lastused);
 
         if(score > highscore) {
           highscore = score;

lib/setopt.c

@@ -2645,6 +2645,12 @@ static CURLcode vsetopt(struct Curl_easy *data, CURLoption option,
       return CURLE_BAD_FUNCTION_ARGUMENT;
     data->set.upkeep_interval_ms = arg;
     break;
+  case CURLOPT_MAXAGE_CONN:
+    arg = va_arg(param, long);
+    if(arg < 0)
+      return CURLE_BAD_FUNCTION_ARGUMENT;
+    data->set.maxage_conn = arg;
+    break;
   case CURLOPT_TRAILERFUNCTION:
 #ifndef CURL_DISABLE_HTTP
     data->set.trailer_callback = va_arg(param, curl_trailer_callback);

lib/url.c

@@ -541,6 +541,7 @@ CURLcode Curl_init_userdefined(struct Curl_easy *data)
   set->fnmatch = ZERO_NULL;
   set->upkeep_interval_ms = CURL_UPKEEP_INTERVAL_DEFAULT;
   set->maxconnects = DEFAULT_CONNCACHE_SIZE; /* for easy handles */
+  set->maxage_conn = 118;
   set->http09_allowed = TRUE;
   set->httpversion =
 #ifdef USE_NGHTTP2
@@ -958,6 +959,25 @@ static void prune_dead_connections(struct Curl_easy *data)
   }
 }
 
+/* A connection has to have been idle for a shorter time than 'maxage_conn' to
+   be subject for reuse. The success rate is just too low after this. */
+
+static bool conn_maxage(struct Curl_easy *data,
+                        struct connectdata *conn,
+                        struct curltime now)
+{
+  if(!conn->data) {
+    timediff_t idletime = Curl_timediff(now, conn->lastused);
+    idletime /= 1000; /* integer seconds is fine */
+
+    if(idletime/1000 > data->set.maxage_conn) {
+      infof(data, "Too old connection (%ld seconds), disconnect it\n",
+            idletime);
+      return TRUE;
+    }
+  }
+  return FALSE;
+}
 /*
  * Given one filled in connection struct (named needle), this function should
  * detect if there already is one that has all the significant details
@@ -981,6 +1001,7 @@ ConnectionExists(struct Curl_easy *data,
   bool foundPendingCandidate = FALSE;
   bool canmultiplex = IsMultiplexingPossible(data, needle);
   struct connectbundle *bundle;
+  struct curltime now = Curl_now();
 
 #ifdef USE_NTLM
   bool wantNTLMhttp = ((data->state.authhost.want &
@@ -1044,7 +1065,7 @@ ConnectionExists(struct Curl_easy *data,
         /* connect-only connections will not be reused */
         continue;
 
-      if(extract_if_dead(check, data)) {
+      if(conn_maxage(data, check, now) || extract_if_dead(check, data)) {
         /* disconnect it */
         (void)Curl_disconnect(data, check, /* dead_connection */TRUE);
         continue;

lib/urldata.h

@@ -866,6 +866,7 @@ struct connectdata {
 
   struct curltime now;     /* "current" time */
   struct curltime created; /* creation time */
+  struct curltime lastused; /* when returned to the connection cache */
   curl_socket_t sock[2]; /* two sockets, the second is used for the data
                             transfer when doing FTP */
   curl_socket_t tempsock[2]; /* temporary sockets for happy eyeballs */
@@ -1553,6 +1554,8 @@ struct UserDefined {
   long accepttimeout;   /* in milliseconds, 0 means no timeout */
   long happy_eyeballs_timeout; /* in milliseconds, 0 is a valid value */
   long server_response_timeout; /* in milliseconds, 0 means no timeout */
+  long maxage_conn;     /* in seconds, max idle time to allow a connection that
+                           is to be reused */
   long tftp_blksize;    /* in bytes, 0 means use default */
   curl_off_t filesize;  /* size of file to upload, -1 means unknown */
   long low_speed_limit; /* bytes/second */