CURLMOPT_MAXCONNECTS: restore functionality

When a connection is no longer used, it is kept in the cache. If the
cache is full, the oldest idle connection is closed. If no connection is
idle, the current one is closed instead.

lib/url.c

@@ -122,6 +122,7 @@ int curl_win32_idn_to_ascii(const char *in, char **out);
 #include "http_proxy.h"
 #include "bundles.h"
 #include "conncache.h"
+#include "multihandle.h"
 
 #define _MPRINTF_REPLACE /* use our functions only */
 #include <curl/mprintf.h>
@@ -131,6 +132,8 @@ int curl_win32_idn_to_ascii(const char *in, char **out);
 #include "memdebug.h"
 
 /* Local static prototypes */
+static struct connectdata *
+find_oldest_idle_connection(struct SessionHandle *data);
 static void conn_free(struct connectdata *conn);
 static void signalPipeClose(struct curl_llist *pipeline, bool pipe_broke);
 static CURLcode do_init(struct connectdata *conn);
@@ -2710,6 +2713,57 @@ static void signalPipeClose(struct curl_llist *pipeline, bool pipe_broke)
   }
 }
 
+/*
+ * This function kills and removes an existing connection in the connection
+ * cache. The connection that has been unused for the longest time.
+ *
+ * Returns the pointer to the oldest idle connection, or NULL if none was
+ * found.
+ */
+static struct connectdata *
+find_oldest_idle_connection(struct SessionHandle *data)
+{
+  struct conncache *bc = data->state.conn_cache;
+  struct curl_hash_iterator iter;
+  struct curl_llist_element *curr;
+  struct curl_hash_element *he;
+  long highscore=-1;
+  long score;
+  struct timeval now;
+  struct connectdata *conn_candidate = NULL;
+  struct connectbundle *bundle;
+
+  now = Curl_tvnow();
+
+  Curl_hash_start_iterate(bc->hash, &iter);
+
+  he = Curl_hash_next_element(&iter);
+  while(he) {
+    struct connectdata *conn;
+
+    bundle = he->ptr;
+
+    curr = bundle->conn_list->head;
+    while(curr) {
+      conn = curr->ptr;
+
+      if(!conn->inuse) {
+        /* Set higher score for the age passed since the connection was used */
+        score = Curl_tvdiff(now, conn->now);
+
+        if(score > highscore) {
+          highscore = score;
+          conn_candidate = conn;
+        }
+      }
+      curr = curr->next;
+    }
+
+    he = Curl_hash_next_element(&iter);
+  }
+
+  return conn_candidate;
+}
 
 /*
  * Given one filled in connection struct (named needle), this function should
@@ -2961,11 +3015,35 @@ ConnectionExists(struct SessionHandle *data,
   return FALSE; /* no matching connecting exists */
 }
 
-/* this connection can now be marked 'idle' */
-static void
-ConnectionDone(struct connectdata *conn)
+/* Mark the connection as 'idle', or close it if the cache is full.
+   Returns TRUE if the connection is kept, or FALSE if it was closed. */
+static bool
+ConnectionDone(struct SessionHandle *data, struct connectdata *conn)
 {
+  /* data->multi->maxconnects can be negative, deal with it. */
+  size_t maxconnects =
+    (data->multi->maxconnects < 0) ? 0 : data->multi->maxconnects;
+  struct connectdata *conn_candidate = NULL;
+
+  /* Mark the current connection as 'unused' */
   conn->inuse = FALSE;
+
+  if(maxconnects > 0 &&
+     data->state.conn_cache->num_connections > maxconnects) {
+    infof(data, "Connection cache is full, closing the oldest one.\n");
+
+    conn_candidate = find_oldest_idle_connection(data);
+
+    if(conn_candidate) {
+      /* Set the connection's owner correctly */
+      conn_candidate->data = data;
+
+      /* the winner gets the honour of being disconnected */
+      (void)Curl_disconnect(conn_candidate, /* dead_connection */ FALSE);
+    }
+  }
+
+  return (conn_candidate == conn) ? FALSE : TRUE;
 }
 
 /*
@@ -4907,6 +4985,7 @@ static CURLcode create_conn(struct SessionHandle *data,
      * This is a brand new connection, so let's store it in the connection
      * cache of ours!
      */
+    conn->inuse = TRUE;
     ConnectionStore(data, conn);
   }
 
@@ -5182,14 +5261,17 @@ CURLcode Curl_done(struct connectdata **connp,
       result = res2;
   }
   else {
-    ConnectionDone(conn); /* the connection is no longer in use */
+    /* the connection is no longer in use */
+    if(ConnectionDone(data, conn)) {
+      /* remember the most recently used connection */
+      data->state.lastconnect = conn;
 
-    /* remember the most recently used connection */
-    data->state.lastconnect = conn;
-
-    infof(data, "Connection #%ld to host %s left intact\n",
-          conn->connection_id,
-          conn->bits.httpproxy?conn->proxy.dispname:conn->host.dispname);
+      infof(data, "Connection #%ld to host %s left intact\n",
+            conn->connection_id,
+            conn->bits.httpproxy?conn->proxy.dispname:conn->host.dispname);
+    }
+    else
+      data->state.lastconnect = NULL;
   }
 
   *connp = NULL; /* to make the caller of this function better detect that