lib: connection filters (cfilter) addition to curl:

- general construct/destroy in connectdata
 - default implementations of callback functions
 - connect: cfilters for connect and accept
 - socks: cfilter for socks proxying
 - http_proxy: cfilter for http proxy tunneling
 - vtls: cfilters for primary and proxy ssl
 - change in general handling of data/conn
 - Curl_cfilter_setup() sets up filter chain based on data settings,
   if none are installed by the protocol handler setup
 - Curl_cfilter_connect() boot straps filters into `connected` status,
   used by handlers and multi to reach further stages
 - Curl_cfilter_is_connected() to check if a conn is connected,
   e.g. all filters have done their work
 - Curl_cfilter_get_select_socks() gets the sockets and READ/WRITE
   indicators for multi select to work
 - Curl_cfilter_data_pending() asks filters if the have incoming
   data pending for recv
 - Curl_cfilter_recv()/Curl_cfilter_send are the general callbacks
   installed in conn->recv/conn->send for io handling
 - Curl_cfilter_attach_data()/Curl_cfilter_detach_data() inform filters
   and addition/removal of a `data` from their connection
 - adding vtl functions to prevent use of Curl_ssl globals directly
   in other parts of the code.

Reviewed-by: Daniel Stenberg
Closes #9855

lib/file.c

@@ -150,9 +150,19 @@ static CURLcode file_connect(struct Curl_easy *data, bool *done)
   char *actual_path;
 #endif
   size_t real_path_len;
+  CURLcode result;
 
-  CURLcode result = Curl_urldecode(data->state.up.path, 0, &real_path,
-                                   &real_path_len, REJECT_ZERO);
+  if(file->path) {
+    /* already connected.
+     * the handler->connect_it() is normally only called once, but
+     * FILE does a special check on setting up the connection which
+     * calls this explicitly. */
+    *done = TRUE;
+    return CURLE_OK;
+  }
+
+  result = Curl_urldecode(data->state.up.path, 0, &real_path,
+                          &real_path_len, REJECT_ZERO);
   if(result)
     return result;
 
@@ -226,6 +236,7 @@ static CURLcode file_connect(struct Curl_easy *data, bool *done)
   file->path = real_path;
   #endif
 #endif
+  Curl_safefree(file->freepath);
   file->freepath = real_path; /* free this when done */
 
   file->fd = fd;