Based on Daniel's patch, provide a Curl_reset_reqproto() function that frees
data->reqdata.proto.* on connection setup if needed (that is if the
SessionHandle was used by a different connection).
---
 lib/file.c    |   28 +++++++++++++++-------------
 lib/ftp.c     |   10 +++++-----
 lib/http.c    |    7 +++++--
 lib/ssh.c     |    7 +++----
 lib/url.c     |   14 ++++++++++++++
 lib/url.h     |    5 +++++
 lib/urldata.h |    2 ++
 7 files changed, 49 insertions(+), 24 deletions(-)

--- lib/file.c.orig
+++ lib/file.c
@@ -125,8 +125,8 @@ const struct Curl_handler Curl_handler_f
  */
 CURLcode Curl_file_connect(struct connectdata *conn)
 {
-  char *real_path = curl_easy_unescape(conn->data, conn->data->reqdata.path, 0,
-                                       NULL);
+  struct SessionHandle *data = conn->data;
+  char *real_path = curl_easy_unescape(data, data->reqdata.path, 0, NULL);
   struct FILEPROTO *file;
   int fd;
 #if defined(WIN32) || defined(MSDOS) || defined(__EMX__)
@@ -137,17 +137,19 @@ CURLcode Curl_file_connect(struct connec
   if(!real_path)
     return CURLE_OUT_OF_MEMORY;
 
-  file = (struct FILEPROTO *)calloc(sizeof(struct FILEPROTO), 1);
-  if(!file) {
-    free(real_path);
-    return CURLE_OUT_OF_MEMORY;
+  /* If there already is a protocol-specific struct allocated for this
+     sessionhandle, deal with it */
+  Curl_reset_reqproto(conn);
+
+  if (!data->reqdata.proto.file) {
+    file = (struct FILEPROTO *)calloc(sizeof(struct FILEPROTO), 1);
+    if(!file) {
+      free(real_path);
+      return CURLE_OUT_OF_MEMORY;
+    }
+    data->reqdata.proto.file = file;
   }
 
-  if (conn->data->reqdata.proto.file)
-    free(conn->data->reqdata.proto.file);
-
-  conn->data->reqdata.proto.file = file;
-
 #if defined(WIN32) || defined(MSDOS) || defined(__EMX__)
   /* If the first character is a slash, and there's
      something that looks like a drive at the beginning of
@@ -186,8 +188,8 @@ CURLcode Curl_file_connect(struct connec
   file->freepath = real_path; /* free this when done */
 
   file->fd = fd;
-  if(!conn->data->set.upload && (fd == -1)) {
-    failf(conn->data, "Couldn't open file %s", conn->data->reqdata.path);
+  if(!data->set.upload && (fd == -1)) {
+    failf(data, "Couldn't open file %s", data->reqdata.path);
     Curl_file_done(conn, CURLE_FILE_COULDNT_READ_FILE, FALSE);
     return CURLE_FILE_COULDNT_READ_FILE;
   }
--- lib/ftp.c.orig
+++ lib/ftp.c
@@ -90,6 +90,7 @@
 #include "parsedate.h" /* for the week day and month names */
 #include "sockaddr.h" /* required for Curl_sockaddr_storage */
 #include "multiif.h"
+#include "url.h"
 
 #if defined(HAVE_INET_NTOA_R) && !defined(HAVE_INET_NTOA_R_DECL)
 #include "inet_ntoa_r.h"
@@ -3047,11 +3048,9 @@ static CURLcode Curl_ftp_connect(struct 
 
   *done = FALSE; /* default to not done yet */
 
-  if (data->reqdata.proto.ftp) {
-    Curl_ftp_disconnect(conn);
-    free(data->reqdata.proto.ftp);
-    data->reqdata.proto.ftp = NULL;
-  }
+  /* If there already is a protocol-specific struct allocated for this
+     sessionhandle, deal with it */
+  Curl_reset_reqproto(conn);
 
   result = ftp_init(conn);
   if(result)
@@ -3602,6 +3601,7 @@ static CURLcode Curl_ftp(struct connectd
     make sure we have a good 'struct FTP' to play with. For new connections,
     the struct FTP is allocated and setup in the Curl_ftp_connect() function.
   */
+  Curl_reset_reqproto(conn);
   retcode = ftp_init(conn);
   if(retcode)
     return retcode;
--- lib/http.c.orig
+++ lib/http.c
@@ -1894,13 +1894,16 @@ CURLcode Curl_http(struct connectdata *c
      the rest of the request in the PERFORM phase. */
   *done = TRUE;
 
+  /* If there already is a protocol-specific struct allocated for this
+     sessionhandle, deal with it */
+  Curl_reset_reqproto(conn);
+
   if(!data->reqdata.proto.http) {
     /* Only allocate this struct if we don't already have it! */
 
-    http = (struct HTTP *)malloc(sizeof(struct HTTP));
+    http = (struct HTTP *)calloc(sizeof(struct HTTP), 1);
     if(!http)
       return CURLE_OUT_OF_MEMORY;
-    memset(http, 0, sizeof(struct HTTP));
     data->reqdata.proto.http = http;
   }
   else
--- lib/ssh.c.orig
+++ lib/ssh.c
@@ -1846,10 +1846,9 @@ static CURLcode Curl_ssh_connect(struct 
   CURLcode result;
   struct SessionHandle *data = conn->data;
 
-  if (data->reqdata.proto.ssh) {
-    Curl_safefree(data->reqdata.proto.ssh);
-    data->reqdata.proto.ssh = NULL;
-  }
+  /* If there already is a protocol-specific struct allocated for this
+     sessionhandle, deal with it */
+  Curl_reset_reqproto(conn);
 
   result = ssh_init(conn);
   if (result)
--- lib/url.c.orig
+++ lib/url.c
@@ -1998,6 +1998,7 @@ static void conn_free(struct connectdata
   if(CURL_SOCKET_BAD != conn->sock[FIRSTSOCKET])
     sclose(conn->sock[FIRSTSOCKET]);
 
+  conn->data->reqdata.current_conn = NULL;
   Curl_safefree(conn->user);
   Curl_safefree(conn->passwd);
   Curl_safefree(conn->proxyuser);
@@ -4446,3 +4447,16 @@ CURLcode Curl_do_more(struct connectdata
 
   return result;
 }
+
+/* Called on connect, and if there's already a protocol-specific struct
+   allocated for a different connection, this frees it that it can be setup
+   properly later on. */
+void Curl_reset_reqproto(struct connectdata *conn)
+{
+  struct SessionHandle *data = conn->data;
+  if (data->reqdata.proto.generic && data->reqdata.current_conn != conn) {
+    free(data->reqdata.proto.generic);
+    data->reqdata.proto.generic = NULL;
+  }
+  data->reqdata.current_conn = conn;
+}
--- lib/url.h.orig
+++ lib/url.h
@@ -84,4 +84,9 @@ CURLcode Curl_doing_fdset(struct connect
                           int *max_fdp);
 #endif
 
+/* Called on connect, and if there's already a protocol-specific struct
+   allocated for a different connection, this frees it that it can be setup
+   properly later on. */
+void Curl_reset_reqproto(struct connectdata *conn);
+
 #endif
--- lib/urldata.h.orig
+++ lib/urldata.h
@@ -807,6 +807,8 @@ struct HandleData {
     void *generic;
     struct SSHPROTO *ssh;
   } proto;
+  /* current user of this HandleData instance, or NULL */
+  struct connectdata *current_conn;
 };
 
 /*