libssh2: handle the SSH protocols done over HTTPS proxy

Reported-by: Robin Douine
Fixes #4295
Closes #6021

lib/vssh/libssh2.c

@@ -3039,6 +3039,42 @@ static CURLcode ssh_setup_connection(struct connectdata *conn)
 static Curl_recv scp_recv, sftp_recv;
 static Curl_send scp_send, sftp_send;
 
+static ssize_t ssh_tls_recv(libssh2_socket_t sock, void *buffer,
+                            size_t length, int flags, void **abstract)
+{
+  struct connectdata *conn = (struct connectdata *)*abstract;
+  ssize_t nread;
+  CURLcode result;
+  (void)flags;
+
+  result = Curl_read(conn, sock, buffer, length, &nread);
+  if(result == CURLE_AGAIN)
+    return -EAGAIN; /* magic return code for libssh2 */
+  else if(result)
+    return -1; /* generic error */
+  if(conn->data->set.verbose)
+    Curl_debug(conn->data, CURLINFO_DATA_IN, (char *)buffer, (size_t)nread);
+  return nread;
+}
+
+static ssize_t ssh_tls_send(libssh2_socket_t sock, const void *buffer,
+                            size_t length, int flags, void **abstract)
+{
+  struct connectdata *conn = (struct connectdata *)*abstract;
+  ssize_t nwrite;
+  CURLcode result;
+  (void)flags;
+
+  result = Curl_write(conn, sock, buffer, length, &nwrite);
+  if(result == CURLE_AGAIN)
+    return -EAGAIN; /* magic return code for libssh2 */
+  else if(result)
+    return -1; /* error */
+  if(conn->data->set.verbose)
+    Curl_debug(conn->data, CURLINFO_DATA_OUT, (char *)buffer, (size_t)nwrite);
+  return nwrite;
+}
+
 /*
  * Curl_ssh_connect() gets called from Curl_protocol_connect() to allow us to
  * do protocol-specific actions at connect-time.
@@ -3060,14 +3096,6 @@ static CURLcode ssh_connect(struct connectdata *conn, bool *done)
      function to make the re-use checks properly be able to check this bit. */
   connkeep(conn, "SSH default");
 
-  if(conn->handler->protocol & CURLPROTO_SCP) {
-    conn->recv[FIRSTSOCKET] = scp_recv;
-    conn->send[FIRSTSOCKET] = scp_send;
-  }
-  else {
-    conn->recv[FIRSTSOCKET] = sftp_recv;
-    conn->send[FIRSTSOCKET] = sftp_send;
-  }
   ssh = &conn->proto.sshc;
 
 #ifdef CURL_LIBSSH2_DEBUG
@@ -3088,6 +3116,53 @@ static CURLcode ssh_connect(struct connectdata *conn, bool *done)
     return CURLE_FAILED_INIT;
   }
 
+  if(conn->http_proxy.proxytype == CURLPROXY_HTTPS) {
+    /*
+     * This crazy union dance is here to avoid assigning a void pointer a
+     * function pointer as it is invalid C. The problem is of course that
+     * libssh2 has such an API...
+     */
+    union receive {
+      void *recvp;
+      ssize_t (*recvptr)(libssh2_socket_t, void *, size_t, int, void **);
+    };
+    union transfer {
+      void *sendp;
+      ssize_t (*sendptr)(libssh2_socket_t, const void *, size_t, int, void **);
+    };
+    union receive sshrecv;
+    union transfer sshsend;
+
+    sshrecv.recvptr = ssh_tls_recv;
+    sshsend.sendptr = ssh_tls_send;
+
+    infof(data, "Uses HTTPS proxy!\n");
+    /*
+      Setup libssh2 callbacks to make it read/write TLS from the socket.
+
+      ssize_t
+      recvcb(libssh2_socket_t sock, void *buffer, size_t length,
+      int flags, void **abstract);
+
+      ssize_t
+      sendcb(libssh2_socket_t sock, const void *buffer, size_t length,
+      int flags, void **abstract);
+
+    */
+    libssh2_session_callback_set(ssh->ssh_session,
+                                 LIBSSH2_CALLBACK_RECV, sshrecv.recvp);
+    libssh2_session_callback_set(ssh->ssh_session,
+                                 LIBSSH2_CALLBACK_SEND, sshsend.sendp);
+  }
+  else if(conn->handler->protocol & CURLPROTO_SCP) {
+    conn->recv[FIRSTSOCKET] = scp_recv;
+    conn->send[FIRSTSOCKET] = scp_send;
+  }
+  else {
+    conn->recv[FIRSTSOCKET] = sftp_recv;
+    conn->send[FIRSTSOCKET] = sftp_send;
+  }
+
   if(data->set.ssh_compression) {
 #if LIBSSH2_VERSION_NUM >= 0x010208
     if(libssh2_session_flag(ssh->ssh_session, LIBSSH2_FLAG_COMPRESS, 1) < 0)