GUACAMOLE-221: Add protocol functions for sending prompt to client.

src/common-ssh/common-ssh/ssh.h

@@ -26,21 +26,16 @@
 #include <libssh2.h>
 
 /**
- * Handler for retrieving additional credentials.
+ * A handler function for retrieving additional credentials for the client.
  * 
  * @param client
  *     The Guacamole Client associated with this need for additional
  *     credentials.
  * 
  * @param cred_name
- *     The name of the credential being requested, which will be shared
+ *     The connection parameter that is being requested from the client.
- *     with the client in order to generate a meaningful prompt.
- * 
- * @return
- *     A newly-allocated string containing the credentials provided by
- *     the user, which must be freed by a call to free().
  */
-typedef char* guac_ssh_credential_handler(guac_client* client, char* cred_name);
+typedef void guac_ssh_credential_handler(guac_client* client, char* cred_name);
 
 /**
  * An SSH session, backed by libssh2 and associated with a particular

src/common-ssh/ssh.c

@@ -360,7 +360,7 @@ static int guac_common_ssh_authenticate(guac_common_ssh_session* common_session)
 
     /* Attempt authentication with username + password. */
     if (user->password == NULL && common_session->credential_handler)
-            user->password = common_session->credential_handler(client, "Password: ");
+        common_session->credential_handler(client, "password");
     
     /* Authenticate with password, if provided */
     if (user->password != NULL) {

src/libguac/guacamole/protocol.h

@@ -794,6 +794,22 @@ int guac_protocol_send_push(guac_socket* socket, const guac_layer* layer);
 int guac_protocol_send_rect(guac_socket* socket, const guac_layer* layer,
         int x, int y, int width, int height);
 
+/**
+ * Sends a "required" instruction over the given guac_socket connection.  This
+ * instruction indicates to the client that one or more additional parameters
+ * is needed to continue the connection.
+ * 
+ * @param socket
+ *     The guac_socket connection to use.
+ * 
+ * @param required
+ *     The name of the parameter that is required.
+ * 
+ * @return
+ *     Zero on success, non-zero on error.
+ */
+int guac_protocol_send_required(guac_socket* socket, const char* required);
+
 /**
  * Sends a reset instruction over the given guac_socket connection.
  *

src/libguac/protocol.c

@@ -961,6 +961,21 @@ int guac_protocol_send_rect(guac_socket* socket,
 
 }
 
+int guac_protocol_send_required(guac_socket* socket, const char* required) {
+    
+    int ret_val;
+    
+    guac_socket_instruction_begin(socket);
+    ret_val =
+            guac_socket_write_string(socket, "8.required,")
+        || __guac_socket_write_length_string(socket, required)
+        || guac_socket_write_string(socket, ";");
+    
+    guac_socket_instruction_end(socket);
+    return ret_val;
+    
+}
+
 int guac_protocol_send_reset(guac_socket* socket, const guac_layer* layer) {
 
     int ret_val;

src/protocols/rdp/Makefile.am

@@ -38,6 +38,7 @@ nodist_libguac_client_rdp_la_SOURCES =  \
     _generated_keymaps.c
 
 libguac_client_rdp_la_SOURCES =                  \
+    argv.c										 \
     beep.c                                       \
     bitmap.c                                     \
     channels/audio-input/audio-buffer.c          \
@@ -82,6 +83,7 @@ libguac_client_rdp_la_SOURCES =                  \
     user.c
 
 noinst_HEADERS =                                 \
+    argv.h										 \
     beep.h                                       \
     bitmap.h                                     \
     channels/audio-input/audio-buffer.h          \

src/protocols/rdp/argv.c

@@ -0,0 +1,189 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#include "config.h"
+#include "argv.h"
+#include "rdp.h"
+
+#include <guacamole/protocol.h>
+#include <guacamole/socket.h>
+#include <guacamole/user.h>
+
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+
+/**
+ * All RDP connection settings which may be updated by unprivileged users
+ * through "argv" streams.
+ */
+typedef enum guac_rdp_argv_setting {
+
+    /**
+     * The username of the connection.
+     */
+    GUAC_RDP_ARGV_SETTING_USERNAME,
+            
+    /**
+     * The password to authenticate the connection.
+     */
+    GUAC_RDP_ARGV_SETTING_PASSWORD,
+            
+    /**
+     * The domain to use for connection authentication.
+     */
+    GUAC_RDP_ARGV_SETTING_DOMAIN
+
+} guac_rdp_argv_setting;
+
+/**
+ * The value or current status of a connection parameter received over an
+ * "argv" stream.
+ */
+typedef struct guac_rdp_argv {
+
+    /**
+     * The specific setting being updated.
+     */
+    guac_rdp_argv_setting setting;
+
+    /**
+     * Buffer space for containing the received argument value.
+     */
+    char buffer[GUAC_RDP_ARGV_MAX_LENGTH];
+
+    /**
+     * The number of bytes received so far.
+     */
+    int length;
+
+} guac_rdp_argv;
+
+/**
+ * Handler for "blob" instructions which appends the data from received blobs
+ * to the end of the in-progress argument value buffer.
+ *
+ * @see guac_user_blob_handler
+ */
+static int guac_rdp_argv_blob_handler(guac_user* user,
+        guac_stream* stream, void* data, int length) {
+
+    guac_rdp_argv* argv = (guac_rdp_argv*) stream->data;
+    
+    /* Calculate buffer size remaining, including space for null terminator,
+     * adjusting received length accordingly */
+    int remaining = sizeof(argv->buffer) - argv->length - 1;
+    if (length > remaining)
+        length = remaining;
+
+    /* Append received data to end of buffer */
+    memcpy(argv->buffer + argv->length, data, length);
+    argv->length += length;
+
+    return 0;
+
+}
+
+/**
+ * Handler for "end" instructions which applies the changes specified by the
+ * argument value buffer associated with the stream.
+ *
+ * @see guac_user_end_handler
+ */
+static int guac_rdp_argv_end_handler(guac_user* user,
+        guac_stream* stream) {
+
+    guac_client* client = user->client;
+    guac_rdp_client* rdp_client = (guac_rdp_client*) client->data;
+    guac_rdp_settings* settings = rdp_client->settings;
+    
+    /* Append null terminator to value */
+    guac_rdp_argv* argv = (guac_rdp_argv*) stream->data;
+    argv->buffer[argv->length] = '\0';
+
+    /* Apply changes to chosen setting */
+    switch (argv->setting) {
+
+        /* Update RDP username. */
+        case GUAC_RDP_ARGV_SETTING_USERNAME:
+            free(settings->username);
+            settings->username = malloc(strlen(argv->buffer) * sizeof(char));
+            strcpy(settings->username, argv->buffer);
+            pthread_cond_broadcast(&(rdp_client->rdp_cond));
+            break;
+            
+        case GUAC_RDP_ARGV_SETTING_PASSWORD:
+            free(settings->password);
+            settings->password = malloc(strlen(argv->buffer) * sizeof(char));
+            strcpy(settings->password, argv->buffer);
+            pthread_cond_broadcast(&(rdp_client->rdp_cond));
+            break;
+            
+        case GUAC_RDP_ARGV_SETTING_DOMAIN:
+            free(settings->domain);
+            settings->domain = malloc(strlen(argv->buffer) * sizeof(char));
+            strcpy(settings->domain, argv->buffer);
+            pthread_cond_broadcast(&(rdp_client->rdp_cond));
+            break;
+            
+    }
+
+    free(argv);
+    return 0;
+
+}
+
+int guac_rdp_argv_handler(guac_user* user, guac_stream* stream,
+        char* mimetype, char* name) {
+
+    guac_rdp_argv_setting setting;
+
+    /* Allow users to update authentication details */
+    if (strcmp(name, "username") == 0)
+        setting = GUAC_RDP_ARGV_SETTING_USERNAME;
+    else if (strcmp(name, "password") == 0)
+        setting = GUAC_RDP_ARGV_SETTING_PASSWORD;
+    else if (strcmp(name, "domain") == 0)
+        setting = GUAC_RDP_ARGV_SETTING_DOMAIN;
+
+    /* No other connection parameters may be updated */
+    else {
+        guac_protocol_send_ack(user->socket, stream, "Not allowed.",
+                GUAC_PROTOCOL_STATUS_CLIENT_FORBIDDEN);
+        guac_socket_flush(user->socket);
+        return 0;
+    }
+
+    guac_rdp_argv* argv = malloc(sizeof(guac_rdp_argv));
+    argv->setting = setting;
+    argv->length = 0;
+
+    /* Prepare stream to receive argument value */
+    stream->blob_handler = guac_rdp_argv_blob_handler;
+    stream->end_handler = guac_rdp_argv_end_handler;
+    stream->data = argv;
+
+    /* Signal stream is ready */
+    guac_protocol_send_ack(user->socket, stream, "Ready for updated "
+            "parameter.", GUAC_PROTOCOL_STATUS_SUCCESS);
+    guac_socket_flush(user->socket);
+    return 0;
+
+}
+

src/protocols/rdp/argv.h

@@ -0,0 +1,41 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+
+#ifndef GUAC_RDP_ARGV_H
+#define GUAC_RDP_ARGV_H
+
+#include "config.h"
+
+#include <guacamole/user.h>
+
+/**
+ * The maximum number of bytes to allow for any argument value received via an
+ * argv stream, including null terminator.
+ */
+#define GUAC_RDP_ARGV_MAX_LENGTH 16384
+
+/**
+ * Handles an incoming stream from a Guacamole "argv" instruction, updating the
+ * given connection parameter if that parameter is allowed to be updated.
+ */
+guac_user_argv_handler guac_rdp_argv_handler;
+
+#endif
+

src/protocols/rdp/client.c

@@ -158,6 +158,10 @@ int guac_client_init(guac_client* client, int argc, char** argv) {
     /* Initalize the lock */
     pthread_rwlock_init(&(rdp_client->lock), NULL);
 
+    /* Init RDP credential lock and condition */
+    pthread_mutex_init(&(rdp_client->rdp_credential_lock), &(rdp_client->attributes));
+    pthread_cond_init(&(rdp_client->rdp_credential_cond), NULL);;
+
     /* Set handlers */
     client->join_handler = guac_rdp_user_join_handler;
     client->free_handler = guac_rdp_client_free_handler;
@@ -219,6 +223,9 @@ int guac_rdp_client_free_handler(guac_client* client) {
     if (rdp_client->audio_input != NULL)
         guac_rdp_audio_buffer_free(rdp_client->audio_input);
     
+    /* Destroy the pthread conditional handler */
+    pthread_cond_destroy(&(rdp_client->rdp_cond));
+
     pthread_rwlock_destroy(&(rdp_client->lock));
 
     /* Free client data */

src/protocols/rdp/rdp.c

@@ -66,6 +66,7 @@
 #include <freerdp/update.h>
 #include <guacamole/audio.h>
 #include <guacamole/client.h>
+#include <guacamole/parser.h>
 #include <guacamole/protocol.h>
 #include <guacamole/socket.h>
 #include <guacamole/timestamp.h>
@@ -227,10 +228,34 @@ static BOOL rdp_freerdp_authenticate(freerdp* instance, char** username,
 
     rdpContext* context = instance->context;
     guac_client* client = ((rdp_freerdp_context*) context)->client;
+    guac_rdp_client* rdp_client = (guac_rdp_client*) client->data;
+    guac_rdp_settings* settings = rdp_client->settings;
+    
+    pthread_mutex_lock(&(rdp_client->rdp_lock));
+    
+    while (settings->username == NULL || strcmp(settings->username, "") == 0) {
+        guac_protocol_send_required(client->socket, "username");
+        guac_socket_flush(client->socket);
+        pthread_cond_wait(&(rdp_client->rdp_cond), &(rdp_client->rdp_lock));
+        *username = settings->username;
+    }
+    
+    while (settings->password == NULL || strcmp(settings->password, "") == 0) {
+        guac_protocol_send_required(client->socket, "password");
+        guac_socket_flush(client->socket);
+        pthread_cond_wait(&(rdp_client->rdp_cond), &(rdp_client->rdp_lock));
+        *password = settings->password;
+    }
+    
+    while (settings->domain == NULL || strcmp(settings->domain, "") == 0) {
+        guac_protocol_send_required(client->socket, "domain");
+        guac_socket_flush(client->socket);
+        pthread_cond_wait(&(rdp_client->rdp_cond), &(rdp_client->rdp_lock));
+        *domain = settings->domain;
+    }
+    
+    pthread_mutex_unlock(&(rdp_client->rdp_lock));
     
-    /* Warn if connection is likely to fail due to lack of credentials */
-    guac_client_log(client, GUAC_LOG_INFO,
-            "Authentication requested but username or password not given");
     return TRUE;
 
 }

src/protocols/rdp/rdp.h

@@ -153,6 +153,18 @@ typedef struct guac_rdp_client {
      */
     guac_common_list* available_svc;
 
+    /**
+     * Lock which is locked and unlocked for each credential required
+     * during the connection process.
+     */
+    pthread_mutex_t rdp_credential_lock;
+    
+    /**
+     * Condition which is used when the pthread needs to wait for a
+     * particular credential to be provided.
+     */
+    pthread_cond_t rdp_credential_cond;
+
     /**
      * Common attributes for locks.
      */

src/protocols/rdp/user.c

@@ -117,6 +117,9 @@ int guac_rdp_user_join_handler(guac_user* user, int argc, char** argv) {
         /* Inbound arbitrary named pipes */
         user->pipe_handler = guac_rdp_pipe_svc_pipe_handler;
         
+        /* Handler for updating parameters during connection. */
+        user->argv_handler = guac_rdp_argv_handler;
+
     }
 
     return 0;

src/protocols/ssh/argv.c

@@ -36,6 +36,7 @@ int guac_ssh_argv_callback(guac_user* user, const char* mimetype,
     guac_client* client = user->client;
     guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
     guac_terminal* terminal = ssh_client->term;
+    guac_ssh_settings* settings = ssh_client->settings;
 
     /* Update color scheme */
     if (strcmp(name, GUAC_SSH_ARGV_COLOR_SCHEME) == 0)

src/protocols/ssh/ssh.c

@@ -57,6 +57,32 @@
 #include <sys/socket.h>
 #include <sys/time.h>
 
+/**
+ * A function used to generate a prompt to gather additional credentials from
+ * the guac_client during a connection, and using the specified parameter to
+ * generate the prompt to the client.
+ * 
+ * @param client
+ *     The guac_client object associated with the current connection
+ *     where additional credentials are required.
+ * 
+ * @param cred_name
+ *     The name of the parameter to prompt for in the client.
+ */
+static void guac_ssh_get_credential(guac_client *client, char* cred_name) {
+
+    guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
+    
+    pthread_mutex_lock(&(ssh_client->term_channel_lock));
+    
+    guac_protocol_send_required(client->socket, cred_name);
+    guac_socket_flush(client->socket);
+    
+    pthread_cond_wait(&(ssh_client->ssh_cond), &(ssh_client->term_channel_lock));
+    pthread_mutex_unlock(&(ssh_client->term_channel_lock));
+    
+}
+
 /**
  * Produces a new user object containing a username and password or private
  * key, prompting the user as necessary to obtain that information.
@@ -77,9 +103,8 @@ static guac_common_ssh_user* guac_ssh_get_user(guac_client* client) {
     guac_common_ssh_user* user;
 
     /* Get username */
-    if (settings->username == NULL)
+    while (settings->username == NULL)
-        settings->username = guac_terminal_prompt(ssh_client->term,
+        guac_ssh_get_credential(client, "username");
-                "Login as: ", true);
 
     /* Create user object from username */
     user = guac_common_ssh_create_user(settings->username);
@@ -103,10 +128,8 @@ static guac_common_ssh_user* guac_ssh_get_user(guac_client* client) {
                     "Re-attempting private key import (WITH passphrase)");
 
             /* Prompt for passphrase if missing */
-            if (settings->key_passphrase == NULL)
+            while (settings->key_passphrase == NULL)
-                settings->key_passphrase =
+                guac_ssh_get_credential(client, "passphrase");
-                    guac_terminal_prompt(ssh_client->term,
-                            "Key passphrase: ", false);
 
             /* Reattempt import with passphrase */
             if (guac_common_ssh_user_import_key(user,
@@ -144,29 +167,6 @@ static guac_common_ssh_user* guac_ssh_get_user(guac_client* client) {
 
 }
 
-/**
- * A function used to generate a terminal prompt to gather additional
- * credentials from the guac_client during a connection, and using
- * the specified string to generate the prompt for the user.
- * 
- * @param client
- *     The guac_client object associated with the current connection
- *     where additional credentials are required.
- * 
- * @param cred_name
- *     The prompt text to display to the screen when prompting for the
- *     additional credentials.
- * 
- * @return 
- *     The string of credentials gathered from the user.
- */
-static char* guac_ssh_get_credential(guac_client *client, char* cred_name) {
-
-    guac_ssh_client* ssh_client = (guac_ssh_client*) client->data;
-    return guac_terminal_prompt(ssh_client->term, cred_name, false);
-    
-}
-
 void* ssh_input_thread(void* data) {
 
     guac_client* client = (guac_client*) data;
@@ -281,6 +281,7 @@ void* ssh_client_thread(void* data) {
     }
 
     pthread_mutex_init(&ssh_client->term_channel_lock, NULL);
+    pthread_cond_init(&(ssh_client->ssh_cond), NULL);
 
     /* Open channel for terminal */
     ssh_client->term_channel =
@@ -495,6 +496,7 @@ void* ssh_client_thread(void* data) {
     guac_client_stop(client);
     pthread_join(input_thread, NULL);
 
+    pthread_cond_destroy(&(ssh_client->ssh_cond));
     pthread_mutex_destroy(&ssh_client->term_channel_lock);
 
     guac_client_log(client, GUAC_LOG_INFO, "SSH connection ended.");

src/protocols/ssh/ssh.h

@@ -90,6 +90,12 @@ typedef struct guac_ssh_client {
      */
     pthread_mutex_t term_channel_lock;
     
+    /**
+     * Condition used when SSH client thread needs to wait for Guacamole
+     * client response.
+     */
+    pthread_cond_t ssh_cond;
+
     /**
      * The current clipboard contents.
      */

src/protocols/vnc/Makefile.am

@@ -29,6 +29,7 @@ ACLOCAL_AMFLAGS = -I m4
 lib_LTLIBRARIES = libguac-client-vnc.la
 
 libguac_client_vnc_la_SOURCES = \
+    argv.c			\
     auth.c                      \
     client.c                    \
     clipboard.c                 \
@@ -41,6 +42,7 @@ libguac_client_vnc_la_SOURCES = \
     vnc.c
     
 noinst_HEADERS =      \
+    argv.h	      \
     auth.h            \
     client.h          \
     clipboard.h       \

src/protocols/vnc/argv.c

@@ -0,0 +1,163 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#include "config.h"
+#include "argv.h"
+#include "vnc.h"
+
+#include <guacamole/protocol.h>
+#include <guacamole/socket.h>
+#include <guacamole/user.h>
+
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+
+/**
+ * All VNC connection settings which may be updated by unprivileged users
+ * through "argv" streams.
+ */
+typedef enum guac_vnc_argv_setting {
+
+    /**
+     * The password for the connection.
+     */
+    GUAC_VNC_ARGV_SETTING_PASSWORD
+
+} guac_vnc_argv_setting;
+
+/**
+ * The value or current status of a connection parameter received over an
+ * "argv" stream.
+ */
+typedef struct guac_vnc_argv {
+
+    /**
+     * The specific setting being updated.
+     */
+    guac_vnc_argv_setting setting;
+
+    /**
+     * Buffer space for containing the received argument value.
+     */
+    char buffer[GUAC_VNC_ARGV_MAX_LENGTH];
+
+    /**
+     * The number of bytes received so far.
+     */
+    int length;
+
+} guac_vnc_argv;
+
+/**
+ * Handler for "blob" instructions which appends the data from received blobs
+ * to the end of the in-progress argument value buffer.
+ *
+ * @see guac_user_blob_handler
+ */
+static int guac_vnc_argv_blob_handler(guac_user* user, guac_stream* stream,
+        void* data, int length) {
+
+    guac_vnc_argv* argv = (guac_vnc_argv*) stream->data;
+
+    /* Calculate buffer size remaining, including space for null terminator,
+     * adjusting received length accordingly */
+    int remaining = sizeof(argv->buffer) - argv->length - 1;
+    if (length > remaining)
+        length = remaining;
+
+    /* Append received data to end of buffer */
+    memcpy(argv->buffer + argv->length, data, length);
+    argv->length += length;
+
+    return 0;
+
+}
+
+/**
+ * Handler for "end" instructions which applies the changes specified by the
+ * argument value buffer associated with the stream.
+ *
+ * @see guac_user_end_handler
+ */
+static int guac_vnc_argv_end_handler(guac_user* user, guac_stream* stream) {
+
+    guac_client* client = user->client;
+    guac_vnc_client* vnc_client = (guac_vnc_client*) client->data;
+    guac_vnc_settings* settings = vnc_client->settings;
+
+    /* Append null terminator to value */
+    guac_vnc_argv* argv = (guac_vnc_argv*) stream->data;
+    argv->buffer[argv->length] = '\0';
+
+    /* Apply changes to chosen setting */
+    switch (argv->setting) {
+        
+        /* Update password */
+        case GUAC_VNC_ARGV_SETTING_PASSWORD:
+            
+            /* Update password in settings */
+            if (settings->password != NULL)
+                free(settings->password);
+            settings->password = malloc(strlen(argv->buffer) * sizeof(char));
+            strcpy(settings->password, argv->buffer);
+            
+            pthread_cond_broadcast(&(vnc_client->argv_cond));
+            break;
+
+    }
+
+    free(argv);
+    return 0;
+
+}
+
+int guac_vnc_argv_handler(guac_user* user, guac_stream* stream, char* mimetype,
+        char* name) {
+
+    guac_vnc_argv_setting setting;
+
+    /* Allow users to update authentication information */
+    if (strcmp(name, "password") == 0)
+        setting = GUAC_VNC_ARGV_SETTING_PASSWORD;
+
+    /* No other connection parameters may be updated */
+    else {
+        guac_protocol_send_ack(user->socket, stream, "Not allowed.",
+                GUAC_PROTOCOL_STATUS_CLIENT_FORBIDDEN);
+        guac_socket_flush(user->socket);
+        return 0;
+    }
+
+    guac_vnc_argv* argv = malloc(sizeof(guac_vnc_argv));
+    argv->setting = setting;
+    argv->length = 0;
+
+    /* Prepare stream to receive argument value */
+    stream->blob_handler = guac_vnc_argv_blob_handler;
+    stream->end_handler = guac_vnc_argv_end_handler;
+    stream->data = argv;
+
+    /* Signal stream is ready */
+    guac_protocol_send_ack(user->socket, stream, "Ready for updated "
+            "parameter.", GUAC_PROTOCOL_STATUS_SUCCESS);
+    guac_socket_flush(user->socket);
+    return 0;
+
+}

src/protocols/vnc/argv.h

@@ -0,0 +1,41 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#ifndef ARGV_H
+#define ARGV_H
+
+#include "config.h"
+
+#include <guacamole/user.h>
+
+
+/**
+ * The maximum number of bytes to allow for any argument value received via an
+ * argv stream, including null terminator.
+ */
+#define GUAC_VNC_ARGV_MAX_LENGTH 16384
+
+/**
+ * Handles an incoming stream from a Guacamole "argv" instruction, updating the
+ * given connection parameter if that parameter is allowed to be updated.
+ */
+guac_user_argv_handler guac_vnc_argv_handler;
+
+#endif /* ARGV_H */
+

src/protocols/vnc/auth.c

@@ -23,12 +23,29 @@
 #include "vnc.h"
 
 #include <guacamole/client.h>
+#include <guacamole/protocol.h>
+#include <guacamole/socket.h>
 #include <rfb/rfbclient.h>
 #include <rfb/rfbproto.h>
 
+#include <pthread.h>
+#include <string.h>
+
 char* guac_vnc_get_password(rfbClient* client) {
     guac_client* gc = rfbClientGetClientData(client, GUAC_VNC_CLIENT_KEY);
-    return ((guac_vnc_client*) gc->data)->settings->password;
+    guac_vnc_client* vnc_client = ((guac_vnc_client*) gc->data);
+    guac_vnc_settings* settings = vnc_client->settings;
+    
+    if (settings->password == NULL || strcmp(settings->password, "") == 0) {
+        pthread_mutex_lock(&(vnc_client->argv_lock));
+        guac_protocol_send_required(gc->socket, "password");
+        guac_socket_flush(gc->socket);
+        pthread_cond_wait(&(vnc_client->argv_cond), &(vnc_client->argv_lock));
+        pthread_mutex_unlock(&(vnc_client->argv_lock));
+    }
+    
+    return settings->password;
+    
 }
 
 rfbCredential* guac_vnc_get_credentials(rfbClient* client, int credentialType) {

src/protocols/vnc/client.c

@@ -50,10 +50,14 @@ int guac_client_init(guac_client* client) {
     client->data = vnc_client;
 
 #ifdef ENABLE_VNC_TLS_LOCKING
-    /* Initialize the write lock */
+    /* Initialize the TLS write lock */
     pthread_mutex_init(&(vnc_client->tls_lock), NULL);
 #endif
     
+    /* Initialize argv lock and condition */
+    pthread_mutex_init(&(vnc_client->argv_lock), NULL);
+    pthread_cond_init(&(vnc_client->argv_cond), NULL);
+
     /* Init clipboard */
     vnc_client->clipboard = guac_common_clipboard_alloc(GUAC_VNC_CLIPBOARD_MAX_LENGTH);
 
@@ -136,6 +140,10 @@ int guac_vnc_client_free_handler(guac_client* client) {
     pthread_mutex_destroy(&(vnc_client->tls_lock));
 #endif
     
+    /* Clean up argv mutex */
+    pthread_cond_destroy(&(vnc_client->argv_cond));
+    pthread_mutex_destroy(&(vnc_client->argv_lock));
+
     /* Free generic data struct */
     free(client->data);
 

src/protocols/vnc/vnc.h

@@ -62,6 +62,16 @@ typedef struct guac_vnc_client {
     pthread_mutex_t tls_lock;
 #endif
     
+    /**
+     * The lock for tracking changes via argv.
+     */
+    pthread_mutex_t argv_lock;
+    
+    /**
+     * The condition for signaling argv updates.
+     */
+    pthread_cond_t argv_cond;
+
     /**
      * The underlying VNC client.
      */