HCLIENT ProxyConnect(
	UINT nProxyType,
	LPCTSTR lpszProxyHost,
	UINT nProxyPort,
	LPCTSTR lpszProxyUser,
	LPCTSTR lpszProxyPassword,
	LPCTSTR lpszRemoteHost,
	UINT nRemotePort,
	UINT nTimeout,
	DWORD dwOptions
);

The ProxyConnect method establishes a connection through a proxy server.

Parameters

nProxyType

An identifier which specifies the type of proxy server that is being connected to. This value must be defined as one of the following values:

Value	Description
FTP_PROXY_NONE	This value specifies that no proxy server is being used. In this case, the Connect method is called directly, ignoring the proxy parameters.
FTP_PROXY_USER	This value specifies that the client is not logged into the proxy server. The USER command is sent in the format username@ftpsite followed by the password. This is the format used with the Gauntlet proxy server.
FTP_PROXY_LOGIN	This value specifies that the client is logged into the proxy server. The USER command is then sent in the format username@ftpsite followed by the password. This is the format used by the InterLock proxy server.
FTP_PROXY_OPEN	This value specifies that the client is not logged into the proxy server. The OPEN command is sent specifying the host name, followed by the username and password.
FTP_PROXY_SITE	This value specifies that the client is logged into the server. The SITE command is sent, specifying the host name, followed by the username and the password.
FTP_PROXY_OTHER	This special proxy type specifies that another, undefined proxy server is being used. The client connects to the proxy host, but does not attempt to authenticate the client. The application is responsible for negotiating with the proxy server, typically using the Command method to send specific command sequences.

lpszProxyHost

The name of the proxy server to connect through; this may be a fully-qualified domain name or an IP address.

nProxyPort

The port number the proxy server is listening on; a value of zero specifies that the default port number should be used.

lpszProxyUser

The user name used to authenticate the client on the proxy server. Not all proxy servers require this information; it is recommended that you consult the proxy server documentation to determine if a username is required.

lpszProxyPassword

The password used to authenticate the client on the proxy server. Not all proxy servers require this information; it is recommended that you consult the proxy server documentation to determine if a password is required.

lpszRemoteHost

The name of the server to connect to; this may be a fully-qualified domain name or an IP address.

nRemotePort

The port number the server is listening on; a value of zero specifies that the default port number should be used. For standard connections, the default port number is 21. For secure connections, the default port number is 990.

nTimeout

The number of seconds that the client will wait for a response from the server before failing the current operation.

dwOptions

An unsigned integer that specifies one or more options. This parameter is constructed by using a bitwise operator with any of the following values:

Value	Description
FTP_OPTION_PASSIVE	This option specifies the client should attempt to establish the data connection with the server. When the client uploads or downloads a file, normally the server establishes a second connection back to the client which is used to transfer the file data. However, if the local system is behind a firewall or a NAT router, the server may not be able to create the data connection and the transfer will fail. By specifying this option, it forces the client to establish an outbound data connection with the server. It is recommended that applications use passive mode whenever possible.
FTP_OPTION_FIREWALL	This option specifies the client should always use the host IP address to establish the data connection with the server, not the address returned by the server in response to the PASV command. This option may be necessary if the server is behind a router that performs Network Address Translation (NAT) and it returns an unreachable IP address for the data connection. If this option is specified, it will also enable passive mode data transfers.
FTP_OPTION_NOAUTH	This option specifies the server does not require authentication, or that it requires an alternate authentication method. When this option is used, the client connection is flagged as authenticated as soon as the connection to the server has been established. Note that using this option to bypass authentication may result in subsequent errors when attempting to retrieve a directory listing or transfer a file. It is recommended that you consult the technical reference documentation for the server to determine its specific authentication requirements.
FTP_OPTION_VIRTUALHOST	This option specifies the server supports virtual hosting, where multiple domains are hosted by a server using the same external IP address. If this option is enabled, the client will send the HOST command to the server upon establishing a connection.
FTP_OPTION_VERIFY	This option specifies that file transfers should be automatically verified after the transfer has completed. If the server supports the XMD5 command, the transfer will be verified by calculating an MD5 hash of the file contents. If the server does not support the XMD5 command, but does support the XCRC command, the transfer will be verified by calculating a CRC32 checksum of the file contents. If neither the XMD5 or XCRC commands are supported, the transfer is verified by comparing the size of the file. Automatic file verification is only performed for binary mode transfers because of the end-of-line conversion that may occur when text files are uploaded or downloaded.
FTP_OPTION_TRUSTEDSITE	This option specifies the server is trusted. The server certificate will not be validated and the connection will always be permitted. This option only affects connections using the TLS protocol.
FTP_OPTION_SECURE	This option specifies the client should attempt to establish a secure connection with the server. This option is the same as specifying FTP_OPTION_SECURE_IMPLICIT which immediately performs the TLS protocol negotiation when the connection is established.
FTP_OPTION_SECURE_IMPLICIT	This option specifies the client should attempt to immediately establish secure TLS connection with the server. This option is typically used when connecting to a server on port 990, which is the default port number used for FTPS.
FTP_OPTION_SECURE_EXPLICIT	This option specifies the client should establish a standard connection to the server and then use the AUTH command to negotiate an explicit secure connection. This option is typically used when connecting to the server on ports other than 990.
FTP_OPTION_SECURE_FALLBACK	This option specifies the client should permit the use of less secure cipher suites for compatibility with legacy servers. If this option is specified, the client will allow connections using TLS 1.0 and cipher suites that use RC4, MD5 and SHA1.
FTP_OPTION_TUNNEL	This option specifies that a tunneled TCP connection and/or port-forwarding is being used to establish the connection to the server. This changes the behavior of the client with regards to internal checks of the destination IP address and remote port number, default capability selection and how the connection is established. This option also forces all connections to be outbound and enables the firewall compatibility features in the client.
FTP_OPTION_KEEPALIVE_DATA	This option specifies the client should attempt to keep the control connection active during a file transfer. Normally, when a data transfer is in progress, no additional commands are issued on the control channel until the transfer completes. Specifying this option automatically enables the FTP_OPTION_KEEPALIVE option and forces the client to continue to issue NOOP commands during the file transfer. This option only applies to FTP and FTPS connections and has no effect on connections using SFTP (SSH).
FTP_OPTION_PREFER_IPV6	This option specifies the client should prefer the use of IPv6 if the server hostname can be resolved to both an IPv6 and IPv4 address. This option is ignored if the local system does not have IPv6 enabled, or when the hostname can only be resolved to an IPv4 address. If the server hostname can only be resolved to an IPv6 address, the client will attempt to establish a connection using IPv6 regardless if this option has been specified.
FTP_OPTION_FREETHREAD	This option specifies the handle returned by this function may be used by any thread, and is not limited to the thread which created it. The application is responsible for ensuring that access to the handle is synchronized across multiple threads.
FTP_OPTION_HIRES_TIMER	This option specifies the elapsed time for data transfers should be returned in milliseconds instead of seconds. This will return more accurate transfer times for smaller files being uploaded or downloaded using fast network connections.
FTP_OPTION_TLS_REUSE	This option specifies that TLS session reuse should be enabled for secure connections. This option is only supported on Windows 8.1 or Windows Server 2012 R2 and later platforms, and it should only be used when explicitly required by the server. This option is not compatible with servers built using OpenSSL 1.0.2 and earlier versions which do not provide Extended Master Secret (EMS) support as outlined in RFC7627.

Return Value

If the method succeeds, the return value is a handle to a client session. If the method fails, the return value is INVALID_CLIENT. To get extended error information, call GetLastError.

Remarks

This method will block the current thread until a connection has been established or the timeout period has elapsed. To prevent it from blocking the main user interface thread, the application should create a background worker thread and establish a connection by calling the ProxyConnect method in that thread. If the application requires multiple simultaneous connections, it is recommended you create a worker thread for each connection.

The username and password that is used to authenticate the client with the proxy server are not the same as those used to login to the target server. Once a connection has been established with the proxy server, the client must call the Login method to actually login to the server and begin a file transfer.

If the FTP_OPTION_KEEPALIVE option is specified, a background worker thread will be created to monitor the command channel and periodically send NOOP commands to the server if no commands have been sent recently. This can prevent the server from terminating the client connection during idle periods where no commands are being issued. However, it is important to keep in mind that many servers can be configured to also limit the total amount of time a client can be connected to the server, as well as the amount of time permitted between file transfers. If the server does not respond to the NOOP command, this option will be automatically disabled for the remainder of the client session.

If the FTP_OPTION_SECURE_EXPLICIT option is specified, the client will first send an AUTH TLS command to the server. If the server does not accept this command, it will then send an AUTH SSL command. If both commands are rejected by the server, an explicit TLS session cannot be established. By default, both the command and data channels will be encrypted when a secure connection is established. To change this, use the SetChannelMode method.

The dwOptions argument can be used to specify the threading model that is used by the class when a connection is established. By default, the client session is initially attached to the thread that created it. From that point on, until the connection is terminated, only the owner may invoke methods in that instance of the class. The ownership of the class instance may be transferred from one thread to another using the AttachThread method.

Specifying the FTP_OPTION_FREETHREAD option enables any thread to call methods in any instance of the class, regardless of which thread created it. It is important to note that this option disables certain internal safety checks which are performed by the class and may result in unexpected behavior unless access to the class instance is synchronized. If one thread calls a method in the class, it must ensure that no other thread will call another method at the same time using the same instance.

Requirements

Minimum Desktop Platform: Windows 7 Service Pack 1
Minimum Server Platform: Windows Server 2008 R2 Service Pack 1
Header File: cstools11.h
Import Library: csftpv11.lib
Unicode: Implemented as Unicode and ANSI versions

See Also

Connect, ConnectUrl, CreateSecurityCredentials, Disconnect, GetSecurityInformation, Login

Copyright © 2025 Catalyst Development Corporation. All rights reserved.