天行健 君子当自强而不息

本篇是使用DirectPlay进行网络互联（3）的续篇。

客户端的处理

客户端并不像服务器端那么复杂，它通常只使用两种消息，即接收数据和终止会话消息，以及需要连接和保持单一连接（服务器端）。另外最主要的就是客户端应用程序必须指定其玩家的位置，以便主机能够检索它们。设置玩家的信息是通过首先将相关数据填入一个DPN_PLAYER_INFO结构体，然后再调用 IDirectPlay8Client:: SetClientInfo函数来实现。

Sets the static settings of a client with an application. Call this method before connecting to relay basic player information to the application. Once the client successfully connects with the application, the server can retrieve information obtained through this method by calling the IDirectPlay8Server::GetClientInfo method.

HRESULT SetClientInfo(
const DPN_PLAYER_INFO *const pdpnPlayerInfo,
PVOID const pvAsyncContext,
DPNHANDLE *const phAsyncHandle,
const DWORD dwFlags
);

Parameters

pdpnPlayerInfo

[in] Pointer to a DPN_PLAYER_INFO structure that contains the client information to set.

pvAsyncContext

[in] Pointer to the user-supplied context, which is returned in the pvUserContext member of the DPN_MSGID_ASYNC_OP_COMPLETE system message.

phAsyncHandle

[in,out] A DPNHANDLE. A value will be returned. However, Microsoft® DirectPlay® 8.1 does not permit cancellation of this operation, so the value cannot be used.

dwFlags

[in] Flag that controls how this method is processed. The following flag can be set for this method.

DPNSETCLIENTINFO_SYNC

Causes the method to process synchronously.

Return Values

Returns S_OK if this method is processed synchronously and is successful. If the request is processed asynchronously, S_OK can return if the method is instantly processed. By default, this method is run asynchronously and generally returns DPNSUCCESS_PENDING or one of the following error values.

DPNERR_NOCONNECTION

DPNERR_INVALIDFLAGS

DPNERR_INVALIDPARAM

 

Remarks

This method can be called at any time during the session.

The dwPlayerFlags member of the DPN_PLAYER_INFO structure must be set to zero.

Transmission of nonstatic information should be handled with the IDirectPlay8Client::Send method because of the high cost of using the IDirectPlay8Client::SetClientInfo method.

You can modify the client information with this method after connecting to the application. Calling this method after connection generates a DPN_MSGID_CLIENT_INFO system message to all players, informing them that data has been updated.

服务器端和客户端都使用相同的应用程序GUID，这样它们才能相互识别。网络应用程序不能连接的主要原因就是没有这样做，所以一定要确保使用相同的应用程序GUID。

设置好客户端的信息后，需要与服务器端建立连接，可以调用 IDirectPlay6Client::Connect来实现。

Establishes the connection to the server. After a connection is established, the communication channel on the interface is open and the application should expect messages to arrive immediately. No messages can be sent by means of the IDirectPlay8Client::Send method until the connection has completed.

Before this method is called, you can obtain an application description by calling IDirectPlay8Client::EnumHosts. When you call EnumHosts, DPN_MSGID_ENUM_HOSTS_RESPONSE messages are sent to your message handler with the IDirectPlay8Address objects and the DPN_APPLICATION_DESC structure for each host found. This information can be passed without modification to the Connect method.

HRESULT Connect(
const DPN_APPLICATION_DESC *const pdnAppDesc,
IDirectPlay8Address *const pHostAddr,
IDirectPlay8Address *const pDeviceInfo,
const DPN_SECURITY_DESC *const pdnSecurity,
const DPN_SECURITY_CREDENTIALS *const pdnCredentials,
const void *const pvUserConnectData,
const DWORD dwUserConnectDataSize,
void *const pvAsyncContext,
DPNHANDLE *const phAsyncHandle,
const DWORD dwFlags
);

Parameters

pdnAppDesc

[in] Pointer to a DPN_APPLICATION_DESC structure that describes the application. The only member of this structure that you must set is the guidApplication member. Only some of the members of this structure are used by this method. The only member that you must set is guidApplication. You can also set guidInstance, pwszPassword, dwFlags, and dwSize.

pHostAddr

[in] Pointer to an IDirectPlay8Address interface that specifies the addressing information to use to connect to the computer that is hosting. The user can be queried for any missing address information if you set the DPNENUMHOSTS_OKTOQUERYFORADDRESSING flag in the dwFlags parameter.

pDeviceInfo

[in] Pointer to an IDirectPlay8Address object that specifies what network adapter (for example, NIC, modem, and so on) to use to connect to the server. Some service providers allow this parameter to be NULL or be an address object containing only the service provider component. In this case, they will use the most appropriate device to reach the designated host. If you set the DPNCONNECT_OKTOQUERYFORADDRESSING flag in dwFlags, the user can be queried for any missing address information.

pdnSecurity

[in] Reserved. Must be NULL.

pdnCredentials

[in] Reserved. Must be NULL.

pvUserConnectData

[in] Pointer to application-specific data provided to the host or server to further validate the connection. DirectPlay will make a copy of this data when the method is called and therefore you can modify or destroy this data once the connection is complete. This data is sent to the DPN_MSGID_INDICATE_CONNECT message in the pvUserConnectData member. This parameter is optional and you can pass NULL to bypass the connection validation provided by the user code.

dwUserConnectDataSize

[in] Variable of type DWORD that specifies the size of the data contained in pvUserConnectData.

pvAsyncContext

[in] Pointer to the user-supplied context, which is returned in the pvUserContext member of the DPN_MSGID_CONNECT_COMPLETE system message. This parameter is optional and can be set to NULL.

phAsyncHandle

[out] A DPNHANDLE. When the method returns, phAsyncHandle will point to a handle that you can pass to IDirectPlay8Client::CancelAsyncOperation to cancel the operation. This parameter must be set to NULL if you set the DPNCONNECT_SYNC flag in dwFlags.

dwFlags

[in] Flag that describes the connection mode. You can set the following flag.

DPNCONNECT_OKTOQUERYFORADDRESSING

Setting this flag will display a standard Microsoft® DirectPlay® dialog box, which queries the user for more information if not enough information is passed in this method.

DPNCONNECT_SYNC

Process the connection request synchronously.

Return Values

Returns S_OK if this method is processed synchronously and is successful. If the request is processed asynchronously, S_OK will be returned if the method is instantly processed. By default, this method is run asynchronously and generally returns DPNSUCCESS_PENDING or one of the following error values.

DPNERR_HOSTREJECTEDCONNECTION

DPNERR_INVALIDAPPLICATION

DPNERR_INVALIDDEVICEADDRESS

DPNERR_INVALIDFLAGS

DPNERR_INVALIDHOSTADDRESS

DPNERR_INVALIDINSTANCE

DPNERR_INVALIDINTERFACE

DPNERR_INVALIDPASSWORD

DPNERR_NOCONNECTION

DPNERR_NOTHOST

DPNERR_SESSIONFULL

DPNERR_ALREADYCONNECTED

 

Remarks

It is not required to enumerate hosts before calling Connect if you know the appropriate host and device information.

If you do call the IDirectPlay8Client::EnumHosts method and you want to ensure better network address translation (NAT) and proxy support when using the TCP/IP service provider or prevent redialing with the modem service provider, keep the enumeration active when calling Connect. To prevent the enumeration from completing, set the dwEnumCount parameter to INFINITE and do not use the IDirectPlay8Client::CancelAsyncOperation to terminate the enumeration before the connect operation has completed. You should also pass the pAddressSender and pAddressDevice address objects in the DPNMSG_ENUM_HOSTS_RESPONSE message without modification into the pHostAddr and pDeviceInfo parameters of the Connect method. To pass the address objects to Connect outside of the callback function, use IDirectPlay8Address::Duplicate or IDirectPlay8Address::AddRef to prevent the object from being destroyed and store the pointers using thread-safe code. DirectPlay will automatically cancel the enumeration when the connect completes with DPN_OK or when IDirectPlay8Client::Close is called.

Although multiple enumerations can be run concurrently and can be run across the duration of a connection, only one connection is allowed per interface. To establish a connection to more than one application, you must create another interface.

When this method is called, a DPN_MSGID_INDICATE_CONNECT message is posted to the server's message handler. On retrieval of this message, the host can pass back connection reply data to the Connect method. Connection reply data can send a message indicating that the host does not approve the connection. The calling application can then handle this reply appropriately.

If Connect is called synchronously, the following outcomes are possible.

• Connection Successful. The application will receive a DPN_MSGID_CONNECT_COMPLETE message containing the success code and the Connect method will return with DPN_OK.
• Connection fails because the server rejects the connection. The application will receive a DPN_MSGID_CONNECT_COMPLETE message containing the DPNERR_HOSTREJECTEDCONNECTION failure code. The Connect method will also return with the error code DPNERR_HOSTREJECTEDCONNECTION. The DPN_MSGID_CONNECT_COMPLETE message provides an opportunity for the client application to inspect any data the server returns with the rejection.
• Connection fails for any other reason. The application will not receive a DPN_MSGID_CONNECT_COMPLETE message, and the Connect method will return with the appropriate error code.

If Connect is called asynchronously, the method returns immediately with DPNSUCCESS_PENDING. A DPN_MSGID_CONNECT_COMPLETE message will follow after the connection is complete, containing the result of the connection. The only time the method does not return DPNSUCCESS_PENDING is when validation of the supplied parameters fails, in which case the appropriate error code is returned.

When the connection request completes, all outstanding enumerations are canceled with the return of DPNERR_USERCANCEL.

The hResultCode on the completion will indicate S_OK if the Connect() attempt was successful, or an error otherwise. If the Host player returned anything other than S_OK from the DPN_MSGID_INDICATE_CONNECT message, the likely error code in the completion will be DPNERR_HOSTREJECTEDCONNECTION.

To close the connection established with this method, call the IDirectPlay8Client::Close method.

Note  If you set the DPNCONNECT_OKTOQUERYFORADDRESSING flag in dwFlags, the service provider might attempt to display a dialog box to ask the user to complete the address information. You must have a visible window present when the service provider tries to display the dialog box, or your application will lock.

最后一个参数dwFlags告诉DirectPlay采用异步（0）还是同步（DPNCONNECT_SYNC）方式进行连接。使用异步连接方式会立即返回控制权，所以需要等待DPN_MSGID_CONNECT_COMPLETE消息来标识和服务器端的成功连接。采用同步连接方式， Connect函数就只会在出现错误或成功连接时才会返回。

下面这个函数演示了如何设置客户端属性并建立与服务器端的连接。
 
发送和接收消息

客户端接收消息和服务器端接收消息的处理方法是一样的，所以只需要关心消息处理函数内部的实现，发送消息需要调用IDirectPlay8Server::Send函数。

Transmits data to the server. The message can be sent synchronously or asynchronously.

HRESULT Send(
const DPN_BUFFER_DESC *const pBufferDesc,
const DWORD cBufferDesc,
const DWORD dwTimeOut,
void *const pvAsyncContext,
DPNHANDLE *const phAsyncHandle,
const DWORD dwFlags
);

Parameters

pBufferDesc

[in] Pointer to a DPN_BUFFER_DESC structure that describes the data to send.

cBufferDesc

[in] Number of DPN_BUFFER_DESC structures pointed to by pBufferDesc. There can only be one buffer in this version of Microsoft® DirectPlay® .

dwTimeOut

[in] Number of milliseconds to wait for the message to send. If the message has not been sent by the dwTimeOut value, it is deleted from the send queue. If you set this parameter to 0, the message remains in the send queue until it is sent or until the link is dropped.

pvAsyncContext

[in] Pointer to the user-supplied context, which is returned in the pvUserContext member of the DPN_MSGID_SEND_COMPLETE system message.

phAsyncHandle

[in,out] A DPNHANDLE. When the method returns, phAsyncHandle will point to a handle that you can pass to IDirectPlay8Client::CancelAsyncOperation to cancel the operation. This parameter must be set to NULL if you set the DPNSEND_SYNC flag in dwFlags.

dwFlags

[in] Flags that describe send behavior. You can set one or more of the following flags.

DPNSEND_SYNC

Process the Send request synchronously.

DPNSEND_NOCOPY

Use the data in the DPN_BUFFER_DESC structure and do not make an internal copy. This may be a more efficient method of sending data to the server. However, it is less robust, because the sender might be able to modify the message before the receiver has processed it. This flag cannot be combined with DPNSEND_NOCOMPLETE.

DPNSEND_NOCOMPLETE

Does not send DPN_MSGID_SEND_COMPLETE to the message handler. This flag may not be used with DPNSEND_NOCOPY or DPNSEND_GUARANTEED. Additionally, when using this flag pvAsyncContext must be NULL.

DPNSEND_COMPLETEONPROCESS

Send DPN_MSGID_SEND_COMPLETE to the message handler when this message has been delivered to the target and the target's message handler returns from indicating its reception. There is additional internal message overhead when this flag is set, and the message transmission process may become significantly slower. If you set this flag, DPNSEND_GUARANTEED must also be set.

DPNSEND_GUARANTEED

Send the message by a guaranteed method of delivery.

DPNSEND_PRIORITY_HIGH

Sets the priority of the message to high. This flag cannot be used with DPNSEND_PRIORITY_LOW.

DPNSEND_PRIORITY_LOW

Sets the priority of the message to low. This flag cannot be used with DPNSEND_PRIORITY_HIGH.

DPNSEND_NOLOOPBACK

Suppress the DPN_MSGID_RECEIVE system message to your message handler if you are sending to yourself.

DPNSEND_NONSEQUENTIAL

If the flag is not set, messages are delivered to the target application in the order that they are sent, which may necessitate buffering out of sequence messages until the missing messages arrive. Messages are simply delivered to the target application in the order that they are received.

Return Values

Returns S_OK if this method is processed synchronously and is successful. By default, this method is run asynchronously and generally returns DPNSUCCESS_PENDING or one of the following error values.

DPNERR_INVALIDFLAGS

DPNERR_TIMEDOUT

Remarks

This method generates a DPN_MSGID_RECEIVE system message in the server's message handler. The data buffer is contained in the pReceiveData member of the associated structure.

Messages can have one of three priorities: low, normal, and high. To specify a low or high priority for the message, set the appropriate flag in dwFlags. If neither of the priority flags is set, the message will have normal priority. See Basic Networking for a discussion of send priorities.

When the Send request is completed, a DPN_MSGID_SEND_COMPLETE system message is posted to the sender's message handler. The success or failure of the request is contained in the hResultCode member of the associate structure. You can suppress the send completion by setting the DPN_NOCOMPLETE flag in dwflags.

If a player joins a game and needs to send multiple messages immediately, the player should first send a message with the DPNSEND_COMPLETEONPROCESS flag set. When the DPN_MSGID_SEND_COMPLETE message is returned, the application can begin sending messages. If the player does not do this, some of the messages might need to be queued on the receiver and, if too much data arrives, the queue can grow faster than the receiver can handle the messages. This might result in lost data. After a player is established in the game, however, throttling in DirectPlay will control the data flow by using message timeouts or the GetSendQueueInfo method. For more information, see Optimizing Network Usage.

Send completions are typically posted on the source computer as soon as the message is sent. In other words, a send completion does not necessarily mean that the message has been processed on the target. It may still be in a queue. If you want to be certain that the message has been processed by the target, set the DPN_COMPLETEONPROCESS flag in dwFlags. This flag ensures that the send completion will not be sent until the target's message handler has processed the message, and returned.

Note  Do not assume that resources such as the data buffer will remain valid until the method has returned. If you call this method asynchronously, the DPN_MSGID_SEND_COMPLETE message may be received and processed by your message handler before the call has returned. If your message handler deallocates or otherwise invalidates a resource such as the data buffer, that resource may become invalid at any time after the method has been called.

下面这两个函数演示了如何发送和接收消息。
   

获得玩家的ID号

当连接到服务器端后，在有些情况下客户端需要使用自己的玩家ID号。要获得玩家的ID号，客户端可以解析连接完成消息（DPN_MSGID_CONNECT_COMPLETE），该消息使用以下数据结构来包含有关客户端到服务器端连接的必要信息。

Microsoft® DirectPlay® generates the DPN_MSGID_CONNECT_COMPLETE message when the connection attempt has been completed in a peer-to-peer or client/server session. This message is generated whether or not the connection was successful.

The DPNMSG_CONNECT_COMPLETE structure contains information for the DPN_MSGID_CONNECT_COMPLETE system message.

typedef struct _DPNMSG_CONNECT_COMPLETE{
 DWORD dwSize;
 DPNHANDLE hAsyncOp;
 PVOID pvUserContext;
 HRESULT hResultCode;
 PVOID pvApplicationReplyData;
 DWORD dwApplicationReplyDataSize;
} DPNMSG_CONNECT_COMPLETE, *PDPNMSG_CONNECT_COMPLETE;

dwSize

Size of this structure.

hAsyncOp

Asynchronous operation handle.

pvUserContext

User context supplied when the IDirectPlay8Peer::Connect or IDirectPlay8Client::Connect methods are called.

hResultCode

HRESULT describing the result of the connection attempt. See the Return Values section in the IDirectPlay8Peer::Connect or IDirectPlay8Client::Connect method for more information. Additionally, DPNERR_PLAYERNOTREACHABLE will be returned if a player has tried to join a peer-to-peer session where at least one other existing player in the session cannot connect to the joining player.

pvApplicationReplyData

Connection reply data returned from the host or server.

dwApplicationReplyDataSize

Size of the data, in bytes, of the pvApplicationReplyData member.

Return Values

Return DPN_OK.

 

当服务器端调用IDirectPlay8Server::DestroyClient来销毁玩家时，客户端会收到消息 DPN_MSGID_TERMINATE_SESSION。

下面这个函数演示了如何处理消息DPN_MSGID_CONNECT_COMPLETE和DPN_MSGID_TERMINATE_SESSION。

 

终止客户端会话

当客户端需要从一次会话中断开连接时，需要明确向DirectPlay传达该消息，以使其按正确的步骤关闭连接。使用IDirectPlay8Client::Close函数，就能将客户端从一次会话中断开连接。

Closes the open connection to a session. This method must be called on any object that is successfully initialized with a call to the IDirectPlay8Client::Initialize method.

HRESULT Close(
const DWORD dwFlags
);

Parameters

dwFlags

[in] Reserved. Must be 0.

Return Values

Returns S_OK if successful, or the following error value.

DPNERR_UNINITIALIZED

 

Remarks

Calling Close will cancel all outstanding operations, including data sent as guaranteed. To make sure all messages are sent, wait for all outstanding Send calls to complete before calling Close.

If you do not want the application to wait, the application should call IDirectPlay8Client::CancelAsyncOperation to cancel all outstanding sends prior to calling IDirectPlay8Client::Close or doing a final release call on the IDirectPlay8Client interface. Failing to do so causes unpredictable results.

下面给出一个完整的代码示例：

点击下载源码和工程

 
该程序必须和使用DirectPlay进行网络互联（3）中提及的服务器端程序配合使用。

运行截图：