[英]Winsock: UDP recvfrom() not filling in the same IP address that was used to send data
I am coding a UDP echo client & server.我正在编写 UDP echo 客户端和服务器。 These are both running on my machine.这些都在我的机器上运行。 The client is set up to send the message to the IP address::1.客户端设置为将消息发送到 IP 地址::1。 At this point my server receives the message and is supposed to print something similar to this.此时,我的服务器收到消息并应该打印类似的内容。
Processing client at::1
Instead the server keeps getting a different IP address.相反,服务器不断获得不同的 IP 地址。
Processing client at 132:e3d5::
Note: The IP address received is different every time.注意:每次收到的IP地址都不一样。
This is causing a problem because I believe when I later try to echo the message back to my client, I can't send it to the correct place because the IP address I received is not the same as::1.这导致了一个问题,因为我相信当我稍后尝试将消息回显给我的客户端时,我无法将其发送到正确的位置,因为我收到的 IP 地址与::1 不同。
Here is some code:这是一些代码:
Client.c客户端.c
void main(int argc, char* argv[]) // argc is # of strings following command, argv[] is array of ptrs to the strings
{
WSADATA wsaData; // contains details about WinSock DLL implementation
struct sockaddr_in6 serverInfo; // standard IPv6 structure that holds server socket info
char* serverIPaddr, * phrase, echoBuffer[RCVBUFSIZ];
int serverPort, msgLen, fromSize, echoLen;
// Verify correct number of command line arguments
if (argc != 4) {
printf("Invalid amount of arguments entered. \nPlease make sure to only enter the following: \n\n <application name> <ip address> <port number> <message>");
exit(1);
}
// Retrieve the command line arguments.
// to be converted from char to int.
serverIPaddr = argv[1];
serverPort = atoi(argv[2]);
phrase = argv[3];
msgLen = strlen(phrase) + 1; // We are sending the null terminator
// Initialize Winsock 2.0 DLL.
if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0) {
// Failed
printf("Couldn't initialize Winsock 2.0 DLL");
exit(1);
}
// Create an IPv6 UPD stream socket. Now that Winsock DLL is loaded, we can signal any errors as shown on next line:
int sock;
sock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
if (sock == INVALID_SOCKET) {
DisplayFatalErr("socket() function failed.");
exit(1);
}
printf("Socket created successfully. Press enter to continue...");
getchar();
memset(&serverInfo, 0, sizeof(serverInfo));
serverInfo.sin6_family = AF_INET6;
serverInfo.sin6_port = htons(serverPort);
inet_pton(AF_INET6, serverIPaddr, &serverInfo.sin6_addr);
if (msgLen == 0) {
DisplayFatalErr("Message was empty, please make sure to include a message.");
exit(1);
}
// Send data to server
if (sendto(sock, phrase, msgLen, 0, (struct sockaddr*) & serverInfo, sizeof(serverInfo)) != msgLen) {
DisplayFatalErr("sendto() function failed.");
exit(1);
}
fromSize = sizeof(serverInfo);
if ((echoLen = recvfrom(sock, echoBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & serverInfo.sin6_addr, &fromSize)) != msgLen) {
// We lost some data check for error first
if (echoLen < 0) {
DisplayFatalErr("recvfrom() function failed.");
exit(1);
}
}
// Output message (Will create soon)
printf("");
printf("\nData was received from the server. Press enter to continue...");
getchar();
if (closesocket(sock) != 0) {
DisplayFatalErr("closesocket() function failed.");
}
printf("socket closed successfully. Press enter to continue...");
getchar();
if (WSACleanup() != 0) {
DisplayFatalErr("WSACleanup() function failed.");
}
exit(0);
}
Server.c服务器.c
void main(int argc, char* argv[]) // argc is # of strings following command, argv[] is array of ptrs to the strings
{
WSADATA wsaData; // contains details about WinSock DLL implementation
struct sockaddr_in6 serverInfo; // standard IPv6 structure that holds server socket info
int serverPort, clientSock, rcvLen, fromSize;
char* rcvBuffer[RCVBUFSIZ];
serverPort = 0;
// Verify correct number of command line arguments
if (argc != 2) {
serverPort = DEFAULT_PORT;
}
else {
serverPort = atoi(argv[1]);
}
// Initialize Winsock 2.0 DLL
if (WSAStartup(MAKEWORD(2, 0), &wsaData) != 0) {
// Failed
printf("Couldn't initialize Winsock 2.0 DLL");
exit(1);
}
// Create an IPv6 UDP stream socket.
int sock;
sock = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
if (sock == INVALID_SOCKET) {
DisplayFatalErr("socket() function failed.");
exit(1);
}
// Don't forget any necessary format conversions.
memset(&serverInfo, 0, sizeof(serverInfo));
serverInfo.sin6_family = AF_INET6;
serverInfo.sin6_port = htons(serverPort);
serverInfo.sin6_addr = in6addr_any;
//inet_pton(AF_INET6, serverIPaddr, &serverInfo.sin6_addr);
// Bind the server socket to the sockadder structure.
if (bind(sock, (struct sockadder*) & serverInfo, sizeof(serverInfo)) == SOCKET_ERROR) {
DisplayFatalErr("bind() function failed.");
exit(1);
}
printf("ST's IPv6 echo server is ready for client connection on port: %i\r\n", serverPort);
// Forever Loop waiting for messages
for (;;) {
struct sockaddr_in6 clientInfo; // Hold client port & adder recvfrom
memset(&clientInfo, 0, sizeof(clientInfo));
clientInfo.sin6_family = AF_INET6;
fromSize = sizeof(clientInfo);
if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo.sin6_addr, &fromSize)) < 0) { //THIS IS WHERE I BELIEVE THE ERROR TO BE. WHEN LOOKING AT THE ADDRESS ON THE DEBUGGER IT DOESN'T MATCH THE ONE I SENT USING THE CLIENT
DisplayFatalErr("recvfrom() function failed.");
}
// Processing Socket
char* clientAddr[INET6_ADDRSTRLEN];
inet_ntop(AF_INET6, &(clientInfo.sin6_addr), clientAddr, INET6_ADDRSTRLEN);
int clientPort = ntohs(clientInfo.sin6_port);
printf("Processing the client at %s, client port %i, server port %i.\r\n", clientAddr, clientPort, serverPort);
printf("Message Received: %s\r\n", rcvBuffer);
// Send data back
if (sendto(sock, rcvBuffer, rcvLen, 0, (struct sockaddr*) & clientInfo, sizeof(clientInfo)) != rcvLen) {
DisplayFatalErr("sendto() function failed.");
}
}
}
Let me know if you need me to provide any other information.如果您需要我提供任何其他信息,请告诉我。
You are correct, the problem is here:你是对的,问题出在这里:
if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo.sin6_addr, &fromSize)) < 0) {
// ^^^^^^^^^^
You are not passing a sockaddr *
, you are passing a struct in6_addr *
.您没有传递sockaddr *
,而是传递了struct in6_addr *
。 Just drop the .sin6_addr
part:只需删除.sin6_addr
部分:
if ((rcvLen = recvfrom(sock, rcvBuffer, RCVBUFSIZ, 0, (struct sockaddr*) & clientInfo, &fromSize)) < 0) {
When the server calls recvfrom()
, you are passing it an in6_addr*
instead of a sockaddr_in6*
in the from
parameter.当服务器调用recvfrom()
时,您将在from
参数中传递一个in6_addr*
而不是sockaddr_in6*
。 You need to pass in a pointer to the whole sockaddr_in6
, not a pointer to just its sin6_addr
field:您需要传入一个指向整个sockaddr_in6
的指针,而不是指向其sin6_addr
字段的指针:
recvfrom(..., (struct sockaddr*) &clientInfo, ...) // <-- NOT &clientInfo.sin6_addr!
There are other problems in the server, too.服务器中还有其他问题。
Once the server has received a message, it is calling inet_ntop()
to convert the client's source IP address to a string.一旦服务器收到消息,它就会调用inet_ntop()
将客户端的源 IP 地址转换为字符串。 However, it passing in a char*[]
array, but it needs to pass in a char[]
array instead:但是,它传入了一个char*[]
数组,但它需要传入一个char[]
数组:
char clientAddr[INET6_ADDRSTRLEN]; // <-- char, NOT char*!
inet_ntop(AF_INET6, &(clientInfo.sin6_addr), clientAddr, INET6_ADDRSTRLEN);
Also, when printing out the received message, you are treating it as a null-terminated string.此外,在打印出接收到的消息时,您会将其视为以空字符结尾的字符串。 Which is fine in this example since your client is sending a null terminator, but that is not a good idea for your server to rely on in general.在此示例中这很好,因为您的客户端正在发送 null 终结器,但这对于您的服务器来说通常不是一个好主意。 That is a good way for malicious clients to cause buffer overflow attacks.这是恶意客户端引发缓冲区溢出攻击的好方法。 You should instead use the actual byte size that recvfrom()
returns:您应该改用recvfrom()
返回的实际字节大小:
printf("Message Received: %.*s\r\n", rcvLen, rcvBuffer);
And when calling sendto()
to echo the message back to the client, you should use the actual fromSize
reported by recvfrom()
instead of using sizeof(clientInfo)
for the client's address size:当调用sendto()
将消息回显给客户端时,您应该使用recvfrom()
报告的实际fromSize
而不是使用sizeof(clientInfo)
作为客户端的地址大小:
sendto(..., (struct sockaddr*) &clientInfo, fromSize)
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