我有一个服务器/客户端应用程序，我试图让服务器读取客户端发送给它的每条消息，然后将其发送回客户端进行打印。到目前为止，我已经让服务器读取了第一条消息并将其发送到客户端，并且可以正常打印，但是当第二条消息从客户端发送时，我尝试通过HandleTcpClient函数对其进行打印以对其进行测试，并且它只打印null，我不确定它是否正确接收
客户代码：
#include <stdio.h> //include standard input/output library
#include <stdlib.h> //include standard libraries
#include <string.h> //include string headers
#include <unistd.h> //add definitions for constansts and functions
#include <sys/types.h> // include definitions for different data types
#include <sys/socket.h> //include socket support
#include <netinet/in.h> //define internet protocol functions
#include <arpa/inet.h> //define internet protocol functions
#include "Practical.h" //include practical header file
int main(int argc, char *argv[]) {
char myIP[16];
unsigned int myPort;
struct sockaddr_in server_addr,myaddr;
char username[] = "CharlieA";
if (argc < 2 || argc > 3) // Test for correct number of arguments
DieWithUserMessage("Parameter(s)",
"<Server Address> [<Server Port>]");
char *servIP = argv[1]; // First arg: server IP address (dotted quad)
// Third arg (optional): server port (numeric). 7 is well-known echo port
in_port_t servPort = atoi(argv[2]); //21
printf("serv port: %d\n",servPort);
// Create a reliable, stream socket using TCP //23
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);//this block of code creates a reliable tcp stream socket and checks what the returned integer is from the socket function, the returned function will give a integer that descibes the socket. if this is 0 then kill the socket and show the user an error message.
if (sock < 0)
DieWithSystemMessage("socket() failed"); //26
// Construct the server address structure //28
struct sockaddr_in servAddr; // Server address
memset(&servAddr, 0, sizeof(servAddr)); // Zero out structure
servAddr.sin_family = AF_INET; // IPv4 address family
// Convert address
int rtnVal = inet_pton(AF_INET, servIP, &servAddr.sin_addr.s_addr);
if (rtnVal == 0)
DieWithUserMessage("inet_pton() failed", "invalid address string");
else if (rtnVal < 0)
DieWithSystemMessage("inet_pton() failed");
servAddr.sin_port = htons(servPort); // Server port
myaddr.sin_addr.s_addr = INADDR_ANY;
// Establish the connection to the echo server
if (connect(sock, (struct sockaddr *) &servAddr, sizeof(servAddr)) < 0)
DieWithSystemMessage("connect() failed");
//get address of bound socket after connect function call (binds automatically with connect method)
bzero(&myaddr,sizeof(myaddr));
int len = sizeof(myaddr);
getsockname(sock,(struct sockaddr *) &myaddr, &len);
inet_ntop(AF_INET, &myaddr.sin_addr, myIP, sizeof(myIP)); //convert network address to string
myPort = ntohs(myaddr.sin_port); //convert from netshort to hostbyte order
//getlocal ip address to be sent to server
char *echoString=(char*)malloc(13*sizeof(char));
sprintf(echoString,"netsrv type0 %s %s-%u\r\n",username,myIP,myPort); //generate request string
size_t echoStringLen = strlen(echoString); // Determine input length //44
size_t iplen = strlen(myIP);
// Send the string to the server
ssize_t numBytes = send(sock,echoString, echoStringLen, 0);
printf("sent: %s", echoString);
if (numBytes < 0) //sending string to server, number of bytes of the message is equal to return value of send function, if the number of bytes is less than 0 then do not send and say to user that the send failed
DieWithSystemMessage("send() failed");
else if (numBytes != echoStringLen)
DieWithUserMessage("send()", "sent unexpected number of bytes"); //51
// if the number of bytes is not equal to the input length of the string parsed as an argument then die with the message to the user saying sent unexpected number of bytes.
//send IP to server
send(sock,myIP,iplen,0); //send client IP
// Receive the same string back from the server //53
unsigned int totalBytesRcvd = 0; // Count of total bytes received
while (totalBytesRcvd < echoStringLen) {
char buffer[BUFSIZE]; // I/O buffer
/* Receive up to the buffer size (minus 1 to leave space for
a null terminator) bytes from the sender */
numBytes = recv(sock, buffer, BUFSIZE - 1, 0);
if (numBytes < 0)
DieWithSystemMessage("recv() failed");
else if (numBytes == 0)
DieWithUserMessage("recv()", "connection closed prematurely");
totalBytesRcvd += numBytes; // Keep tally of total bytes
buffer[numBytes] = '\0'; // Terminate the string!
fputs("Received: ", stdout); // Setup to print the echoed string
fputs(buffer, stdout); // Print the echo buffer
}
fputc('\n', stdout); // Print a final linefeed //70
close(sock);
exit(0);
}
//closing off connections to clean up data left over.
第二条消息是发送客户端IP注释行
服务器：
#include <stdio.h> //include standard input/output library
#include <stdlib.h> //include standard libraries
#include <string.h> //include string headers
#include <sys/types.h> //add definitions for constansts and functions
#include <sys/socket.h> // include definitions for different data types
#include <netinet/in.h> //define internet protocol functions
#include <arpa/inet.h> //define internet protocol functions
#include "Practical.h" //include pactical
static const int MAXPENDING = 5; // Maximum outstanding connection requests
static const int servPort = 48031;
int main(int argc) {//run on command line = "echoSvr <port>";argc = 2 command and parameter- argv[0] = echoSvr and argv[1] = <port>
// Create socket for incoming connections
int servSock; // Socket descriptor for server
if ((servSock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
DieWithSystemMessage("socket() failed");
// this block of code is creating a socket stream to accept the incoming connections from clients
// Construct local address structure
struct sockaddr_in servAddr; // Local address; internet socket address structure
memset(&servAddr, 0, sizeof(servAddr)); // Zero out structure
servAddr.sin_family = AF_INET; // IPv4 address family
servAddr.sin_addr.s_addr = htonl(INADDR_ANY); // Any incoming interface; host to network long[integer]
servAddr.sin_port = htons(servPort); // Local port; host to network short[integer]
// Bind to the local address
if (bind(servSock, (struct sockaddr*) &servAddr, sizeof(servAddr)) < 0)//cast servaddr as generic socket address structure
DieWithSystemMessage("bind() failed");
// Mark the socket so it will listen for incoming connections
if (listen(servSock, MAXPENDING) < 0)
DieWithSystemMessage("listen() failed");
setvbuf (stdout, NULL, _IONBF, 0);
printf("Listening on port: %d \n" , servPort);
printf("awaiting connection from client.... \n");
// this block of code binds the socket to the address of the server and tells the binded to socket to begin listening in for connections coming from client machines
for (;;) { // Run forever
struct sockaddr_in clntAddr; // Client address
// Set length of client address structure (in-out parameter)
socklen_t clntAddrLen = sizeof(clntAddr);
// Wait for a client to connect
int clntSock = accept(servSock, (struct sockaddr *) &clntAddr, &clntAddrLen);
if (clntSock < 0)
DieWithSystemMessage("accept() failed");
//this block of code waits for a client to connect to the socket and then accepts the connection from the client and prints the clients details out to screen
// clntSock is connected to a client!
char clntName[INET_ADDRSTRLEN]; // String to contain client address
if (inet_ntop(AF_INET, &clntAddr.sin_addr.s_addr, clntName,
sizeof(clntName)) != NULL)
printf("Handling client %s/%d\n", clntName, ntohs(clntAddr.sin_port));
else
puts("Unable to get client address");
HandleTCPClient(clntSock);
}
}
HandleTCPClient函数：
void HandleTCPClient(int clntSocket) {
char buffer[BUFSIZE]; // Buffer for echo string
char *clientIP;
unsigned int clientPort;
// Receive message from client
ssize_t numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);
if (numBytesRcvd < 0)
DieWithSystemMessage("recv() failed");
//get ip and port of clntSocket to apply to greeting string
// Send greeting string and receive again until end of stream
while (numBytesRcvd > 0) { // 0 indicates end of stream
// Echo message back to client
ssize_t numBytesSent = send(clntSocket, buffer, numBytesRcvd, 0);
if (numBytesSent < 0)
DieWithSystemMessage("send() failed");
else if (numBytesSent != numBytesRcvd)
DieWithUserMessage("send()", "sent unexpected number of bytes");
// See if there is more data to receive
numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);
if (numBytesRcvd < 0)
DieWithSystemMessage("recv() failed");
//recv client ip and assign to variable to hold
recv(clntSocket,clientIP,100,0);
printf("clientIP : %s" ,clientIP);
}
close(clntSocket); // Close client socket
}
我正在尝试使用printf函数打印clientIP，这就是我得到null的地方，它似乎没有收到它，这里有很多代码，我将其全部发布以防万一是
答案 0 :(得分：0)
这是很多代码，所以我没有看大部分。但是，我确实注意到了：
char *echoString=(char*)malloc(13*sizeof(char));
sprintf(echoString,"netsrv type0 %s %s-%u\r\n",username,myIP,myPort);
您无法解释这13个字符的来源，但显然不足以容纳sprintf将产生的格式化字符串。容纳12个字符的字符串（加上NUL终止符）就足够了，您最多可以使用netsrv type0。这需要解决，因为sprintf会破坏不属于它的随机内存，但这可能不是您的直接问题。 （使用snprintf。如果使用的是Linux / OSX / FreeBSD，更简单的是asprintf。）
我认为您的问题可能是这样的：
numBytesRcvd = recv(clntSocket, buffer, BUFSIZE, 0);
//recv client ip and assign to variable to hold
recv(clntSocket,clientIP,100,0);
printf("clientIP : %s" ,clientIP);
您永远不会查看第一次recv()调用所收到的数据。也许您会误以为每个send都以某种方式标记了要发送的数据，因此recv仅能准确读取一个send发送的数据。事实并非如此。 TCP是一种流协议。数据只是一系列不可区分的字节，每个recv()都会接收可用的内容，但要视调用的大小限制而定。因此，两个send()调用的结果很有可能会出现在第一个recv()调用中。
我认为这可能在您用来编写该代码的任何文本/教程/指南中都有解释，但是如果没有，我强烈建议您找到W. R. Stevens' Unix Network Programming的副本。
简而言之：如果要发送“消息”，则需要弄清楚如何对它们进行定界，以使接收者可以分辨出一条消息在哪里结束而下一条消息在哪里开始。许多较旧的Internet协议使用的一种非常简单的策略是，以一条换行符结束每条消息，并确保每条消息中都没有换行符。