套接字编程:C 中的 UDP 客户端-服务器 [英] Socket Programming: UDP Client-Server in C
问题描述
我正在尝试使用 UDP 和等待并停止编写客户端服务器程序，但我还没有到那部分，我仍在尝试弄清楚这两个进程(服务器和客户端) 通信，因为在我的客户端程序中，用户需要输入服务器名称或IP地址，以及端口名称，然后发送服务器应该计算的表达式.但是，我在互联网上挖了一些教程，在进行相应的编码后(或者我是这样认为的)，我无法让客户端与服务器进行通信.下面是我的代码，如果是bind()、sendto()、recvfrom()，请指教我做错了什么或 socket()，或所有这些.我看不出到底出了什么问题.我知道客户端不应该无限循环运行，但到目前为止我想让程序相互通信，然后我会改进我的代码.谢谢！
I'm trying to write a client server program using UDP, and wait-and-stop, but I haven't got to that part, I'm still trying to figure it out how the two processes (server and client) communicate, because on my client program, the user needs to enter the server name or IP address, and a port name, and then send an expression that the server should calculate. However, I dug some tutorials in the internet and after coding accordingly (or I thought so) I can't make the client communicate with the server. Below is my code, please enlighten me what I'm doing wrong, if it's the bind(), sendto(), recvfrom() or socket(), or all of them. I can't see what exactly is wrong. I know that the client-side shouldn't run on a infinite loop, but so far I want to make the programs communicate with each other, afterwards I'll polish my code. Thanks!
客户端代码:
#include <stdio.h> // Default System Calls
#include <stdlib.h> // Needed for OS X
#include <string.h> // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h> // To control the timeout mechanism
#define EXPR_SIZE 1024
#define BUFLEN 512
#define TRUE 1
#define FALSE 0
#define SERVERLEN 1024
int main(int argc, char **argv){
long portNum; // Since it's possible to input a value bigger
// than 65535 we'll be using long to
// avoid overflows
char expr[EXPR_SIZE];
char server[SERVERLEN];
int fd; // file descriptor for the connected socket
int buf[512];
struct hostent *h; // information of the host
unsigned int addrLen; // address length after getting the port number
struct sockaddr_in myaddr; // address of the client
struct sockaddr_in servaddr; // server's address
unsigned int exprLen;
socklen_t slen = sizeof(servaddr);
printf("Enter server name or IP address:");
scanf("%s",server);
printf("Enter port:");
scanf("%ld",&portNum);
if ((portNum < 0) || (portNum > 65535)) {
printf("Invalid port number. Terminating.");
return 0;
}
printf("Enter expression:");
scanf("%s",expr);
if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
perror("cannot create socket");
return 0;
}
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
myaddr.sin_port = htons(0);
if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
perror("cannot bind");
return 0;
}
/*
// Discovering the port number the OS allocated
addrLen = sizeof(myaddr);
if(getsockname(fd, (struct sockaddr *)&myaddr, &addrLen) < 0){
perror("cannot getsockname");
return 0;
}
printf("local port number = %d
", ntohs(myaddr.sin_port));
*/
memset((char*)&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htonl(portNum);
exprLen = sizeof(expr);
while(TRUE){
printf("Sending message to %s port %ld
",server, portNum);
if (sendto(fd, expr, strlen(expr), 0, (struct sockaddr *)&servaddr, slen) < 0) {
perror("cannot sendto()");
}
printf("Success
");
}
return 0;
}
服务端代码:
#include <stdio.h> // Default System Calls
#include <stdlib.h> // Needed for OS X
#include <string.h> // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h> // To control the timeout mechanism
#define EXPR_SIZE 1024
#define BUFLEN 512
#define TRUE 1
#define SERVERLEN 1024
int main(int argc, char **argv){
struct sockaddr_in myaddr; // address of the server
struct sockaddr_in claddr; // address of the client
char buf[BUFLEN];
int fd;
long recvlen;
socklen_t clientlen;
if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
perror("cannot create socket");
return 0;
}
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
myaddr.sin_port = htons(0);
if(bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0){
perror("cannot bind");
return 0;
}
clientlen = sizeof(claddr);
while (TRUE) {
recvlen = recvfrom(fd, buf, BUFLEN, 0, (struct sockaddr *)&claddr, &clientlen);
if (recvlen < 0) {
perror("cannot recvfrom()");
return 0;
}
printf("Received %ld bytes
",recvlen);
buf[recvlen] = 0;
printf("Received message: "%s"
",buf);
}
return 0;
}
服务端程序不输出任何东西，而客户端输出直到进程中断:
The server program doesn't output anything, while the client outputs until the process is interrupted:
Enter server name or IP address:127.0.0.1
Enter port:30
Enter expression:2+2
Sending message to 127.0.0.1 port 30
cannot sendto(): Can't assign requested address
我尝试将服务器名称更改为 localhost 和其他端口，但无济于事.
I tried changing the server name to localhost, and other ports, but to no avail.
推荐答案
在开发网络软件时(尤其是在使用 BSD 套接字接口时)，在您建立基本通信之前保持事情尽可能简单很重要.然后，您可以逐步添加功能，同时确保在此过程中不会破坏任何内容.
When developing networking software (especially when using the BSD socket interface), it's important to keep things as simple as possible until you've established basic communication. Then you can incrementally add functionality, while making sure that you don't break anything along the way.
在客户端，保持简单意味着
On the client side, keeping things simple means
不要在客户端调用
bind.操作系统会选择一个合适的接口并随机分配一个端口号，所以不需要绑定套接字.
Don't call
bindin the client. The OS will choose an appropriate interface and assign a random port number, so there's no need tobindthe socket.
使用硬编码的服务器地址(例如 127.0.0.1).地址127.0.0.1(0x7f000001)是本地主机地址，适合向同一台机器上的服务器发送数据包.
Use a hard-coded server address (e.g. 127.0.0.1). Address 127.0.0.1 (0x7f000001) is the local host address, suitable for sending packets to a server on the same machine.
使用硬编码的端口号(例如 50037).临时端口号应大于 0xC000 十六进制(十进制 49152).
Use a hard-coded port number (e.g. 50037). Ephemeral port numbers should be greater than 0xC000 hex (49152 decimal).
使用硬编码的消息，例如你好".
Use a hard-coded message, e.g. "hello".
考虑到这一点，这就是客户端软件的样子
With that in mind, here's what the client software looks like
int main( void )
{
int fd;
if ( (fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket failed");
return 1;
}
struct sockaddr_in serveraddr;
memset( &serveraddr, 0, sizeof(serveraddr) );
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons( 50037 );
serveraddr.sin_addr.s_addr = htonl( 0x7f000001 );
for ( int i = 0; i < 4; i++ ) {
if (sendto( fd, "hello", 5, 0, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0 ) {
perror( "sendto failed" );
break;
}
printf( "message sent
" );
}
close( fd );
}
在服务器端，保持简单意味着
On the server side, keeping things simple means
- 绑定到
INADDR_ANY，即让操作系统选择合适的接口. - 绑定到硬编码端口，例如50037(必须与客户端使用的端口相同).
- 不要向
recvfrom请求地址信息，即传递NULL, 0作为最后两个参数.
- Bind to
INADDR_ANY, i.e. let the OS pick an appropriate interface. - Bind to a hard-coded port, e.g. 50037 (must be the same port the client uses).
- Don't request the address information from
recvfrom, i.e. passNULL, 0as the last two parameters.
考虑到这一点，这是服务器软件的样子
With that in mind, here's what the server software looks like
int main( void )
{
int fd;
if ( (fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror( "socket failed" );
return 1;
}
struct sockaddr_in serveraddr;
memset( &serveraddr, 0, sizeof(serveraddr) );
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons( 50037 );
serveraddr.sin_addr.s_addr = htonl( INADDR_ANY );
if ( bind(fd, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0 ) {
perror( "bind failed" );
return 1;
}
char buffer[200];
for ( int i = 0; i < 4; i++ ) {
int length = recvfrom( fd, buffer, sizeof(buffer) - 1, 0, NULL, 0 );
if ( length < 0 ) {
perror( "recvfrom failed" );
break;
}
buffer[length] = ' ';
printf( "%d bytes: '%s'
", length, buffer );
}
close( fd );
}
这篇关于套接字编程:C 中的 UDP 客户端-服务器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
