套接字编程：C语言中的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编写客户端服务器程序，然后等待并停止，但是我还没有涉及到那部分，我仍在尝试弄清楚这两个过程（服务器和客户端）的过程）进行通信，因为在我的客户端程序上，用户需要输入服务器名称或IP地址以及端口名称，然后发送服务器应计算的表达式。但是，我在互联网上挖了一些教程，并进行了相应的编码（或者我认为是这样）之后，我无法使客户端与服务器通信。下面是我的代码，如果它是 bind（）， sendto（）， recvfrom（）或 socket（）或全部。我看不出到底有什么问题。我知道客户端不应该在无限循环中运行，但是到目前为止，我想使程序彼此通信，然后再完善代码。
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\n", 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\n",server, portNum);
if (sendto(fd, expr, strlen(expr), 0, (struct sockaddr *)&servaddr, slen) < 0) {
perror("cannot sendto()");
}
printf("Success\n");
}
return 0;
}
服务器端代码：
#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\n",recvlen);
buf[recvlen] = 0;
printf("Received message: \"%s\"\n",buf);
}
return 0;
}
服务器程序不输出任何内容，而客户端则输出直到该过程中断：
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），在建立基本通信之前，使事情尽可能简单是很重要的。然后，您可以逐步添加功能，同时确保一路上不会破坏任何东西。
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。操作系统将选择适当的接口并分配一个随机端口号，因此无需绑定套接字。
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，适合将数据包发送到同一台计算机上的服务器。
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）。 星号端口号应大于0xC000十六进制（十进制为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".
请记住，这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\n" );
}
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）。
- 不要从
recvfrom请求地址信息，即传递NULL，最后两个参数为0。
- 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.
请牢记这一点服务器软件看起来像
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] = '\0';
printf( "%d bytes: '%s'\n", length, buffer );
}
close( fd );
}
这篇关于套接字编程：C语言中的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！
