c - 如何在C中的新任意端口上重定向客户端程序
问题描述
我正在尝试在 C 中实现客户端-服务器程序。我希望客户端在特定端口 5555 上连接到服务器。服务器接受连接后,我希望服务器将任意端口发送回客户端。为了将客户端重定向到客户端可以发送信息的端口。我的问题是客户端收到新端口但无法通过该端口连接到服务器
客户端源代码如下(graham.c):
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#define PORT 5555
#define MAX_USERNAME_SIZE 16
#define MAX_FILENAME_SIZE 255
#define BUFFSIZE 1024
char *extract_filename_from_path(char *pathname);
char *extract_filename_from_path(char *pathname)
{
char *last = strrchr(pathname, '/');
return (last != NULL) ? last + 1 : pathname;
}
int main(int argc, char *argv[])
{
int sockfd1, sockfd2, numbytes;
struct sockaddr_in their_addr;
struct hostent *he;
FILE *photo;
char buff[BUFFSIZE];
short status = 1;
// verifier le nombre d'arguments
if (argc != 7)
{
fprintf(stderr, "Compléter sa commande de la façon suivante:\n"
"graham ip_serveur nom_utilisateur_dans_le_pool"
" /chemin/vers/la/photo année mois jour");
return EXIT_FAILURE;
}
if ((he = gethostbyname(argv[1])) == NULL)
{
perror("Client: gethostbyname");
return EXIT_FAILURE;
}
// initialiser le socket 1
if ((sockfd1 = socket(PF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Client: socket");
return EXIT_FAILURE;
}
their_addr.sin_family = AF_INET;
their_addr.sin_port = htons(PORT);
their_addr.sin_addr = *((struct in_addr*)he->h_addr);
memset(&(their_addr.sin_zero), '\0', 8);
if (connect(sockfd1, (struct sockaddr *)&their_addr,
sizeof(struct sockaddr)) == -1)
{
perror("Client: connect 1");
return EXIT_FAILURE;
}
// get port
short int port;
if (recv(sockfd1, &port, sizeof(short int), 0) == -1)
{
perror("Client: recv port");
return EXIT_FAILURE;
}
printf("recieved port: %d\n", ntohs(port));
close(sockfd1);
// changer de port
// initialiser le socket 2
if ((sockfd2 = socket(PF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Client: socket");
return EXIT_FAILURE;
}
their_addr.sin_family = AF_INET;
their_addr.sin_port = port;
their_addr.sin_addr = *((struct in_addr*)he->h_addr);
memset(&(their_addr.sin_zero), '\0', 8);
if (connect(sockfd2, (struct sockaddr *)&their_addr,
sizeof(struct sockaddr)) == -1)
{
perror("Client: connect 2");
return EXIT_FAILURE;
}
// 2) envoyer le nom d'utilisateur
if (send(sockfd2, argv[2], MAX_USERNAME_SIZE, 0) == -1)
{
perror("Client: send username");
return EXIT_FAILURE;
}
// 3) envoyer la date de prise
if (send(sockfd2, argv[4], 5, 0) == -1)
{
perror("Client: send year");
return EXIT_FAILURE;
}
if (send(sockfd2, argv[5], 3, 0) == -1)
{
perror("Client: send month");
return EXIT_FAILURE;
}
if (send(sockfd2, argv[6], 3, 0) == -1)
{
perror("Client: send day");
return EXIT_FAILURE;
}
// 4) envoyer le nom de l'image
if (send(sockfd2, extract_filename_from_path(argv[3]), MAX_FILENAME_SIZE, 0) == -1)
{
perror("Client: send filename");
return EXIT_SUCCESS;
}
// 5) envoyer l'image au client
if ((photo = fopen(argv[3], "r")) == NULL)
{
perror("Client: fopen");
return EXIT_FAILURE;
}
do
{
if ((numbytes = write(sockfd2, buff, BUFFSIZE)) > 0)
{
for (int i = 0; i < numbytes; i++)
{
buff[i] = getc(photo);
}
}
else
{
break;
}
}while(1);
fclose(photo);
// 6) recevoir et traiter le code de retour
if ((numbytes = recv(sockfd2, &status, sizeof(short int), 0)) == -1)
{
perror("Client: recv return code");
return EXIT_FAILURE;
}
if ((status = ntohs(status)))
{
fprintf(stderr, "Echec de la transaction");
}
close(sockfd2);
return EXIT_SUCCESS;
}
服务器源代码是(spbx.c):
#include "spbx.h"
int my_read(FILE *target, const int source_fd)
{
char buff[BUFFSIZE];
memset(buff, '\0', BUFFSIZE);
int numbytes;
int status = 0;
if ((numbytes = read(source_fd, buff, BUFFSIZE)) > 0)
{
for (int i = 0; i < numbytes; i++)
{
putc(buff[i], target);
}
}
else
{
status = -1;
}
return status;
}
int my_mkdir(const char *path, mode_t mode)
{
struct stat s;
int status = 0;
if (stat(path, &s) == -1)
{
if (mkdir(path, mode) == -1 && errno != EEXIST)
{
status = -1;
}
}
else
{
errno = ENOTDIR;
status = -1;
}
return status;
}
int init_socket(int *sockfd, const short int port)
{
struct sockaddr_in my_addr;
int yes = 1;
if ((*sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Serveur: socket");
return -1;
}
if (setsockopt(*sockfd, SOL_SOCKET,
SO_REUSEADDR, &yes, sizeof(int)) == -1)
{
perror("Serveur: setsockopt");
return -1;
}
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(port);
my_addr.sin_addr.s_addr = INADDR_ANY;
memset(&(my_addr.sin_zero), '\0', 8);
if (bind(*sockfd, (struct sockaddr *)&my_addr,
sizeof(struct sockaddr)) == -1)
{
perror("Serveur: bind");
return -1;
}
if (listen(*sockfd, BACKLOG) == -1)
{
perror("Serveur: listen");
return -1;
}
return 0;
}
int recv_date(int new_fd, char **year, char **month, char **day)
{
int numbytes;
if ((numbytes = recv(new_fd, year, 5, 0)) == -1)
{
perror("Serveur: recv year");
return -1;
}
if ((numbytes = recv(new_fd, month, 3, 0)) == -1)
{
perror("Serveur: recv month");
return -1;
}
if ((numbytes = recv(new_fd, day, 3, 0)) == -1)
{
perror("Serveur: recv day");
return -1;
}
return 0;
}
int main(int argc, char *argv[])
{
// ecouter sur sockfd et etablir la nouvelle
// connexion sur new_fd
int sockfd1, sockfd2, new_fd, numbytes, photo_tmp_fd;
struct sockaddr_in their_addr;
unsigned int sin_size;
char username[MAX_USERNAME_SIZE];
char filename[MAX_FILENAME_SIZE];
char path_tmp[MAX_FILEPATH_SIZE];
char path[MAX_FILEPATH_SIZE];
memset(path, '\0', MAX_FILEPATH_SIZE);
char year[5], month[3], day[3];
FILE *photo_tmp;
FILE *photo;
short int status = 1;
fd_set readfds;
int max;
// verifier le nombre d'arguments
if (argc != 2)
{
fprintf(stderr, "Donner le chemin vers le pool 2\n");
return EXIT_FAILURE;
}
// initialiser les socket
if(init_socket(&sockfd1, MY_PORT) == -1) return EXIT_FAILURE;
if(init_socket(&sockfd2, 0) == -1) return EXIT_FAILURE;
struct sockaddr_in my_addr;
if (getsockname(sockfd2, (struct sockaddr*)&my_addr, &sin_size) == -1)
{
perror("Serveur: getsockname");
return EXIT_FAILURE;
}
sin_size = sizeof(struct sockaddr_in);
while (1)
{
//initialisation du fd_set
FD_ZERO(&readfds);
FD_SET(sockfd1, &readfds);
FD_SET(sockfd2, &readfds);
max = (sockfd1 < sockfd2)? sockfd2 : sockfd1;
select(max + 1, &readfds, NULL, NULL, NULL);
if (FD_ISSET(sockfd1, &readfds))
{
// on envoie le port
if ((new_fd = accept(sockfd1,
(struct sockaddr *)&their_addr,
&sin_size)) == -1)
{
perror("Serveur: accept 1");
return EXIT_FAILURE;
}
printf("Serveur: connexion reçue du client %s\n",
inet_ntoa(their_addr.sin_addr));
if (fork() == 0)
{
close(sockfd1);
if (send(new_fd, &my_addr.sin_port, sizeof(short int), 0) == -1)
{
perror("Serveur: send port");
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
close(new_fd);
}
else if (FD_ISSET(sockfd2, &readfds))
{
if ((new_fd = accept(sockfd2,
(struct sockaddr *)&their_addr, &sin_size)) == -1)
{
perror("Serveur: accept 2");
return EXIT_FAILURE;
}
printf("Serveur: connexion reçue du client %s redirigé vers le port %d\n",
inet_ntoa(their_addr.sin_addr), ntohs(my_addr.sin_port));
if (fork() == 0)
{
close(sockfd1);
close(sockfd2);
// 2) recevoir l'utilisateur du pool sous forme
// de chaîne de caractères
if ((numbytes = recv(new_fd, &username, MAX_USERNAME_SIZE, 0)) == -1)
{
perror("Serveur: recv username");
return EXIT_FAILURE;
}
// 3) récevoir la date de prise de vue
if(recv_date(new_fd, (char **) &year, (char **)&month, (char **) &day) == -1)
return EXIT_FAILURE;
// 4) recevoir le nom du fichier
if ((numbytes = recv(new_fd, &filename, MAX_FILENAME_SIZE, 0)) == -1)
{
perror("Serveur: recv filename");
return EXIT_FAILURE;
}
// 5) recevoir l'image téléversée par le client
sprintf(path_tmp, "/tmp/%s", filename);
if ((photo_tmp = fopen(path_tmp, "w")) == NULL)
{
perror("Serveur: fopen");
return EXIT_FAILURE;
}
do
{
if (my_read(photo_tmp, sockfd2) == -1) break;
}while(1);
fclose(photo_tmp);
// 6) creer l'arborescence
sprintf(path, "%s/%s", argv[1], username);
my_mkdir(path, MODE);
sprintf(path, "%s/%s/%s", argv[1], username, year);
my_mkdir(path, MODE);
sprintf(path, "%s/%s/%s/%s", argv[1], username, year, month);
my_mkdir(path, MODE);
sprintf(path, "%s/%s/%s/%s/%s", argv[1], username, year, month, day);
my_mkdir(path, MODE);
sprintf(path, "%s/%s/%s/%s/%s/%s", argv[1], username, year, month, day, filename);
// 7) Enregistrement de la photographie
if ((photo = fopen(path, "w")) == NULL
|| (photo_tmp_fd = open(path_tmp, O_WRONLY)) == -1)
{
perror("Serveur: fopen");
return EXIT_FAILURE;
}
do
{
if (my_read(photo, photo_tmp_fd) == -1) break;
}while(1);
close(photo_tmp_fd);
fclose(photo);
// 8) enoyer le code 0 en cas de success
status = htons(0);
if (send(new_fd, &status, sizeof(short int), 0) == -1)
{
perror("Serveur: send code");
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
close(new_fd);//9) deconnexion
}
else
{
fprintf(stderr, "erreur de select\n");
}
}
return EXIT_SUCCESS;
}
当我运行服务器并尝试使用客户端程序连接到它两次时,我得到以下结果:
服务器端:
Serveur: connexion reçue du client 127.0.0.1
Serveur: connexion reçue du client 127.0.0.1
客户端:
recieved port: 4645
Client: connect 2: Connection refused
recieved port: 4645
Client: connect 2: Connection refused
我唯一注意到的是,对于服务器的相同执行和客户端的多次执行,端口保持不变。但我不知道我做错了什么。提前致谢。
解决方案
如@ChrisTurner 所述,我应该在客户端连接后创建新套接字。所以我移动了以下几行:
if(init_socket(&sockfd2, 0) == -1) return EXIT_FAILURE;
if (getsockname(sockfd2, (struct sockaddr*)&my_addr, &sin_size) == -1)
{
perror("Serveur: getsockname");
return EXIT_FAILURE;
}
就在第一个accept()
和fork()
服务器程序之前。
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