【发布时间】：2018-01-20 10:07:11
【问题描述】：
所以我正在尝试解决这个玩具客户端文件服务器问题。
迭代版本运行良好，但是当我尝试在服务器代码中分叉每个新连接时，客户端代码在 recv 调用上挂起。
我很确定问题出在 peer_socket 上，但我一直找不到我的错误。
如果我用 Ctrl-c 访问服务器，它就可以完成。
客户代码：
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netinet/in.h>
#define PORT_NUMBER 5108
#define SERVER_ADDRESS "localhost"
//#define FILENAME "test.txt"
int main(int argc, char **argv)
{
int client_socket;
ssize_t len;
struct sockaddr_in remote_addr;
char buffer[BUFSIZ];
char filename[256];
char local_filename[256];
int file_size;
FILE *received_file;
int remain_data = 0;
/* Zeroing remote_addr struct */
memset(&remote_addr, 0, sizeof(remote_addr));
memset(local_filename, 0, sizeof(local_filename));
if(argc >1){
strncpy(local_filename, argv[1], 256);
}
/* Construct remote_addr struct */
remote_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERVER_ADDRESS, &(remote_addr.sin_addr));
remote_addr.sin_port = htons(PORT_NUMBER);
/* Create client socket */
client_socket = socket(AF_INET, SOCK_STREAM, 0);
if (client_socket == -1)
{
fprintf(stderr, "Error creating socket --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
//Prompt for file to retrieve
printf("Enter file name: ");
fgets(filename,sizeof(filename),stdin);
printf("Getting file %s", filename);
/* Connect to the server */
if (connect(client_socket, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1)
{
fprintf(stderr, "Error on connect --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
//Send filename to server
/*if(!send(client_socket,filename, sizeof(filename))) {
printf("Error sending filename\n");
exit(EXIT_FAILURE);
}*/
send(client_socket,filename, sizeof(filename),0);
printf("success\n");
/* Receiving file size */
memset(&buffer, 0, sizeof(buffer));
recv(client_socket, buffer, sizeof(buffer), 0);
file_size = atoi(buffer);
fprintf(stdout, "\nFile size : %d\n", file_size);
if(!local_filename[0]) {
received_file = fopen("test2.txt", "w");
}else{
received_file = fopen(local_filename, "w");
}
if (received_file == NULL)
{
fprintf(stderr, "Failed to open file foo --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
remain_data = file_size;
//THIS IS THE LOOP THAT HANGS!
while (((len = recv(client_socket, buffer, BUFSIZ, 0)) > 0) && (remain_data > 0))
{
fwrite(buffer, sizeof(char), len, received_file);
remain_data -= len;
fprintf(stdout, "Receive %d bytes and we hope :- %d bytes\n", len, remain_data);
}
printf("did we reach here in the code?\n");
fclose(received_file);
printf("did we reach here in the code?\n");
close(client_socket);
return 0;
}
服务器代码：
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <signal.h>
#define PORT_NUMBER 5108
#define SERVER_ADDRESS "localhost"
//#define FILE_TO_SEND "hello.c"
int main(int argc, char **argv)
{
int server_socket;
socklen_t global_sock_len;
struct sockaddr_in server_addr;
struct sockaddr_in peer_addr;
/* Create server socket */
server_socket = socket(AF_INET, SOCK_STREAM, 0);
if (server_socket == -1)
{
fprintf(stderr, "Error creating socket --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Zeroing server_addr struct */
memset(&server_addr, 0, sizeof(server_addr));
/* Construct server_addr struct */
server_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERVER_ADDRESS, &(server_addr.sin_addr));
server_addr.sin_port = htons(PORT_NUMBER);
/* Bind */
if ((bind(server_socket, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))) == -1)
{
fprintf(stderr, "Error on bind --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Listening to incoming connections */
if ((listen(server_socket, 5)) == -1)
{
fprintf(stderr, "Error on listen --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
//attempt multiple connections via fork
int peer_socket;
int fid;
while(1) {
bool servexit = false;
printf("did we reach HERE in the code?%d\n",getpid());
peer_socket = accept(server_socket, (struct sockaddr *) &peer_addr, &global_sock_len);
//printf("did we reach HERE in the code?\n");
if (peer_socket == -1) {
fprintf(stderr, "Error on accept --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
if((fid = fork()) == -1) {
printf("error\n");
close(peer_socket);
//continue;
}else if(fid > 0){
printf("parent\n");
close(peer_socket);
//continue;
}else if(fid == 0) {
printf("child\n");
socklen_t sock_len;
ssize_t len;
int fd;
int sent_bytes = 0;
char FILE_TO_SEND[256];
char file_size[256];
struct stat file_stat;
off_t offset;
int remain_data;
//int peer_socket = peer_socket;
recv(peer_socket, FILE_TO_SEND, sizeof(FILE_TO_SEND), 0);
printf("Client requested %s", FILE_TO_SEND);
if (strlen(FILE_TO_SEND) > 1) {
strtok(FILE_TO_SEND, "\n");
}
//check for server close command from client
if(strcmp(FILE_TO_SEND,"quit") == 0){
servexit = true;
printf("Quiting server\n");
close(server_socket);
close(peer_socket);
pid_t pid = getppid();
kill(pid, SIGKILL);
exit(0);
}else {
fd = open(FILE_TO_SEND, O_RDONLY);
if (fd == -1) {
fprintf(stderr, "Error opening file --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Get file stats */
if (fstat(fd, &file_stat) < 0) {
fprintf(stderr, "Error fstat --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(stdout, "File Size: \n%d bytes\n", file_stat.st_size);
sock_len = sizeof(struct sockaddr_in);
fprintf(stdout, "Accept peer --> %s\n", inet_ntoa(peer_addr.sin_addr));
sprintf(file_size, "%d", file_stat.st_size);
/* Sending file size */
len = send(peer_socket, file_size, sizeof(file_size), 0);
if (len < 0) {
fprintf(stderr, "Error on sending greetings --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(stdout, "Server sent %d bytes for the size\n", len);
//fflush((FILE*)peer_socket);
offset = 0;
remain_data = file_stat.st_size;
/* Sending file data */
while (((sent_bytes = sendfile(peer_socket, fd, &offset, BUFSIZ)) > 0) && (remain_data > 0)) {
fprintf(stdout,
"1. Server sent %d bytes from file's data, offset is now : %d and remaining data = %d\n",
sent_bytes, offset, remain_data);
remain_data -= sent_bytes;
fprintf(stdout,
"2. Server sent %d bytes from file's data, offset is now : %d and remaining data = %d\n",
sent_bytes, offset, remain_data);
}
}
break;
}
}
return 0;
}
【问题讨论】：
-
父级应该在分叉后关闭对等套接字。否则，当子进程退出时，客户端永远不会得到 EOF。
-
由于某种原因，您将该行注释掉了。取消注释。
-
谢谢，我意识到应该取消注释这些行，但它们并没有影响我的特定问题（还）。事实证明，问题在于 sendfile() 的行为与 send() 的行为方式不同，这是我没有预料到的。如果返回 -1(error) 而不是退出，则修复它的问题是重试客户端中的 recv() 调用。
-
int sent_bytes和int len是用于保存来自send()和sendfile()的返回值的错误类型。sendfile()和send()都返回ssize_t而不是int。sprintf(file_size, "%d", file_stat.st_size);是错误的，请参阅 stackoverflow.com/questions/586928/… 以获取正确的printf()样式格式的off_t。使用正确的类型很重要。如果您遇到大于 2 GB 的文件和/或如果您在 64 位平台上编译您的代码，您所使用的内容将会惨遭失败。 -
第一个要解决的问题是客户端和服务器代码都不能干净地编译。事实上，服务器代码有一些它使用的未定义名称，例如
false和 'true' 所以服务器代码缺少以下语句：#include <stdbool.h>