C文件服务器和客户端卡在recv上

Question

所以我正在尝试解决这个玩具客户端文件服务器问题。

迭代版本工作正常，但是当我尝试在服务器代码中 fork 每个新连接时，客户端代码会挂起在 recv 调用上。

我相当确定问题出在peer_socket上，但我一直无法找到我的错误。

如果我使用 Ctrl-c 访问服务器，它就可以很好地完成。

客户端代码:

#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;

}

Answer 1

好吧，事实证明，在这种情况下，sendfile() 的表现不如 send() 好。我发现了两个修复。

1.) 使用send()代替sendfile()

2.) 如果任一返回 -1(错误)，则在 sendfile()(服务器)和 recv()(客户端)中重试