modify c socket program to send file from server to client

Question

Modify the following socket program and let the server send a file to the client.

I'm stuck with this i can't figure this out. below is the server and client that where given to me. right now the server will send the client the time stamp.

Socket Server Example (server.c)

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>

int main(int argc, char *argv[])
{
    int listenfd = 0, connfd = 0;
    struct sockaddr_in serv_addr;

    char sendBuff[1025];
    time_t ticks;

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    memset(&serv_addr, '0', sizeof(serv_addr));
    memset(sendBuff, '0', sizeof(sendBuff));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(5000);

    bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

    listen(listenfd, 10);

    while(1)
    {
        connfd = accept(listenfd, (struct sockaddr*)NULL, NULL);

        ticks = time(NULL);
        snprintf(sendBuff, sizeof(sendBuff), "%.24s\r\n", 
     ctime(&ticks));
        write(connfd, sendBuff, strlen(sendBuff));

        close(connfd);
        sleep(1);
     }
 }

Socket Client Example (client.c)

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    int sockfd = 0, n = 0;
    char recvBuff[1024];
    struct sockaddr_in serv_addr;

    if(argc != 2)
    {
        printf("\n Usage: %s <ip of server> \n",argv[0]);
        return 1;
    }

    memset(recvBuff, '0',sizeof(recvBuff));
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("\n Error : Could not create socket \n");
        return 1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(5000);

    if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
    {
        printf("\n inet_pton error occured\n");
        return 1;
    }

    if( connect(sockfd, (struct sockaddr *)&serv_addr, 
    sizeof(serv_addr)) < 0)
    {
       printf("\n Error : Connect Failed \n");
       return 1;
    }

    while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
    {
        recvBuff[n] = 0;
        if(fputs(recvBuff, stdout) == EOF)
        {
            printf("\n Error : Fputs error\n");
        }
    }

    if(n < 0)
    {
        printf("\n Read error \n");
    }

    return 0;
} 

Answer 1

Read the content of the file you wish to send, and save it into a string:

char *loadFileContent(char *fileName, size_t *len){
    FILE* input_file               = fopen(fileName, "rb");
    size_t stat;
    if(!input_file){
        OCSP_ERR_INDEX = OCSP_LOG_ERR_load_file_fail;
        return NULL;
    }
    fseek(input_file, 0, SEEK_END);
    long int input_file_size       = ftell(input_file);
    rewind(input_file);
    char *file_contents            = malloc((input_file_size + 1) * (sizeof(char)));
    stat = fread(file_contents, sizeof(char), (size_t) input_file_size, input_file);
    if(stat<1){
        OCSP_ERR_INDEX = OCSP_LOG_ERR_load_file_fail;
        return NULL;
    }
    fclose(input_file);
    file_contents[input_file_size] = 0;
    *len                           = (size_t) input_file_size;
    return file_contents;
}

In your code, modify the line in server that is supposed to send response to client. So this line write(connfd, sendBuff, strlen(sendBuff)); becomes:

size_t len;
char *text = loadFileContent("myfile.txt", &len);
write(connfd, text, len);

Answer 2

If you don't want to or can't read the whole content of the file you wish to send at once into memory, use a loop with your buffer:

    #include <fcntl.h>
    if (argv[1])    // or whereever you get the file name from
    {
        int fd = open(argv[1], O_RDONLY);
        if (fd < 0) perror(argv[1]);
        else
        {
            ssize_t n;
            while (n = read(fd, sendBuff, sizeof sendBuff), n > 0)
                if (send(connfd, sendBuff, n, MSG_NOSIGNAL) < 0)
                { perror("send"); break; }
            close(fd);
            if (n < 0) perror("read");
        }
    }

In the client use a similar loop. Be aware that the file might contain NUL characters, so functions like fputs, operating on C strings, are inept.

    while ((n = read(sockfd, recvBuff, sizeof recvBuff)) > 0)
        if (write(1, recvBuff, n) < 0) perror("write");