Сервер передачи файлов/клиент, использующий сокет

Я пытаюсь сделать передачу файлов между сервером и клиентом, но работает очень плохо. В основном, что должно произойти:
1) Клиент отправляет txt файл на сервер (я назвал его "quotidiani.txt" )
2) Сервер сохраняет его в другом txt файле ( "receive.txt" )
3) Сервер запускает script на нем, который изменяет его и сохраняет его с другим именем ( "output.txt" )
4) Сервер отправляет файл обратно клиенту, который сохраняет его (в том же сокете) с именем (final.txt)

Проблема в том, что первый файл (quotidiani.txt) читается только для небольшой части, а затем есть некоторые ошибки. Я хочу, чтобы кто-то помог мне понять и исправить мои ошибки.

Здесь мой код:

client.c:

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

#define PORT 20000
#define LENGTH 512 


void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
    /* Variable Definition */
    int sockfd; 
    int nsockfd;
    char revbuf[LENGTH]; 
    struct sockaddr_in remote_addr;

    /* Get the Socket file descriptor */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor! (errno = %d)\n",errno);
        exit(1);
    }

    /* Fill the socket address struct */
    remote_addr.sin_family = AF_INET; 
    remote_addr.sin_port = htons(PORT); 
    inet_pton(AF_INET, "127.0.0.1", &remote_addr.sin_addr); 
    bzero(&(remote_addr.sin_zero), 8);

    /* Try to connect the remote */
    if (connect(sockfd, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1)
    {
        fprintf(stderr, "ERROR: Failed to connect to the host! (errno = %d)\n",errno);
        exit(1);
    }
    else 
        printf("[Client] Connected to server at port %d...ok!\n", PORT);

    /* Send File to Server */
    //if(!fork())
    //{
        char* fs_name = "/home/aryan/Desktop/quotidiani.txt";
        char sdbuf[LENGTH]; 
        printf("[Client] Sending %s to the Server... ", fs_name);
        FILE *fs = fopen(fs_name, "r");
        if(fs == NULL)
        {
            printf("ERROR: File %s not found.\n", fs_name);
            exit(1);
        }

        bzero(sdbuf, LENGTH); 
        int fs_block_sz; 
        while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs)) > 0)
        {
            if(send(sockfd, sdbuf, fs_block_sz, 0) < 0)
            {
                fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
                break;
            }
            bzero(sdbuf, LENGTH);
        }
        printf("Ok File %s from Client was Sent!\n", fs_name);
    //}

    /* Receive File from Server */
    printf("[Client] Receiveing file from Server and saving it as final.txt...");
    char* fr_name = "/home/aryan/Desktop/progetto/final.txt";
    FILE *fr = fopen(fr_name, "a");
    if(fr == NULL)
        printf("File %s Cannot be opened.\n", fr_name);
    else
    {
        bzero(revbuf, LENGTH); 
        int fr_block_sz = 0;
        while((fr_block_sz = recv(sockfd, revbuf, LENGTH, 0)) > 0)
        {
            int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
            if(write_sz < fr_block_sz)
            {
                error("File write failed.\n");
            }
            bzero(revbuf, LENGTH);
            if (fr_block_sz == 0 || fr_block_sz != 512) 
            {
                break;
            }
        }
        if(fr_block_sz < 0)
        {
            if (errno == EAGAIN)
            {
                printf("recv() timed out.\n");
            }
            else
            {
                fprintf(stderr, "recv() failed due to errno = %d\n", errno);
            }
        }
        printf("Ok received from server!\n");
        fclose(fr);
    }
    close (sockfd);
    printf("[Client] Connection lost.\n");
    return (0);
}

server.c

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

#define PORT 20000 
#define BACKLOG 5
#define LENGTH 512 

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main ()
{
    /* Defining Variables */
    int sockfd; 
    int nsockfd; 
    int num;
    int sin_size; 
    struct sockaddr_in addr_local; /* client addr */
    struct sockaddr_in addr_remote; /* server addr */
    char revbuf[LENGTH]; // Receiver buffer

    /* Get the Socket file descriptor */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
    {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Obtaining socket descriptor successfully.\n");

    /* Fill the client socket address struct */
    addr_local.sin_family = AF_INET; // Protocol Family
    addr_local.sin_port = htons(PORT); // Port number
    addr_local.sin_addr.s_addr = INADDR_ANY; // AutoFill local address
    bzero(&(addr_local.sin_zero), 8); // Flush the rest of struct

    /* Bind a special Port */
    if( bind(sockfd, (struct sockaddr*)&addr_local, sizeof(struct sockaddr)) == -1 )
    {
        fprintf(stderr, "ERROR: Failed to bind Port. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Binded tcp port %d in addr 127.0.0.1 sucessfully.\n",PORT);

    /* Listen remote connect/calling */
    if(listen(sockfd,BACKLOG) == -1)
    {
        fprintf(stderr, "ERROR: Failed to listen Port. (errno = %d)\n", errno);
        exit(1);
    }
    else
        printf ("[Server] Listening the port %d successfully.\n", PORT);

    int success = 0;
    while(success == 0)
    {
        sin_size = sizeof(struct sockaddr_in);

        /* Wait a connection, and obtain a new socket file despriptor for single connection */
        if ((nsockfd = accept(sockfd, (struct sockaddr *)&addr_remote, &sin_size)) == -1) 
        {
            fprintf(stderr, "ERROR: Obtaining new Socket Despcritor. (errno = %d)\n", errno);
            exit(1);
        }
        else 
            printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));

        /*Receive File from Client */
        char* fr_name = "/home/aryan/Desktop/receive.txt";
        FILE *fr = fopen(fr_name, "a");
        if(fr == NULL)
            printf("File %s Cannot be opened file on server.\n", fr_name);
        else
        {
            bzero(revbuf, LENGTH); 
            int fr_block_sz = 0;
            while((fr_block_sz = recv(nsockfd, revbuf, LENGTH, 0)) > 0) 
            {
                int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
                if(write_sz < fr_block_sz)
                {
                    error("File write failed on server.\n");
                }
                bzero(revbuf, LENGTH);
                if (fr_block_sz == 0 || fr_block_sz != 512) 
                {
                    break;
                }
            }
            if(fr_block_sz < 0)
            {
                if (errno == EAGAIN)
                {
                    printf("recv() timed out.\n");
                }
                else
                {
                    fprintf(stderr, "recv() failed due to errno = %d\n", errno);
                    exit(1);
                }
            }
            printf("Ok received from client!\n");
            fclose(fr); 
        }

        /* Call the Script */
        system("cd ; chmod +x script.sh ; ./script.sh");

        /* Send File to Client */
        //if(!fork())
        //{
            char* fs_name = "/home/aryan/Desktop/output.txt";
            char sdbuf[LENGTH]; // Send buffer
            printf("[Server] Sending %s to the Client...", fs_name);
            FILE *fs = fopen(fs_name, "r");
            if(fs == NULL)
            {
                fprintf(stderr, "ERROR: File %s not found on server. (errno = %d)\n", fs_name, errno);
                exit(1);
            }

            bzero(sdbuf, LENGTH); 
            int fs_block_sz; 
            while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs))>0)
            {
                if(send(nsockfd, sdbuf, fs_block_sz, 0) < 0)
                {
                    fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
                    exit(1);
                }
                bzero(sdbuf, LENGTH);
            }
            printf("Ok sent to client!\n");
            success = 1;
            close(nsockfd);
            printf("[Server] Connection with Client closed. Server will wait now...\n");
            while(waitpid(-1, NULL, WNOHANG) > 0);
        //}
    }
}