transport endpoint is not connected recv socket

Question

i've made a simple program that change a string from lowercase to uppercase and from uppercase to lowercase. Server works until start client, after client run server give this error: "recv server fallita: Transport endpoint is not connected" why? i think that stream closed too soon or not? below there is code of server:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <ctype.h>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#define MAXLENGTH 80
#define SERVERPORT 1313


void minuscolatore (int in,int out){
    char inputline[MAXLENGTH];
    int len,i;
    while((len=recv(in,inputline,MAXLENGTH,0))>0){
        for(i=0;i<len;i++){
            inputline[i]=tolower(inputline[i]);
        }
        if (strcmp(inputline,"fine")==0){
            break;
        }
        send(out,inputline,len,0);
    }
}
void maiuscolatore(int in,int out){
    char inputline[MAXLENGTH];
    int len,i;
    while((len=recv(in,inputline,MAXLENGTH,0))>0){
        for(i=0;i<len;i++){
            inputline[i]=toupper(inputline[i]);
        }
        if (strcmp(inputline,"FINE")==0){
            break;
        }
        send(out,inputline,len,0);
    }
}
int main(){
    int sock,client_len,fd;
    char c;
    struct sockaddr_in client, server = {AF_INET,htons(SERVERPORT),INADDR_ANY};
    if((sock=socket(AF_INET,SOCK_STREAM,0))==-1){
        perror("Socket fallita");
        exit(1);
    }
    if(bind(sock,(struct sockaddr *)&server,sizeof server)==-1){
        perror("Bind fallita");
        exit(2);
    }
    listen(sock,5);
    while(1){
        client_len=sizeof(client);
        if((fd=accept(sock,(struct sockaddr *)&client,&client_len))<0){
            perror("accept fallita");
            exit(3);
        }
        if (recv(sock,&c,1,0)==-1){
            perror("recv server fallita");
            exit(4);
        }
        if (c=='+'){
        switch(fork()){
            case -1:
                perror("Fork fallita");
                exit(4);
            case 0:
                printf("Aperta connessione\n");
                send(fd,"Benvenuto al maiuscolatore, minuscolatore\n",27,0);
                maiuscolatore(fd,fd);
                printf("Chiusa connessione\n");
        }
    }
        else if (c=='-'){
        switch(fork()){
            case -1:
                perror("Fork fallita");
                exit(4);
            case 0:
                printf("Aperta connessione\n");
                send(fd,"Benvenuto al maiuscolatore, minuscolatore\n",27,0);
                minuscolatore(fd,fd);
                printf("Chiusa connessione\n");
        }   
        }
    }
    close(fd);
}

and after client:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <ctype.h>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#define MAXLENGTH 80
#define SERVERPORT 1313

int main(){
    int sockfd;
    struct sockaddr_in server={AF_INET,htons(SERVERPORT),INADDR_ANY};
    int i=0, len;
    char buf[MAXLENGTH],c,d;
    if ((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1){
        perror("socket fallita");
        exit(1);
    }
    if (connect(sockfd, (struct sockaddr *) &server,sizeof server)==-1){
        perror("connect fallita");
        exit(2);
    }
    printf("\nDigita una stringa :");
    while((c=getchar())!='\n' && i<MAXLENGTH)
        buf[i++]=c;

    buf[i]='\0';
    len=strlen(buf);
    printf("\nScrivi + se vuoi tutto maiuscolo e - se vuoi tutto minuscolo:");
    d=getchar();
    if (send(sockfd,&d,1,0)==-1){
        perror("send d fallita");
        exit(4);
    }
    printf("\nInvio la stringa al server...\n");
    if(send(sockfd,buf,len,0)==-1){
        perror("send fallita");
        exit(4);
    }
    if(recv(sockfd,buf,len,0)>0){
        printf("Ho ricevuto la risposta: %s\n",buf);
    }
    else{
        perror("seconda receive fallita");
        exit(3);
    }
    close(sockfd);
    exit(0);
}

Answer 1

The fd from your accept is the file handle to recv from, not sock