Client receiving wrong message from server (UDP) - c

Question

I am writing a private chat using UDP, but I have some problems while implementing the registration service. When the client writes the ID and password he wants to use, the server checks if the ID already exists(IDs and password are saved in a file), if it doesn't exist yet, the client can start chatting with other users(I still haven't implemented this part), if the ID is already in use I want to tell the user to choose another ID. In this scenario, I send the message "ID already in use" to the client using sendto but the recvfrom sometimes riceives other messages. Precisely the first time the user chooses a wrong ID, he receives the right message, then, if he chooses again an ID already in use, from the message he has received from the server he reads the ID he tried to choose and not the error message.The strangest thing is that at a third wrong attempt, the error message is correct.
Messages and related functions are defined in a file called utils.h
typedef struct Message{
int type; //Message's type: 0->registration; 1->login; 2->message; 3->ack
char* dest;
char* mitt; //source
char msg[1024];
}Message;
//createMsg is used to fill message struct
int createMsg(int type, char* dest, char* mitt, char * msg, struct Message* message){ //char msg[1024]
//printf("Sono in createMsg\n");
memset(message,0,sizeof(*message));
message->type = type;
message->dest = dest;
message->mitt = mitt;
//printf("msg to write: %s\n",msg);
strcpy(message->msg,msg);
//printf("msg written: %s\n",message->msg);
}
//print messages
void printMsg(struct Message* message){
if(strlen(message->msg)!=0) printf("type: %d, dest: %s, mitt:%s, msg: %s\n",message->type,message->dest,message->mitt,message->msg);
printf("dim msg tot: %lu\n",sizeof(*message));
printf("type dim: %lu, dest dim: %lu, mitt dim:%lu, msg dim: %lu, dim tot msg: %lu\n",sizeof(message->type),sizeof(message->dest),sizeof(message->mitt),strlen(message->msg),sizeof(message->msg));
}
//Set message's field to zero
void setToZeroMsg(struct Message* message){
message->type = 0;
message->dest = NULL;
message->mitt = NULL;
int i=0;
for(i=0;i<strlen(message->msg);i++){
message->msg[i]=0;
}
//memset(message->msg,0,strlen(message->msg));
}
This is the server:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <arpa/inet.h> // htons()
#include <netinet/in.h> // struct sockaddr_in
#include <sys/socket.h>
//#include "utente.h"
#include "utils.h"
#define MAX_CONNECTIONS 5
#define MAX_MESSAGE 1024
int main(){
int sockfd, ret;
char buffer[MAX_MESSAGE];
size_t buf_len = sizeof(buffer);
struct sockaddr_in server_addr, client_addr;
int serv_addr_len = sizeof(server_addr);
int client_addr_len = sizeof(client_addr);
//socket file descriptor
sockfd = socket(AF_INET, SOCK_DGRAM,0);
if(sockfd < 0){
perror("Errore nel creare la socket!");
exit(EXIT_FAILURE);
}
//Setting structure's content to zero
memset(&server_addr,0,serv_addr_len);
memset(&client_addr,0,client_addr_len);
//Server addr
server_addr.sin_family = AF_INET; //IPv4
server_addr.sin_addr.s_addr = INADDR_ANY;
server_addr.sin_port = htons(5500);
//Bind
ret = bind(sockfd, (const struct sockaddr *)&server_addr, serv_addr_len);
if(ret < 0){
perror("Errore nella bind!");
exit(EXIT_FAILURE);
}
struct Message* newmsg = (struct Message*)malloc(sizeof(struct Message));
//Start comunication with clients
//int num_clients = 0;
while(1){
setToZeroMsg(newmsg); //Cancel previous messages
printf("waiting for a message from a client...\n");
//Receiving a message
ret = recvfrom(sockfd, newmsg, sizeof(*newmsg), 0, (struct sockaddr*)&client_addr, &client_addr_len);
if(ret == -1){
perror("Errore nella recvfrom!");
}
printMsg(newmsg);
int type = newmsg->type;
if(type == 0){ //Type==0 -> register request
printf("register request\n");
int newID = 0; //if is set to -1 the ID already exist
size_t msg_len=sizeof(newmsg->msg);
FILE* file = fopen("utenti.txt","r+");
if(file==NULL){
perror("Errore nell'apertura del file");
}
char* newuser = strcpy(newser,newmsg->msg);
strtok(newuser,";");
int size_newuser = sizeof(newuser);
while(1){
char* res = fgets(buffer,32,file);
if(res==NULL) break;
//printf("%s",buffer);
char* user = strtok(buffer,";");
//printf("%s\n",user);
int size_user = sizeof(user);
int size = (size_newuser > size_user)? size_newuser : size_user;
if(strncmp(newuser,user,size) == 0){
//printf("This name is already in use!\n");
/*memset(newmsg,0,sizeof(Message));
newmsg->type = 3;
newmsg->dest = NULL;
strcpy(newmsg->msg, "This ID is already taken!\n");
printf("mess: %s",newmsg->msg);*/
//Error message to client
creaMsg(3, NULL, NULL, "This ID is already taken!\n", newmsg); //buffer
printMsg(newmsg);
printf("msg: %s\n",newmsg->msg);
//ret = sendto(sockfd, (struct Message*)newmsg, sizeof(*newmsg), 0, (struct sockaddr*)&client_addr, (socklen_t) client_addr_len);
ret = sendto(sockfd,newmsg->msg,sizeof(newmsg->msg),0,(struct sockaddr*)&client_addr, (socklen_t) client_addr_len );
if(ret == -1){
perror("Errore nella sendto!");
exit(EXIT_FAILURE);
}
newID = -1;
break;
}
}
if(newID != -1){
ret = fprintf(file,newmsg->msg,msg_len);
if(ret == -1){
perror("Errore nella scrittura su file");
}
}
if(fclose(file) == -1) perror("Errore nella chiusura del file");
}
else if(type==1){
}
else if(type==2){
}
//This part is not implemented yet
/*ret = sendto(sockfd, buffer, buf_len,0,(const struct sockaddr*)&client_addr, (socklen_t) client_addr_len);
if(ret == -1){
perror("Errore nella sendto!");
}*/
}
close(sockfd);
return 0;
}
And this is the client file:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <arpa/inet.h> // htons()
#include <netinet/in.h> // struct sockaddr_in
#include <sys/socket.h>
//#include "utente.h"
#include "utils.h"
#define MAX_MESSAGE 1024
#define quit_command "QUIT"
int main(){
int sockfd, ret;
struct sockaddr_in server_addr;
int serv_addr_len = sizeof(server_addr);
char buffer[MAX_MESSAGE];
size_t buf_len = sizeof(buffer);
size_t msg_len;
int quit_command_len = strlen(quit_command);
//Message struct
struct Message message = {};
setToZeroMsg(&message);
//socket file descriptor
sockfd = socket(AF_INET, SOCK_DGRAM,0);
if(sockfd < 0){
perror("Errore nel creare la socket!");
exit(EXIT_FAILURE);
}
//Structures to zero
memset(&server_addr,0,serv_addr_len);
//Initialize server_addr
server_addr.sin_family = AF_INET; //IPv4
server_addr.sin_addr.s_addr = INADDR_ANY;
server_addr.sin_port = htons(5500);
printf("Welcome in Private Chat!\n");
while(1){
char buf_credentials[32];
memset(buf_credentials,0,sizeof(buf_credentials));
memset(buffer,0,sizeof(buffer));
//setToZeroMsg(&message);
printf("If you want to register write 'r', to login type 'l':\n");
if (fgets(buffer, MAX_MESSAGE, stdin) != (char*)buffer) {
fprintf(stderr, "Error while reading from stdin, exiting...\n");
exit(EXIT_FAILURE);
}
if(!memcmp(buffer, "l", 1)){
printf("not implemented yet");
break;
}
else if(!memcmp(buffer,"r",1)){
printf("To register choose an ID and a password.\n");
printf("ID:\n");
if (fgets(buffer, 15, stdin) != (char*)buffer) {
fprintf(stderr, "Error while reading from stdin, exiting...\n");
exit(EXIT_FAILURE);
}
//printf("%s\n",buffer);
strncpy(buf_credentials,buffer,strlen(buffer)-1);
strcat(buf_credentials,";");
printf("Inserire password:\n");
if (fgets(buffer, 15, stdin) != (char*)buffer) {
fprintf(stderr, "Error while reading from stdin, exiting...\n");
exit(EXIT_FAILURE);
}
strcat(buf_credentials,buffer);
printf("utente+pass: %s",buf_credentials);
//Message struct
/*
struct Message message = {
};*/
setToZeroMsg(&message);
strcpy(message.msg, buf_credentials);
//send ID e password to server
ret = sendto(sockfd, (struct Message*)&message, sizeof(message), 0, (struct sockaddr*)&server_addr, (socklen_t) serv_addr_len);
if(ret == -1){
perror("Errore nella sendto!");
continue;
}
setToZeroMsg(&message);
printf("msg: %s\n",message.msg);
//ret = recvfrom(sockfd, (struct Message*)&message, sizeof(message), 0, (struct sockaddr*)&server_addr, (socklen_t*)&serv_addr_len);
ret = recvfrom(sockfd, message.msg, sizeof(message.msg), 0, (struct sockaddr*)&server_addr, (socklen_t*)&serv_addr_len);
printMsg(&message);
printf("msg: %s\n",message.msg);
if(ret == -1){
perror("Errore nella recvfrom!");
}
continue;
}
else{ //User didn't type 'r' or 'l'
printf("Wrong, you have to type 'r' o 'l'\n");
}
memset(buffer,0,MAX_MESSAGE);
}
//Chatting with server
while(1){
memset(buffer,0,MAX_MESSAGE);
printf("Type the message for the server, QUIT to leave the chat:\n");
if (fgets(buffer, MAX_MESSAGE, stdin) != (char*)buffer) {
fprintf(stderr, "Error while reading from stdin, exiting...\n");
exit(EXIT_FAILURE);
}
printf("You wrote: %s\n", buffer);
msg_len=strlen(buffer);
//Send Message
ret = sendto(sockfd, buffer, MAX_MESSAGE, 0, (struct sockaddr*)&server_addr, (socklen_t) serv_addr_len);
if(ret == -1){
perror("Errore nella sendto!");
continue;
}
//Server wrote back
memset(buffer,0,MAX_MESSAGE);
ret = recvfrom(sockfd, buffer, buf_len, 0, (struct sockaddr*)&server_addr, &serv_addr_len);
if(ret == -1){
perror("Errore nella recvfrom!");
}
printf("Message received from server: %s\n",buffer);
//Controlla se il messaggio ricevuto è QUIT
if (msg_len == quit_command_len+1 && !memcmp(buffer, quit_command, quit_command_len)) break;
}
printf("Closing connection!\n");
close(sockfd);
return 0;
}
ID and password are stored in the file "utenti.txt", separated by semicolons, in this way:
ID1;password1
ID2;password2
...
I hope I have been clear about my problem, thank you for helping me!