Download a file from server using TCP - c

Question

I'm trying to write a C program for a client which can download a file from the server using TCP. The client will print and save the file content after it receives the file from the server. To compile the client program it needs IP address and port number of the server. I implemented it in Linux but it displayed 0s after the received texts. The saved text file was the same. I have no idea how to output the text only. Maybe there are wrongs in the receive buffer?
Code for server:
#include <stdio.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <pthread.h>
#define portnum 12345
#define FILE_SIZE 500
#define BUFFER_SIZE 1024
void *client_fun(void * fd);
int main()
{
int new_fd;
pthread_t thread_id;
int server_fd=socket(AF_INET,SOCK_STREAM,0);
if(-1==server_fd)
{
perror("socket");
exit(1);
}
struct sockaddr_in server_addr;
server_addr.sin_family=AF_INET;
server_addr.sin_port=htons(portnum);
(server_addr.sin_addr).s_addr=htonl(INADDR_ANY);
if(-1==bind(server_fd,(struct sockaddr *)&server_addr,sizeof(server_addr)))
{
perror("bind");
close(server_fd);
exit(6);
}
if(-1==listen(server_fd,5))
{
perror("listen");
close(server_fd);
exit(7);
}
while(1)
{
struct sockaddr_in client_addr;
int size=sizeof(client_addr);
new_fd=accept(server_fd,(struct sockaddr *)&client_addr,&size);
if(new_fd < 0)
{
perror("accept");
continue;
}
printf("accept client ip锛?s:%d\n",inet_ntoa(client_addr.sin_addr),client_addr.sin_port);
//printf("new_fd=%d\n",new_fd);
if (new_fd > 0)
{
pthread_create(&thread_id, NULL, client_fun, (void *)&new_fd);
pthread_detach(thread_id);
}
}
close(server_fd);
return 0;
}
void *client_fun(void *arg)
{
int new_fd = *((int *)arg);
int file2_fp;
int len;
char buffer[BUFFER_SIZE];
memset( buffer,0, sizeof(buffer) );
while(1)
{
if((len=recv(new_fd, buffer, sizeof(buffer), 0)) <= 0)
{
continue;
}
char file_name[FILE_SIZE];
memset( file_name,0, sizeof(file_name) );
strncpy(file_name, buffer, strlen(buffer)>FILE_SIZE?FILE_SIZE:strlen(buffer));
memset( buffer,0, sizeof(buffer) );
printf("Client requests file %s\n", file_name);
if( strcmp(file_name,"exit")==0 )
{
break;
}
file2_fp = open(file_name,O_RDONLY,0777);
if(file2_fp<0)
{
printf("File %s Not Found\n", file_name);
char* err_info = "File not found\n";
if (write(new_fd, err_info, sizeof(err_info)) < 0)
{
printf("Send error information failed\n");
break;
}
continue;
}
else
{
int length = 0;
memset( buffer,0, sizeof(buffer) );
while( (length = read(file2_fp, buffer, sizeof(buffer))) > 0 )
{
if( write(new_fd, buffer, length) < 0)
{
printf("Send File %s Failed.\n", file_name);
break;
}
memset( buffer,0, sizeof(buffer) );
}
close(file2_fp);
printf("Transfer file %s successfully!\n", file_name);
}
}
close(new_fd);
}
Code for client:
#include <stdio.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <pthread.h>
int main(int argc, char *argv[])
{
int sockfd = 0;
char recvBuff[1024];
char file_name[500];
char *serverIP=argv[1];
int portno=atoi(argv[2]);
printf("IP Addresses: %s Port Number: %s\n", argv[1], argv[2]);
memset(recvBuff,'0',sizeof(recvBuff));
struct sockaddr_in server_addr;
/* Creat a socket*/
sockfd = socket(AF_INET, SOCK_STREAM, 0);
/*Initialize sockaddr_in structure*/
server_addr.sin_family=AF_INET;
server_addr.sin_port=htons(portno);
(server_addr.sin_addr).s_addr=inet_addr(serverIP);
/*Attempt a connection*/
printf("Connect status: ");
if (connect(sockfd,(struct sockaddr *)&server_addr,sizeof(server_addr))<0)
{
printf("fail\n");
return 0;
}
printf("success\n");
/*Request file from server*/
while(1)
{
printf("Input the file name to be requested from the server: ");
fgets(file_name,500, stdin);
char *p=strchr(file_name,'\n');
if (p) *p=0;
if (send(sockfd, file_name, strlen(file_name), 0)<0)
{
printf("Send failed.\n");
break;
}
printf("Send success.\n");
if (strcmp(file_name,"exit")==0)
break;
int length=0;
printf("Send status: ");
if (length=read(sockfd, recvBuff, sizeof(recvBuff))<0)
{
printf("fail\n");
continue;
}
else if (strcmp(recvBuff,"File not found\n")==0)
{
printf("fail\n");
continue;
}
else
{
printf("success\n");
/*Create file where text will be stored*/
FILE *fp;
fp=fopen("received_file.txt","w");
printf("Open file status: ");
if (fp==NULL)
{
printf("fail\n");
continue;
}
printf("success\n");
printf("Received text: ");
if (fprintf(fp, "%s", recvBuff)<0)
{
printf("Save status: fail\n");
continue;
}
fflush(fp);
printf("%s",recvBuff);
memset(recvBuff,0,1024);
while ((length=read(sockfd, recvBuff, sizeof(recvBuff)))>0)
{
if (fprintf(fp, "%s", recvBuff)<0)
{
printf("Save status: fail\n");
break;
}
fflush(fp);
printf("%s",recvBuff);
memset(recvBuff,0,1024);
}
printf("Save status: success");
}
}
}
Another question is that the client is supposed to keep asking for files until it sends an 'exit'. But it stopped asking the client to input the file name after the first file was received. What's wrong with the loop?

Answer 1

you have several issues.
first: - comparison operator has precedence over assignment so length gets FALSE(0) value instead of the real number of received data
if (length=read(sockfd, recvBuff, sizeof(recvBuff))<0)
it should be:
if ((length=read(sockfd, recvBuff, sizeof(recvBuff)))<0)
second: you are operating with zero terminated strings but you do not send zero ('\0') from server and client does not set it at the end of the data block.
So you need to set it explicitly at client side here
if ((length=read(sockfd, recvBuff, sizeof(recvBuff)))<0)
{
printf("fail\n");
continue;
}
else if (strcmp(recvBuff,"File not found\n")==0)
{
printf("fail\n");
continue;
}
else
{
recvBuff[length]='\0';
and here:
while ((length=read(sockfd, recvBuff, sizeof(recvBuff)))>0){
recvBuff[length]='\0';