Simple FTP With Sockets Sending Empty File Back To Client - c

Question

I am trying to implement the following code for a simple FTP between a client and a server. The problem is, when the server sends the file to the client, the file is empty. I'm not sure what the problem is. I'm assuming the problem lies when the server sends the file. Below is the code.
/*Server Code*/
#ifndef unix
#define WIN32
#include <windows.h>
#include <winsock.h>
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <netdb.h>
#endif
#include <stdio.h>
#include <string.h>
#define PROTOPORT 5193 /* default protocol port number */
#define QLEN 6 /* size of request queue */
int visits = 0; /* counts client connections */
main(argc, argv)
int argc;
char *argv[];
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold server.s address */
struct sockaddr_in cad; /* structure to hold client.s address */
int sd, sd2; /* socket descriptors */
int port; /* protocol port number */
int alen; /* length of address */
char buf_recv[1000],buf_send[1000]; /* buffer for string the server sends */
char file_buffer[10000],f_buffer[1000];
int n;
FILE *fp;
#ifdef WIN32
WSADATA wsaData;
WSAStartup(0x0101, &wsaData);
#endif
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
sad.sin_addr.s_addr = INADDR_ANY; /* set the local IP address */
if (argc > 1) { /* if argument specified */
port = atoi(argv[1]);
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for illegal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,"bad port number %s\n",argv[1]);
exit(1);
}
/* Map TCP transport protocol name to protocol number */
if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Create a socket */
sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (sd < 0) {
fprintf(stderr, "socket creation failed\n");
exit(1);
}
/* Bind a local address to the socket */
if (bind(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"bind failed\n");
exit(1);
}
/* Specify size of request queue */
if (listen(sd, QLEN) < 0) {
fprintf(stderr,"listen failed\n");
exit(1);
}
alen = sizeof(cad);
if ( (sd2=accept(sd, (struct sockaddr *)&cad, &alen)) < 0) {
fprintf(stderr, "accept failed\n");
exit(1);
}
sprintf(buf_send,"Please enter the file name: ");
send(sd2,buf_send,strlen(buf_send),0);
n=recv(sd2,buf_recv,1000,0);
buf_recv[n]='\0';
printf("%s\n",buf_recv);
fflush(stdout);
if((fp = fopen(buf_recv,"r"))==NULL)
{
sprintf(buf_send,"File could not be found!!!");
exit(0);
} else
sprintf(buf_send,"File found!!!\n");
send(sd2,buf_send,strlen(buf_send),0);
n=recv(sd2,buf_recv,1000,0);
printf("%s",buf_recv);
fflush(stdout);
while(!feof(fp)) {
fgets(f_buffer,1000,fp);
if (feof(fp))
break;
strcat(file_buffer,f_buffer);
}
fclose(fp);
send(sd2,file_buffer,strlen(file_buffer),0);
closesocket(sd2);
exit(0);
}
The Client Code:
/*Client Code*/
#ifndef unix
#define WIN32
#include <windows.h>
#include <winsock.h>
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif
#include <stdio.h>
#include <string.h>
#define PROTOPORT 5193 /* default protocol port number */
extern int errno;
char localhost[] = "localhost"; /* default host name */
main(argc, argv)
int argc;
char *argv[];
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold an IP address */
int sd; /* socket descriptor */
int port; /* protocol port number */
char *host; /* pointer to host name */
int n; /* number of characters read */
char buf_recv[1000],buf_send[100]; /* buffer for data from the server */
char *filename;
char file_buffer[10000];
FILE *fp;
#ifdef WIN32
WSADATA wsaData;
WSAStartup(0x0101, &wsaData);
#endif
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
if (argc > 2) { /* if protocol port specified */
port = atoi(argv[2]); /* convert to binary */
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for legal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,"bad port number %s\n",argv[2]);
exit(1);
}
/* Check host argument and assign host name. */
if (argc > 1) {
host = argv[1]; /* if host argument specified */
} else {
host = localhost;
}
/* Convert host name to equivalent IP address and copy to sad. */
ptrh = gethostbyname(host);
if ( ((char *)ptrh) == NULL ) {
fprintf(stderr,"invalid host: %s\n", host);
exit(1);
}
memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);
/* Map TCP transport protocol name to protocol number. */
if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Create a socket. */
sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (sd < 0) {
fprintf(stderr, "socket creation failed\n");
exit(1);
}
/* Connect the socket to the specified server. */
if (connect(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"connect failed\n");
exit(1);
}
n = recv(sd, buf_recv, sizeof(buf_recv), 0);
buf_recv[n]='\0';
printf("%s",buf_recv);
scanf("%s",buf_send);
send(sd,buf_send,strlen(buf_send),0);
n = recv(sd, buf_recv, sizeof(buf_recv), 0);
buf_recv[n]='\0';
printf("%s",buf_recv);
fflush(stdout);
sprintf(buf_send,"Client acknowledges, Sending file now.\n");
send(sd,buf_send, strlen(buf_send),0);
n=recv(sd, file_buffer, sizeof(file_buffer), 0);
file_buffer[n]='\0';
fflush(stdout);
fp = fopen("transferredFile.TXT","w");
fputs(file_buffer,fp);
fclose(fp);
closesocket(sd);
exit(0);
}
Is the problem coming from the server sending or is it the client receiving? Thanks!

Answer 1

Server: 'strcat(file_buffer,f_buffer);' - concat to uninitialized array.
Server and Client: assumptions that data contains no nulls, ie. system cannnot transfer binary data, only text.
Server and Client - assumptions that all the file data will fit in one line.
Server and Client - assumptions that TCP can transfer messages larger than one byte.
Probably other bugs associated with TCP streaming and C null-terminated strings.