Send file size and then the file itself - c

Question

client-side code:
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
void error(char * msg){
perror(msg);
exit(0);
}
// Returns an string array from function
char *buff(const char *path){
int end = 0;
unsigned char * buf;
int f_write = open(path,O_RDONLY);
end = lseek(f_write,0,SEEK_END);
lseek(f_write,0,SEEK_SET);
buf =(char*)malloc(sizeof(char*)*(end+1));
read(f_write,buf,end);
close(f_write);
buf[end+1]= '\0';
return buf;
}
//connects to the socket
int connection(int portno,struct hostent * server,int sockfd){
struct sockaddr_in serv_addr;
int conn =0;
bzero((char *)&serv_addr,sizeof(serv_addr));
serv_addr.sin_family= AF_INET;
bcopy((char*)server->h_addr,(char *)&serv_addr.sin_addr.s_addr,server->h_length);
serv_addr.sin_port = htons(portno);
conn = connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
return conn;
}
int main(int argc, char *argv[]) {
int sockfd = -1;
int check =0;
char projname[100]= "project1";
int portno = -1;
int conn = -1;
int file_size =0;
ssize_t len;
int n = -1;
struct hostent *server;
char buffer[256];
int fd =0;
if(argc < 3){
fprintf(stderr,"usage %s hostname port\n",argv[0]);
exit(0);
}
// getting the portnumber
portno = atoi(argv[2]);
sockfd = socket(AF_INET,SOCK_STREAM,0);
if(sockfd < 0){
error("Error opening socket");
}
// getting the hostname
server = gethostbyname(argv[1]);
if(server == NULL){
fprintf(stderr,"Error no such host\n");
exit(0);
}
conn = connection(portno,server,sockfd);
if(conn < 0){
printf("%s\n",strerror(errno));
}
int path = open("text.txt",O_CREAT | O_WRONLY, 0644);
if(path < 0){
printf("%s\n",strerror(errno));
}
int remain_data = file_size;
printf("Printing out the file size ");
printf("%d\n",file_size);
char *buffer1 = (char*)malloc(sizeof(char)*file_size+1);
len = recv(sockfd,buffer1,BUFSIZ,0);
printf("%d",len);
buffer1[file_size]= '\0';
printf("printing the sentence\n");
printf("%s\n",buffer1);
int total_read_bytes =0;
int nread =0;
return 0;
}
server-side code
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <sys/socket.h>
void error(char * msg){
perror(msg);
exit(1);
}
int main(int argc, char const *argv[]){
int sockfd =-1;
int newsockfd = -1;
int portno = -1;
int clilen = -1;
int remain_data =0;
char buffer[300];
char buffer1[300];
int peer_socket = -1;
struct sockaddr_in serv_addr,cli_addr;
int n = -1;
struct stat file_stat;
char file_size[256];
ssize_t len;
int sent_bytes =0;
int path = open("project1/text.txt",O_RDONLY);
read(path,buffer1,30);
buffer1[31]= '\0';
printf("%s\n",buffer1);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd <0){
error("Error opening socket");
}
bzero((char*) &serv_addr,sizeof(serv_addr));
portno=atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
if(bind(sockfd,(struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0){
error("Error on Binding");
}
listen(sockfd,5);
int fd = open("project1/text.txt",O_RDONLY);
fstat(fd,&file_stat);
clilen = sizeof(cli_addr);
peer_socket = accept(sockfd,(struct sockaddr *)&cli_addr, &clilen);
sprintf(file_size,"%d",file_stat.st_size);
//sends file size
len = send(peer_socket,file_size,sizeof(file_size),0);
if(peer_socket <0){
error("Error on accept");
}
off_t offset = 0;
remain_data = file_stat.st_size;
//send the file
while(((sent_bytes=sendfile(peer_socket,fd,&offset,remain_data))>0) &&( remain_data>0)){
fprintf(stdout,"1.Server sent %d bytes from files data, offset is now : %d and remaining data = %d\n",sent_bytes, offset,remain_data);
remain_data -=sent_bytes;
fprintf(stdout, "2. Server sent %d bytes from files data, offest is not: %d and remaing data = %d\n",sent_bytes, offset,remain_data);
}
return 0;
}
I am able to get the size of my file from server side but I am unable to get file content from my server on client side. My client prints out an empty space where the data of the file is supposed to be, I don't know if I am using the recv function correctly the file correctly.
P.S I understand that I must close the sockets when finished.

Answer 1

For safety and robustness, you must check the return values of all the standard library functions you call to check for errors. For recv() and read(), however, you must check and appropriately handle return values for correctness. These functions do not guarantee to transfer the full number of bytes requested, and for network connections it is reasonably common that they don't. If you want to fully transfer a specific number of bytes then you must be prepared to use multiple recv() or read() calls to do so, generally by calling the function in a loop.
You do not check the return value of your recv() call, so if you have a short read -- or if there is an error or if the remote side closes the connection without sending anything -- then your client will not notice, and will simply output whatever garbage happens to be in the buffer.