Socket Programming - Message receive not correct - c++

Question

I'm a newbie in socket programming. I'm trying to make a server/ client program to download a file.
Firstly, i init some step that i usually do in other program for set up a connection form client to server.
Next, From server side, I'm try to in put number of bytes that send to client to set up the receive buffer's size. From client side, I receive the number in string type. I convert it to long type and set it to buffer size.
Then, From client side, I enter the name of file that need to download from server. Server receive the name and check if it exist or not.
Last step ( THE PROBLEM STEP, i think ) server try to open file. if file is opened, send the file name back to client. client check file name if it same what it sent or not.
======> my problem is file name sent back to client:
- From server side: I print it out and check. it's correct.
- From client: I print buffer out right after read from server. It's not correct. sometimes, it's empty. sometimes, it's some-random-value.
I have done exactly like previous step.
Server.cpp
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
int sockfd, newsockfd, portno;
socklen_t clilen;
struct sockaddr_in serv_addr, cli_addr;
int n;
if (argc < 2)
{
perror("you have to input port");
exit(1);
}
// init sockfd
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
{
perror("sockfd perror");
exit(1);
}
// sockopt
int opt = 1;
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt)))
{
perror("setsockopt");
exit(EXIT_FAILURE);
}
// init server
bzero(&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);
// bind port
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
{
perror("ERROR on binding");
exit(1);
}
listen(sockfd, 5);
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd,
(struct sockaddr *) &cli_addr,
&clilen);
if (newsockfd < 0)
{
perror("ERROR on accept");
exit(1);
}
char buffer[256];
// write buff size
int buffsize;
printf("Input recive buffsize in Byte: ");
scanf("%d", &buffsize);
if (buffsize <= 0)
{
perror("Buffer size must be > 0");
exit(1);
}
bzero(buffer, sizeof(buffer));
bcopy(to_string(buffsize).c_str(), buffer, sizeof(buffer));
n = write(newsockfd, buffer, sizeof(buffer));
if (n < 0)
{
perror("fail to send buffer size");
exit(0);
}
//read file name
bzero(buffer, sizeof(buffer));
n = read(newsockfd, buffer, sizeof(buffer));
if (n < 0)
{
perror("ERROR reading from socket");
exit(1);
}
// open file:
char filename[strlen(buffer) + 1];
bcopy(buffer, filename, sizeof(filename));
FILE *pf;
unsigned long fsize;
pf = fopen(filename, "rb");
if (pf == NULL)
{
bzero(buffer, sizeof(buffer));
bcopy("File not found", buffer, sizeof(buffer));
n = write(newsockfd, buffer, sizeof(buffer));
if (n < 0)
{
perror("ERROR writing to socket");
exit(1);
}
printf("File not found!\n");
return 1;
}
else
{
printf("File %s is openned \n", filename);
fseek(pf, 0, SEEK_END);
fsize = ftell(pf);
rewind(pf);
printf("File has %ld bytes!\n", fsize);
}
// write OK response file name
bzero(buffer, sizeof(buffer));
bcopy(filename, buffer, sizeof(buffer));
printf("\n\n\n\n%s\n\n\n\n", buffer);
n = write(newsockfd, buffer, sizeof(buffer));
if (n < 0)
{
perror("ERROR writing to socket");
exit(1);
}
close(newsockfd);
close(sockfd);
return 0;
}
Client.cpp
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;
int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
if (argc < 3)
{
fprintf(stderr, "usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
// init sockfd
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
{
perror("sockfd error");
exit(1);
}
// init server
server = gethostbyname(argv[1]);
if (server == NULL)
{
fprintf(stderr, "ERROR, no such host\n");
exit(0);
}
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
serv_addr.sin_port = htons(portno);
// connect
if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
{
perror("ERROR connecting");
exit(1);
}
// recive and set buffer size:
char tempBuff[10];
bzero(tempBuff, 10);
n = read(sockfd, tempBuff, sizeof(tempBuff));
if (n < 0)
{
perror("fail to recive buffer size");
exit(1);
}
char buffer[stol(string(tempBuff))];
printf("Connect succes, Buffer size is %ld Bytes\n", sizeof(buffer));
// input file:
printf("Input file name to download: ");
string filename;
cin >> filename;
// Send filename
bzero(buffer, sizeof(buffer));
bcopy(filename.c_str(), buffer, filename.length());
n = write(sockfd, buffer, strlen(buffer));
if (n < 0)
{
perror("ERROR writing to socket");
}
// read file name response
bzero(buffer, sizeof(buffer));
n = read(sockfd, buffer, sizeof(buffer));
if (n < 0)
{
perror("ERROR reading from socket");
}
printf("\n\n\n\n%s, %ld\n\n\n\n", buffer, strlen(buffer));
// if (strcmp(buffer, filename.c_str()) == 0)
// {
// printf("OK!\n");
// }
// else
// {
// perror("Wrong filename");
// printf("server msg: %s\n", buffer);
// exit(1);
// }
close(sockfd);
return 0;
}
RUN CODE WITH FOLLOWING COMMAND:
Client: ./client [server ip] [port]
Server: ./server [port]
My result:
Update 1: problem disappear when i remove these line:
// write buff size
int buffsize;
printf("Input recive buffsize in Byte: ");
scanf("%d", &buffsize);
if (buffsize <= 0)
{
perror("Buffer size must be > 0");
exit(1);
}
at server.cpp
and these line:
// recive and set buffer size:
bzero(tempBuff, sizeof(tempBuff));
n = read(sockfd, tempBuff, sizeof(tempBuff));
if (n < 0)
{
perror("fail to recive buffer size");
exit(1);
}
// char buffer[stol(string(tempBuff))];
at client.cpp

Answer 1

I solved it. this problem occur due to tempBuff is too small. it's just 10 bytes. Using bigger tempBuff will solve the problem.