trying to send a mmaped file in chat using sockets in c - c

Question

my assignment was to build a chat server and client with the beej's guide examples so the client can upload a file to the server.
the instructions were to mmap the file and send the data using send().
iv'e tried first just to send simple txt file but it wont work.
for some reason when debug the program and execcutes it line by line it works.
maybe someone can point out what am i missing?
client code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define PORT "6667" // the port client will be connecting to
#define MAXDATASIZE 256 // max number of bytes we can get at once
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(int argc, char *argv[])
{
fd_set master; // master file descriptor list
fd_set read_fds; // temp file descriptor list for select()
int sockfd, numbytes;
char buf[MAXDATASIZE];
struct addrinfo hints, *servinfo, *p;
int rv;
char s[INET6_ADDRSTRLEN];
struct stat mystat;
char* pmap;
int fdin;
if (argc != 2) {
fprintf(stderr,"usage: client hostname\n");
exit(1);
}
FD_ZERO(&master); // clear the master and temp sets
FD_ZERO(&read_fds);
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and connect to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("client: socket");
continue;
}
if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("client: connect");
continue;
}
break;
}
if (p == NULL) {
fprintf(stderr, "client: failed to connect\n");
return 2;
}
inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
s, sizeof s);
printf("client: connecting to %s\n", s);
freeaddrinfo(servinfo); // all done with this structure
FD_SET(sockfd,&master);
FD_SET(0,&master);
for(;;)
{
read_fds = master;
if (select(sockfd+1, &read_fds, NULL, NULL, NULL) == -1)
{
perror("select");
exit(4);
}
if (FD_ISSET(0,&read_fds))
{
//reads messege form user
scanf ("%[^\n]%*c", buf);
//if it is upload
if (0 == strncmp(buf,"/upload ",8)) {
//sendFile(sockfd,buf);
if (send(sockfd,buf ,strlen(buf),0) == -1)
perror("send");
if ((fdin = open(buf + 8,O_RDONLY)) < 0)
perror("open");
fstat (fdin,&mystat);
pmap = mmap (0, mystat.st_size, PROT_READ, MAP_SHARED, fdin, 0);
if (send(sockfd,pmap,(int)mystat.st_size,0))
perror("send");
close(fdin);
}
else if (send(sockfd,buf,strlen(buf),0) == -1)
perror("send");
}
else if (FD_ISSET(sockfd, &read_fds))
{
if ((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1)
{
perror("recv");
exit(1);
}
buf[numbytes] = '\0';
printf("%s\n",buf);
}
}
close(sockfd);
return 0;
}
server code:
#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 <arpa/inet.h>
#include <netdb.h>
#include <libgen.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#define PORT "6667" // port we're listening on
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(void)
{
struct User *usersPtr = NULL; //ptr to users list
struct File *filesPtr = NULL; //ptr to files list
fd_set master; // master file descriptor list
fd_set read_fds; // temp file descriptor list for select()
int fdmax; // maximum file descriptor number
int listener; // listening socket descriptor
int newfd; // newly accept()ed socket descriptor
struct sockaddr_storage remoteaddr; // client address
socklen_t addrlen;
char buf[256]; // buffer for client data
char msg[256]; //string to deal with message
int nbytes;
char remoteIP[INET6_ADDRSTRLEN];
int yes=1; // for setsockopt() SO_REUSEADDR, below
int i, j, rv;
struct addrinfo hints, *ai, *p;
char path[100],data[1000];
int fdout;
char* pmap;
int pid;
FD_ZERO(&master); // clear the master and temp sets
FD_ZERO(&read_fds);
// get us a socket and bind it
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
if ((rv = getaddrinfo(NULL, PORT, &hints, &ai)) != 0) {
fprintf(stderr, "selectserver: %s\n", gai_strerror(rv));
exit(1);
}
for(p = ai; p != NULL; p = p->ai_next) {
listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (listener < 0) {
continue;
}
// lose the pesky "address already in use" error message
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));
if (bind(listener, p->ai_addr, p->ai_addrlen) < 0) {
close(listener);
continue;
}
break;
}
// if we got here, it means we didn't get bound
if (p == NULL) {
fprintf(stderr, "selectserver: failed to bind\n");
exit(2);
}
freeaddrinfo(ai); // all done with this
// listen
if (listen(listener, 10) == -1) {
perror("listen");
exit(3);
}
// add the listener to the master set
FD_SET(listener, &master);
// keep track of the biggest file descriptor
fdmax = listener; // so far, it's this one
// main loop
for(;;) {
read_fds = master; // copy it
if (select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
perror("select");
exit(4);
}
// run through the existing connections looking for data to read
for(i = 0; i <= fdmax; i++) {
if (FD_ISSET(i, &read_fds)) { // we got one!!
if (i == listener) {
// handle new connections
addrlen = sizeof remoteaddr;
newfd = accept(listener,(struct sockaddr *)&remoteaddr,&addrlen);
if (newfd == -1) {
perror("accept");
}
else {
FD_SET(newfd, &master); // add to master set
if (newfd > fdmax) { // keep track of the max
fdmax = newfd;
}
printf("selectserver: new connection from %s on "
"socket %d\n",inet_ntop(remoteaddr.ss_family,get_in_addr((struct sockaddr*)&remoteaddr),
remoteIP, INET6_ADDRSTRLEN),newfd);
}
}
else {
// handle data from a client
if ((nbytes = recv(i, buf, sizeof buf, 0)) <= 0) {
// got error or connection closed by client
if (nbytes == 0) {
// connection closed
printf("selectserver: socket %d hung up\n", i);
}
else {
perror("recv");
}
close(i); // bye!
FD_CLR(i, &master); // remove from master set
}
else { // we got some data from a client
buf[nbytes] = '\0';
else if (0 == strncmp(buf,"/upload ",8)) {
sprintf(path,"%s",basename(buf + 8));
if((fdout = open (path, O_RDWR | O_CREAT | O_TRUNC, 0777)) < 0)
perror("open");
if ((nbytes = recv(i,data,sizeof data,0)) == -1)
perror("recive");
data[nbytes] = '\0';
lseek (fdout, nbytes - 1, SEEK_SET);
write (fdout, "", 1);
pmap = mmap (0, nbytes, PROT_READ | PROT_WRITE, MAP_SHARED, fdout, 0);
memcpy (pmap , data, nbytes);
close(fdout);
}
else {
for(j = 0; j <= fdmax; j++) { // send to everyone!
if (FD_ISSET(j, &master)) {
if (j != listener && j != i) {
if (send(j, buf, nbytes, 0) == -1) {
perror("send");
}
}
}
}
}
}
} // END handle data from client
} // END got new incoming connection
} // END looping through file descriptors
} // END for(;;)
return 0;
}

Answer 1

Sockets are streams of data, sending 30 bytes then 100 will not result in the server reading 30 bytes then 100, it could read any amount up to 130 bytes. If your file is short, you will probably get the command and the data in one recv.
To get it working for short files containing text (not the complete solution).
The command must be \0 terminated for strlen to give the right size in the server so in the client change:
if (send(sockfd,buf ,strlen(buf),0) == -1)
to
if (send(sockfd,buf ,strlen(buf)+1,0) == -1)
The server will get the command and data together in buf, so in the server change:
char path[100],data[1000];
to
char path[100], *data;
and use data to point to the data in the buffer by changing:
if ((nbytes = recv(i,data,sizeof data,0)) == -1)
perror("recive");
data[nbytes] = '\0';
to
buf[nbytes] = '\0';
data = buf + strlen(buf) + 1;
nbytes = strlen(data);
The full solution is to loop receiving data and to look for the /upload command in stream. You could still look for the \0 as a delimiter, but you should then send the length of the file and use this to determine the number of bytes to read. This will cope with binary files too.