I'm building a app TCP server client, i want to send binary to the server/client (so i don't want to use send and recv) and i have a problem, i want to read the file descriptor of my client it's doesn't working i don't understand why because the server accept the client correctly so i have make this function:
bool accept_and_read_client(){
struct sockaddr_in new_client = { 0 };
socklen_t length = sizeof(new_client);
int val_return = accept(sock_fd, (struct sockaddr*)&new_client, &length);
if(val_return < 0){
syserr("error of accept");
return true;
}
printf("accept of client successful\n");
client_array[0].fd = val_return;
size_t nbread;
client_array[0].file = fdopen(client_array[0].fd, "w+");
nbread = fread(&val_return, sizeof(char), sizeof(MAX_BUFF), client_array[0].file);
if(nbread < -1){
syserr("fread");
return true;
}
printf("number i read : %ld\n", nbread);
return false;
}
when i start the server, the server wait client and when i make ./client test the server said:
accept of client successful
fread: Success
so the function fread fails.
on the client.c i do a fwrite like this:
...
FILE* fdc = fdopen(sock_fd, "w+");
if(fdc == NULL){
syserr("error of fdopen");
return 1;
}
printf("%s\n", argv[1]);
size_t nb_write = fwrite(argv[1], sizeof(*argv), strlen(argv[1]), fdc);
printf("number i write: %ld\n", nb_write);
if(fflush(fdc)){
syserr("fflush");
}
if you want to see the client structure:
struct client{
int fd;
// char buffer[MAX_BUFF];
FILE* file;
};
struct client client_array[MAX_CLIENTS];
if somebody have a idea why fread don't work tell me please
The fread function probably doesn't fail, instead it's your check that is flawed:
size_t nbread;
...
if(nbread < -1)
The type size_t is unsigned so when you compare nbread with -1 the value -1 will be converted to an unsigned value as well. And that unsigned value will be very large, so nbread will always be smaller than -1.
The fread function will not return -1 or EOF on error, instead it will return a value smaller than the count argument (the third argument). That's the condition you need to check (nbread < sizeof(MAX_BUFF) with the possibly wrong code you currently show).
Related
In an exercise problem, I am required to build a client program (write first) that opens a .txt file, put each line and the total bytes of each line into a struct variable and then send it out to the server program (read first). Right after this is done, the client program will also receive a struct file (similarly only has char * and int attributes) from the server program.
// Below are global variables in both programs
#define BUFSIZE 1024
struct info_pack
{
char line[BUFSIZE]; // the line to receive messages
int bytes; // the bytes of data transferred
};
char fifo_path[] = "./my_fifo";
struct info_pack info_w; // the info_pack for writing each line in text.txt
struct info_pack info_r; // the info_pack for reading feedback info_pack sent from the server program
First is the client program:
// the main() in the client program
int main()
{
int fd;
int i = 0, index = 1, bytes = 0, line_length, fifo_read;
char *file_path = "/home/text.txt";
FILE *fd2;
mkfifo(fifo_path, 0666);
if ((fd2 = fopen(file_path, "r")) < 0)
{
perror("Opening file");
return -1;
}
else
{
printf("Successfully open the target file\n");
while (fgets(info.line, BUFSIZE, fd2) != NULL)
// the "segmentation fault" error appears right after this line
{
info_w.bytes = strlen(line);
fd = open(fifo_path, O_WRONLY);
printf("The %d th line sent out is: %s\n%d bytes are sent\n\n",
index, info_w.line, info_w.bytes);
write(fd, &info_w, sizeof(info_w) + 1);
close(fd);
fd = open(fifo_path, O_RDONLY);
fifo_read = read(fd, &info_r, sizeof(info_r));
close(fd);
if (fifo_read > 0)
{
printf("Feedback: %s\nand %d bytes are returned\n", info_r.line, info_r.bytes);
}
}
printf("All data is successfully transfered\n");
}
return 0;
}
Then is the server program
// the main() in the server program
int main()
{
int fd, fifo_read;
int line_length;
char *feedback = "SUCCESS";
strcpy(info_w.line, feedback);
info_w.bytes = strlen(feedback);
// define a constant info_pack variable to send to the client program
if (mkfifo(fifo_path, 0666) < 0)
{
perror("client end: ");
exit(-1);
}
while (1)
// This server program will wait for any one single client's message
// This server program can only be terminated by manually input signals (like ^\)
{
fd = open(fifo_path, O_RDONLY);
printf("waiting for client's message\n");
fifo_read = read(fd, &info_r, sizeof(info_r));
close(fd);
if (fifo_read > 0)
// if receive the struct variable, print all of its attributes
{
if (info_r == NULL)
printf("Found no lines sent from the client\n");
else
printf("Read from fifo:\n %s\n(in info)%d bytes read (actually)%d bytes read\n", info_r.line, info_r.bytes, fifo_read);
}
else
{
sleep(1);
printf("Fail to read data from the client\n");
}
// Because of the error in client program this server program
// always pause here
fd = open(fifo_path, O_WRONLY);
printf("Now writing feedback to the client\n");
write(fd, info_w, sizeof(info_w));
close(fd);
}
}
Could anyone explain why the segmentation fault error appears in the client program? Then I can test if the both the client and the server can co-op properly.By the way, I read this post already but, in this post, it is a one-time data stream and I cannot find any hints in it.
I am trying to learn C and I can't get these apps working. I am creating 2 apps client/server, where the client connects to a server via specified port, and sends a file name (text) to the server. The server then takes the file name, runs it through a word count function and then responds to the client with filename/line/word/character count. I have gotten the client and the server to connect and communicate but my problem is that I can't seem to pass the client input to the wordcount function properly. Also, I'm not sure my function will return properly as I haven't found an appropriate method of returning a crafted string. Any help would be appreciated. Thanks!
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
void error(const char *msg){
perror(msg);
exit(1);
}
char * wordcount(char *cfile){
int i = 0;
int ccount = 0;
int wcount = 0;
int lcount = 0;
char *fn = malloc(strlen(cfile+7));
sprintf(fn, "/Files/%s", cfile);
FILE *cfilename = fopen (fn, "r");
while ((i = fgetc(cfilename)) != EOF){
if (i == '\n') {
lcount++;
}
if (i == '\t' || i == ' '){
wcount++;
}
ccount++;
}
printf("%c contains %d words, %d characters and %d lines.\n", cfile, wcount, ccount, lcount);
return 0;
}
int main(int argc, char *argv[]){
int sock, newSock, portno, n;
struct sockaddr_in serv_addr, cli_addr;
socklen_t clilen;
char buffer[256];
int index = 5;
int lowPortNum = 2500 + (10 * index);
int highPortNum = 2500 + (10 * index) + 9;
/* Check for proper amount of args */
if (argc < 2){
fprintf(stderr, "ERROR: No port specified. Exiting...\n");
printf("NOTE: Port must be between %d & %d.\n",lowPortNum,highPortNum);
exit(1);
}
/* Create socket by using args to form components */
sock = socket(AF_INET , SOCK_STREAM , 0);
if (sock < 0){
error("ERROR: Could not create 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(sock, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0){
error("ERROR: Binding failed.");
return 1;
}
/* Start listening on socket */
listen(sock, 5);
puts("Server is waiting for connection...");
clilen = sizeof(cli_addr);
/* Accept connection from incoming client */
newSock = accept(sock, (struct sockaddr *) &cli_addr, &clilen);
if (newSock < 0){
error("ERROR: Accept failed.");
}
/* Read message from the client */
bzero(buffer, 256);
if (read(newSock, buffer, 255) < 0){
error("ERROR: Cannot read from socket.");
}
//debug
printf("client msg read: %s\n",buffer);
/* Send message to the client */
//wordcount(buffer);
if (write(newSock , wordcount(buffer) , 100) < 0){
error("ERROR: Cannot write to socket.");
}
close(newSock);
close(sock);
return 0;
}
Firstly, I think you've made a mistake here:
char *fn = malloc(strlen(cfile+7));
sprintf(fn, "/Files/%s", cfile);
You probably meant this:
char fn[strlen(cfile) + 8];
sprintf(fn, "/Files/%s", cfile);
You might notice that I've rearranged it a little; I think you wanted to add 7 to the return value of strlen, not to the argument of strlen. I've written 8 instead, because the extra 1 is for a '\0' which goes at the end of your string; that's extremely important. When you're crafting strings, always remember to make space for the '\0'.
Additionally, I've changed your malloc to a variable-length array. You really don't need to use dynamic storage duration (e.g. malloc) for this; try to prefer automatic storage duration unless you absolutely need dynamic storage duration.
Especially considering that your code leaks memory (which is the precise reason to avoid it unless you absolutely need it). Perhaps valgrind would be a useful tool in your development environment? Always remember to free any memory you have mallocd.
There's another error here:
FILE *cfilename = fopen (fn, "r");
while ((i = fgetc(cfilename)) != EOF){
Supposing fopen returns NULL (probably to indicate that the file doesn't exist), the calls to fgetc following it are clearly going to fail in disastrous ways. I think you meant something like this:
FILE *cfilename = fopen (fn, "r");
if (cfilename == NULL) {
/* XXX: HANDLE THIS ERROR! We'll get to this later... */
}
while ((i = fgetc(cfilename)) != EOF){
... and similarly, you've forgotten to fclose that file that was fopend. Always remember to fclose files that you have fopend.
... my problem is that I can't seem to pass the client input to the wordcount function properly
Providing the mistakes mentioned earlier are fixed, you should be able to safely pass the message received from your socket to wordcount as you have in your comment, without crashes or resource leaks: wordcount(buffer);...
You can try that if you like, but bear with me for a moment longer because you have other requirements to assess.
I'm not sure my function will return properly as I haven't found an appropriate method of returning a crafted string.
Think about how standard library functions handle this. You've used one of them here: sprintf(fn, "/Files/%s", cfile);. By accepting the destination (fn) for the string as an argument, sprintf allows you to use whichever storage duration you like. Additionally, this allows sprintf to return some other int value (which you can look up in the sprintf manual in your own time)...
If you design your function to write to a destination pointed to by an argument, like sprintf (and others) do, you'll be able to use your function however you like (e.g. automatic or dynamic storage duration?), too. You'll be able to return an int value indicating success or failure (e.g. when the fopen call fails), too.
Consider the following function, which doesn't even need a return value because there are no error modes:
typedef unsigned long long ullong;
void fcount(FILE *f, ullong *char_count, ullong *word_count, ullong *line_count)
{
rewind(f);
*char_count = 0;
*word_count = 0;
*line_count = 0;
for (;;) {
int c = fgetc(f);
switch (c) {
case EOF: return;
case '\n': (*line_count)++;
case '\t':
case ' ': (*word_count)++;
default: (*char_count)++;
}
}
}
Now consider this wrapper of that function, which does require a return value
int count(char *destination, char *filename) {
char fn[strlen(filename) + 8];
sprintf(fn, "/files/%s", filename);
FILE *f = fopen(fn, "r");
if (f == NULL) {
/* Note: This exit code is defined within <stdlib.h> */
return EXIT_FAILURE;
}
ullong char_count, word_count, line_count;
count(f, &char_count, &word_count, &line_count);
fclose(f);
sprintf(destination, "%s contains %llu words, %llu characters and %llu lines.\n", filename, word_count, char_count, line_count);
return EXIT_SUCCESS;
}
Now you can tell if your function fails or succeeds, just like many of the standard library functions! Yay!
char buf[128];
count(buf, file_name);
printf("%s", buf);
You can also access the string you intended to write... Is this all flowing together?
I'm trying to implement a working HTTP Client-Server application just to make practice with network programming.
The 2 programs have to follow this basic algorithm:
CLIENT - send a GET request
SERVER - send "+OK\r\n"
SERVER - send file size in bytes
SERVER - send file
CLIENT - send ACK
I'm having a lot of troubles in the reading part, probably because i perform some dirty read on the stream.
These are the 2 reading function that i'm using:
/* Reads a line from stream socket s to buffer ptr
The line is stored in ptr including the final '\n'
At most maxlen chasracters are read*/
int readline (SOCKET s, char *ptr, size_t maxlen)
{
size_t n;
ssize_t nread;
char c;
for (n=1; n<maxlen; n++)
{
nread=recv(s, &c, 1, 0);
if (nread == 1)
{
*ptr++ = c;
if (c == '\n')
break;
}
else if (nread == 0) /* connection closed by party */
{
*ptr = 0;
return (n-1);
}
else /* error */
return (-1);
}
*ptr = 0;
return (n);
}
and:
int readNumber(SOCKET s, long *num, int maxRead)
{
size_t n;
ssize_t nread;
int totRead;
long number=0;
for (n=1; n<maxRead+1; n++)
{
nread=recv(s, &number, sizeof(number), 0);
if (nread == sizeof(number))
{
totRead+=nread;
*num = number;
}
else if (nread == 0) /* connection closed by party */
{
*num = 0;
return (n-1);
}
else /* error */
{
printf("nread = %d\n", nread);
return (-1);
}
}
return (totRead);
}
this is the snippet of the main where i receive the +OK message and then the file size:
memset(rbuf,0,sizeof(rbuf)); //rbuf is the buffer where is store the read
printf("waiting for response...\n");
result = readline(s, rbuf, sizeof(rbuf)); //reading function is above
printf("Byte read(okMsg) = %d\n", result);
if (result <= 0)
//ERROR MANAGEMENT
{
printf("Read error/Connection closed\n");
closesocket(s);
SockCleanup();
exit(1);
}
else
{
long fileLength=0;
unsigned char *fBuf;
//RECEIVE OK
if(!strcmp(rbuf,"+OK\r\n"))
{
puts("+OK\n");
//RECEIVE FILE LEN
int nw = readNumber(s, &fileLength, 1); //reading function is above
printf("Byte read(fDim) = %d\n", nw);
printf("File is %ld bytes long\n", fileLength);
if(nw >0)
{
// RECEIVE FILE
}
}
}
When i send the "+OK\r\n" string the server tells me that it sends 8 bytes, but when i read i find the '\0' char only after 6 bytes.
By the way it reads correctly the message, but when i try to read the file size (that is a long) it gives me back a wrong number.
My opinion is that the stream buffer is dirty, and that i'm reading 2 bytes that are not part of the file size, but i'm not understanding why this happens.
Please ask me more info if i'm not clear enough.
SOLVED:
Thank you all for your answers!!!
You put me in the right mindset to understand what was wrong.
Look like the problem was this declaration in the server:
char *okMsg = "+OK\r\n";
instead of
char okMsg[] = "+OK\r\n";
that lead me to an undefined behavior.
long number=0;
for (n=1; n<maxRead+1; n++)
{
nread=recv(s, &number, sizeof(number), 0);
You forgot to design and implement a protocol to carry the data between your server and your client. Because TCP provides a stream of bytes, your protocol should be defined as a stream of bytes.
How many bytes convey this number? Is "however many bytes a 'long' happens to occupy on my platform" a good answer? What's the semantic meaning of the first byte? Is "whatever the first byte of a 'long' happens to mean on my platform" a good answer?
A good answer would be, "The size shall be conveyed as a 4-byte unsigned integer in little-endian byte order". Then make absolutely sure your code sends and receives in that format.
I'm writing a small and simple server (in C language for Linux stations).
A client requests a file to my server, my server asks this file to another server which sends it to my server.
My server should NOT receive ALL the file before sending it to the client BUT must send the bytes of the file so as they arrive.
This is an exercise in school so I can not dissociate myself from this requirement.
I have implemented the function explained below. The problem is that the client receives a non-deterministic number of bytes and NEVER the entire file.
int Recv_and_send_file (int socketa, int socketb, char *buffer, size_t file_size){
size_t n;
ssize_t nread;
ssize_t nwritten;
char c;
for (n=1; n<file_size; n++)
{
nread=recv(socketa, &c, 1, 0);
if (nread == 1)
{
nwritten = send(socketb,&c,1,0);
}
else if (nread == 0)
{
*buffer = 0;
return (-1); /* Errore */
}
else
return (-1); /* Errore */
}
}
*buffer = 0;
return (n);
}
Someone could kindly tell me where I'm wrong?
Is it an stupid idea to change the values SO_SNDBUF and SO_RCVBUF on both the server and the client?
Assuming the file_size is the total number of bytes you want to send, then your for loop will only send file_size - 1 bytes. In other words, you are off by one. Start from 0 instead to fix this:
for (n=0; n<file_size; n++)
{ //..
You capture the return value of send(), but you do not check to see if it was successful or not.
You are treating a 0 return value from recv() the same as an error. Since you do not show what you do after returning -1 from your function, I don't know if this may be contributing to your problem or not.
Certain errors on send() and recv() are "soft", in that you are allowed to retry the operation for those particular errors. One such error is EINTR, but check the documentation on your system to see if there are others.
In order to optimize performance and simplify your code, you can use splice()+pipes. Sendfile enables you to "forward" data between file descriptors, without the copy to user space.
Are you sure you have copied the correct code? That part as it is would not compile, there is a } in the last else which don't match with a corresponding {.
Also, how you get to know the file size? if it's send thru the socket as an integer, bear in mind the possible byte order of the source and destination machines.
Anyway, you are reading one byte at a time, you should improve it this way:
EDIT: use buffer and not the extra buff[2048];
int Recv_and_send_file (int socketa, int socketb, char *buffer, size_t file_size){
ssize_t nread;
ssize_t nwritten;
ssize_t bLeft=file_size;
while (bLeft > 0)
{
nread=recv(socketa, buffer, bleft, 0);
if (nread > 0)
{
nwritten = send(socketb, buffer, nread, 0);
bLeft -= nread;
buffer+=nread;
}
else if (nread == 0)
{
// I think this could raise a memory exception, read below
*buffer = 0;
return (-1); /* Errore */
}
else
{
return (-1); /* Errore */
}
}
// If buffer is allocated with file_size bytes this one will raise a memory exception
// *buffer = 0;
return (file_size-bLeft);
}
there's something strange in my client/server socket using RSA.
If i test it on localhost, everithing goes fine, but if i put client on a pc and server on othe pc, something gone wrong.
Client after call connect, call a method for public keys exchange with server. This part of code works fine.
After this, client send a request to server:
strcpy(send_pack->op, "help\n");
RSA_public_encrypt(strlen(send_pack->op), send_pack->op,
encrypted_send->op, rsa_server, padding);
rw_value = write(server, encrypted_send, sizeof (encrypted_pack));
if (rw_value == -1) {
stampa_errore(write_error);
close(server);
exit(1);
}
if (rw_value == 0) {
stampa_errore(no_response);
close(server);
exit(1);
}
printf("---Help send, waiting for response\n");
set_alarm();
rw_value = read(server, encrypted_receive, sizeof (encrypted_pack));
alarm(0);
if (rw_value == -1) {
stampa_errore(read_error);
exit(1);
}
if (rw_value == 0) {
stampa_errore(no_response);
close(server);
exit(1);
}
RSA_private_decrypt(RSA_size(rsa), encrypted_receive->message,
receive_pack->message, rsa, padding);
printf("%s\n", receive_pack->message);
return;
}
but when server try to decrypt the receive message on server side, the "help" string doesn't appear. This happen only on the net, on localhost the same code works fine...
EDIT:
typedef struct pack1 {
unsigned char user[encrypted_size];
unsigned char password[encrypted_size];
unsigned char op[encrypted_size];
unsigned char obj[encrypted_size];
unsigned char message[encrypted_size];
int id;
}encrypted_pack;
encrypted_size is 512, and padding used is RSA_PKCS1_PADDING
You are assuming that you read the whole thing, 512 sizeof (encrypted_pack) bytes, in one go. This doesn't always happen. You can get less than that, so you should read(2) in a loop until you have your complete application message.
Edit 0:
You are trying to decrypt not complete message. TCP is a stream of bytes, and you have to treat it as such. It doesn't know about your application message boundaries. You should be doing something like this:
char buffer[sizeof( encrypted_pack )];
size_t to_read = sizeof( encrypted_pack );
size_t offset = 0;
while ( true ) {
ssize_t rb = ::read( fd, buffer + offset, to_read - offset );
if ( rb == -1 ) { /* handle error */ }
else if ( rb == 0 ) { /* handle EOF */ }
else {
offset += rb;
to_read -= rb;
if ( to_read == 0 ) break;
}
}
// handle complete message in buffer
You should do the same - write bytes into the socket in a loop - on the sending side too.
It "works" over loopback because MTU of that virtual interface is usually around 16K vs. 1500 for normal ethernet, so TCP transfers your data in one chunk. But you cannot rely on that.