Socket not completely filling receive buffer - c

I'm building my own netcat style listener in C for a project that I'm working on.
The client (linux in this case) connects to the listener using netcat, and from the listener I'm able to send linux commands back. When running commands which give a small output (e.g. whoami, uname, pwd) the output comes back fine. However, when running a command that can give a substantial output (e.g. ls -la), I only get partial output until I send another command, which then means subsequent commands are executing the previous command. Screenshot:
Fig 1: Start of output
Fig 2: Entering another command to force output to finish
Fig 3: Now I'm one command behind, giving incorrect output.
Code as follows (includes/defines/other functions left out for brevity):
int main(int argc, char *argv[])
{
char readbuff[262144];
char user_input[1024] = "";
struct sockaddr_in srv, cln;
int bnd, checkrtr, len, lstn, new_sfd, rd, result, sfd, val;
if(argc != 2)
{
fprintf(stderr, "[*]Usage: %s <target_router>\n", argv[0]);
return -1;
}
check_router(argv[1]);
// Start a listener on port 8888
// Create the socket
sfd = socket(AF_INET, SOCK_STREAM, 0);
if(sfd == -1)
{
fprintf(stderr, "\n[*]socket: %s (%d)", strerror(errno), errno);
return -1;
}
else
{
fprintf(stdout, "\n[*]Socket created.");
}
val = 1;
result = 0;
result = setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
if(result == -1)
{
fprintf(stderr, "\n[*]setsockopt: %s (%d)", strerror(errno), errno);
}
else
{
fprintf(stdout, "\n[*]Address reuse set");
}
srv.sin_family = AF_INET;
srv.sin_addr.s_addr = inet_addr(IP);
srv.sin_port = htons(atoi(LPORT));
len = sizeof(srv);
bnd = bind(sfd, (struct sockaddr*)&srv, len);
if(bnd != 0)
{
fprintf(stderr, "\n[*]bind: %s (%d)", strerror(errno), errno);
return -1;
}
else
{
fprintf(stdout, "\n[*]Socket bound");
}
lstn = listen(sfd, 10);
if(lstn != 0)
{
fprintf(stderr, "\n[*]listen: %s (%d)", strerror(errno), errno);
return -1;
}
else
{
fprintf(stdout, "\n[*]Server listening on %s:%s", IP, LPORT);
}
socklen_t len_c = sizeof(cln);
new_sfd = accept(sfd, (struct sockaddr*)&cln, &len_c);
if(new_sfd == -1)
{
fprintf(stderr, "\n[*]accept: %s (%d)", strerror(errno), errno);
return -1;
}
else
{
char *ip_c = inet_ntoa(cln.sin_addr);
fprintf(stdout, "\n[*]New connection from client: %s:%d\n", ip_c, ntohs(cln.sin_port));
while(1)
{
memset(readbuff, 0x00, sizeof(readbuff));
memset(user_input, 0x00, sizeof(user_input));
fgets(user_input, sizeof(user_input), stdin);
if(user_input[0] == '\n')
{
continue;
}
int send_data = send(new_sfd, user_input, sizeof(user_input), 0);
if(send_data == -1)
{
fprintf(stderr, "\n[*]send: %s (%d)", strerror(errno), errno);
continue;
}
rd = read(new_sfd, readbuff, sizeof(readbuff));
fprintf(stdout, "\n size of rd: %d", rd);
fprintf(stdout, "\n size of readbuff: %ld", sizeof(readbuff));
if(rd > 0)
{
fprintf(stdout, "\n%s", readbuff);
}
else if(rd == 0)
{
fprintf(stdout, "\n[*]Client connection closed.\n");
continue;
//break;
}
else
{
fprintf(stderr, "\n[*]recv: %s (%d)", strerror(errno), errno);
continue;
}
}
}
}
Is anyone able to give me a reason why the output stops partway through please?

That's quite to be expected.
A single read can only read as much data as has been received so far (or otherwise it would need to bend time and space). The other end may also not have sent off everything they have to send by the time you issue read, so a single read won't be able to read everything either (because, well, it may not have been sent).
Since TCP is a stream protocol, you will need to devise a way to know how many bytes to expect for a single "message" from the other end, and read exactly that many bytes so you know you've gotten everything the other end has to say; I'd recommend some sort of Type-Length-Value scheme, even if you didn't need more than 1 type at present.

Related

ssh_channel_read_nonblocking( ) just echoback the given command?

I am trying to implement an ssh client using libssh but output seems to just be an echo of whatever been sent main part of program is :
do {
printf("Enter Command or q to exit: ");
fgets(command, 100, stdin);
command[strlen(command)-1] = 0;
if (ssh_channel_write(channel, command, strlen(command)) != strlen(command)) {
fprintf(stderr, "Unable to execute command\n");
exit(1);
}
printf("Data Sent: %s\n", command);
sleep(1);
while ((bytes_recieved = ssh_channel_read_nonblocking(channel, output, 2024, 0))) {
if (bytes_recieved < 1) {
fprintf(stderr, "Error Reading Output or End Of Data\n");
break;
}
printf("Data Recieved(%d): %.*s\n", bytes_recieved, bytes_recieved, output);
}
}while (strcmp(command, "q")!=0 ||strcmp(command, "Q")!=0 );
first command result in what I guess the banner to be sent althought I guess the banner is supposed to be sent before connection , this is output for only the first command after that anything i type is just echod back.
Welcome to Ubuntu 20.04 LTS (GNU/Linux 5.4.0-40-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
* "If you've been waiting for the perfect Kubernetes dev solution for
macOS, the wait is over. Learn how to install Microk8s on macOS."
https://www.techrepublic.com/article/how-to-install-microk8s-on-macos/
65 updates can be installed immediately.
0 of these updates are security updates.
To see these additional updates run: apt list --upgradable
Your Hardware Enablement Stack (HWE) is supported until April 2025.
sshd_config files (server side) have been edited to include this as highlights:
AllowTcpForwarding no
PasswordAuthentication yes
PermitRootLogin prohibit-password
AllowUsers user_name
Whole code is here for anyone if he want's to use or test on it just change your username in ssh_options_set( ) part of the code.
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <libssh/libssh.h>
int main(int argc, char* argv[])
{
printf("libssh version: %s\n", ssh_version(0));
if (argc < 2){
fprintf(stderr, "USAGE command hostname\n");
exit(1);
}
char* hostname = argv[1];
int port = 22;
ssh_session ssh = ssh_new();
ssh_options_set(ssh, SSH_OPTIONS_HOST, hostname);
ssh_options_set(ssh, SSH_OPTIONS_PORT, &port);
// TODO: Enable it in the future
int verbosity = SSH_LOG_PROTOCOL;
ssh_options_set(ssh, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
int error_code = ssh_connect(ssh);
if (error_code != SSH_OK){
fprintf(stderr, "Error creating connection with error %d", error_code);
exit(1);
}
printf("Connected to %s on port %d.\n", hostname, port);
printf("banner %s\n", ssh_get_serverbanner(ssh));
ssh_key key;
if(ssh_get_server_publickey(ssh, &key) != SSH_OK) {
fprintf(stderr,"Couldnt get server key\n");
exit(1);
}
unsigned char* hash;
size_t hash_len;
if(ssh_get_publickey_hash(key, SSH_PUBLICKEY_HASH_SHA1, &hash, &hash_len)!=SSH_OK){
fprintf(stderr, "Error Calculating Hash\n");
exit(1);
}
printf("Host public key hash:\n");
ssh_print_hash(SSH_PUBLICKEY_HASH_SHA1, hash, hash_len);
ssh_key_free(key);
ssh_clean_pubkey_hash(&hash);
enum ssh_known_hosts_e known = ssh_session_is_known_server(ssh);
switch (known) {
case SSH_KNOWN_HOSTS_OK:printf("known Host\n");break;
case SSH_KNOWN_HOSTS_NOT_FOUND:printf("no host file\n");break;
case SSH_KNOWN_HOSTS_CHANGED:printf("Host Changed\n");break;
case SSH_KNOWN_HOSTS_ERROR:
printf("Host error. %s\n", ssh_get_error(ssh)); return 1;
case SSH_KNOWN_HOSTS_UNKNOWN: printf("Unknown Host verify please\n");break;
}
if(known == SSH_KNOWN_HOSTS_CHANGED){
printf("Server key changed Exiting\n");
exit(1);
}
if (
known == SSH_KNOWN_HOSTS_OTHER ||
known == SSH_KNOWN_HOSTS_UNKNOWN ||
known == SSH_KNOWN_HOSTS_NOT_FOUND)
{
printf("Do you want to trust this host\n");
char answer[10];
fgets(answer, 10, stdin);
if(answer[0] == 'y' || answer[0] == 'Y'){
ssh_session_update_known_hosts(ssh);
}else{
printf("Not trusting it\n");
exit(1);
}
}
ssh_options_set(ssh, SSH_OPTIONS_USER, "my_user");
printf("Enter password: ");
char pass[20];
fgets(pass, 20, stdin);
pass[strlen(pass)-1] = 0 ;
if(ssh_userauth_password(ssh, 0, pass) != SSH_AUTH_SUCCESS){
fprintf(stderr, "Unable to Authentication\n");
exit(1);
}else {
printf("Authentication successful!\n");
}
int err = ssh_userauth_publickey_auto(ssh, NULL, NULL);
if (err == SSH_AUTH_ERROR){
fprintf(stderr, "Unable to Authunticate\n");
exit(1);
}
ssh_channel channel = ssh_channel_new(ssh);
if(!channel){
fprintf(stderr, "Couldnt create a channel\n");
exit(1);
}
if(ssh_channel_open_session(channel) != SSH_OK){
fprintf(stderr, "Error Openning Session\n");
exit(1);
}
if (ssh_channel_request_pty(channel) != SSH_OK){
fprintf(stderr, "Can't initiate terminal\n");
exit(1);
}
if(ssh_channel_change_pty_size(channel, 80, 400) != SSH_OK){
fprintf(stderr, "Error Changing size of terminal\n");
exit(1);
}
if(ssh_channel_request_shell(channel) != SSH_OK){
fprintf(stderr, "Couldn't request a shell\n");
exit(1);
}
char command[100];
char output[2024];
int bytes_recieved;
do {
printf("Enter Command or q to exit: ");
fgets(command, 100, stdin);
command[strlen(command)-1] = 0;
if (ssh_channel_write(channel, command, strlen(command)) != strlen(command)) {
fprintf(stderr, "Unable to execute command\n");
exit(1);
}
printf("Data Sent: %s\n", command);
sleep(1);
while ((bytes_recieved = ssh_channel_read_nonblocking(channel, output, 2024, 0))) {
if (bytes_recieved < 1) {
fprintf(stderr, "Error Reading Output or End Of Data\n");
break;
}
printf("Data Recieved(%d): %.*s\n", bytes_recieved, bytes_recieved, output);
}
}while (strcmp(command, "q")!=0 ||strcmp(command, "Q")!=0 );
ssh_channel_send_eof(channel);
ssh_channel_close(channel);
ssh_channel_free(channel);
ssh_disconnect(ssh);
ssh_free(ssh);
return 0;
}

How to reconnect to TCP server after network goes down and comes back up again?

I have a raspberry pi that connects to a TCP server and sends some data every couple of seconds, I want to be able to handle all kind of failures and disconnects, so at the moment I am trying a test where I disconnect the Huawei USB dongle that I am connecting through.
I have a thread that runs in the background and check the connection periodically. The code does not reconnect when I remove the USB dongle and plug it back in sometime later, I need help on how to make this more robust. At the moment on the server side I see that after I plug back in the USB dongle I see the client connect but immediately disconnect from it.
The thread is called KeepSocketOpen and inside here I call a ping function to 8.8.8.8 to see if the connection is still active and here is my code, I'm kind of new to socket programming so excuse the mess:
int ping(char *ipaddr)
{
char *command = NULL;
FILE *fp;
int x, match=0;
char* result = NULL;
size_t len = 0;
asprintf (&command, "%s %s -p 50 -r 3", "fping", ipaddr);
//printf ("%s %s -q 2>&1", "fping", ipaddr);
fp = popen(command, "r");
if (fp == NULL) {
fprintf(stderr, "Failed to execute fping command\n");
free(command);
return -1;
}
while(getline(&result, &len, fp) != -1) {
fputs(result, stdout);
//printf("%s",result);
}
for(x=0;x<len;x++)
{
if(x>5 && result[x]=='e'&& result[x-1]=='v'&& result[x-2]=='i'&& result[x-3]=='l'&& result[x-4]=='a')
{
match=1;
break;
}
}
if(match==0)
sleep(5);
free(result);
fflush(fp);
if (pclose(fp) != 0) {
perror("Cannot close stream.\n");
}
free(command);
//printf("%s\r\n",result);
if(match==0)
return -1;
else
return 1;
}
void* KeepSocketOpen(void *arg)
{
pthread_t id= pthread_self();
char tcprxbuff[1024];
int numbytes, status=0,attempts,reuse=1;
struct timeval timeout={0};
timeout.tv_sec=10;
timeout.tv_usec=0;
printf("in sock thread\r\n");
while(1)
{
if(is_socket_connected==0)
{
sock=socket(AF_INET,SOCK_STREAM,0);
addr.sin_family = AF_INET;
addr.sin_port = htons(34879);
addr.sin_addr.s_addr=inet_addr("X.X.X.X");
attempts=0;
setsockopt(sock,SOL_SOCKET,SO_SNDTIMEO,(char *)&timeout,sizeof(timeout));
setsockopt(sock,SOL_SOCKET,SO_RCVTIMEO,(char *)&timeout,sizeof(timeout));
setsockopt(sock, SOL_SOCKET,SO_REUSEADDR,&reuse,sizeof(reuse));
status=connect(sock, (struct sockaddr *) &addr,sizeof (addr));
// wait for 5s and see if the socket has connected
do
{
delay(5);
}
while(errno && attempts++<1000);
if (attempts >=1000 || errno) // this is the fail case
{
printf("socket not connected %s\r\n",strerror(errno));
is_socket_connected=0;
close(sock);
//shutdown(sock,SHUT_RDWR);
sleep(30);
}
else
{
// fcntl(sock, F_SETFL, O_NONBLOCK);
printf("socket reconnected %d,%s\r\n",attempts,strerror(errno));
is_socket_connected=1;
write(sock, "HI FROM RASPI", strlen("HI FROM RASPI"));
}
}
else
{
numbytes=read(sock,tcprxbuff,sizeof(tcprxbuff));
if(numbytes==0)// if this is zero, socket was closed by server
{
is_socket_connected=0;
while(close(sock)==-1);
}
else
{
printf("socket connected:%d\r\n",numbytes);
status = ping("8.8.8.8");
if (status!=-1) {
printf("socket still connected:%d\r\n",status);
is_socket_connected=1;
} else {
printf("socket disconnected:%d\r\n",status);
is_socket_connected=0;
//shutdown(sock,SHUT_RDWR);
while(close(sock)==-1);
}
}
sleep(30);
}
}
}

libssh tunnel echoing input

I've created my own SSH reverse tunnel using libssh by following the tutorials at http://api.libssh.org/master/libssh_tutorial.html and piecing things together from various other samples. However, now, all I get is the client echoing back whatever is inputted via the tunnel connection. I'm trying to get to the point where I can execute commands through the reverse tunnel (ex: ls -al).
The reverse tunnel (initiated on the client side):
int reverse_loop(ssh_session session){
ssh_channel channel;
int rc;
int nbytes, nwritten;
char buf[256];
int port = 0;
rc = ssh_channel_listen_forward(session, NULL, 43434, NULL);
if (rc != SSH_OK){
fprintf(stderr, "Error opening remote port %s\n", ssh_get_error(session));
return rc;
}
channel = ssh_channel_accept_forward(session, 60000, &port);
if (channel == NULL){
fprintf(stderr, "Error waiting for incoming connection: %s\n", ssh_get_error(session));
return SSH_ERROR;
}
while(1){
printf("In loop\n");
nbytes = ssh_channel_read(channel, buf, sizeof(buf), 0);
if (nbytes < 0){
fprintf(stderr, "Error reading incoming data: %s\n", ssh_get_error(session));
ssh_channel_send_eof(channel);
ssh_channel_free(channel);
return SSH_ERROR;
}
printf("read channel\n");
if (nbytes > 0){
nwritten = ssh_channel_write(channel, buf, nbytes);
if (nwritten != nbytes){
fprintf(stderr, "Error sending answer: %s\n", ssh_get_error(session));
ssh_channel_send_eof(channel);
ssh_channel_free(channel);
return SSH_ERROR;
}
printf("Wrote channel\n");
}
printf("sent answer!\n");
}
// close_channel
ssh_channel_send_eof(channel);
ssh_channel_free(channel);
return SSH_OK;
}
Running this, the reverse session is initiated. So, from the SSH server, I can run:
> nc localhost 43434
ls (this is what I sent)
ls (this is what I receive)
pwd (this is what I sent)
pwd (this is what I receive)
Then on the client side, I see this output:
In loop
read channel
Wrote channel
sent answer!
In loop
What I'm looking for are the actual results of running ls or pwd (or whatever system command the user inputs, not the echo. Can anyone direct me on the step that I missed to do this?
Thanks!

Strtok() returning NULL randomly

I am trying to create a client that communicate with a server by sending 2 types of messages:
The word QUIT that communicate to the server to close the connection.
An operation with the following syntax: operator first_operand second_operand. For example: + 3 3, - 5 6 etc. (the operands must be positive integers, and there must be only 2 operands).
If the server receive an operation, it executes it and returns the result to the client. The problem is that the first operation I send returns the right result, while the following ones work randomly (sometimes they return the right result, other times the function strtok() doesn't get the second operand and returns NULL...).
This is code of the client that process the message written by the user in the prompt and that scan the message to check if the operation is written with the correct syntax (WARNING: the code is written in an extremely unprofessional and unclean way).
The code part that creates the problem is inside the while(1).
#define MAXLENGTH 256
int main (int argc, char *argv[]) {
int simpleSocket = 0;
int simplePort = 0;
int returnStatus = 0;
char first[10], second[10];
char* operator;
char buffer[MAXLENGTH] = "";
char message[50];
char terminationCommand[] = "QUIT\n";
char space[2] = " ";
struct sockaddr_in simpleServer;
if (3 != argc) {
fprintf(stderr, "Usage: %s <server> <port>\n", argv[0]);
exit(1);
}
/* create a streaming socket */
simpleSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (simpleSocket == -1) {
fprintf(stderr, "Could not create a socket!\n");
exit(1);
} else {
fprintf(stderr, "Socket created!\n");
}
/* retrieve the port number for connecting */
simplePort = atoi(argv[2]);
/* setup the address structure */
/* use the IP address sent as an argument for the server address */
//bzero(&simpleServer, sizeof(simpleServer));
memset(&simpleServer, '\0', sizeof(simpleServer));
simpleServer.sin_family = AF_INET;
//inet_addr(argv[2], &simpleServer.sin_addr.s_addr);
simpleServer.sin_addr.s_addr=inet_addr(argv[1]);
simpleServer.sin_port = htons(simplePort);
/* connect to the address and port with our socket */
returnStatus = connect(simpleSocket, (struct sockaddr *)&simpleServer, sizeof(simpleServer));
if (returnStatus == 0) {
fprintf(stderr, "Connect successful!\n\n");
} else {
fprintf(stderr, "Could not connect to address!\n");
close(simpleSocket);
exit(1);
}
/* get the message from the server */
returnStatus = read(simpleSocket, buffer, sizeof(buffer));
if (returnStatus > 0) {
printf("%s\n", &buffer[3]);
} else {
fprintf(stderr, "Return Status = %d \n", returnStatus);
}
memset(&buffer, '\0', sizeof(buffer));
printf("You can execute 2 commands:\n");
printf("1. Operations ( +, -, *, /, % ) with the following syntax: operator + first operand + second operand.\n");
printf("Example: + 5 2 \n");
printf("2. Termination of the connection with the following syntax: QUIT + press Enter.\n");
while(1) {
printf("\nEnter a command:\n");
fgets(message, 1000, stdin);
// the if with the termination command works fine
if (strcmp(message, terminationCommand) == 0) {
if (send(simpleSocket, message, strlen(message), 0) < 0) {
printf("Send failed.");
return 1;
}
returnStatus = read(simpleSocket, buffer, sizeof(buffer));
if (returnStatus > 0) {
printf("%s\n", &buffer[4]);
} else {
fprintf(stderr, "Return Status = %d \n", returnStatus);
}
close(simpleSocket);
exit(1);
}
operator = strtok(message, space);
if (strcmp(operator, "+") == 0 || strcmp(operator, "-") == 0 || strcmp(operator, "/") == 0 || strcmp(operator, "%") == 0 || strcmp(operator, "*") == 0) {
char *first_operand = strtok(NULL, space);
if (first_operand != NULL) {
if (strcmp(first_operand, "ANS") == 0)
strcpy(first, "ANS");
else
strcpy(first, first_operand);
printf("%s\n", operator);
printf("%s\n", first);
char *second_operand = strtok(NULL, space);
printf("%s\n", second_operand);
if (second_operand != NULL && strtok(NULL, space) == NULL && (atoi(first) > 0 || strcmp(first, "ANS") == 0)) {
if (strcmp(second_operand, "ANS\n") == 0)
strcpy(second, "ANS");
else {
strcpy(second, second_operand);
}
if (atoi(second) > 0 || strcmp(second, "ANS") == 0) {
printf("OK\n");
char operation[] = "";
strcat(operation, operator);
strcat(operation, " ");
strcat(operation, first);
strcat(operation, " ");
strcat(operation, second);
if (send(simpleSocket, operation, strlen(operation), 0) < 0) {
printf("Send failed.");
return 1;
}
returnStatus = read(simpleSocket, buffer, sizeof(buffer));
if (returnStatus > 0) {
printf("%s\n", buffer);
} else {
fprintf(stderr, "Return Status = %d \n", returnStatus);
}
}
}
}
}
// after everything I reset the buffers I use to memorize the message and the elements of the message
memset(&buffer, '\0', sizeof(buffer));
memset(&first, '\0', sizeof(first));
memset(&second, '\0', sizeof(second));
memset(&message, '\0', sizeof(message));
memset(operator, '\0', sizeof(operator));
}
}
Can someone tell me why the second strtok() acts weird 90% of the times? What am I doing wrong?
There are multiple issues in you program:
You send newline terminated messages and you assume on the other end the read will return exactly the bytes sent by the other party, which is an incorrect assumption for the TCP/IP communications, only the order of bytes received is guaranteed, but the messages can be split on the way and received in chunks different from the sending sequence. You should instead read the socket into a buffer and only handle it once you receive a newline.
In your case, there is another problem which is more pressing: the buffer into which you read the data is not null terminated, so you should not pass it to standard C functions such as strtok().

C 3G File Transfer Client/Server Linux

I have a problem that I'm hoping is a mistake as I am a bit new to linux C.
I have a server, that sends a file to a client. The code works perfectly fine over a wired connection, 100% success rate every time. However, when I try to run that same code over a 3G USB connection at -65dB (Strong), the client will usually only receive the first 1 or 2 thousand bytes of the file. (Forgive the syntax errors won't let me space properly)
// CLIENT CODE
char* fs_name = "/target/to/send";
char sdbuf[LENGTH]; // Send buffer, LENGTH == 512
printf("Sending %s to the Client... \n", fs_name);
FILE *fs = fopen(fs_name, "r");
if(fs == NULL)
{
fprintf(stderr, "ERROR: File %s not found on server. (errno = %d)\n", fs_name, errno);
exit(1);
}
bzero(sdbuf, LENGTH);
int fs_block_sz;
while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs))>0)
{
if(send(client, sdbuf, fs_block_sz, 0) < 0)
{
fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
exit(1);
}
bzero(sdbuf, LENGTH);
}
printf("File send Success\n");
// SERVER CODE
char* fr_name = "/home/file/to/save";
FILE *fr = fopen(fr_name, "a");
if(fr == NULL)
printf("File %s Cannot be opened.\n", fr_name);
else
{
// zero out bytes
bzero(revbuf, LENGTH);
int fr_block_sz = 0;
while((fr_block_sz = recv(sd, revbuf, LENGTH, 0)) > 0) //LENGTH == 512
{
int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
if(write_sz < fr_block_sz)
{
error("File write failed.\n");
}
bzero(revbuf, LENGTH);
if (fr_block_sz == 0 || fr_block_sz != 512)
{
break;
}
}
// error checking
if(fr_block_sz < 0)
{
if (errno == EAGAIN)
{
printf("recv() timed out.\n");
}
else
{
fprintf(stderr, "recv() failed due to errno = %d\n", errno);
}
fclose(fr);
If anyone out there could shed some light on what I'm doing wrong I would be most appreciative. Thanks for reading.
EDIT: The server is Ubuntu 10.04 and the client is Arch Linux ARM and the type of file being sent is an ARM binary.
I think your main problem is here in your code labeled server but which really looks to be the client. You assume that the recv is going to get all 512 bytes on each recv but that's not true - you can and will get short reads. A little below you break out of the read loop if you haven't read exactly LENGTH (i.e. 512). That explains why your pgm quits after a couple of thousand bytes.
while ((fr_block_sz = recv(sd, revbuf, LENGTH, 0)) > 0) //LENGTH == 512
{
int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
if (write_sz < fr_block_sz)
{
error("File write failed.\n");
}
bzero(revbuf, LENGTH);
if (fr_block_sz == 0 || fr_block_sz != 512)
{
break;
}
}
You want something more like this:
while ((fr_block_sz = recv(sd, revbuf, LENGTH, 0)) > 0) //LENGTH == 512
{
if (fr_block_sz < 0)
if (errno == EAGAIN)
continue;
else
error;
if (fr_block_sz == 0)
break; //done
int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
if (write_sz < fr_block_sz)
{
error("File write failed.\n");
}
bzero(revbuf, LENGTH);
}

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