I'm working on a project with a C++ client and a Python server.
int connecting(SOCKET s){
WSADATA wsa;
struct sockaddr_in server;
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
std::cout<<"WSA error";
return 1;
}
if((s=socket(AF_INET, SOCK_STREAM, 0))==INVALID_SOCKET){
std::cout<<"invalid socket";
return 1;
}
server.sin_addr.s_addr = inet_addr("192.168.1.10");
server.sin_family = AF_INET;
server.sin_port = htons(2424);
if(connect(s , (struct sockaddr *)&server , sizeof(server))!=0){
std::cout<<"error connecting";
return 1;
}
else{
return 0;
}
}
void recv_data(SOCKET socket){
char buf[buflen];
recv(socket, buf, buflen, 0);
std::cout<<buf;
}
int main(int argc, char* argv[]){
SOCKET s;
connecting(s);
recv_data(s);
}
Here's the very basic Python server.
import socket
import struct
s=socket.socket()
s.bind(("192.168.1.10", 2424))
s.listen(1)
c, a=s.accept()
print(f"{a}")
data="Hi from server"
c.send(data.encode())
After establishing the connection in the server, the a variable is printed. Nothing is received nor printed in the client-side. I tried putting in a loop the recv() function in the client but it does not work.
You misunderstood argument passing by value...
void f(int x) {
x = 5;
}
int main() {
int j = 7;
f(j);
printf("%d\n", j);
}
What is j? NOT 5! The number 7 was passed into f, where it was stored in the variable x, and then the number 5 was stored in the variable x, which is not the variable j, so j was not changed.
You have this in your program:
int main(int argc, char* argv[]){
SOCKET s;
connecting(s);
recv_data(s);
}
After the call connecting(s) what is s? NOT A SOCKET! Only the variable s inside the function connecting held a socket handle, and the variable s in main is not that variable, so it never got to hold a socket handle. You pass some uninitialized value to recv_data.
The function recv probably reads this random uninitialized value and returns an error code meaning "hey, that isn't a socket handle" but since your code never checked whether it returned an error code, you wouldn't know about this.
Related
I am trying to make a messenger program (that currently has a ton of bugs so please dismiss them) and for some reason, the server wont let the clients connect. I have tried changing the port, but nothing works. I get the following error (for my client, which is in python) (this is on a mac, but I have tried the client on a windows computer, still nothing):
Traceback (most recent call last):
File "msgclient.py", line 31, in <module>
Program()
File "msgclient.py", line 8, in __init__
self.s.connect((IP, PORT))
ConnectionRefusedError: [Errno 61] Connection refused
Here is the code for the server (written in c):
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <unistd.h>
#include <sys/types.h>
#define MAXCLIENTS 256
#define MAXMSG 269
#define PORT 9989
void forward(int clientslist[MAXCLIENTS], char* msg) {
int x;
for (x=0; x < MAXCLIENTS; x++){
send(clientslist[x], msg, sizeof(msg), 0);
}
return;
}
int main(){
int s = socket(AF_INET, SOCK_STREAM, 0);
int clients[MAXCLIENTS];
int clientcounter = 0;
fd_set socketlist, readlist;
FD_ZERO(&socketlist);
FD_SET(s, &socketlist);
struct sockaddr_in server;
server.sin_family = AF_INET;
server.sin_port = htons(PORT);
server.sin_addr.s_addr = INADDR_ANY;
bind(s, (struct sockaddr*) &server, sizeof(server));
listen(s, MAXCLIENTS);
int clientsocket;
int i;
int rc;
int max = s;
void* msg = (char *) malloc(MAXMSG+1);
void* usr = (char *) malloc(14);
while (1){
readlist = socketlist;
select(FD_SETSIZE, &readlist, NULL, NULL, NULL);
for (i=0; i<max+1; i++){
if(FD_ISSET(i, &readlist)){
if (i == s){
clientsocket = accept(s, NULL, NULL);
FD_SET(clientsocket, &socketlist);
clients[clientcounter] = clientsocket;
clientcounter++;
rc = recv(clientsocket, usr, 10, 0);
printf("Connection received from %s\n", usr);
usr = "\0";
if (clientsocket > max+1){
max = clientsocket;
}
} else {
rc = recv(i, msg, MAXMSG, 0);
if (rc > 0){
forward(clients, msg);
} else{
close(i);
msg = "\0";
}
}
}
}
}
return 0;
}
and the client (written in python):
import socket
class Program:
def __init__(self):
IP = socket.gethostbyname(socket.gethostname())
PORT = 9989
self.s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.s.connect((IP, PORT))
self.user = self.username()
self.s.send(bytes(self.user, "utf-8"))
while True:
received = self.s.recv(269)
received = received.decode("utf-8")
print(received)
self.enter()
def username(self):
name = str(input("Enter a username (10 character max): "))
if len(name) > 10:
print("Username is larger than 10; try again")
self.username()
return name;
def enter(self):
msg = str(input("Enter a message>> "))
if msg != "":
self.s.send(bytes(f"{self.user}>> {msg}", "utf-8"))
if __name__ == "__main__":
Program()
regarding the function:
void forward(int clientslist[MAXCLIENTS], char* msg)
and
send(clientslist[x], msg, sizeof(msg), 0);
The expression: sizeof(msg) will return a value (depending on your underlying hardware and certain compiler parameters) of 4 or 8, Not what you want. Suggest passing the actual number of bytes to transmit.
regarding the function:
void forward(int clientslist[MAXCLIENTS], char* msg)
and the statement:
return;
The return; statement is completely unnecessary. Suggest removing that statement.
regarding:
int s = socket(AF_INET, SOCK_STREAM, 0);
This statement can fail. Always check (if socket < 0) then handle the error
regarding:
server.sin_addr.s_addr = INADDR_ANY;
INADDR_ANY has the value: "0.0.0.0" which cannot be directly assigned. Suggest:
server.sin_addr.s_addr = htonl(INADDR_ANY);
OT: regarding:
bind(s, (struct sockaddr*) &server, sizeof(server));
and
listen(s, MAXCLIENTS);
These functions can fail. Always check the returned value to assure the operation was successful.
OT: regarding:
void* msg = (char *) malloc(MAXMSG+1);
and similar statements. In C, the returned type is void* which can be assigned to any pointer. Casting just clutters the code and is error prone. even this statement has an error in the cast. Suggest removing that cast.
regarding:
readlist = socketlist;
select(FD_SETSIZE, &readlist, NULL, NULL, NULL);
for (i=0; i<max+1; i++)
{
if(FD_ISSET(i, &readlist))
{
if (i == s)
{
This code sequence forces serial handling of the incoming sockets. Much better to generate a 'thread pool', then use accept() and pass the resulting client socket to an idle thread. The thread then performs all the communication with the client, then, when finishing with the client, closes the client socket.
regarding:
select(FD_SETSIZE, &readlist, NULL, NULL, NULL);
There must already be an open socket to the client, which there is none, so no communication occurs.
there may be other problems, but this should aim you in the right direction.
I would like to send over a message structure from a DLL-callback function to a python application so I can log the messages.
For this I would like to use ZeroMQ. Sadly I am unable to get the messages to python using the example provided by ZeroMQ.
DLL:
// dllmain.cpp : Defines the entry point for the DLL application.
#include "pch.h"
#include <windows.h>
#include <stdio.h>
#include <string.h>
#include <zmq.h>
HHOOK tHook;
HMODULE hinstDLL;
void* requester;
void* context;
LRESULT CALLBACK meconnect(int code, WPARAM wParam, LPARAM lParam) {
if (code == HC_ACTION) {
LPMSG data = (LPMSG)lParam;
UINT message = data->message;
switch (message)
{
case WM_POINTERUPDATE:
if (!IS_POINTER_INCONTACT_WPARAM(wParam))
break;
case WM_POINTERDOWN:
case WM_POINTERUP:
POINTER_INFO pointerInfo = {};
GetPointerInfo(GET_POINTERID_WPARAM(wParam), &pointerInfo);
int request_nbr;
for (request_nbr = 0; request_nbr != 10; request_nbr++) {
char buffer[10];
printf("Sending Hello %d…\n", request_nbr);
zmq_send(requester, data, 5, 0);
zmq_recv(requester, buffer, 10, 0);
printf("Received World %d\n", request_nbr);
}
}
}
return(CallNextHookEx(tHook, code, wParam, lParam));
}
extern "C" __declspec(dllexport) BOOL ConnectServer() {
printf("Connecting to hello world server…\n");
static void* context = zmq_ctx_new();
static void* requester = zmq_socket(context, ZMQ_REQ);
zmq_connect(requester, "tcp://127.0.0.1:5555");
printf("connected");
return TRUE;
}
extern "C" __declspec(dllexport) BOOL DisconnectServer() {
zmq_close(requester);
zmq_ctx_destroy(context);
return TRUE;
}
extern "C" __declspec(dllexport) BOOL SetHook()
{
tHook = SetWindowsHookEx(WH_GETMESSAGE, meconnect, hinstDLL, 0);
if (tHook == NULL)
return FALSE;
else
return TRUE;
}
extern "C" __declspec(dllexport) BOOL UnHook()
{
return UnhookWindowsHookEx(tHook);
}
BOOL APIENTRY DllMain(HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
hinstDLL = hModule;
break;
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
Python:
context = zmq.Context()
socket = context.socket(zmq.REP)
socket.bind("tcp://127.0.0.1:5555")
def message_msg_loop():
while True:
# Wait for next request from client
message = socket.recv()
print("Received request: %s" % message)
# Do some 'work'
time.sleep(1)
# Send reply back to client
socket.send(b"World")
def pointer_msg_loop():
global lib
lib = cdll.LoadLibrary(r'C:\Users\Braun\Documents\BA_Thesis\ba-oliver-braun-logging-tool-code\MessagesDll\x64\Release\HOOKDLL.dll')
print(lib)
res = lib.ConnectServer()
res = lib.SetHook()
pythoncom.PumpMessages()
res = lib.UnHook()
Basically my plan was to detect a certain event through windows messages and pass the message structure from the DLL-callback over to the server in Python, so I can handle the data there and put them into a log file. It does not seem to work though.
In case one has never worked with ZeroMQ,one may here enjoy to first look at "ZeroMQ Principles in less than Five Seconds"before diving into further details
Simplicity helps us start,rather than remain headbanging into Complexity First
Best avoid all the complexities :
- set .setsockopt( zmq.LINGER, 0 ) # ALWAYS, never know what version will try to join the Club
- prototype with PUSH/PULL(it a) meets the spec.+b) does not block in a mutual deadlock as all REQ/REP do )
- never share a socket ( yes, the requester ought be a private, non-shared instance )
- always read-in and assert-eval the return-codes from the ZeroMQ API calls ( detect many issues on-spot )
Can you POSACK / prove the both of the module-level declarations
...
void* requester;
void* context;
LRESULT CALLBACK meconnect(...) {...}
...
actually work as expected, or does the ConnectServer(){...}'s internal, in-scope declarations mask both of these globals ?
extern "C" __declspec(dllexport) BOOL ConnectServer() {
printf("Connecting to hello world server…\n");
static void* context = zmq_ctx_new(); // shadows out void* context
static void* requester = zmq_socket(context, ZMQ_REQ); // shadows out void* requester
zmq_connect(requester, "tcp://127.0.0.1:5555");
printf("connected");
return TRUE;
}
I have written code to set default gateway using ioctl in C. I have a function to set the gateway and the usual main function. When I compile and run the code it works fine, but when I turn it into a library and call the main function from python using ctypes the ioctl call fails. Why is this?
Note: Before using ctypes method, I tried to set gateway from python using fcntl, ioctl and socket but it failed with OSError saying invalid arguments.
gateway.c
int setDefaultGW( int sockfd, char* gatewatStr)
{
struct sockaddr_in *dst, *gw, *mask;
struct rtentry route;
in_addr_t gip;
fprintf( stderr,"socket %d\n", sockfd);
fprintf( stderr,"Address %s\n", gatewatStr);
gip = inet_addr(gatewatStr);
fprintf( stderr,"Address %d\n", gip);
memset(&route,0,sizeof(struct rtentry));
dst = (struct sockaddr_in *)(&(route.rt_dst));
gw = (struct sockaddr_in *)(&(route.rt_gateway));
mask = (struct sockaddr_in *)(&(route.rt_genmask));
/* Make sure we're talking about IP here */
dst->sin_family = AF_INET;
gw->sin_family = AF_INET;
mask->sin_family = AF_INET;
/* Set up the data for adding the default route */
dst->sin_addr.s_addr = inet_addr("0.0.0.0");
gw->sin_addr.s_addr = gip;
mask->sin_addr.s_addr = inet_addr("0.0.0.0");
route.rt_metric = 100;
route.rt_flags = RTF_UP | RTF_GATEWAY;
/* Remove this route if it already exists */
ioctl(sockfd,SIOCDELRT,&route);
/* Add the default route */
if( ioctl(sockfd,SIOCADDRT,&route) < 0 )
{
fprintf( stderr,"Adding default route: %d\n", errno);
return -1;
}
fprintf( stdout,"Added default route successfully.\n" );
return 0;
}
int main(){
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == -1)
{
perror("socket creation failed\n");
return;
}
setDefaultGW(sockfd, "192.168.6.1");
return 0;
}
net.py
gatewayFun = ctypes.CDLL("./libgateway.so")
gatewayFun.main()
Running the C binary:
./gateway
socket 3
Address 192.168.6.1
Address 17213632
Added default route successfully.
Running the python script:
# python3 net.py
socket 4
Address 192.168.6.1
Address 17213632
Adding default route: 101
I'm having a project to use pyserial to send a number to an Arduino. This number is RPM (round per minute). Arduino will receive this number to control the motor (in here I use PID Controller) and then send the number Arduino received back to Python console. The problem is, I tried to send float number to Arduino, but it receives nothing. Here is the problem:
#include <TimerOne.h>
#include <Encoder.h>
#define A 2 //Encoder pins
#define B 3
Encoder encoder(2,3);
//Config pins for motor control:
int pinAIN1 = 9; //Direction
int pinAIN2 = 8; //Direction
int pinPWMA = 5; //Speed
int pinSTBY = 4; //Stanby
float receive;
float tsamp = 0.01;
float xung = 0;
float last_xung = 0;
float current_speed = 0;
float ref_speed ; //The reference speed
float error = 0;
float last_error = 0;
float PID,last_PID;
float Kp =0.15 , Ki =0, Kd = 0.01;
void dotocdo()
{
if ( ref_speed >= 0)
{
digitalWrite(pinAIN1, 1);
digitalWrite(pinAIN2, 0);
analogWrite(pinPWMA, PID);
}
if ( ref_speed < 0)
{
digitalWrite(pinAIN1, 0);
digitalWrite(pinAIN2, 1);
analogWrite(pinPWMA, abs(PID));
}
float P;
static float I,D;
current_speed = 60*(xung-last_xung)/(tsamp*374*4);
last_xung = xung;
Serial.println(current_speed);
error=abs(ref_speed)-abs(current_speed);
P = Kp*error;
D = Kd*(error - last_error)/tsamp;
I = Ki*error*tsamp;
PID = last_PID + P + I + D;
last_error = error;
last_PID = PID;
if (PID >= 255) {PID = 255;}
if (PID <= -255) {PID = -255;}
}
void setup() {
Serial.begin(115200);
pinMode(pinPWMA, OUTPUT);
pinMode(pinAIN1, OUTPUT);
pinMode(pinAIN2, OUTPUT);
pinMode(pinSTBY, OUTPUT);
pinMode(A, INPUT);
pinMode(B, INPUT);
digitalWrite(pinSTBY, 1);
Timer1.initialize(10000);
Timer1.attachInterrupt(dotocdo);
}
void loop()
{
if (Serial.available())
{
receive= Serial.parseFloat();
ref_speed=receive;
Serial.println(receive);
}
xung=encoder.read();
}
And here is the Python code on Raspberry:
import time
import socket
import sys
import serial
import struct
UNO_1 = serial.Serial('/dev/ttyUSB0', 115200)
while (1):
n=float(25)
UNO_1.write(bytes(b'%f'%n))
receive=UNO_1.readline()
print(receive)
This is the error (Arduino receives nothing):
Does anyone know how to fix this problem?
Has any communication worked before?
Double-check your connections (swapped TX and RX, forgot GND)
Try using a serial terminal (I think pyserial has a demo included) to send data manually.
Your Python script may just be timing out.
Your Python script might be sending too many zeroes or control characters that Serial.parseFloat() does not like (it stops if it does not like something).
Alternativley, just get started with echo programs that don't actually try to parse numbers to see if any data comes through: try this.
I am trying to implement a UDP communication protocol between a C program and a python program. The C program has a structure that it sends through the UDP port (tx_port) as binary data. This program also listens on another port (rx_port) for any received data, and then prints the received binary output to the screen.
The python program listens on tx_port and unpacks the received data and prints it to the screen. Then it repacks the data and sends it back through UDP port (rx_port).
Here are the C and Python programs that I used.
C program
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>
#include <pthread.h>
#define BUFLEN 4096
#define RX_PORT 8888
#define TX_PORT 8889
// Structure data
struct data {
long frame_number;
double time;
} tx_data, rx_data;
int dlen = sizeof(tx_data);
struct sockaddr_in si_me, si_other;
int tx_soc;
int slen = sizeof(si_other);
int recv_len;
char* buf;
pthread_t rx_thread;
void* receiver_thread(void *arg)
{
int i =0;
while (1) {
recv_len = recvfrom(tx_soc, buf, sizeof(rx_data), 0, (struct sockaddr *) &si_other, &slen);
printf("\nReceived data : %d\n", recv_len);
for (i = 0; i < recv_len; i++) {
printf("%x ", buf[i]);
}
printf("\n");
fflush(stdout);
};
}
void data_init(void) {
tx_data.frame_number = 0;
tx_data.time = 0;
};
int main(void)
{
// Initialize data
data_init();
//create a UDP socket
if ((tx_soc=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
{
printf("Socket error!");
exit(0);
}
// zero out the structure
memset((char *) &si_me, 0, sizeof(si_other));
memset((char *) &si_other, 0, sizeof(si_other));
// Host socket address
si_me.sin_family = AF_INET;
si_me.sin_port = htons(RX_PORT);
si_me.sin_addr.s_addr = htonl(INADDR_ANY);
// Remote socket address
si_other.sin_family = AF_INET;
si_other.sin_port = htons(TX_PORT);
si_other.sin_addr.s_addr = htonl(INADDR_ANY);
//bind sockets to the ports
if( bind(tx_soc, (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)
{
printf("Binding error!");
}
// Start reader thread.
if (pthread_create(&rx_thread, NULL, &receiver_thread, NULL) != 0) {
printf("\ncan't create thread");
}
//keep listening for data
while(1)
{
// Allocate memory for receive buffer.
buf = (char*) malloc(sizeof(rx_data));
// Update data value.
tx_data.frame_number++;
printf("\nFrame numner: %ld", tx_data.frame_number);
fflush(stdout);
// Send data.
if (sendto(tx_soc, (char*)&tx_data, dlen, 0, (struct sockaddr*) &si_other, slen) == -1)
{
printf("Sending error!");
}
sleep(1);
}
close(tx_soc);
return 0;
}
Python program
from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
import struct
# Packet format string
packet_fmt = ''.join(['i', # Frame number
'd', # Frame time stamp
])
s = struct.Struct(packet_fmt)
class Echo(DatagramProtocol):
def datagramReceived(self, data, (host, port)):
new_data = s.unpack(data)
print new_data
echo_data = s.pack(*new_data)
self.transport.write(echo_data, (host, port))
reactor.listenUDP(8889, Echo())
reactor.run()
When I execute the two programs, I am able to receive data on both sides. I am able to unpack data in python, print it, repack and send it.
But on the C side, the received data does not match the sent data. I have checked on the python side to make sure the repacked data matches the original data.
Here is a sample output from the C and Python programs. I started the python programs first, and then the C program.
What is the mistake I might be making?