I'm a newbie, and I was trying to test the code here (which uses Redis event loop)
But when i make a request to 127.0.0.1:8000, the server doesn't send the response, it hangs. Do i need to make some changes ? I just need the request to be echoed back, which the example intends to do.
Why do you think this thing is a HTTP server? It is not. It is a broken TCP echo server.
It is broken, because the write operation is not under the control of the event loop. Some bytes will be lost if the non blocking write operation cannot send all the bytes (you have no such guarantee).
Now, if you use a proper client, this program can still be demonstrated:
$ telnet 127.0.0.1 8000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
toto
toto
titi
titi
tutu
tutu
... while the output of the program itself is:
Accepted 127.0.0.1:48645
If you want to play with event loops, I would suggest picking one among the following list. They are probably much better documented than the first random ae hack found on github ...
libevent
libev
libuv
Related
I am facing some issues to solve a problem. A server program is giving 4 random unsigned integer numbers everytime I connect to it. My job is to add the 4 numbers and send back the sum. But the time is restricted. So if I want to use a calculator to do the job, it is not possible. Thus I have to take resort to scripting. I want to connect to the the server using netcat, retrieve the 16 bytes, pipe the data to my C program(which will parse the data into 4 unsigned int variables and print out the sum) and again redirect this program output to netcat
netcat <server> <port> | myProg | netcat <server> <port>
But the tcp socket netcat is opening second time is not the previous socket. So a different set of 4 numbers would be presented this time, which defeats the entire effort. My question is: Is it possible by any means(using netcat) to use the previous socket (opened by netcat) to pump the calculated sum back to the server?
I dont want to use C to do socket programming as it is very tough for me.
Also I know
echo 3<>/dev/tcp/server/port
cat <&3 | ./myprog | more >&3
probably will solve my purpose (correct me if I am wrong). But I would like to do it the netcat way. Thanks in advance.
Use socat instead of netcat.
socat can spawn the command itself, with input and output both redirected (you don't use shell redirection, let socat handle it)
socat TCP:server,port SYSTEM:myProg
I'm trying to build a python client to interact with my C server. Here's the code for the client:
import socket
s = socket.socket()
s.connect(("127.0.0.1", 12209))
print "preparing to send"
s.send("2")
s.send("mmm2.com")
s.send("mypwd")
s.send("5120")
print "Sent data"
root = s.recv(256)
print root
When I run this code on the interactive shell (the GUI IDLE) of course line by line, everything runs very fine. But when i save this code in a file and try to run it, it hangs and stops responding according to windows, what's it that I'm just not doing?
If you type it line by line, the sent strings are likely received by the server one after another in separate recv() calls.
When you execute it in a script, all the send() calls run immediately after each other without delay and the server will probably receive all the data in one bulk in a single recv() call. So the server will see "2mmm2.commypwd5120", and maybe not handle that correctly. It might wait for more input from the client.
You will need some explicit separation between the values, for example newline characters, so that the server can parse the received data correctly.
I have 2 files Client Side & Server Side
I send a string over the socket from client to server. I have to execute this string as one does in a terminal. The output of the command is to be displayed on the client side.
Server Side Code : this loop runs on each thread created by pthread_create
while((n=recv(sock,client_message,2000,0))>0)
{
send(sock,server_out,n,0);
}
I need to run the string i recieve in client_message as a terminal command and fetch the output of the command and send it back via the server_out string buffer.
How do i go about this ?
So - you have two or three different tasks to accomplish.
The first one is to run the command line you received on the server. For that, you can start reading the system() function. It's very straightforward to use.
But then you need to get it's output. You can read about this two points in this question.
Lastly, send that data back to the server - once you have the output stream, it's just send()ing that via the socket. You can implement some mini-protocol for telling the other side how many bytes to expect, some error detection/correction if you want, etc.
Once the data arrives the client, then you can do whatever you want with it - print it on the screen, save to a file, you name it.
Read about this things, take your chances, and come back to continue asking if you need it - good luck!
This is a very beginner-level question in C.
Don't know where to start looking/searching.
So, if I have a program continuously running in C, what is the best way to accept input through the command line into the program?
EX, mysql is already running, but you can process a command call
mysql SELECT * FROM *
Do I need a different program to write to file/stdin?enter code here
Clarification:
So, mysql seems to be able to take in commands while it is already running... is that possible in C?
Goal:
I have some hooks into open gl es, and I want to run a continuous draw loop in the background, while having the ability to call commands such as
glhookprogram make "object1" model "triangle" program "default"
glhookprogram attr "object1" position "1.0, 1.0, 0.0" scale "2.0" rotation "45, 0, 0"
this way, I can have a node server run hw-accelerated animations in javascript on the rpi.
Looks like this is what you need (and I'm sorry - I won't be going into too much details as there are plenty of sources on the Web about that):
A "server" - that would be your background process that stays running in memory and can accept and process commands (requests)
A "client" - a (short-running?) process that can accept commands from user (GUI, command-line. Network? Other process?) and send requests to your "server"
This is not a trivial task for a beginner. I would suggest googling for "server-client" and for "inter-process communications" first and go from there.
The range of options to "accept input" into your server includes (but is not limited to) the following:
(Windows) messages
Shared memory and a command queue (producer-consumer)
Shared file (just listing it here for completeness, I'd advise against this particular one for your case)
Named pipes
Sockets (thanks for reminding me of those in the comments, can't believe I missed that!)
My situation is the following: I've got a lot of small gizmos ( pretty close to routers, not exactly but anyway that's irrelevant) ; they are running a bare-bones MIPS-based Linux distro.
To control them, one can telnet there ( thru serial port ) and issue commands to an interactive bash-like shell which then writes back some output. The shell's input and output are both attached to /dev/ttyAS0.
Now, I'd like to automate all of this, i.e. write a program that will run inside the gizmo, be a small server listening on some port, and which would pass on any command to the said shell, capture shell's output and relay it back to whoever contacted to server.
I:
1) can install (small, <500KB) programs inside the gizmo
2) can't modify the OS, startup scripts, the shell, anything
3) have root access
4) know how to write a SOAP server
5) know how to get a SOAP message, translate it to a command and inject it into /dev/ttyAS0
6) DONT KNOW how to capture the shell's reply
7) know how to, having shell's reply, translate it back to a SOAP message and reply to the original inquirer.
So basically, the problem is 6) : how to, having injected a string to /dev/ttyAS0 and thus having made the shell execute it, capture the shell's output ?
I am aware of
http://etbe.coker.com.au/2008/02/27/redirecting-output-from-a-running-process/
i.e. I know that I could change the shell's stdout if I had GDB ( or strace ) running inside the box, but I can't install it there - it's too big and anyway this approach seems too much like a hack.
So, summarizing:
How root can capture stdout of an already running process, IN PURE C, without gdb or strace, with no access to the way the process is started?
Or - almost equivalently - how to capture what's being written to a terminal, IN PURE C ?
You might want to take a look at reptyr. It will probably need some adaptation to work for your system though
Have you tried driving the serial port with a kermit script? I would probably forgo trying to insert a more clever proxy on the device and just try and drive the existing interface.
If you really want to get it on the device, you may be able to look at the source to something like screen or kermit to get a sense of how they interact with ttys.