I am now coding a telnet proxy which forwards the message between the client and the telnet server and will forbid some instructions from the client.
I am confused about the transform mode in telnet.If the server and the client both agree to the TRANSMIT-BINARY option,then when the client want to send a char which is 255 to the server,what will it send?Sending 255 255 for escape?
If it is so,then when the client want to send a telnet command to the server,what will it send?Just as usual sending the 255 x x (that is IAC verb option)?
Thanks for your help!
Related
I'm experimenting with LuaSocket for a project I'm working on. I've chosen UDP as my protocol.
Looking for docs and tutorials online, I've attempted to create a client-server pair for testing and learning.
According to what I've read, the following code should work. However, only the server seems to be working properly. The client sends a message, but it will not receive the reply from the server.
Thank you for any help anyone can provide.
Server:
-- Server
#!/usr/bin/env lua5.1
local socket = require("socket")
udp = socket.udp()
udp:setsockname("*", 53474)
udp:settimeout(0)
while true do
data, ip, port = udp:receivefrom()
if data then
print("Received: ", data, ip, port)
udp:sendto(data, ip, port)
end
socket.sleep(0.01)
end
Client:
-- Client
#!/usr/bin/env lua5.1
local socket = require("socket")
udp = socket.udp()
udp:setpeername("127.0.0.1", 53474)
udp:settimeout(0)
udp:send("Data!")
data = udp:receive()
if data then
print("Received: ", data)
end
The timeout value you set is 0, which causes the client timeout every time.
To fix it, give it a positive timeout value:
udp:settimeout(1)
Or set it to nil or a negative value, so it blocks indefinitely:
udp:settimeout()
or
udp:settimeout(-1)
I am making a simple UDP P2P Chat Program with a well known server.
The client's send and recieve data from server and clients through a single IdUDPServer.
The clients as of now can login and logout i.e. they can send data to the server.
Whenever the server sends any data it gets dropped at the NIC side of the node as the embedded ip header checksum is 0x00 as notified by wireshark.
IdUDPServer Settings (Client/Server)
Active : True
Bindings :
Broadcast : False
BufferSize : 8192
DefaultPort : 10000
IPVersion : Id_IPv4
ThreadedEvent : False
Command Used
only one command is used within
UDPServer.SendBuffer ( ED_Host.Text, StrToInt ( ED_Port.Text ), Buffer );
A similar configuration is working perfectly in another program of mine.
Most NICs will perform checksum validation and generation these days instead of the os network stack. This is to improve performance and is known as checksum offloading. As such wiresshark will report the fact the checksum is missing as an error but it can usually be ignored or the error turned off in the wire shark settings.
Some NIC drivers allow you to turn off checksum offloading. Try this and retest the code
I want to build a small script in python which needs to fetch an url. The server is a kind of crappy though and replies pure ASCII without any headers.
When I try:
import urllib.request
response = urllib.request.urlopen(url)
print(response.read())
I obtain a http.client.BadStatusLine: 100 error because this isn't a properly formatted HTTP response.
Is there another way to fetch an url and get the raw content, without trying to parse the response?
Thanks
It's difficult to answer your direct question without a bit more information; not knowing exactly how the (web) server in question is broken.
That said, you might try using something a bit lower-level, a socket for example. Here's one way (python2.x style, and untested):
#!/usr/bin/env python
import socket
from urlparse import urlparse
def geturl(url, timeout=10, receive_buffer=4096):
parsed = urlparse(url)
try:
host, port = parsed.netloc.split(':')
except ValueError:
host, port = parsed.netloc, 80
sock = socket.create_connection((host, port), timeout)
sock.sendall('GET %s HTTP/1.0\n\n' % parsed.path)
response = [sock.recv(receive_buffer)]
while response[-1]:
response.append(sock.recv(receive_buffer))
return ''.join(response)
print geturl('http://www.example.com/') #<- the trailing / is needed if no
other path element is present
And here's a stab at a python3.2 conversion (you may not need to decode from bytes, if writing the response to a file for example):
#!/usr/bin/env python
import socket
from urllib.parse import urlparse
ENCODING = 'ascii'
def geturl(url, timeout=10, receive_buffer=4096):
parsed = urlparse(url)
try:
host, port = parsed.netloc.split(':')
except ValueError:
host, port = parsed.netloc, 80
sock = socket.create_connection((host, port), timeout)
method = 'GET %s HTTP/1.0\n\n' % parsed.path
sock.sendall(bytes(method, ENCODING))
response = [sock.recv(receive_buffer)]
while response[-1]:
response.append(sock.recv(receive_buffer))
return ''.join(r.decode(ENCODING) for r in response)
print(geturl('http://www.example.com/'))
HTH!
Edit: You may need to adjust what you put in the request, depending on the web server in question. Guanidene's excellent answer provides several resources to guide you on that path.
What you need to do in this case is send a raw HTTP request using sockets.
You would need to do a bit of low level network programming using the socket python module in this case. (Network sockets actually return you all the information sent by the server as it as, so you can accordingly interpret the response as you wish. For example, the HTTP protocol interprets the response in terms of standard HTTP headers - GET, POST, HEAD, etc. The high-level module urllib hides this header information from you and just returns you the data.)
You also need to have some basic information about HTTP headers. For your case, you just need to know about the GET HTTP request. See its definition here - http://djce.org.uk/dumprequest, see an example of it here - http://en.wikipedia.org/wiki/HTTP#Example_session. (If you wish to capture live traces of HTTP requests sent from your browser, you would need a packet sniffing software like wireshark.)
Once you know basics about socket module and HTTP headers, you can go through this example - http://coding.debuntu.org/python-socket-simple-tcp-client which tells you how to send a HTTP request over a socket to a server and read its reply back. You can also refer to this unclear question on SO.
(You can google python socket http to get more examples.)
(Tip: I am not a Java fan, but still, if you don't find enough convincing examples on this topic under python, try finding it under Java, and then accordingly translate it to python.)
urllib.urlretrieve('http://google.com/abc.jpg', 'abc.jpg')
I am developing a chat application.
But Right now chatting is possible with only google because I know only google's port no.
xmppClient = [[XMPPClient alloc] init];
[xmppClient addDelegate:self];
// Replace me with the proper domain and port.
// The example below is setup for a typical google talk account.
[xmppClient setDomain:#"talk.google.com"];
[xmppClient setPort:5222];
You can see that, google has set 5222 as port number.
Same way I want to set port no for yahoo, windows messenger & other popular sites, How can I get all these?
(Is it something like that - "XMPP is specific for Google ones" ? ? )
Kraken's Openfire Properties Page has the port and domain information you need. Just re-use and try with your application.
5222/tcp is the default port for XMPP, but your implementation may have a different one. To find out, you do a DNS SRV query for _xmpp-client._tcp.YOURDOMAIN, where you replace YOURDOMAIN with the domain you're trying to connect to. This will return 0+ records that have hostname/port combinations for how to connect. If you get 0 records back, assume port 5222.
For example, I want to connect to the GoogleTalk server, and log in with the account foo#gmail.com. My client performs the lookup that can be simulated with dig on the command line like this:
% dig +short -t SRV _xmpp-client._tcp.gmail.com.
20 0 5222 talk1.l.google.com.
20 0 5222 talk4.l.google.com.
5 0 5222 talk.l.google.com.
20 0 5222 talk3.l.google.com.
20 0 5222 talk2.l.google.com.
The result with the lowest priority number is 5 0 5222 talk.l.google.com., which means you open a TCP connection to talk.l.google.com on port 5222.
To make SRV queries from code, check out this answer, which relies on DNSServiceQueryRecord.
5222 is the default port for XMPP, but
your implementation may have a
different one. To find out, you do a
DNS server query for
_xmpp-client._tcp.DOMAIN_Name, where you replace DOMAIN_Name with the
domain you're trying to connect to(ex.
gmail.com,google.com,yahoo.com). This
will return 0+ records that have
hostName/port combinations for how to
connect. If you get 0 records back,
assume port 5222.
i want to check my server connection to know if its available or not to inform the user..
so how to send a pkg or msg to the server (it's not SQL server; it's a server contains some serviecs) ...
thnx in adcvance ..
With all the possibilities for firewalls blocking ICMP packets or specific ports, the only way to guarantee that a service is running is to do something that uses that service.
For instance, if it were a JDBC server, you could execute a non-destructive SQL query, such as select * from sysibm.sysdummy1 for DB2. If it's a HTTP server, you could create a GET packet for index.htm.
If you actually have control over the service, it's a simple matter to create a special sub-service to handle these requests (such as you send through a CHECK packet and get back an OKAY response).
That way, you avoid all the possible firewall issues and the test is a true end-to-end one. PINGs and traceroutes will be able to tell if you can get to the machine (firewalls permitting) but they won't tell you if your service is functioning.
Take this from someone who's had to battle the network gods in a corporate environment where machines are locked up as tight as the proverbial fishes ...
If you can open a port but don't want to use ping (i dont know why but hey) you could use something like this:
import socket
host = ''
port = 55555
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((host, port))
s.listen(1)
while 1:
try:
clientsock, clientaddr = s.accept()
clientsock.sendall('alive')
clientsock.close()
except:
pass
which is nothing more then a simple python socket server listening on 55555 and returning alive