Problems Returning an HTTP 200 Ok Message
Hi Folks,
I'm having some issues with an small socket based server I'm writing,
and I was hoping I could get some help.
My code (attached below) us supposed to read an HTTP Post message
coming from a power meter, parse it, and return a proper HTTP 200 Ok
message. The problem is that the socket fails to send the entire
message as one message, creating a fragmented message which the power
meter then fails to read and accept.
Is there any way to force the socket to send the entire message at
once? Am I doing anything wrong? Is there an easier way to implement
this functionality?
Thanks,
Guy Davidson
Code:
# server application to read data from power meter
# listens on port 80
# receives HTTP POST messages
# author: Maria Kazandjieva <[EMAIL PROTECTED]>, Guy Davidson
<[EMAIL PROTECTED]>
# updated: July 7th, 2008: staring to add database writing
functionality
import time
import datetime #datetime for response message
from socket import * #socket module
import DataPacket #local file with data packet class
import library
import MySQLdb
#formats a proper response message
myHost = ""
myPort = 80
#response = "HTTP/1.1 200 OK\r\nDate: Fri, 20 June 2008 20:40:34 GMT\r
\nServer:SING\r\nX-Powered-By: maria\r\nContent-Length: 7\r
\nConnection:close\r\nContent-Type: text/html\r\n\r\n[0!:20]\n"
#initializing the socket:
s = socket(AF_INET, SOCK_STREAM)# create a TCP socket
s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1) # allow port reuse? I hope
s.bind((myHost, myPort))# bind it to the server port
s.listen(50)# allow 50 simultaneous
pending connections
print('Socket initialized')
#intializing the database
db = MySQLdb.connect(host='localhost', user='powernet',
passwd='jplicks', db='test')
cursor = db.cursor()
print('Database cursor intialized')
while 1:
print('In while 1')
connection, address = s.accept()# connection is a new socket
print('Accepted a connection')
# TODO:
# verify connection is from powernet so we don't get random
connections to port 80
# best way to get the data would be:
# read until we get all the headers
# parse Content header to get length of data
# read for that many additional bytes
while 1:
print('In while 1 2')
data = connection.recv(4096)# receive up to 4K bytes
print('First set of data receieved:')
#print(data)
'''
if data:
print data
#connection.send(response) #send response; OK 200
HTTP message
else:
break
'''
if data:
# second read should recieve the rest of the packet
# finding how long the content is
length = data.find('Content-Length: ')
print('Index of "Content-Length" = ' + str(length))
length = int(data[length+16:length+18])
# adding the bytes from the "Content-Type section:"
length += 51
data += connection.recv(length)
print('Second set of data received:')
print(data)
if data:
#print('Found data:')
#print data #print the string data
packet = DataPacket.DataPacket(data) #use the
string data to
create a DataPacket object
print(packet) #print the contents of the
object, I hope :)
#we have a packet, let's write it to the mysql
DB
packet.mysql_insert(cursor)
#connection.send(response) #send response;
OK 200 HTTP
message
print('Sending response')
response = library.response_message() #get the
response message
totalsent = 0 #initialize a variable to track
how much we've sent
so far
while totalsent < len(response): #while we
haven't sent everything
sent =
connection.send(response[totalsent:]) #send whatever we
can starting where we stopped
totalsent += sent #increment the count
of how much we've sent.
else:
print('No data')
break
else:
print('No data')
break
--
http://mail.python.org/mailman/listinfo/python-list
Re: Problems Returning an HTTP 200 Ok Message
On Jul 10, 12:38 pm, samwyse <[EMAIL PROTECTED]> wrote: > On Jul 10, 1:50 pm, Guy Davidson <[EMAIL PROTECTED]> wrote: > > > Hi Folks, > > > I'm having some issues with an small socket based server I'm writing, > > and I was hoping I could get some help. > > > My code (attached below) us supposed to read an HTTP Post message > > coming from a power meter, parse it, and return a proper HTTP 200 Ok > > message. The problem is that the socket fails to send the entire > > message as one message, creating a fragmented message which the power > > meter then fails to read and accept. > > > Is there any way to force the socket to send the entire message at > > once? Am I doing anything wrong? Is there an easier way to implement > > this functionality? > > By 'message', do you mean a single IP datagram? In general, the > answer is no. Each call to 'connection.send()' will (in general, see > the next paragraph) transmit as much data as will fit into a single IP > datagram, given the current MTU for the transmission circuit. The > fact that you're calling it in a loop indicates that the data being > sent may be larger than will fit into a datagram. > > Or, by 'message', do you mean a single TCP segment? Again, the answer > is no. Your network stack will try to make the TCP segments the right > size to fit within a single IP datagram, leading to the same result as > above. > > From your description, I get the feeling that your power meter has a > broken network stack, and you're trying to program around it. You > need to repair the meter. Here's the weird thing. I know it should be able to be done. Let me try and explain in some more depth what I'm trying to do: The meter sends HTTP Post messages, and expects, as a reply, an HTTP 200/Ok message. I try to send the following message, using the socket.send() command: 'HTTP/1.1 200 OK\r\nDate: Thu, 10 July 2008 14:07:50 GMT\r\nServer: Apache/2.2.8 (Fedora)\r\nX-Powered-By: PHP/5.2.4\r\nContent-Length: 4\r \nConnection: close\r\nContent-Type: text/html; charset=UTF-8\r\n\r \n[0]\n' However, when I snoop on the packets in wireshark, here's what I see: HTTP/1.1 200 Ok: HTTP/1.1 200 OK Date: Wed, 09 July 2008 14:55:50 GMT Server: Apache/2.2.8 (Fedora) X-Powered-By: Continuation or non-HTTP traffic: PHP/5.2.4 Content-Length: 4 Connection: close Content-Type: text/html; charset=UTF-8 [0] It splits into two packages, which the meter can't read, and the communication breaks down there. Any ideas? Thanks. -- http://mail.python.org/mailman/listinfo/python-list
