Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 1 ■ INTRODUCTION TO CLIENT/SERVER NETWORKING
reply = json.loads(rawreply)
print reply['Placemark'][0]['Point']['coordinates'][:-1]
In this listing, all references to the idea of a URL have disappeared—in fact, none of Python’s URLrelated
libraries are imported at all! Instead, we are here directly manipulating the HTTP protocol: asking
it to connect to a specific machine, to issue a GET request with a path that we have constructed, and
finally to read the reply directly from the HTTP connection. Instead of being able to conveniently
provide our query parameters as separate keys-and-values in a dictionary, we are having to embed them
directly, by hand, in the path that we are requesting by first writing a question mark (?) followed by the
parameters in the format name=value and all separated by & characters.
The result of running the program, however, is much the same as for the programs shown
previously:
$ python search3.py
[-84.3063479, 41.5228242]
As we will see throughout this book, HTTP is just one of many protocols for which the Python Standard
Library provides a built-in implementation. In search3.py, instead of having to worry about all of the
details of how HTTP works, our code can simply ask for a request to be sent and then take a look at the
resulting response. The protocol details that the script has to deal with are, of course, more primitive than
those of search2.py, because we have stepped down another level in the protocol stack, but at least we are
still able to rely on the Standard Library to handle the actual network data and make sure we get it right.
A Raw Network Conversation
But, of course, HTTP cannot simply send data between two machines using thin air. Instead, the HTTP
protocol must operate by using some even simpler abstraction. In fact, it uses the capacity of modern
operating systems to support a plain-text network conversation between two different programs across
an IP network. The HTTP protocol, in other words, operates by dictating exactly what the text of the
messages will look like that pass back and forth between two hosts implementing the protocol.
When we move beneath HTTP to look at what happens below it, we are dropping down to the very
lowest level of the network stack that we can still access easily from Python. Take a careful look at
search4.py. It makes exactly the same networking request to Google Maps as our previous three programs,
but it does so by sending a raw text message across the Internet and receiving a bundle of text in return.
Listing 1–4. Talking to Google Maps Through a Bare Socket
#!/usr/bin/env python
# Foundations of Python Network Programming - Chapter 1 - search4.py
import socket
sock = socket.socket()
sock.connect(('maps.google.com', 80))
sock.sendall(
» 'GET /maps/geo?q=207+N.+Defiance+St%2C+Archbold%2C+OH'
» '&output=json&oe=utf8&sensor=false HTTP/1.1\r\n'
» 'Host: maps.google.com:80\r\n'
» 'User-Agent: search4.py\r\n'
» 'Connection: close\r\n'
» '\r\n')
rawreply = sock.recv(4096)
print rawreply
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