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

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CHAPTER 18 ■ RPC 8.0 If this response looks a bit verbose for the amount of data that it is transmitting, then you will be happy to learn about the RPC mechanism that we tackle next. JSON-RPC The bright idea behind JSON is to serialize data structures to strings that use the syntax of the JavaScript programming language. This means that JSON strings can be turned back into data in a web browser simply by using the eval() function. By using a syntax specifically designed for data rather than adapting a verbose document markup language like XML, this remote procedure call mechanism can make your data much more compact while simultaneously simplifying your parsers and library code. Purpose: Remote procedure calls Standard: http://json-rpc.org/wiki/specification Runs atop: HTTP THE JSON-RPC PROTOCOL Data types: int; float; unicode; list; dict with unicode keys; None Libraries: many third-party, including lovely.jsonrpc JSON-RPC is not supported in the Python Standard Library (at least at the time of writing), so you will have to choose one of the several third-party distributions available. You can find these distributions on the Python Package Index. My own favorite is lovely.jsonrpc, contributed to the Python community by Lovely Systems GmBH in Austria. If you install it in a virtual environment (see Chapter 1), then you can try out the server and client shown in Listings 18–5 and 18–6. Listing 18–5. A JSON-RPC Server #!/usr/bin/env python # Foundations of Python Network Programming - Chapter 18 - jsonrpc_server.py # JSON-RPC server from wsgiref.simple_server import make_server import lovely.jsonrpc.dispatcher, lovely.jsonrpc.wsgi def lengths(*args): » results = [] » for arg in args: » » try: » » » arglen = len(arg) » » except TypeError: » » » arglen = None » » results.append((arglen, arg)) » return results 313
CHAPTER 18 ■ RPC dispatcher = lovely.jsonrpc.dispatcher.JSONRPCDispatcher() dispatcher.register_method(lengths) app = lovely.jsonrpc.wsgi.WSGIJSONRPCApplication({'': dispatcher}) server = make_server('localhost', 7002, app) print "Starting server" while True: » server.handle_request() You can see that the Lovely Systems package — which was written recently using modern Python technology — offers a WSGI wrapper around its JSON-RPC dispatcher, making it easy to incorporate into modern Python web application stacks, or to deploy stand-alone using the Standard Library’s wsgiref package. The server code is quite simple, as an RPC mechanism should be. As with XML-RPC, we merely need to name the functions that we want offered over the network, and they become available for queries. (You can also pass an object, and its methods will be registered with the server all at once.) Listing 18–6. JSON-RPC Client #!/usr/bin/env python # Foundations of Python Network Programming - Chapter 18 - jsonrpc_client.py # JSON-RPC client from lovely.jsonrpc import proxy proxy = proxy.ServerProxy('http://localhost:7002') print proxy.lengths((1,2,3), 27, {'Sirius': -1.46, 'Rigel': 0.12}) Writing client code is also quite simple. Sending several objects whose lengths we want measured — and having those data structures sent right back by the server — enables us to see several details about this particular protocol. First, note that the protocol allowed us to send as many arguments as we wanted; it was not bothered by the fact that it could not introspect a static method signature from our function. This is similar to XML-RPC, but it is very different from XML-RPC mechanisms built for traditional, staticallytyped languages. Second, note that the None value in the server’s reply passes back to us unhindered. This is because this value is supported natively by the protocol itself, without our having to activate any non-standard extensions: $ python jsonrpc_server.py Starting server [In another command window:] $ python jsonrpc_client.py [[3, [1, 2, 3]], [None, 27], [2, {'Rigel': 0.12, 'Sirius': -1.46}]] Third, note that there is only one kind of sequence supported by JSON-RPC, which means that the tuple sent by our client had to be coerced to a list to make it across. Of course, the biggest difference between JSON-RPC and XML-RPC — that the data payload in this case is a small, sleek JSON message that knows natively how to represent each of our data types — is not even visible here. This is because both mechanisms do such a good job of hiding the network from our code. Running Wireshark on my localhost interface while running this example client and server, I can see that the actual messages being passed are as follows: {"version": "1.1", "params": [[1, 2, 3], 27, {"Rigel": 0.12, "Sirius": -1.46}], "method": "lengths"} {"result": [[3, [1, 2, 3]], [null, 27], [2, {"Rigel": 0.12, "Sirius": -1.46}]]} 314
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Foundations of Python Network Progr
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To the Python community for creatin
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Contents ■Contents at a Glance ..
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■ CONTENTS Asking getaddrinfo() W
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■ CONTENTS Using Message Queues f
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■ CONTENTS Parsing Dates ........
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■ CONTENTS Telnet ...............
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About the Authors ■ Brandon Craig
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Acknowledgements This book owes its
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■ INTRODUCTION If you do know som
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C H A P T E R 1 ■ ■ ■ Introdu
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CHAPTER 1 ■ INTRODUCTION TO CLIEN
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C H A P T E R 2 ■ ■ ■ UDP The
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CHAPTER 2 ■ UDP server with SSH.
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CHAPTER 2 ■ UDP them anywhere in
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CHAPTER 2 ■ UDP command-line argu
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CHAPTER 2 ■ UDP » » » » raise
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CHAPTER 2 ■ UDP world itself give
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CHAPTER 2 ■ UDP socket that is no
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CHAPTER 2 ■ UDP So binding to an
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CHAPTER 2 ■ UDP s.connect((hostna
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CHAPTER 2 ■ UDP else: » print >>
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C H A P T E R 3 ■ ■ ■ TCP The
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CHAPTER 3 ■ TCP situation), and t
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CHAPTER 3 ■ TCP » reply = recv_a
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CHAPTER 3 ■ TCP guess when the in
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CHAPTER 3 ■ TCP the system has no
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CHAPTER 3 ■ TCP » » » print '\
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CHAPTER 3 ■ TCP $ python tcp_dead
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CHAPTER 3 ■ TCP Using TCP Streams
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CHAPTER 4 ■ SOCKET NAMES AND DNS
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CHAPTER 5 ■ NETWORK DATA AND NETW
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C H A P T E R 6 ■ ■ ■ TLS and
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CHAPTER 6 ■ TLS AND SSL systems a
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CHAPTER 6 ■ TLS AND SSL • He wi
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CHAPTER 6 ■ TLS AND SSL discussio
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CHAPTER 6 ■ TLS AND SSL • The s
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CHAPTER 6 ■ TLS AND SSL The Links
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C H A P T E R 7 ■ ■ ■ Server
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CHAPTER 7 ■ SERVER ARCHITECTURE P
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CHAPTER 7 ■ SERVER ARCHITECTURE
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CHAPTER 7 ■ SERVER ARCHITECTURE N
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CHAPTER 7 ■ SERVER ARCHITECTURE L
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CHAPTER 7 ■ SERVER ARCHITECTURE F
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CHAPTER 7 ■ SERVER ARCHITECTURE p
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CHAPTER 7 ■ SERVER ARCHITECTURE N
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CHAPTER 7 ■ SERVER ARCHITECTURE L
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CHAPTER 7 ■ SERVER ARCHITECTURE s
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CHAPTER 7 ■ SERVER ARCHITECTURE c
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C H A P T E R 8 ■ ■ ■ Caches,
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CHAPTER 8 ■ CACHES, MESSAGE QUEUE
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C H A P T E R 9 ■ ■ ■ HTTP Th
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CHAPTER 9 ■ HTTP Here, the URL sp
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CHAPTER 9 ■ HTTP Relative URLs Ve
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CHAPTER 9 ■ HTTP From now on, I a
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CHAPTER 9 ■ HTTP • 303 See Othe
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CHAPTER 9 ■ HTTP You cannot tell
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CHAPTER 9 ■ HTTP Instead of stuff
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CHAPTER 9 ■ HTTP POST And APIs Al
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CHAPTER 9 ■ HTTP Content Type Neg
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CHAPTER 9 ■ HTTP HTTP Caching Man
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CHAPTER 9 ■ HTTP If the connectio
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CHAPTER 9 ■ HTTP >>> import cooki
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CHAPTER 9 ■ HTTP So the technique
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C H A P T E R 10 ■ ■ ■ Screen
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CHAPTER 10 ■ SCREEN SCRAPING Figu
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CHAPTER 10 ■ SCREEN SCRAPING cont
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CHAPTER 10 ■ SCREEN SCRAPING Thir
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CHAPTER 10 ■ SCREEN SCRAPING Ther
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CHAPTER 10 ■ SCREEN SCRAPING Beau
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CHAPTER 10 ■ SCREEN SCRAPING If y
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CHAPTER 10 ■ SCREEN SCRAPING Cond
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C H A P T E R 11 ■ ■ ■ Web Ap
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CHAPTER 11 ■ WEB APPLICATIONS Thi
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CHAPTER 11 ■ WEB APPLICATIONS But
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CHAPTER 11 ■ WEB APPLICATIONS the
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CHAPTER 11 ■ WEB APPLICATIONS •
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CHAPTER 11 ■ WEB APPLICATIONS hig
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CHAPTER 11 ■ WEB APPLICATIONS The
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CHAPTER 11 ■ WEB APPLICATIONS the
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CHAPTER 11 ■ WEB APPLICATIONS The
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C H A P T E R 12 ■ ■ ■ E-mail
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CHAPTER 12 ■ E-MAIL COMPOSITION A
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C H A P T E R 13 ■ ■ ■ SMTP A
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CHAPTER 13 ■ SMTP anyway. Outgoin
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CHAPTER 13 ■ SMTP How SMTP Is Use
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CHAPTER 13 ■ SMTP This mechanism
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CHAPTER 13 ■ SMTP s = smtplib.SMT
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CHAPTER 13 ■ SMTP ETRN STARTTLS X
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CHAPTER 13 ■ SMTP » s = smtplib.
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CHAPTER 13 ■ SMTP exchange mail o
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CHAPTER 13 ■ SMTP username = sys.
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C H A P T E R 14 ■ ■ ■ POP PO
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CHAPTER 14 ■ POP ■ Caution! Whi
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CHAPTER 14 ■ POP finally: » p.qu
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CHAPTER 14 ■ POP Subject: Backup
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CHAPTER 15 ■ IMAP THE IMAP PROTOC
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CHAPTER 15 ■ IMAP '(\\HasNoChildr
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CHAPTER 15 ■ IMAP Examining Folde
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CHAPTER 15 ■ IMAP Listing 15-5. D
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CHAPTER 15 ■ IMAP key that IMAP h
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CHAPTER 15 ■ IMAP » » print def
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CHAPTER 15 ■ IMAP » From: Brando
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CHAPTER 15 ■ IMAP • \Flagged: T
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CHAPTER 15 ■ IMAP An IMAP message
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Page 340 and 341: ■ INDEX mod_python, 194 Qpid, 131
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