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

Recommendations

Info

CHAPTER 11 ■ WEB APPLICATIONS the WSGI standard specifies its behavior rather than its inheritance tree (duck typing).The Standard Library includes two other HTTP servers: • CGIHTTPServer takes the SimpleHTTPServer and, instead of just serving static files off of the disk, it adds the ability to run CGI scripts (which we will cover in the next section). • SimpleXMLRPCServer and DocXMLRPCServer each provide a server endpoint against which client programs can make XML-RPC remote procedure calls, as demonstrated in Chapter 18 and Listing 22-1. This protocol uses XML files submitted through HTTP requests. Note that none of the preceding servers is typically intended for production use; instead, they are useful for small internal tasks for which you just need a quick HTTP endpoint to be used by other services internal to a system or subnet. And while most Python web frameworks will provide a way to run your application from the command line for debugging, most follow the lead of Django in recommending against using the development platform for debugging. However, a few Python web frameworks exist that not only provide their own built-in HTTP servers, but have also worked on their security and performance, so that they can be recommended for use in production. These pure-Python web servers can be very useful if you are writing an application that users will be installing locally, and you want to provide a web interface without having to ship a separate web server like Apache or nginx. Frameworks that offer a pure-Python integrated web server include CherryPy; Zope, and thus Grok and BFG; web2py; and web.py. CGI When the first experiments were taking place with dynamically generated web pages, developers would write an external program and have their web server run the program every time a matching HTTP request arrived. This resembled the behavior of the traditional inetd server (Chapter 7), which could run an external command to answer each incoming TCP or UDP connection on a listening socket. Many of these early web servers lacked the ability to designate entire sections of a web site as dynamic; for example, you could not tell them, “all URLs beneath /cart should be handled by my application.” Instead, scripts were simply designated as a new type of content, and then placed right next to static pages, images, and archive files in directories that were already browsable from the web. Just as servers had been told that .html files should be delivered as text/html content and that .jpg files should be returned as images, they were now told that executable .cgi files should be run and their output returned to the HTTP client. Obviously, a calling convention was necessary, and so the Common Gateway Interface (CGI) was defined. It allowed programs in all sorts of languages—C, the various Unix shells, awk, Perl, Python, PHP, and so forth—to be partners in generating dynamic content. Today, the design of CGI is considered something of a disaster. Running a new process from scratch is just about the most expensive single operation that you can perform on a modern operating system, and requiring that this take place for every single incoming HTTP request is simply madness. You should avoid CGI under all circumstances. But it is possible you might someday have to connect Python code to a legacy HTTP server that does not support at least FastCGI or SCGI, so I will outline CGI's essential features. Three standard lines of communication that already existed between parent and child processes on Unix systems were used by web servers when invoking a CGI script: 193
CHAPTER 11 ■ WEB APPLICATIONS • The Unix environment—a list of strings provided to each process upon its invocation that traditionally includes things like TZ=EST (the time zone) and COLUMNS=80 (user's screen width)—was instead stuffed full of information about the HTTP request that the CGI script was being called upon to answer. The various parts of the request's URL; the user agent string; basic information about the web server; and even a cookie could be included in the list of colon-separated keyvalue pairs. • The standard input to the script could be read to end-of-file to receive whatever data had been submitted in the body of the HTTP request using POST. Whether a request was indeed a POST could be checked by examining the REQUEST_METHOD environment variable. • Finally, the script would produce content, which it did by writing HTTP headers, a blank line, and then a response body to its standard output. To be a valid response, a Content-Type header was generally necessary at a minimum—though in its absence, some web servers would instead accept a Location header as a signal that they should send a redirect. Should you ever need to run Python behind an HTTP server that only supports CGI, then I recommend that you use the CGIHandler module from the wsgiref Standard Library package. This lets you use a normal Python web framework to write your service—or, alternatively, to roll up your sleeves and write a raw WSGI application—and then offer the HTTP server a CGI script, as shown here: import CGIHandler, MyWSGIApp my_wsgi_app = MyWSGIApp() # configuration necessary here? CGIHandler().run(my_wsgi_app) Be sure to check whether your web framework of choice already provides a way to invoke it as a CGI script; if so, your web framework will already know all of the steps involved in loading and configuring your application. For complex web frameworks, it might be tedious to run all of the steps manually in a script like this one. The Python Standard Library also includes two more ancient modules related to the CGI protocol. Old CGI scripts written with Python imported the cgi module; this module contains a number of helpers and utilities for interpreting both the standard CGI environment variables and also for parsing GET or POST form parameters, so that you can access them like a dictionary. And, believe it or not, there is actually a CGIHTTPServer module in the Standard Library, so that Python can actually be used as a CGI-enabled HTTP server. Like many other web servers of its era, this module interprets URLs as paths into a directory tree and serves static files directly while invoking CGI scripts as separate processes. mod_python As it became clear that CGI was both inefficient and inflexible—CGI scripts could not flexibly set the HTTP return code, for example—it became fashionable to start embedding programming languages directly in web servers. Earlier in this chapter, we discussed how embedding Python is possible today with mod_wsgi under Apache. (We also noted that this is usually only desirable if you have another web server in front of Apache that can handle static requests with workers that are not bloated by including their own Python interpreter!) Back in the early days, embedding was also possible, through a somewhat different approach that actually made Python an extension language for much of the internals of Apache itself. The module that supported this was mod_python, and for years it was by far the most popular way to connect Python to the World Wide Web. 194
Page 2 and 3:
Foundations of Python Network Progr
Page 4 and 5:
To the Python community for creatin
Page 6 and 7:
Contents ■Contents at a Glance ..
Page 8 and 9:
■ CONTENTS Asking getaddrinfo() W
Page 10 and 11:
■ CONTENTS Using Message Queues f
Page 12 and 13:
■ CONTENTS Parsing Dates ........
Page 14 and 15:
■ CONTENTS Telnet ...............
Page 16 and 17:
About the Authors ■ Brandon Craig
Page 18 and 19:
Acknowledgements This book owes its
Page 20 and 21:
■ INTRODUCTION If you do know som
Page 22 and 23:
C H A P T E R 1 ■ ■ ■ Introdu
Page 24 and 25:
CHAPTER 1 ■ INTRODUCTION TO CLIEN
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
C H A P T E R 2 ■ ■ ■ UDP The
Page 38 and 39:
CHAPTER 2 ■ UDP server with SSH.
Page 40 and 41:
CHAPTER 2 ■ UDP them anywhere in
Page 42 and 43:
CHAPTER 2 ■ UDP command-line argu
Page 44 and 45:
CHAPTER 2 ■ UDP » » » » raise
Page 46 and 47:
CHAPTER 2 ■ UDP world itself give
Page 48 and 49:
CHAPTER 2 ■ UDP socket that is no
Page 50 and 51:
CHAPTER 2 ■ UDP So binding to an
Page 52 and 53:
CHAPTER 2 ■ UDP s.connect((hostna
Page 54 and 55:
CHAPTER 2 ■ UDP else: » print >>
Page 56 and 57:
C H A P T E R 3 ■ ■ ■ TCP The
Page 58 and 59:
CHAPTER 3 ■ TCP situation), and t
Page 60 and 61:
CHAPTER 3 ■ TCP » reply = recv_a
Page 62 and 63:
CHAPTER 3 ■ TCP guess when the in
Page 64 and 65:
CHAPTER 3 ■ TCP the system has no
Page 66 and 67:
CHAPTER 3 ■ TCP » » » print '\
Page 68 and 69:
CHAPTER 3 ■ TCP $ python tcp_dead
Page 70 and 71:
CHAPTER 3 ■ TCP Using TCP Streams
Page 72 and 73:
CHAPTER 4 ■ SOCKET NAMES AND DNS
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
CHAPTER 5 ■ NETWORK DATA AND NETW
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
C H A P T E R 6 ■ ■ ■ TLS and
Page 108 and 109:
CHAPTER 6 ■ TLS AND SSL systems a
Page 110 and 111:
CHAPTER 6 ■ TLS AND SSL • He wi
Page 112 and 113:
CHAPTER 6 ■ TLS AND SSL discussio
Page 114 and 115:
CHAPTER 6 ■ TLS AND SSL • The s
Page 116 and 117:
CHAPTER 6 ■ TLS AND SSL The Links
Page 118 and 119:
C H A P T E R 7 ■ ■ ■ Server
Page 120 and 121:
CHAPTER 7 ■ SERVER ARCHITECTURE P
Page 122 and 123:
CHAPTER 7 ■ SERVER ARCHITECTURE
Page 124 and 125:
CHAPTER 7 ■ SERVER ARCHITECTURE N
Page 126 and 127:
CHAPTER 7 ■ SERVER ARCHITECTURE L
Page 128 and 129:
CHAPTER 7 ■ SERVER ARCHITECTURE F
Page 130 and 131:
Page 132 and 133:
CHAPTER 7 ■ SERVER ARCHITECTURE p
Page 134 and 135:
CHAPTER 7 ■ SERVER ARCHITECTURE N
Page 136 and 137:
CHAPTER 7 ■ SERVER ARCHITECTURE L
Page 138 and 139:
Page 140 and 141:
CHAPTER 7 ■ SERVER ARCHITECTURE s
Page 142 and 143:
CHAPTER 7 ■ SERVER ARCHITECTURE c
Page 144 and 145:
C H A P T E R 8 ■ ■ ■ Caches,
Page 146 and 147:
CHAPTER 8 ■ CACHES, MESSAGE QUEUE
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
C H A P T E R 9 ■ ■ ■ HTTP Th
Page 158 and 159:
CHAPTER 9 ■ HTTP Here, the URL sp
Page 160 and 161:
CHAPTER 9 ■ HTTP Relative URLs Ve
Page 162 and 163: CHAPTER 9 ■ HTTP From now on, I a
Page 164 and 165: CHAPTER 9 ■ HTTP • 303 See Othe
Page 166 and 167: CHAPTER 9 ■ HTTP You cannot tell
Page 168 and 169: CHAPTER 9 ■ HTTP Instead of stuff
Page 170 and 171: CHAPTER 9 ■ HTTP POST And APIs Al
Page 172 and 173: CHAPTER 9 ■ HTTP Content Type Neg
Page 174 and 175: CHAPTER 9 ■ HTTP HTTP Caching Man
Page 176 and 177: CHAPTER 9 ■ HTTP If the connectio
Page 178 and 179: CHAPTER 9 ■ HTTP >>> import cooki
Page 180 and 181: CHAPTER 9 ■ HTTP So the technique
Page 182 and 183: C H A P T E R 10 ■ ■ ■ Screen
Page 184 and 185: CHAPTER 10 ■ SCREEN SCRAPING Figu
Page 186 and 187: CHAPTER 10 ■ SCREEN SCRAPING cont
Page 188 and 189: CHAPTER 10 ■ SCREEN SCRAPING Thir
Page 190 and 191: CHAPTER 10 ■ SCREEN SCRAPING Ther
Page 192 and 193: CHAPTER 10 ■ SCREEN SCRAPING Beau
Page 194 and 195: CHAPTER 10 ■ SCREEN SCRAPING If y
Page 196 and 197: CHAPTER 10 ■ SCREEN SCRAPING Cond
Page 198 and 199: C H A P T E R 11 ■ ■ ■ Web Ap
Page 200 and 201: CHAPTER 11 ■ WEB APPLICATIONS Thi
Page 202 and 203: CHAPTER 11 ■ WEB APPLICATIONS But
Page 204 and 205: CHAPTER 11 ■ WEB APPLICATIONS the
Page 206 and 207: CHAPTER 11 ■ WEB APPLICATIONS •
Page 208 and 209: CHAPTER 11 ■ WEB APPLICATIONS hig
Page 210 and 211: CHAPTER 11 ■ WEB APPLICATIONS The
Page 214 and 215: CHAPTER 11 ■ WEB APPLICATIONS The
Page 216 and 217: C H A P T E R 12 ■ ■ ■ E-mail
Page 218 and 219: CHAPTER 12 ■ E-MAIL COMPOSITION A
Page 236 and 237: C H A P T E R 13 ■ ■ ■ SMTP A
Page 238 and 239: CHAPTER 13 ■ SMTP anyway. Outgoin
Page 240 and 241: CHAPTER 13 ■ SMTP How SMTP Is Use
Page 242 and 243: CHAPTER 13 ■ SMTP This mechanism
Page 244 and 245: CHAPTER 13 ■ SMTP s = smtplib.SMT
Page 246 and 247: CHAPTER 13 ■ SMTP ETRN STARTTLS X
Page 248 and 249: CHAPTER 13 ■ SMTP » s = smtplib.
Page 250 and 251: CHAPTER 13 ■ SMTP exchange mail o
Page 252 and 253: CHAPTER 13 ■ SMTP username = sys.
Page 254 and 255: C H A P T E R 14 ■ ■ ■ POP PO
Page 256 and 257: CHAPTER 14 ■ POP ■ Caution! Whi
Page 258 and 259: CHAPTER 14 ■ POP finally: » p.qu
Page 260 and 261: CHAPTER 14 ■ POP Subject: Backup
Page 262 and 263:
CHAPTER 15 ■ IMAP THE IMAP PROTOC
Page 264 and 265:
CHAPTER 15 ■ IMAP '(\\HasNoChildr
Page 266 and 267:
CHAPTER 15 ■ IMAP Examining Folde
Page 268 and 269:
CHAPTER 15 ■ IMAP Listing 15-5. D
Page 270 and 271:
CHAPTER 15 ■ IMAP key that IMAP h
Page 272 and 273:
CHAPTER 15 ■ IMAP » » print def
Page 274 and 275:
CHAPTER 15 ■ IMAP » From: Brando
Page 276 and 277:
CHAPTER 15 ■ IMAP • \Flagged: T
Page 278 and 279:
CHAPTER 15 ■ IMAP An IMAP message
Page 280 and 281:
CHAPTER 15 ■ IMAP display or summ
Page 282 and 283:
CHAPTER 16 ■ TELNET AND SSH cloud
Page 284 and 285:
CHAPTER 16 ■ TELNET AND SSH Unix
Page 286 and 287:
CHAPTER 16 ■ TELNET AND SSH Do yo
Page 288 and 289:
CHAPTER 16 ■ TELNET AND SSH As we
Page 290 and 291:
CHAPTER 16 ■ TELNET AND SSH tabif
Page 292 and 293:
CHAPTER 16 ■ TELNET AND SSH repla
Page 294 and 295:
CHAPTER 16 ■ TELNET AND SSH Listi
Page 296 and 297:
CHAPTER 16 ■ TELNET AND SSH def p
Page 298 and 299:
CHAPTER 16 ■ TELNET AND SSH We wi
Page 300 and 301:
CHAPTER 16 ■ TELNET AND SSH • p
Page 302 and 303:
CHAPTER 16 ■ TELNET AND SSH You w
Page 304 and 305:
CHAPTER 16 ■ TELNET AND SSH » »
Page 306 and 307:
CHAPTER 16 ■ TELNET AND SSH Listi
Page 308 and 309:
CHAPTER 16 ■ TELNET AND SSH Summa
Page 310 and 311:
CHAPTER 17 ■ FTP The biggest prob
Page 312 and 313:
CHAPTER 17 ■ FTP f.login() print
Page 314 and 315:
CHAPTER 17 ■ FTP if os.path.exist
Page 316 and 317:
CHAPTER 17 ■ FTP f = FTP(host) f.
Page 318 and 319:
CHAPTER 17 ■ FTP Windows servers
Page 320 and 321:
CHAPTER 17 ■ FTP » try: » » f.
Page 322 and 323:
C H A P T E R 18 ■ ■ ■ RPC Re
Page 324 and 325:
CHAPTER 18 ■ RPC sort of proxy ex
Page 326 and 327:
CHAPTER 18 ■ RPC The SimpleXMLRPC
Page 328 and 329:
CHAPTER 18 ■ RPC Traceback (most
Page 330 and 331:
CHAPTER 18 ■ RPC 8.0 If this
Page 332 and 333:
CHAPTER 18 ■ RPC Note that the po
Page 334 and 335:
CHAPTER 18 ■ RPC up being, simply
Page 336 and 337:
CHAPTER 18 ■ RPC such as Python i
Page 338 and 339:
CHAPTER 18 ■ RPC • Google Proto
Page 340 and 341:
■ INDEX mod_python, 194 Qpid, 131
Page 342 and 343:
■ INDEX Common Gateway Interface.
Page 344 and 345:
■ INDEX international characters
Page 346 and 347:
■ INDEX front-end web servers, 17
Page 348 and 349:
■ INDEX deleting folders, 260 del
Page 350 and 351:
■ INDEX mechanize, 138, 163 Memca
Page 352 and 353:
■ INDEX pausing terminal output,
Page 354 and 355:
■ INDEX resources. See also RFCs
Page 356 and 357:
■ INDEX shutdown(), 48 shutting d
Page 358 and 359:
■ INDEX terminals, 270-74 bufferi
Page 360 and 361:
■ INDEX ■ V validating cached r
show all

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

Create successful ePaper yourself

Delete template?

Save as template?