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Web Server Design Week 14. Old Dominion University Department of Computer Science CS 495/595 Spring 2010 Martin Klein 4/14/10. GET /foo.cgi HTTP/1.1. foo.cgi. 200 OK. Common Gateway Interface. A method for remotely invoking executable programs on a server - PowerPoint PPT Presentation
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Web Server Design
Week 14
Old Dominion UniversityDepartment of Computer Science
CS 495/595 Spring 2010
Martin Klein <[email protected]>
4/14/10
Common Gateway Interface
• A method for remotely invoking executable programs on a server– A long-time convention
• http://web.archive.org/web/20071023072800/http://hoohoo.ncsa.uiuc.edu/cgi/
– finally defined in RFC 3875
client serverGET /foo.cgi HTTP/1.1
foo.cgi200 OK
CGI Invocation
• How Apache does it:– http://httpd.apache.org/docs/2.0/mod/mod_cgi.html
• We’ll live slightly more dangerously:– any executable (non-directory) file can be invoked as CGI with:•POST•GET w/ query string
– e.g. /a/b/c.cgi?var1=foo&var2=bar
CGI Operation• The CGI program is responsible for returning (on STDOUT) some combination of its own headers:– Content-type– Location– Status– and other locally-defined headers
• Script-returned headers are:– collected by the server– processed; e.g.:
• “Location” -> HTTP/1.1 302 Found• Status -> HTTP response code line
– combined with the server’s headers
• Resulting headers are returned to the client
Status% more status.cgi #!/usr/bin/perl
print "Status: 678 This is not a real HTTP status code\n\n";
mk$ telnet www.cs.odu.edu 80Trying 128.82.4.2...Connected to xenon.cs.odu.edu.Escape character is '^]'.GET /~mklein/teaching/cs595-s10/cgi/status.cgi HTTP/1.1Host: www.cs.odu.edu Connection: close
HTTP/1.1 678 This is not a real HTTP status codeDate: Wed, 14 Apr 2010 13:55:05 GMTServer: Apache/2.2.14 (Unix) DAV/2 PHP/5.2.11Content-Length: 0Connection: closeContent-Type: text/plain
Connection closed by foreign host.
Location% more location.cgi #!/usr/bin/perl
print "Location: http://www.cs.odu.edu/~mklein/\n\n";
mk$ telnet www.cs.odu.edu 80Trying 128.82.4.2...Connected to xenon.cs.odu.edu.Escape character is '^]'.GET /~mklein/teaching/cs595-s10/cgi/location.cgi HTTP/1.1Host: www.cs.odu.edu Connection: close
HTTP/1.1 302 FoundDate: Wed, 14 Apr 2010 13:58:01 GMTServer: Apache/2.2.14 (Unix) DAV/2 PHP/5.2.11Location: http://www.cs.odu.edu/~mklein/Content-Length: 309Connection: closeContent-Type: text/html; charset=iso-8859-1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><html><head><title>302 Found</title></head><body><h1>Found</h1><p>The document has moved <a href="http://www.cs.odu.edu/~mklein/">here</a>.</p><hr><address>Apache/2.2.14 (Unix) DAV/2 PHP/5.2.11 Server at www.cs.odu.edu Port 80</address></body></html>Connection closed by foreign host.
Content-type% more ls.cgi#!/usr/bin/perl
print "Content-type: text/plain\n\n";
$ls = `ls -alR`;
print "$ls\n";
mk$ telnet www.cs.odu.edu 80Trying 128.82.4.2...Connected to xenon.cs.odu.edu.Escape character is '^]'.HEAD /~mklein/teaching/cs595-s10/cgi/ls.cgi HTTP/1.1Host: www.cs.odu.edu Connection: close
HTTP/1.1 200 OKDate: Wed, 14 Apr 2010 14:01:57 GMTServer: Apache/2.2.14 (Unix) DAV/2 PHP/5.2.11Connection: closeContent-Type: text/plain
Connection closed by foreign host.
CGI Environment
• Section 4.1, RFC 3875– AUTH_TYPE, CONTENT_LENGTH, CONTENT_TYPE, GATEWAY_INTERFACE, PATH_INFO, PATH_TRANSLATED, QUERY_STRING, REMOTE_ADDR, REMOTE_HOST, REMOTE_IDENT, REMOTE_USER, REQUEST_METHOD, SCRIPT_NAME, SERVER_NAME, SERVER_PORT, SERVER_PROTOCOL, SERVER_SOFTWARE
• In practice, slightly different:– http://www.cs.odu.edu/~mklein/teaching/cs595-s10/
cgi/env.cgi
How to Customize the Environment?
• C:– fork() & execve()
• Perl:– set %ENV– fork() & exec()
• Python:– set %ENV– fork () & execve()
• Others???– please share w/ the list
ENV & CGI Examples#!/usr/bin/perl
print "Content-type: text/html\n\n";
foreach $key (keys (%ENV)) {
print "$key = $ENV{$key} <br>\n";
}
while (<STDIN>) {
print "$_<br>\n";
}
http://www.cs.odu.edu/~mklein/teaching/cs595-s10/cgi/
{GET, POST} X {multipart/form-data, application/x-form-www-urlencoded}
Advanced Topics: “Soft 404s”
• foo.edu/lookup.php?key=123456• what http status code do you return if:
– script “lookup.php” exists and has no syntax errors
– but key 123456 is deleted or invalid
• Semantic events:– http - 200– database - bad key
• reading:– “Sic Transit Gloria Telae: Towards an Understanding of the Web’s Decay”• http://doi.acm.org/10.1145/988672.988716
