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CIT 383: Administrative Scripting

HTTP and HTML. CIT 383: Administrative Scripting. Topics. HTTP URLs Cookies Base64. Web Client/Server Interaction. Server. Browser. HTTP Request (form submission) ‏. User waits. Server processing. HTTP Response (new web page) ‏. User interaction. HTTP Request (form submission) ‏.

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CIT 383: Administrative Scripting

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  1. CIT 383: Administrative Scripting HTTP and HTML CIT 383: Administrative Scripting

  2. CIT 383: Administrative Scripting Topics • HTTP • URLs • Cookies • Base64

  3. CIT 383: Administrative Scripting Web Client/Server Interaction Server Browser HTTP Request (form submission)‏ User waits Server processing HTTP Response (new web page)‏ User interaction HTTP Request (form submission)‏ Server processing User waits HTTP Response (new web page)‏

  4. CIT 383: Administrative Scripting HTTP: HyperText Transfer Protocol Simple request/respond protocol • Request methods: GET, POST, HEAD, etc. • Protocol versions: 1.0, 1.1 Stateless • Each request independent of previous requests, i.e. request #2 doesn’t know you auth’d in #1. • Applications responsible for handling state.

  5. CIT 383: Administrative Scripting HTTP Request GET http://www.google.com/ HTTP/1.1 Host: www.google.com User-Agent: Mozilla/5.0 (Windows NT 5.1) Gecko/20060909 Firefox/1.5.0.7 Accept: text/html, image/png, */* Accept-Language: en-us,en;q=0.5 Cookie: rememberme=true; PREF=ID=21039ab4bbc49153:FF=4 Method URL Protocol Version Headers Blank Line No Data for GET method

  6. CIT 383: Administrative Scripting HTTP Response HTTP/1.1 200 OK Cache-Control: private Content-Type: text/html Server: GWS/2.1 Date: Fri, 13 Oct 2006 03:16:30 GMT <HTML> ... (page data) ... </HTML> Protocol Version HTTP Response Code Headers Blank Line Web Page Data

  7. CIT 383: Administrative Scripting HTTP Methods HEAD Same as GET, but only asks for headers, not body. GET Requests a representation of the resource. Most common method. Should not cause server to modify (write, delete) any resources. POST Submits data to be processed to the resource. The data is included in the body of the request. This may result in the creation of a new resource or the updates of existing resources or both. PUT Uploads a representation of the specified resource. DELETE Deletes the specified resource. TRACE Echoes back the received request, so that a client can see what intermediate servers are adding or changing in the request.

  8. CIT 383: Administrative Scripting HTTP Request Headers

  9. CIT 383: Administrative Scripting HTTP Response Headers

  10. CIT 383: Administrative Scripting HTTP Response Codes

  11. CIT 383: Administrative Scripting Net::HTTP Class Net::HTTP.get(host, path): returns resource from host, path as a string. Net::HTTP.get_response(host, path): returns HTTP response object, includes body + headers. Net::HTTP.post_form(host, path,{parameters}): returns resource from host, path as a string using POST instead of GET, sending form parameters as a hash.

  12. CIT 383: Administrative Scripting Redirection Example def fetch(uri) response = Net::HTTP.get_response(uri) case response when Net::HTTPSuccess then response when Net::HTTPRedirection then fetch(response['location']) else response.error! end end end

  13. CIT 383: Administrative Scripting URI Format <proto>://<user>@<host>:<port>/<path>?<qstr> • Whitespace marks end of URL • “@” separates userinfo from host • “?” marks beginning of query string • “&” separates query parameters • %HH represents character with hex values • ex: %20 represents a space http://username:password@www.auth.com:8001/a%20spaced%20path

  14. CIT 383: Administrative Scripting URI Class URI.extract(string): returns array of URI strings extracted from string. URI.extract("text http://example.com/ and mailto:test@example.com and text here also.") => ["http://example.com/", "mailto:test@example.com"] URI.join(string,string,...): joins two or more strings into a URI. URI.parse(string): creates URI object f/ string. URI.split(uri): splits URI string into protocol, host, path, query, etc. components.

  15. CIT 383: Administrative Scripting Cookies Server to Client Content-type: text/html Set-Cookie: foo=bar; path=/; expires Fri, 20-Feb-2004 23:59:00 GMT Client to Server Content-type: text/html Cookie: foo=bar

  16. CIT 383: Administrative Scripting Base64 Encoding How do you send binary data using text? • Email attachments (MIME). • Cookies (HTTP). Base64: encode 3 bytes as 4 text characters • Use characters A-Za-z0-9+/ to store 6 bits of data. • Byte has 8 bits, so 3 bytes = 24 bits • 4 base64 chars (6 bits each) = 24 bits • Use = to pad output if input not multiple of 3 bytes.

  17. CIT 383: Administrative Scripting Base64 Class encode = Base64.encode64(‘informatics‘) decode = Base64.decode64(‘aW5mb3JtYXRpY3M=‘)

  18. CIT 383: Administrative Scripting Topics • Evolution of HTML • HTML Structure • Regular Expressions v Parsing • HPricot • XPath

  19. CIT 383: Administrative Scripting Evolution of HTML 1991 HTML created (only 22 tags) 1995 HTML 2.0 1996 Tables added to HTML 2.0 Jan 1997 HTML 3.2 published by W3C Dec 1997 HTML 4.0 2000 XHTML 1.0 2008 HTML 5.0 working draft published.

  20. CIT 383: Administrative Scripting HTML Structure <html> <title>My title</title> <body> <a href=“...”>My link</a> <h1>My header</h1> </body> </html>

  21. CIT 383: Administrative Scripting HTML Structure

  22. CIT 383: Administrative Scripting Why Not Regular Expressions? Angle-bracket tags are difficult to deal with. Tag regexp: <\w+\s+[^>]*> Matches <img alt=“ruby” src=“rb.png”> Doesn’t: <img alt=“ruby>” src=“rb.png”> Solution:check for > in attributes. Have to match every form of attribute name=“value” name=‘value’ name=value name

  23. CIT 383: Administrative Scripting Hpricot h = Hpricot(html-string) Creates a new HPricot::Doc object. el = h.at(string) Finds first matching Hpricot::Elements object. el = h.search(string or XPath expression) Returns array of matching objects. el.inner_html Returns HTML enclosed in element.

  24. CIT 383: Administrative Scripting XPath Searches h.search("p") Find all paragraph tags in document. doc.search("/html/body//p") Find all paragraph tags within the body tag. doc.search("//a[@src]") Find all anchor tags with a src attribute. doc.search("//a[@src='google.com']") Find all a tags with a src attribute of google.com.

  25. CIT 383: Administrative Scripting Final Exam Comprehensive exam like midterm • 20% concepts (focus on classes + exceptions) • 80% programs (at least 2 programs like labs) Study • Review the midterm practice problems. • Work out your lab programs again. • Solve un-assigned lab programs. • Review concepts, esp. classes + exceptions.

  26. CIT 383: Administrative Scripting Going Further Ruby Quiz • Assignment-scale problems + solutions. • http://rubyquiz.com/ Practical Ruby for System Administration • If Admin Scripting II existed, this would be the text. General Ruby Books • The Ruby Way, 2nd edition • The Ruby Programming Language

  27. CIT 383: Administrative Scripting References • Michael Fitzgerald, Learning Ruby, O’Reilly, 2008. • David Flanagan and Yukihiro Matsumoto, The Ruby Programming Language, O’Reilly, 2008. • Hal Fulton, The Ruby Way, 2nd edition, Addison-Wesley, 2007. • Robert C. Martin, Clean Code, Prentice Hall, 2008. • Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005.

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