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CIT 383: Administrative Scripting
HTTP and HTML CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Topics HTTP URLs Cookies Base64 CIT 383: Administrative Scripting
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Web Client/Server Interaction
Browser Server 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) CIT 383: Administrative Scripting
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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. CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTTP Request Method URL Protocol Version Headers GET HTTP/1.1 Host: User-Agent: Mozilla/5.0 (Windows NT 5.1) Gecko/ Firefox/ Accept: text/html, image/png, */* Accept-Language: en-us,en;q=0.5 Cookie: rememberme=true; PREF=ID=21039ab4bbc49153:FF=4 Blank Line No Data for GET method CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTTP Response Protocol Version HTTP Response Code HTTP/ OK Cache-Control: private Content-Type: text/html Server: GWS/2.1 Date: Fri, 13 Oct :16:30 GMT <HTML> ... (page data) ... </HTML> Headers Blank Line Web Page Data CIT 383: Administrative Scripting
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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. From CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTTP Request Headers Header Description Example Accept Acceptable content types. Accept: text/plain Authorization HTTP authentication credentials. Authorization: Basic QWxhZGRpbjpvcGVuIHNl c2FtZQ== Cache-Control Caching directives Cache-Control: no cache Cookie Cookie data for server. Cookie: color=red Date Date and time sent Date: 29 Oct :02:03 Host Name of server Host: cs.nku.edu If-Modified- Since Allows a 304 Not Modified to be returned for caching. If-Modified-Since: 29 Oct :02:03 GMT User-Agent Browser description string Mozilla/5.0 (X11; U; Linux i686; en-US; rv: ) Ubuntu/8.04 Firefox/3.1 CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTTP Response Headers Header Description Example Cache-Control Caching directives Cache-Control: no cache Content- Encoding Type of encoding used. Content-Encoding: gzipSer Content-Length Length of data returned. Content-Length: 1024 Content-Type Type of data returned. Content-Type: text/html Date Date and time response sent. Date: 29 Oct :02:03 Expires Date after which data expired. Expires: 1 Nov :02:03 Location Used in redirection Location: Server Server identification string. Server: Apache/2.0.55 Set-Cookie Cookie created by server. Set-Cookie: color=red CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTTP Response Codes Code Description Meaning 200 OK Standard success response. 201 Created New resource created. 301 Moved permanently Permanent redirect to new URI. 304 Not modified Safe to use page stored in cache. 307 Temporary redirect Use new URI now; try old later. 401 Unauthorized Authentication failed. 403 Forbidden Disallowed, auth will not help. 404 Not found Resource was not found. 405 Method not allowed Used GET when should use POST. 500 Internal server error Internal server error. CIT 383: Administrative Scripting
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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. CIT 383: Administrative Scripting
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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 CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
URI Format 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 RFC 1738 for URL definitions CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
URI Class URI.extract(string): returns array of URI strings extracted from string. URI.extract("text and and text here also.") => [" 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. CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Cookies Server to Client Content-type: text/html Set-Cookie: foo=bar; path=/; expires Fri, 20-Feb :59:00 GMT Client to Server Cookie: foo=bar RFC 2109 CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Base64 Encoding How do you send binary data using text? 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. CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Base64 Class encode = Base64.encode64(‘informatics‘) decode = Base64.decode64(‘aW5mb3JtYXRpY3M=‘) CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Topics Evolution of HTML HTML Structure Regular Expressions v Parsing HPricot XPath CIT 383: Administrative Scripting
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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. CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTML Structure <html> <title>My title</title> <body> <a href=“...”>My link</a> <h1>My header</h1> </body> </html> CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
HTML Structure Image from CIT 383: Administrative Scripting
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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 CIT 383: Administrative Scripting
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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. CIT 383: Administrative Scripting
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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. Find all anchor tags with a src attribute. Find all a tags with a src attribute of google.com. CIT 383: Administrative Scripting
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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. CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
Going Further Ruby Quiz Assignment-scale problems + solutions. 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 CIT 383: Administrative Scripting
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CIT 383: Administrative Scripting
References Michael Fitzgerald, Learning Ruby, O’Reilly, 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, Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005. CIT 383: Administrative Scripting
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