HTTP and HTML: Request and Response

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HTTP and HTML Request and Response
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• HTTP the most important protocol of the Internet
• Ideas but not Technology is the key part of the
  story
• Created tremendous network effect n2 value,
  which makes the widespread (HTTP) dominate

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Why a new protocol?

• Existing protocols
• HTTP must provide
• File transfer
• Request an index search
• Automatic format negotiation
• Refer the client to another server
  

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Http Client / Browser

• Has URL Request to server
• Gets back data Response HTML, JPEG
• Displays that data
• Processes Clicks, etc. to make further requests

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URL Request to the Server

• http//www.stanford.edu/class/cs193i/index.html
• http
• Protocol ask scheme
• www.standford.edu
• Host Server to contact
• /class/cs193i/index.html
• Path identifies document on that host

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URL, URN URI

• All of the three identify documents, but
• URL depends on the name of the server and
  other details of where the document is stored
• URN only depends on the server?
• URI URLs URNs?

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• HTTP Server
• Document Root on Server
• Client Request
• Request Example?
• Server Response

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HTML Most often Response to HTTP

• Hypertext Markup Language
• Portable Content
• HTML structure the Browser appearance
• Text and tags tags only OR tags paired to
  enclose some text
• HTML plain text
• Whitespace

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What Defines Appearance?

• The setting of the browser
• Example for pours into http//cslibrary.dtanfor
  d.edu/104/
• An example on different tags.

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Uniform Resource Locator URL

• Specify the location
• Anchor Tag ltagt
• e.g. lta href http//www.duke.edugtdukeltagt
• Encoding?
• Page relative URL lookup
• Two examples
• Root Relative

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Uniform Resource Locator URL

• Image Tag
• ltimg src URL of imagegt
• Image Files
• JPEG .jpg or .jpeg
• GIF .gif
• PNG Portable Network Graphics
• Image Style
• Name Tags lta name spotgt

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HTTP Request/Response

• stateless request and response
• HTTP Request
• Get Request?
• Complex URLs

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HTTP Request

• Example http//foo.com/a/b/bar.html?hello.thereb
  inky
• http ? scheme or protocol
• foo.com ? host
• /a/b/bar.html ? path
• ?hello.there ? query
• binky ? fragment

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HTTP Request

• Basic GET?
• The Empty Request URLs without path/query
  section
• Other requests POST, PUT, DELETE

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HTTP Response

• A header section ? a blank line ? the document
  data
• Content-Length Size
• Content-Type mime-type
• HTTP 1.0 Example
• Status Codes
• Not-Found Example

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HTTP Response

• MIME (Multipurpose Internet Mail Extensions)
  Types
• content-type/sub-type aux-info

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• Empty Request
• Server URL Mapping
• username
• Directories
• Client Side Unawareness
• The Trailing Slash and 300 redirects