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HTTP (HTTP Mesages (Headers (Request (Informational (Client-IP From Host…

- - - - Idempotent
        Yields the same results regardless of whether it's executed once or many times
        GET, HEAD, PUT, DELETE, TRACE, OPTIONS
        
        Safe
        Read only
        GET, HEAD
      - GET
        HEAD - Returns header information without the body
        PUT - Deposit data into a resource on the server
        POST - Designed to send input data to server
        DELETE
        OPTIONS
        TRACE
      - Extension Methods
        Not defined in specification
        
        Server may respond with
        501 Not Implemented status code
        
        Examples
        
        PATCH
        
        COPY
        
        MOVE
  - - - :warning: 100 Continue
      - Success
        
        200 - ok
        201 - created
        202 - accepted
        203 - non-authoritative info
        204 - no content
        205 - reset content
        206 - partial content
      - Redirect
        
        300 - multiple choices
        301 - moved permanently
        302 - found
        303 - see other
        304 - not modified
        305 - use proxy
        306 - unused
        307 - temporary redirect
        
        :warning: Servers need to check a client's HTTP version to properly select which redirect status code to send in a redirect response
      - Client Error
        
        400 - bad request
        401 - unauthorized
        402 - payment required
        403 - forbidden
        404 - not found
        405 - method not allowed
        406 - not acceptable
        407 - proxy authentication required
        408 - request timeout
        409 - conflict
        410 - gone
        411 - length required
        412 - precondition failed
        413 - request entity too large
        414 - request URI too long
        415 - unsupported media type
        416 - requested range not satisfiable
        417 - expectation failed
      - Server Error
        
        500 - internal server error
        501 - not implemented
        502 - bad gateway
        503 - service unavailable
        504 - gateway timeout
        505 - HTTP version not supported
  - - - Connection
        Date
        MIME-Version
        Trailer
        Transfer-Encoding
        Upgrade
        Via
        Cache-Control
        Pragma
    - - Informational
        
        Client-IP
        From
        Host
        Referer
        UA-Color
        UA-CPU
        UA-Disp
        UA-OS
        UA-Pixels
        User-Agent
      - Accept
        
        Accept
        Accept-Charset
        Accept-Encoding
        Accept-Language
        TE
      - Conditional
        
        Expect
        If-Match
        If-Modified-Since
        If-Range
        If-Unmodified-Since
        Range
      - Security
        
        Authorization
        Cookie
        Cookie2
      - Proxy
        
        Max-Forwards
        Proxy-Authorization
        Proxy-Connection
    - - Informational
        
        Age
        Public
        Retry-After
        Server
        Title
        Warning
      - Negotation
        
        Accept-Ranges
        Vary
      - Security
        
        Proxy-Authenticate
        Set-Cookie
        Set-Cookie2
        WWW-Authenticate
    - - Informational
        
        Allow
        Locations
      - Content
        
        Content-Base
        Content-Encoding
        Content-Language
        Content-Length
        Content-Location
        Content-MD5
        Content-Range
        Content-Type
      - Caching
        
        ETag
        Expires
        Last-Modified
  - - - https://letsencrypt.org/
- - - - Doesn't always speed up page transfer, but increases the perceived speed
        
        Examples
        
        Multiple images loading at the same time
        
        Low-resolution approximations of images with gradual increase in resolution
      - Disadvantages
        
        Connection phase overhead for each connection
        
        TCP slow start untuned for each connection
        
        Limit on number of open parallel connections
    - - Advantages
        Connection phase overhead reduced
        TCP slow start remains tuned
      - HTTP/1.0 Keep-alive
        
        Connection: Keep-Alive Keep-Alive: max=5, timeout=120
        
        :!: Blind relay problem
        
        Keep-Alive
      - HTTP1.1 Persistent Connections
        phases out HTTP/1.0 keep-alive
        
        Enabled by default
        
        Connection: close
      - Pipelined, persistent connection
        
        Allows for parallel transactions, where keep-alive and persistent connections are serial
        
        :!: Clients should not pipeline nonidempotent requests
    - - Single, persistent connection
        Multiplexing
        Header compression
        Prioritization
        SSL encryption
      - :warning: HTTP/1.x w/o SSL may offer better performance for large file transfers and streaming with videos and audio
      - Overhead with SSL but is offset by overall performance gains
- - - - Filtering
        Block access to certain content
      - Access control
      - Web cache
      - Anonymizer
        Strips identifying data from HTTP message
      - Reverse proxy
        stand in for web server
      - Security firewall
        Inspect ingress and egress traffic
    - - TRACE /index.html HTTP/1.1 ...
      - GET /index.html HTTP/1.1 ... Via: proxy1, proxy2, ...n
- - - - URL syntax
        scheme://host:port/path?query#fragment