title: HTTP & HTML notebook: Computer Systems layout: note date: 2020-03-19 15:25 tags: ...

HTTP & HTML

Table of Contents

1.1
1.2
1.3
1.4
1.5
1.6
2.1
2.2

1.1

1.2

1.3

1.4

meaning of HTTP headers
how many bytes to implement this page?
how many requests are there? 23!
what is each request for?
- GET requests to get HTML, images, ad services, javascript
- POST request to beacon
response status codes
- 200: successful
- 302: resource temporarily moved (redirects)
- 204: no content
which ones are cacheable?
- GET, HEAD, and POST can be cached (in general)
- Cache-Control header holds instructions for caching, and can be in both requests and responses. Some examples from the page:
  - Cache-Control: private: response is for a single user and mustn't be stored by a shared cache, but can be stored by private cache e.g. browser cache
  - Cache-Control: no-store: don't store anything
how many different domain names are used to build the page

1.5

Javascript executes code in browser to provide dynamic content
in this case, the JS is making requests for images that then get embedded webpage

1.6

http://info.cern.ch/hypertext/WWW/TheProject.html

<HEADER></HEADER>: header
<TITLE></TITLE>: page title (shown in the tab description)
<NEXTID>: used to generate automatic NAME identifiers for anchors; obsolete
<BODY></BODY>: main body of the page
<A></A>: anchor; hyperlink
<DL></DL>: description list
<DT></DT>: description term (in description list)

2.1

2.2

ARC: Authenticated Received Chain: email authentication to allow intermediate mail server e.g. mailing list to sign an email's original authentication results
- allows receiving service to validate an email
- ARC-Seal: instance number + signature of previous headers + validity of prior ARC entries
- ARC-Message-Signature: instance number + signature of entire message except seal headers
- ARC-Authentication-Results: instance number + validation results