Notes/Web Engineering/Foundations of the Web.md

type
practical

The web \neq The internet

As portrayed in CN

URIs

A URI (Uniform Resource Identifier) identifies a resource, either by its name or location, and includes both URLs and URNs. A URL (Uniform Resource Locator) is a type of URI that specifies the exact location of a resource on the web, including its access method (e.g., HTTP, FTP).

Bad naming...

• URLs and URNs are URI Schemes
• URLs - transport://user:password@host:port/path[?search][#fragmentid]
• URNs - Is a logical address of a resource

HTTP

• Port 80 usually
• TCP

MIME

MIME (Multipurpose Internet Mail Extensions) is a standard that extends email and web protocols to support text in character sets other than ASCII, as well as attachments like images, audio, video, and other file types.

HTTP does not have these built-in!

• No state retained between request/response pairs
• Connections can persist

Term	Explanation
Origin Server	Server where resources reside
Proxy	Program that can act on behalf of origin server
Gateway	Intermediary for some other server
Tunnel	Relay between two connections (blindly)

---

Content negotiation

• Content can be available in multiple variants
• Representation is to be served based on the content negotiation mechanism

Type of content negotiation	Description
Server-driven	Client includes headers and server tries to find stuff based on them
Client-driven	Server responds with a list of available types and client picks

---

Messages & methods

Cool diagram expressing how protocols are being nested:

Request message (BNF)

HTTP-message = request-line | status-line message-header* CRLF message-body? message-header = general-header | entity-header | request-header | response-header (general | entity | request | response)-header = field-name ":" field-content CRLF

General Headers

• Cache-Control: Caching directives.
• Connection: Manage persistent connections.
• Transfer-Encoding: Encoding (e.g., chunked, gzip).
• Via: Tracks intermediaries and routing.

Entity Headers

• Content-Encoding: Compression (e.g., gzip).
• Content-MD5: Body integrity check.
• Expires: Response expiry date.
• Last-Modified: Last entity update timestamp.

Request methods

• GET, DELETE, POST, PUT, etc.
• They NEED to be used accordingly, although you are not forced to do it at all
• Idempotent¹ requests are side-effects free

---

1. Describing an action which, when performed multiple times, has no further effect on its subject after the first time it is performed. ↩︎