90 lines
3.1 KiB
Markdown
90 lines
3.1 KiB
Markdown
---
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type: practical
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---
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The web $\neq$ The internet
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As portrayed in CN
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## URIs
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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).
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Bad naming...
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* URLs and URNs are **URI Schemes**
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* URLs - `transport://user:password@host:port/path[?search][#fragmentid]`
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* URNs - Is a logical address of a resource
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## HTTP
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- Port 80 usually
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- TCP
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### MIME
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**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.
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**HTTP does not have these built-in!**
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- No state retained between request/response pairs
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- Connections **can** persist
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| Term | Explanation |
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| ------------- | ----------------------------------------------- |
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| Origin Server | Server where resources reside |
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| Proxy | Program that can act on behalf of origin server |
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| Gateway | Intermediary for some other server |
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| Tunnel | Relay between two connections (blindly) |
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---
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### Content negotiation
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- Content can be available in multiple variants
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- Representation is to be served based on the **content negotiation mechanism**
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| Type of content negotiation | Description |
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| --------------------------- | -------------------------------------------------------------------- |
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| Server-driven | Client includes headers and server tries to find stuff based on them |
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| Client-driven | Server responds with a list of available types and client picks |
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---
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### Messages & methods
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Cool diagram expressing how protocols are being nested:
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#### Request message (BNF)
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```js
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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
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```
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#### **General Headers**
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- `Cache-Control`: Caching directives.
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- `Connection`: Manage persistent connections.
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- `Transfer-Encoding`: Encoding (e.g., `chunked`, `gzip`).
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- `Via`: Tracks intermediaries and routing.
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#### **Entity Headers**
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- `Content-Encoding`: Compression (e.g., `gzip`).
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- `Content-MD5`: Body integrity check.
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- `Expires`: Response expiry date.
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- `Last-Modified`: Last entity update timestamp.
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### Request methods
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- GET, DELETE, POST, PUT, etc.
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- They NEED to be used accordingly, although you are not forced to do it at all
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- Idempotent[^1] requests are side-effects free
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[^1]: Describing an action which, when performed multiple times, has no further effect on its subject after the first time it is performed. |