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188 lines
7.1 KiB
Markdown
188 lines
7.1 KiB
Markdown
---
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marp: true
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paginate: true
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math: mathjax
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theme: buutti
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title: 2. HTTP
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---
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# HTTP
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<!-- headingDivider: 5 -->
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<!-- class: invert -->
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## Contents
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1) What is HTTP?
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2) HTTP Requests
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3) HTTP Responses
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4) IP address and ports
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## What is HTTP?
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* **_HTTP_** (Hypertext Transfer Protocol) is a TCP/IP based communication protocol, which provides a standardized way for computers to communicate with each other
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* The communication happens between a client (browser, application…) and a server
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* The client sends a **_request_**, and the server returns a **_response_**
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* HTTP is *__connectionless__*:
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* The client and server are only aware of each other during the request-response phase
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* After that, each new request is sent through a new connection
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### But what is TCP/IP?
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* It is known as the [Internet protocol suite](https://en.wikipedia.org/wiki/Internet_protocol_suite)
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* Framework used for organizing communication protocols over the Internet
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* TCP = Transmission Control Protocol
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* Controlled stream of bytes between applications communicating via an IP network
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* IP = Internet Protocol
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* Delivering packets from host to destination with IP addresses
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### HTTP structure
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<div class='columns' markdown='1'>
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<div markdown='1'>
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</div>
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<div markdown='1'>
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* The HTTP protocol acts as a communication bus between the web client (e.g. web browser) and the web server
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* There can be multiple clients connected to the server simultaneously
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* The clients are not connected to each other but only to the server
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</div>
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</div>
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## HTTP requests
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* HTTP defines a set of request methods
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* The most common requests are `GET`, `POST`, `PUT` and `DELETE`
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* These are needed to create a basic CRUD app *(Create, Read, Update, Delete)*
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* More requests are listed in the [mdn web docs](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Methods)
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| HTTP Method | Usage | Example Use |
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|-------------|:---------------------|:------------------------------------------|
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| `GET` | Retrieve content | Browser fetching a webpage |
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| `POST` | Add new data | Submitting a form to create a new account |
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| `PUT` | Update existing data | Updating user profile information |
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| `DELETE` | Remove existing data | Deleting a user account |
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### Note: URI vs URL
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* The website address is more formally known as the ***URL (uniform resource locator)***
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* `https://maps.google.com`
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* `https://maps.google.com/maps?q=Oulu` (includes a ***query***)
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* It is a subset of an ***URI (uniform resource identifier)***
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* This identifies any type of a resource
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* `mailto:info@example.com` (an email address)
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* `https://www.example.com/index.html#date` (A section of a website)
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### HTTP request format
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* Request line: `<request method> <request URI>`
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* Example: `GET https://example.com/products`
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* Headers (optional)
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* Example: `Date: Mon, 07 Sep 2020 08:39:33 GMT`
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* Example: `Content-Type: application/json`
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* Body (optional)
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* Example in the JSON format:
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```json
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{
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"date": "2020-09-08T11:39:34.2837813+03:00",
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"temperatureC": 11,
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"temperatureF": 51,
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"summary": "Cool"
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}
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```
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### HTTP request examples
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| Method | URI | Headers | Body |
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|:---------|:--------------------------------|:---------------------------------|:--------------------|
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| `GET` | `http://server.com/` | | |
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| `GET` | `http://server.com/10` | | |
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| `POST` | `http://server.com/users` | `Content-Type: application/json` | `{"name": "Dan"}` |
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| `PUT` | `http://server.com/users/2` | `Content-Type: application/json` | `{"name": "Danny"}` |
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| `DELETE` | `http://server.com/users/2` | | |
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## HTTP response format
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* HTTP responses have the following format:
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* Status line: `<HTTP version> <status code> <reason phrase>`
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* Example:`HTTP/1.1 200 OK`
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* Headers (optional)
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* `Date: Mon, 07 Sep 2020 08:39:33 GMT`
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* `Content-Type: application/json`
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* Body (optional)
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```json
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{
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"date": "2020-09-08T11:39:34.2837813+03:00",
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"temperatureC": 11,
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"temperatureF": 51,
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"summary": "Cool"
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}
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```
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### HTTP status codes
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* The status line of HTTP a response sent by an API should accurately describe the status of what happened on the server after each request:
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* Did the operation succeed? (`2xx` status codes)
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* Was there an error with the request? (`4xx` status codes)
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* E.g., the request line was malformed, or the server doesn't support it
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* Did a server-side exception occur? (`5xx` status codes)
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* This is never the client's fault!
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### Status codes for a CRUD app
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* Your APIs should use the following status codes for responses to CRUD operations
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* See [Restfulapi.net](https://restfulapi.net/http-status-codes/) and [Wikipedia](https://en.wikipedia.org/wiki/List_of_HTTP_status_codes) HTTP status code listings
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| `2xx SUCCESS` | `4xx CLIENT ERROR` | `5xx SERVER ERROR` |
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|:-------------------|:---------------------|:------------------------------|
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| `200 - OK` | `400 - Bad Request` | `500 - Internal Server Error` |
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| `201 - Created` | `401 - Unauthorized` | |
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| `204 - No Content` | `403 - Forbidden` | |
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| | `404 - Not Found` | |
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| | `409 - Conflict` | |
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## IP and ports
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### IP addresses
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* Every node, or ***host*** on a computer network needs an IP (Internet Protocol) address
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* These can be public or private
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* Serves two functions: identifies and provides the location of the host
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* The old 32-bit IPv4 addresses are of the form `192.0.2.1`
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* The 128-bit IPv6 addresses are of the form `2001:0db8:0000:0000:0000:8a2e:0370:7334` (can be shortened to `2001:db8::8a2e:370:7334`)
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### Port numbers
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<!-- Note: older version in the backend-basics repo -->
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* The IP address is often followed by a ***port*** number separated by a colon: `192.0.2.1:8080`
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* The port number (16-bit unsigned integer) defines the port through which communication to your application happens
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* Ports allow multiple applications to be located on the same host
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* The client connects to this port in some server (defined by an IP address), so the client and the server are able to communicate
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* Computers have several different ports at their disposal
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### Reserved ports
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<div class='columns' markdown='1'>
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<div markdown='1'>
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* Some of them are reserved and your application might not be able to assign those ports to itself
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* Ports from 0 to 1023 are ***system ports***
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* There are restrictions in manually assigning applications to use them
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* Generally, ports from 1024 to 65535 are available for the user to assign for applications
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</div>
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<div markdown='1'>
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</div>
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</div>
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