#### What is an API?
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#### Section 1: What is an API?

**Definition:**
An API (Application Programming Interface) is like a restaurant menu. It defines what services (or "dishes") are available and how you can request them.

- **Restaurant Menu (API):** The menu lists all available dishes (services).
- **Customer (Client):** You are the customer requesting food (client making requests to the API).
- **Waiter (Server):** The waiter takes your order (API request) and brings back your dish (API response) from the kitchen (the backend system).

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#### **Section 2: Key API Terminology**

- **API Endpoint:** The URL or address where the API is available, like the kitchen door where orders go in.
- **Example:** `https://api.restaurant.com/v1/orders` (Here, `/orders` is the endpoint)

- **HTTP Methods:** The different ways you can interact with the API.
- **GET:** Request data (e.g., look at the menu).
- **POST:** Send data (e.g., place an order).
- **PUT:** Update data (e.g., modify your order).
- **DELETE:** Remove data (e.g., cancel your order).

- **API Parameters:** These are additional details included in the API request, similar to asking for a steak with a specific sauce.
- **Example:** `/orders?dish=pasta&size=large`

- **API Response:** The data sent back by the API after processing your request, similar to receiving the meal you ordered.

- **Directory Fuzzing:** This is the process of brute-forcing the paths in a website or API to find hidden or unsecured directories or files.
- **Example:** Searching for `/api/v1/admin` on an API to check if there's an unsecured admin panel.

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#### **Section 3: Types of APIs (The Types of Restaurants)**

1. **REST (Represent The State Transfer)**
**Characteristics:**
- Stateless (each request is independent, like ordering a meal without remembering previous orders).
- Supports HTTP methods (GET, POST, PUT, DELETE).
- Returns data in formats like JSON or XML.
- URL-based structure (resource-focused).

**Analogy:** A fast-food restaurant where each order is handled individually without remembering previous ones.

2. **SOAP (Simple Object Access Protocol)**
**Characteristics:**
- Protocol-based and uses XML for communication.
- Strict structure with formal rules for request/response.
- Supports advanced security features and transactions.

**Analogy:** A fine-dining restaurant with a detailed reservation process, where the interaction is more formal and follows strict protocols.

3. **GraphQL**
**Characteristics:**
- Allows clients to specify the exact data they need in a query.
- Fetches multiple resources in a single request (more efficient).
containing flexibility for requesting data fields.

**Analogy:** A restaurant where you can custom order exactly what ingredients you want on your plate without any extras.

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#### **Section 4: Tools for API Testing**

**GUI-based Tools**
1. **Postman:**
- User-friendly interface for making API requests.
- Supports automated testing and creating collections of requests.
- Ideal for beginners and for testing REST APIs.

2. **Insomnia:**
- Clean interface for testing REST, GraphQL, and SOAP APIs.
- Strong collaboration features for teams.

**CLI-based Tools**
1. **cURL:**
- Command-line tool for making API requests, commonly used for quick testing.
- Supports various HTTP methods (GET, POST, PUT, DELETE).

**Example:**

   curl -X GET 'https://api.restaurant.com/v1/orders?dish=pasta'

2. **HTTPie:**
- A more user-friendly alternative to cURL, making API requests simpler with a readable output.
- Can be used directly from the command line.

**Example:**

   http GET 'https://api.restaurant.com/v1/orders?dish=pasta'

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#### **Section 5: Summary of API Testing Types**

**1. Functional Testing**
Verifies whether the API functions correctly according to specifications (e.g., testing different menu options in the restaurant analogy).

**2. Load Testing**
Tests how the API behaves under heavy traffic (similar to a restaurant serving many customers at once).

**3. Security Testing**
Ensures that the API is secure against threats such as unauthorized access, similar to checking that the kitchen staff (server) only accepts orders from customers (clients) with valid tickets.

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#### Helpful API Resources

- [Official Postman Documentation](https://learning.postman.com/docs/getting-started/introduction/)
- [HTTPie Command-line Documentation](https://httpie.io/docs/cli)
- [Understanding REST APIs](https://restfulapi.net/)

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