JavaScript Web Concepts, Part7 - HTTP Headers

What are different HTTP headers?

HTTP headers are key-value pairs sent in HTTP requests and responses that provide essential information about the request, response, or the data being transmitted. They play a critical role in HTTP communication by allowing clients and servers to share metadata. Here’s an overview of different categories and commonly used HTTP headers:

1. General Headers

These headers apply to both requests and responses and provide information about the communication.

1. Cache-Control: Specifies caching policies, like no-cache, no-store, max-age, etc.
2. Connection: Controls whether the network connection stays open after the current transaction (e.g., keep-alive).
3. Date: Indicates the date and time at which the message was sent.
4. Transfer-Encoding: Specifies how the message body is encoded, such as chunked for streaming data.

2. Request Headers

These headers are used in HTTP requests and provide information about the client, resource preferences, and more.

1. Accept: Specifies the media types the client can process, like text/html, application/json.
2. Accept-Encoding: Lists acceptable content-encoding methods like gzip or deflate for data compression.
3. Authorization: Contains credentials for authenticating the client (e.g., Bearer <token>).
4. Cookie: Sends stored cookies to the server for session management and tracking.
5. Host: Specifies the domain name and port number of the server to which the request is directed.
6. Referer: Indicates the previous page that referred the user to the current request URL.
7. User-Agent: Contains information about the client software, including browser and operating system details.

3. Response Headers

These headers are used in HTTP responses to provide additional information about the response and the server.

1. Location: Used for redirection, indicating the new URL to which the client should go.
2. Set-Cookie: Sends cookies from the server to the client to store for future requests.
3. Server: Provides information about the server software handling the request.
4. WWW-Authenticate: Used in responses to request authentication credentials from the client.

4. Entity Headers (also known as Representation Headers)

These headers provide information about the body of the resource in the request or response.

1. Content-Type: Indicates the media type of the body (e.g., application/json, text/html).
2. Content-Length: Specifies the size of the body in bytes.
3. Content-Encoding: States the encoding applied to the body, like gzip.
4. Content-Language: Specifies the natural language of the body’s content, such as en-US.
5. Content-Location: Gives an alternative location for the returned data.

5. Security Headers

These headers enhance security by controlling content behavior and browser policies.

1. Strict-Transport-Security (HSTS): Enforces HTTPS for future requests to prevent man-in-the-middle attacks.
2. Content-Security-Policy: Restricts sources for scripts, styles, images, etc., to protect against XSS attacks.
3. X-Frame-Options: Controls whether the browser should allow a page to be displayed in an iframe, mitigating clickjacking attacks.
4. X-Content-Type-Options: Prevents browsers from MIME-type sniffing, reducing exposure to drive-by downloads.

6. Custom Headers

Custom headers are headers that developers create for application-specific purposes. They generally start with X- to distinguish them from standard headers (e.g., X-Custom-Header), although modern best practices encourage using clear names without the X- prefix.

Each type of HTTP header plays a unique role, enhancing the communication and functionality between clients and servers while ensuring data integrity, security, and flexibility.

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