HTTP headers explained in 10 points

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HTTP headers

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In the Internet world, HTTP headers are an essential part of the Hypertext Transfer Protocol (HTTP), which governs communication between web clients and servers.

These headers contain crucial information to facilitate this communication and ensure its smooth operation.

Why use HTTP headers?

HTTP headers are mainly used to transmit additional data during an HTTP request or response. They are also used to control the behaviour of exchanges between the client and the server. Headers play a major role in :

• Authentication
• Safety
• Cookie management
• Redirects
• Other aspects of the HTTP protocol

The different types of HTTP header

There are several categories of HTTP headers:

1. General headers They apply to both HTTP requests and responses and provide general information about the communication.
2. Request headers They accompany an HTTP request sent by the client and provide details of the request to the server.
3. Response headers As their name suggests, they are included in HTTP responses sent by the server to the client and provide details of the response.
4. Entity headers They describe the characteristics of an entity (request or response body) such as its MIME type, size, etc.

Examples of common HTTP headers

Here are some frequently used HTTP headers with a brief description:

• Content-Type indicates the content type (MIME) of the request or response body.
• Accept provides the server with a list of acceptable content types for the client.
• Authorization transmits client authentication information to the server.
• Cache-Control Cache: specifies the caching directives to be followed by the client and server.
• Rental URL: indicates the URL to which the client should be redirected (used mainly in redirect responses).

How are HTTP headers structured?

An HTTP header consists of two parts separated by a colon:

1. Le name header (for example, Content-Type)
2. La value associated with this header (for example, text/html)

Thus, an HTTP header will generally look like this:

Name-Entee: value

Example of an HTTP request with headers

GET /example.html HTTP/1.1
Host : www.example.com
User-Agent : Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36
Accept : text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Cache-Control : no-cache

Modifying HTTP headers on the client and server sides

HTTP headers can be customised as required on both the client and server sides using appropriate programming languages.

• For the client sidewe can use JavaScript and more specifically XMLHttpRequest or Fetch API to modify and add headers to the HTTP request before sending it
• For the server sideYou can use different languages, such as PHP, Node.js, Python, etc., to modify the response headers to suit your needs.

Customised headers

In addition to standard headers, it is also possible to create custom headers:

1. They must begin with "X-" to comply with HTTP standards.
2. Custom headers can be used to transmit information specific to an application or service

However, it is advisable to use them sparingly and to prefer existing standard headers wherever possible.

HTTP headers and SEO

Several HTTP headers have a direct or indirect influence on the optimisation of the referencing a website :

• Content-Type Make sure you always use the correct MIME type for your resources so that search engines can interpret them correctly.
• Cache-Control caching: the right caching guidelines can improve the speed and performance of your site, which has a positive impact on search engine rankings
• Rental redirects are important for the SEOso use this header correctly to redirect customers to the correct URL
• Vary This header tells proxy servers and caches that a different version of a resource must be provided depending on certain parameters (such as acceptable types), thus ensuring that visitors receive the correct version of the page.

Security and HTTP headers

HTTP headers can also help to improve the security of a website:

• Strict-Transport-Security header: this header forces the use of the HTTPS for exchanges between the client and the server
• Content-Security-Policy It allows you to define strict rules for authorised sources of content (such as images, scripts, etc.) and helps protect against Cross-Site Scripting (XSS) attacks.
• X-XSS-Protection this header activates protection against XSS attacks in certain browsers
• X-Content-Type-Options This header prevents browsers from incorrectly modifying the MIME type of a resource, which could lead to security problems.

HTTP headers are essential for the Web to function properly

In short, HTTP headers play a fundamental role in communications between web clients and servers. They transmit important information relating to HTTP requests and responses, and influence various aspects of the Web such as security, referencing, performance and cookie management. Knowing and understanding these headers is crucial to the successful development and operation of a website or web application.