Headers play a vital role in the communication between a client and a server by providing essential information about the request or response. In this blog, we’ll dive deep into what headers are, why they matter, and some of the most commonly used headers in REST APIs.
What are HTTP Headers?
HTTP headers are key-value pairs sent in the request or response of an HTTP transaction. These headers convey information about the request or response, such as the type of data being sent, the encoding method used, authentication credentials etc.
Headers are used at both request and response time. They facilitate smooth, secure, and efficient communication between the client and server in REST APIs.
Request Headers
Contain more information about the resource to be fetched, or about the client requesting the resource.
| Header | Example | Use Case |
|---|---|---|
| Authorization | Authorization: Bearer | Sends credentials to authenticate the client with the server. |
| Content-Type | Content-Type: application/json | Specifies the media type of the data being sent by the client. |
| Accept | Accept: application/json | Indicates the content types the client can process. |
| User-Agent | User-Agent: Mozilla/5.0 | Identifies the client software making the request. |
| Cache-Control | Cache-Control: no-cache | Directs how the request should be cached by the server or caches. |
| Host | Host: example.com | Specifies the domain name of the server the client is requesting. |
| Accept-Encoding | Accept-Encoding: gzip, deflate | Lists the encoding methods the client can handle. |
| Accept-Language | Accept-Language: en-US | Indicates the preferred languages for the response. |
| Referer | Referer: https://example.com | Provides the URL of the resource from which the request was initiated. |
| Origin | Origin: https://example.com | Identifies the origin of the request, especially for CORS. |
Response Headers
Hold additional information about the response, like its location or about the server providing it.
| Header | Example | Use Case |
|---|---|---|
| Content-Type | application/json | Indicates the media type of the resource in the response body. |
| Cache-Control | max-age=3600 | Defines caching directives for the client and intermediate caches. |
| Location | /new-resource | Indicates the URL to redirect a client to another resource. |
| Set-Cookie | sessionId=abc123 | Sends cookies from the server to the client for session management. |
| WWW-Authenticate | Basic realm="Resource" | Defines the authentication method for accessing a resource. |
| Content-Encoding | gzip | Specifies the encoding method used on the response data. |
| Content-Length | 348 | Indicates the size of the response body in bytes. |
| Expires | Wed, 21 Oct 2024 | Gives the date/time after which the response is considered stale. |
| ETag | "34a64d..." | Provides a unique identifier for a specific version of a resource. |
| Last-Modified | Tue, 15 Nov 2023 | Indicates the date and time the resource was last modified. |
Conclusion
Understanding and properly using request and response headers is fundamental to building REST APIs. These headers give information about security, authentication, caching, content negotiation, and API usability.
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