What are ETags?
Entity Tags, often referred to as ETags, are a mechanism used in web applications and servers to determine if a particular resource has been modified. They are a part of the HTTP protocol and are primarily used in caching and resource validation.
An ETag is a unique identifier assigned to a specific version of a resource. It provides a way for servers to track changes to a resource and inform clients about it. When a client requests a resource, the server includes the ETag value associated with that resource in the response headers.
Meaning of ETags
ETags serve as a metadata component that represents the current state of a resource. They are typically generated based on the content of the resource and can be any string, such as a hash value or a version number. The client stores the received ETag value, and for subsequent requests, it can include this value in the headers as the “If-None-Match” field.
If the server receives a request with an ETag, it compares it with the current ETag value for that resource. If they match, the server responds with a “304 Not Modified” status, indicating that the client’s version of the resource is up to date. This saves bandwidth and network resources since the server doesn’t need to transmit the entire resource again.
If the ETags don’t match, it implies that the resource has been modified. In this case, the server sends the complete resource with a new ETag, and the client updates its stored ETag value accordingly.
Application of Entity Tags
ETags are commonly used in web caching to improve performance and reduce network latency. When a client requests a resource, it can store the response and the associated ETag. The next time the client needs that resource, it can send the ETag in the request headers. If the resource hasn’t changed, the server can respond with a lightweight “304 Not Modified” response, saving time and reducing server load.
Furthermore, ETags are used in conditional requests. Clients can include an ETag in the “If-Match” or “If-None-Match” headers to perform actions based on the resource’s current state. For example, a client can send an ETag in the “If-Match” header when updating a resource, ensuring that the server executes the request only if the resource hasn’t been modified by another user in the meantime.
In conclusion, ETags are an integral part of the HTTP protocol, empowering servers and clients to efficiently handle resource updates, validate the state of resources, and optimize performance in web applications.
Reference Articles
Read also
[Google Chrome] The definitive solution for right-click translations that no longer come up.