LastModifiedIfModifiedSince

LastModifiedIfModifiedSince is a concept related to HTTP caching. When a client requests a resource, the server can respond with a Last-Modified header, indicating the date and time the resource was last changed. The client then stores this information along with the resource.

On subsequent requests for the same resource, the client can include an If-Modified-Since header in its request. This header contains the date and time from the previously received Last-Modified header. The server then checks if the resource has been modified since that specified date.

If the resource has not been modified, the server responds with a 304 Not Modified status code. This indicates that the client can use its cached version of the resource, saving bandwidth and reducing server load. If the resource has been modified, the server sends the updated resource with a 200 OK status code and a new Last-Modified header. This mechanism is crucial for efficient web browsing and API interactions, ensuring that clients only download resources when they are actually new or changed. It helps to improve performance by minimizing unnecessary data transfer.