The ConditionalHeaders plugin (previously known as feature) avoids sending the body of content if it has not changed since the last request. This is achieved by using the following headers:
Last-Modifiedresponse header contains a resource modification time. For example, if the client request contains the
If-Modified-Sincevalue, Ktor will send a full response only if a resource has been modified after the given date. Note that for static files Ktor appends the
Last-Modifiedheader automatically after installing
Etagresponse header is an identifier for a specific resource version. For instance, if the client request contains the
If-None-Matchvalue, Ktor won't send a full response in case this value matches the
Etag. You can specify the
Etagvalue when configuring
To install the
ConditionalHeaders plugin, pass it to the
install function in the application initialization code. Depending on the way used to create a server, this can be the
embeddedServer function call ...
... or a specified module.
ConditionalHeaders, you need to call the version function inside the
install block. This function provides access to a list of resource versions for a given OutgoingContent. You can specify the required versions by using the EntityTagVersion and LastModifiedVersion class objects.
The code snippet below shows how to add a
Last-Modified headers for CSS:
You can find the full example here: conditional-headers.