Conditional GET

Creates a conditional GET handler for a specific HTTP path, using a supplied etag function for the current representation. If the server's ETag and client's 'If-None-Match' headers match, a 304 Not Modified response is sent, short-circuiting downstream handlers. This reduces the need to recompute responses for paths where the data has not changed since the last client request.

Usage

api_cget(api, path, etag_fn)

Arguments

api

a plumber2::plumber2 api object.

path

the path to short circuit.

etag_fn

a function that takes no arguments and returns a single value used to derive the ETag.

Details

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Conditional_requests for more information.

Annotation Reference

The etag function is specified by @etag fn where fn is the function name. Functions can also be defined in-line like @etag \() x + 1.

increment_x <- \() {
    x <<- x + 1L
    later::later(increment_x, delay = 10L)
}
x <- 1L
increment_x()
#* @get /
#* @etag \() x
function() {
 x
}