How do I define asynchronous API endpoints in plumber?
I didn't really find plumber-specific documentation on the topic except this example and this GitHub issue
When I try to reproduce the example, I get an error that R doesn't know how to turn a promise into JSON (at least that's what I think the problem is):
<simpleError: No method asJSON S3 class: promise>
Example
library(promises)
sleep_count <- 5
# add 5 seconds of sleep time
add_async_sleep <- function(p) {
n <- 20
for (i in 1:(sleep_count * n)) {
p <- then(p, function(value) {
Sys.sleep(1/n)
"" # return value
})
}
p
}
# use name_ as a placeholder for name when there are extra args
time <- function(name_, name = name_) {
paste0(name, ": ", Sys.time())
}
new_promise <- function() {
promise(function(resolve, reject){ resolve(NULL) })
}
#' @get /async
function() {
new_promise() %>%
add_async_sleep() %...>%
time("async")
}
Say this code lives in file plumber.R, then you should be able to start the API server and bring up Swagger with
r <- plumber::plumb(here::here("plumber.R"))
r$run()
Once I try out the endpoint /async, my R console reports
Starting server to listen on port 7361
Running the swagger UI at http://127.0.0.1:7361/__swagger__/
<simpleError: No method asJSON S3 class: promise>
and Swagger looks like this:
Disclaimer
I'm new to future and promises and only made it mid-way through the docs on https://rstudio.github.io/promises/ yet.
