plumber::forward() is a nightmare to handle

[schloerke]

Related: #907 (comment)

The code in Meztez's comment is something that I'd like to require... that forward() (or which ever method we use) be returned from the filter.

library(plumber)
library(future)
plan("multisession")

#* @filter future
function(req) {
  print(req$PATH_INFO)
  if (req$PATH_INFO=="/echo1") {
    future::future({
      Sys.sleep(10)
      plumber::forward()
    })
  } else {
    plumber::forward()
  }
}

#* @serializer text
#* @get /echo1
function(msg) {
  msg
}

#* @serializer text
#* @get /echo2
function(msg) {
  msg
}

• I believe this should be done if/when we add middlware.
• I believe it should have a new function name as it has different functionality than plumber::forward().

[thomasp85]

In fiery/routr I simply used TRUE/FALSE return values to indicate whether further handling should be performed