This method allows serializers to return preexec, postexec, and aroundexec (
) hooks in addition to a serializer.
This is useful for graphics device serializers which need a preexec and postexec hook to capture the graphics output.
endpoint_serializer( serializer, preexec_hook = NULL, postexec_hook = NULL, aroundexec_hook = NULL )
Arguments
| serializer | Serializer method to be used. This method should already have its initialization arguments applied. |
|---|---|
| preexec_hook | Function to be run directly before a PlumberEndpoint calls its route method. |
| postexec_hook | Function to be run directly after a PlumberEndpoint calls its route method. |
| aroundexec_hook | Function to be run around a PlumberEndpoint call. Must handle a |
Details
preexec and postexec hooks happened directly before and after a route is executed.
These hooks are specific to a single PlumberEndpoint's route calculation.
Examples
# The definition of `serializer_device` returns # * a `serializer_content_type` serializer # * `aroundexec` hook print(serializer_device)#> function (type, dev_on, dev_off = grDevices::dev.off) #> { #> stopifnot(!missing(type)) #> stopifnot(!missing(dev_on)) #> stopifnot(is.function(dev_on)) #> stopifnot(length(formals(dev_on)) > 0) #> if (!any(c("filename", "...") %in% names(formals(dev_on)))) { #> stop("`dev_on` must contain an arugment called `filename` or have `...`") #> } #> stopifnot(is.function(dev_off)) #> endpoint_serializer(serializer = serializer_content_type(type), #> aroundexec_hook = function(..., .next) { #> tmpfile <- tempfile() #> dev_on(filename = tmpfile) #> device_id <- dev.cur() #> dev_off_once <- once(function() dev_off(device_id)) #> success <- function(value) { #> dev_off_once() #> if (!file.exists(tmpfile)) { #> stop("The device output file is missing. Did you produce an image?", #> call. = FALSE) #> } #> con <- file(tmpfile, "rb") #> on.exit({ #> close(con) #> }, add = TRUE) #> img <- readBin(con, "raw", file.info(tmpfile)$size) #> img #> } #> cleanup <- function() { #> dev_off_once() #> on.exit({ #> unlink(tmpfile) #> }, add = TRUE) #> } #> async <- FALSE #> on.exit({ #> if (!async) { #> cleanup() #> } #> }, add = TRUE) #> result <- promises::with_promise_domain(createGraphicsDevicePromiseDomain(device_id), #> { #> .next(...) #> }) #> if (is.promising(result)) { #> async <- TRUE #> result %>% then(success) %>% finally(cleanup) #> } #> else { #> success(result) #> } #> }) #> } #> <bytecode: 0x7ff88647e208> #> <environment: namespace:plumber>