Read json file continuously - r

Question

I want to read a json file continuously, e.g. every 1000 ms.
One option my be reactiveFileReader
reactiveFileReader(intervalMillis, session, filePath, readFunc, ...)
described here.
This function seems only working with csv files and not for json files:
file_data <- reactiveFileReader(intervalMillis = 1000, NULL, filePath = json_path, readFunc = read.json)
observe({
View(file_data())
})
Error in View : object read.json not found
With reactivePoll like here:
getJsonData <- reactivePoll(1000, session,
checkFunc = function() {
if (file.exists(path))
file.info(path)$mtime[1]
else
""
},
valueFunc = function() {
read_json(path)
}
I get nearly what I want, but this function is not working in my context. How do I force the program to read the file every second and not only when the content of the file is changing?
Are there other possibilities I not have thought about yet?

Answer 1

In your first way, you wrote read.json instead of read_json.
With your second way, you could replace file.info(path)$mtime[1] with runif(1, 0, 1e6). You would be very unlucky if runif returns the same number two consecutive times.
Finally, a third way could be:
server <- function(input, output, session){
autoInvalidate <- reactiveTimer(1000)
getJsonData <- reactive({
autoInvalidate()
read_json("path/to/file.json")
})
}

Answer 2

Here is a reprex on how to use reactiveFileReader with a json file.
I used a future to detach the writing process from the shiny session - you can simply replace this with your json input.
library(shiny)
library(jsonlite)
library(datasets)
library(promises)
library(future)
plan(multisession(workers = 2))
ui <- fluidPage(
uiOutput("printResult")
)
server <- function(input, output, session) {
json_path <- tempfile(fileext = ".json")
write_json(NULL, json_path)
# async file writing process
future({
for(i in seq_len(nrow(iris))){
Sys.sleep(1)
write_json(iris[i,], json_path)
}
})
file_data <- reactiveFileReader(intervalMillis = 1000, NULL, filePath = json_path, readFunc = read_json)
output$printResult <- renderUI({
req(file_data())
})
}
shinyApp(ui, server)