Run a Shiny app in a background process

Starts a Shiny app – a directory or an app file – in a background R process and returns a handle for its lifecycle. One app can back any number of pages: pass the handle to pz_open() for each page. Closing those pages leaves the app running.

Usage

pz_serve_shiny(app, ..., envvars = NULL, shiny_options = list(), timeout = 10)

Arguments

app

A path to a Shiny app directory or an app file (anything shiny::runApp() accepts as a path).

...

Reserved; must be empty.

envvars

Named character vector of environment variables set in the app process, on top of the inherited environment. NULL adds no environment overrides.

shiny_options

Additional options for shiny::runApp(), e.g. list(test.mode = TRUE). appDir is reserved; use app to select the app. host and port are managed by paparazzi: host defaults to "127.0.0.1", and port (default NULL) picks a random free port. If startup fails because the port was taken, a new port is tried.

timeout

Seconds to wait for the app to start listening; defaults to 10.

Value

A PaparazziServe handle with public fields url and port and methods stop(), logs(), and is_running().

Details

The handle has $stop() and $logs() methods and a print() method showing the URL, port, and status – the one place the paparazzi API uses methods rather than pz_*() functions. $stop() interrupts, waits, then kills, and is idempotent, so withr::defer(app$stop()) is a safe cleanup. A finalizer stops the app as a last resort.

App stdout and stderr go to a temporary log file (never an undrained pipe), readable mid-run with $logs().

Examples

if (FALSE) { # paparazzi:::examples_run("shiny")
app <- pz_serve_shiny(pz_example("tasks-app"))
app

# Pages opened on a handle share the app, here at two screen sizes
desktop <- pz_open(app, width = 1280)
phone <- pz_open(app, width = 390, mobile = TRUE)
pz_get_text(phone, target = "#summary")
pz_close(desktop)
pz_close(phone)

# Closing the pages leaves the app running until you stop it
app$is_running()
head(app$logs())
app$stop()
}