feat: override port via environment variable

[JosiahParry]

My understanding is that the environment variable SHINY_PORT can be used to override the port used by a shiny app. However this doesn't seem to be the case and, instead, leads to a spurious warning when used.

See the following repro. It results in the following warning message:

Warning in runApp(x) :
  Shiny Server v0.3.4 or later is required; please upgrade!

Listening on http://127.0.0.1:9001

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(

  # Application title
  titlePanel("Old Faithful"),

  # Sidebar with a slider input for number of bins
  sidebarLayout(
    sidebarPanel(
      sliderInput("bins",
        "Number of bins:",
        min = 1,
        max = 50,
        value = 30
      )
    ),

    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("distPlot")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  output$distPlot <- renderPlot({
    # generate bins based on input$bins from ui.R
    x <- faithful[, 2]
    bins <- seq(min(x), max(x), length.out = input$bins + 1)

    # draw the histogram with the specified number of bins
    hist(x,
      breaks = bins, col = "darkgray", border = "white",
      xlab = "Waiting time to next eruption (in mins)",
      main = "Histogram of waiting times"
    )
  })
}

Sys.setenv("SHINY_PORT" = "3000")
# Run the application
shinyApp(ui = ui, server = server, options = list(port = 9001))

[gadenbuie]

My understanding is that the environment variable SHINY_PORT can be used to override the port used by a shiny app.

Did you see this somewhere in the Shiny docs? It'd be useful to track down and to understand.

From a quick code search here, SHINY_PORT isn't used to set the port used by Shiny. It appears to be an environment variable set by Shiny Server for its own purposes and within the R package we use its presence as a signal that the app is being run by Shiny server.

shiny/R/server.R

Lines 510 to 514 in 55b37fd

	# Returns TRUE if we're running in Shiny Server or other hosting environment,
	# otherwise returns FALSE.
	inShinyServer <- function() {
	nzchar(Sys.getenv('SHINY_PORT'))
	}

The error you encounter is expected from these lines

shiny/R/runapp.R

Lines 203 to 213 in 55b37fd

	if (inShinyServer()) {
	# If SHINY_PORT is set, we're running under Shiny Server. Check the version
	# to make sure it is compatible. Older versions of Shiny Server don't set
	# SHINY_SERVER_VERSION, those will return "" which is considered less than
	# any valid version.
	ver <- Sys.getenv('SHINY_SERVER_VERSION')
	if (utils::compareVersion(ver, .shinyServerMinVersion) < 0) {
	warning('Shiny Server v', .shinyServerMinVersion,
	' or later is required; please upgrade!')
	}
	}

because Shiny thinks it's running inside Shiny Server and does a version check.

I think there's clearly room for improvement, but it could be tricky to handle in a way that doesn't break assumptions across Shiny packages and services.

Personally, I'd use a different environment variable passed directly to shinyApp() (untested, port might need to be coerced to int/numeric):

shinyApp(ui = ui, server = server, options = list(port = Sys.setenv("APP_PORT", 9001))