From 8ccd142b83c3eab4bb190794aca37d1b2e3d0157 Mon Sep 17 00:00:00 2001
From: JosiahParry <josiah.parry@gmail.com>
Date: Fri, 2 Oct 2026 08:20:42 -0700
Subject: [PATCH] add launch_sever for _server.yml standad

---
 R/server-yml.R                          | 92 +++++++++++++++++++++++++
 inst/examples/12_server_yml/_server.yml |  7 ++
 inst/examples/12_server_yml/app.R       | 59 ++++++++++++++++
 3 files changed, 158 insertions(+)
 create mode 100644 R/server-yml.R
 create mode 100644 inst/examples/12_server_yml/_server.yml
 create mode 100644 inst/examples/12_server_yml/app.R

diff --git a/R/server-yml.R b/R/server-yml.R
new file mode 100644
index 0000000000..61328c80ec
--- /dev/null
+++ b/R/server-yml.R
@@ -0,0 +1,92 @@
+#' Launch a Shiny app using the _server.yml standard
+#'
+#' Implements the `_server.yml` standard for R web frameworks for \pkg{shiny}.
+#'
+#' @param settings path to the `_server.yml` file.
+#' @inheritParams runApp host port
+#'
+#' @details
+#' The provided shiny app must be located next to `_server.yml` or in a subdirectory of its containing path.
+#' Configuration options from the `_server.yml` file are passed directly to `runApp()`.
+#'
+#' A valid `_server.yml` file has the following structure:
+#'
+#' ```yaml
+#' engine: shiny
+#'   options:host:"127.0.0.1"
+#'   port: null
+#'   app_dir: null
+#'   quiet: false
+#' ```
+#' @keywords internal
+#' @noRd
+#' @examples
+#' shiny:::launch_server(system.file(
+#'   "examples/12_server_yml/_server.yml",
+#'   package = "shiny"
+#' ))
+#' @seealso [runApp()]
+launch_server <- function(
+  settings = "_server.yml",
+  host = getOption("shiny.host", "127.0.0.1"),
+  port = getOption('shiny.port')
+) {
+  # ensure yaml is installed to read the file
+  rlang::check_installed("yaml", "to read '_server.yml' settings.")
+
+  # early abort based on _settings path
+  if (!file.exists(settings)) {
+    cli::cli_abort(c(
+      "File {.file {settings}} does not exist.",
+      "i" = " {.arg settings} must point to a {.file _server.yml} file."
+    ))
+  }
+
+  # type check the host and port
+  if (!rlang::is_string(host) && !is.null(host)) {
+    cli::cli_abort("{.arg host} must be a string.")
+  }
+
+  if (!rlang::is_integerish(port, 1L) && !is.null(port)) {
+    cli::cli_abort("{.arg port} must be an integer.")
+  }
+
+  # extract config
+  config <- yaml::read_yaml(settings)
+
+  # host precedence env_var > config > default
+  host <- if (!nzchar(Sys.getenv("HOST"))) {
+    config$options$host %||% host
+  }
+
+  # if PORT env var can't coerced into integer we fallback to config then port
+  port_env <- Sys.getenv("PORT")
+  port <- if (is.na(as.integer(port_env))) {
+    config$options$port %||% port
+  }
+
+  # extract directory name of the _settings.yml file
+  # according to standard, app must be relative to the _server.yml file
+  containing_dir <- dirname(settings)
+
+  # extract app_dir from config fall back to parent of _server.yml
+  app_dir <- config$options$app_dir %||% containing_dir
+
+  is_contained <- startsWith(
+    normalizePath(app_dir, mustWork = TRUE),
+    normalizePath(containing_dir, mustWork = TRUE)
+  )
+
+  if (!is_contained) {
+    cli::cli_abort(
+      "The {.file _server.yml}'s {.arg app_dir} option must be relative to it."
+    )
+  }
+
+  runApp(
+    app_dir,
+    port = port,
+    host = host,
+    quiet = config$options$quiet %||% FALSE
+  )
+}
diff --git a/inst/examples/12_server_yml/_server.yml b/inst/examples/12_server_yml/_server.yml
new file mode 100644
index 0000000000..6c28562af1
--- /dev/null
+++ b/inst/examples/12_server_yml/_server.yml
@@ -0,0 +1,7 @@
+engine: shiny
+options:
+    host: "127.0.0.1"
+    port: null
+    app_dir: null
+    quiet: false
+
diff --git a/inst/examples/12_server_yml/app.R b/inst/examples/12_server_yml/app.R
new file mode 100644
index 0000000000..887c50576d
--- /dev/null
+++ b/inst/examples/12_server_yml/app.R
@@ -0,0 +1,59 @@
+library(shiny)
+
+# Define UI for app that draws a histogram ----
+ui <- fluidPage(
+
+  # App title ----
+  titlePanel("Hello Shiny!"),
+
+  # Sidebar layout with input and output definitions ----
+  sidebarLayout(
+
+    # Sidebar panel for inputs ----
+    sidebarPanel(
+
+      # Input: Slider for the number of bins ----
+      sliderInput(inputId = "bins",
+                  label = "Number of bins:",
+                  min = 1,
+                  max = 50,
+                  value = 30)
+
+    ),
+
+    # Main panel for displaying outputs ----
+    mainPanel(
+
+      # Output: Histogram ----
+      plotOutput(outputId = "distPlot")
+
+    )
+  )
+)
+
+# Define server logic required to draw a histogram ----
+server <- function(input, output) {
+
+  # Histogram of the Old Faithful Geyser Data ----
+  # with requested number of bins
+  # This expression that generates a histogram is wrapped in a call
+  # to renderPlot to indicate that:
+  #
+  # 1. It is "reactive" and therefore should be automatically
+  #    re-executed when inputs (input$bins) change
+  # 2. Its output type is a plot
+  output$distPlot <- renderPlot({
+
+    x    <- faithful$waiting
+    bins <- seq(min(x), max(x), length.out = input$bins + 1)
+
+    hist(x, breaks = bins, col = "#75AADB", border = "white",
+         xlab = "Waiting time to next eruption (in mins)",
+         main = "Histogram of waiting times")
+
+    })
+
+}
+
+# Create Shiny app ----
+shinyApp(ui = ui, server = server)