Write a snapshot to a file and read it back

snap_write() saves a snapshot; snap_read() loads one. The canonical format is JSON (see snap_serialize()): plain text, readable, diffable, and safe to open. The "zip" format is a bundle: a zip archive holding the same JSON as manifest.json plus the files of any fileInput() uploads (under attachments/) and, with unsupported = "rds", opaque R objects (under objects/); it needs the zip package. The "rds" format stores the R object with saveRDS(); it is neither readable nor safe across versions, and reading it requires trust = TRUE because unserializing a file runs arbitrary code paths.

Usage

snap_write(
  x,
  path,
  format = c("auto", "json", "zip", "rds"),
  pretty = TRUE,
  ...
)

snap_read(
  path,
  format = c("auto", "json", "zip", "rds"),
  trust = FALSE,
  unknown_types = c("error", "keep"),
  ...
)

Arguments

x

A snapshot object, or a list with (some of) a snapshot's fields (see snap_serialize()).

path

The file path.

format

"auto" picks the format from the extension (.json, .zip, or .rds); otherwise the format to use regardless of the extension.

pretty

Pretty-print JSON (the default) or write one compact line.

...

Passed on to snap_serialize() (unsupported, verbose).

trust

Decode embedded serialized R objects and allow the "rds" format? Only set this to TRUE for files from a source you trust.

unknown_types

What to do with a "$type" the reader does not know: "error" (the default) or "keep" to keep the raw parsed value.

Value

snap_write() returns path invisibly; snap_read() returns a snapshot object.

Details

Reading a bundle checks the archive for path traversal and caps its uncompressed size at getOption("shinysnap.max_bundle_bytes", 100 * 1024^2) bytes, then extracts it into a fresh temporary directory; snap_attachment() returns the local paths of the extracted uploads and bundled objects are decoded only with trust = TRUE.

Examples

snap <- snap_unserialize('{"format": 1, "inputs": {"n": 100, "rate": 0.025}}')
path <- tempfile(fileext = ".json")
snap_write(snap, path)
cat(readLines(path), sep = "\n")
#> {
#>   "format": 1,
#>   "app": {"name": null, "version": null},
#>   "created": "2026-09-18T07:05:19Z",
#>   "producer": {"shinysnap": "0.1.0", "shiny": "1.14.0", "r": "4.6.1"},
#>   "inputs": {"n": 100, "rate": 0.025},
#>   "values": {},
#>   "bindings": {},
#>   "meta": {}
#> }
identical(snap_inputs(snap_read(path)), snap_inputs(snap))
#> [1] TRUE