Convert a snapshot to and from JSON text — snap

snap_serialize() writes a snapshot as JSON text in the canonical shinysnap format; snap_unserialize() reads it back. These are the in-memory counterparts of snap_write() and snap_read().

Usage

snap_serialize(
  x,
  format = "json",
  pretty = TRUE,
  unsupported = c("error", "rds"),
  verbose = FALSE
)

snap_unserialize(
  text,
  format = "json",
  trust = FALSE,
  unknown_types = c("error", "keep")
)

Arguments

x: A snapshot object, as returned by snap_take() or snap_unserialize(), or a list with (some of) a snapshot's fields, for example list(inputs = list(n = 5)).
format: The text format. Only "json" is available.
pretty: Pretty-print with two-space indentation (the default) or emit compact JSON on one line.
unsupported: What to do with values the JSON format cannot describe: "error" (the default) or "rds" to embed them as serialized R objects.
verbose: Print a message about what was converted or dropped.
text: JSON text: a single string or a character vector of lines.
trust: Decode embedded serialized R objects ("$type": "rds")? Only set this to TRUE for files from a source you trust.
unknown_types: What to do with a "$type" the reader does not know: "error" (the default) or "keep" to keep the raw parsed value.

Value

snap_serialize() returns a single string. snap_unserialize() returns a snapshot object of class shinysnap.

Details

The JSON format is designed to be read and edited by people: doubles are written with the fewest digits that read back to the same value, integers as plain digit runs, and everything JSON cannot express directly (the type of an empty vector, NA, Inf, names, dates, matrices, factors, data frames) as a small object with a "$type" key.

Values that the format cannot describe (environments, functions, S4 and R6 objects, unknown classes) are an error by default. With unsupported = "rds" they are embedded as base64 serialized R objects instead; because unserializing arbitrary data is unsafe, reading them back requires trust = TRUE, otherwise they decode to NULL with a warning.

Examples

text <- '{
  "format": 1,
  "app": {"name": "myapp", "version": "2.4.1"},
  "inputs": {
    "dates": {"$type": "Date", "value": ["2024-01-01", "2024-03-01"]},
    "method": "b",
    "n": 100,
    "rate": 0.025,
    "weights": [0.5, 0.75]
  }
}'
snap <- snap_unserialize(text)
snap
#> <shinysnap>
#>   app:         myapp (version 2.4.1)
#>   created:     <unset>
#>   inputs:      5 (dates, method, n, rate, weights)
#>   values:      0
#>   attachments: 0
str(snap_inputs(snap))
#> List of 5
#>  $ dates  : Date[1:2], format: "2024-01-01" "2024-03-01"
#>  $ method : chr "b"
#>  $ n      : int 100
#>  $ rate   : num 0.025
#>  $ weights: num [1:2] 0.5 0.75
cat(snap_serialize(snap))
#> {
#>   "format": 1,
#>   "app": {"name": "myapp", "version": "2.4.1"},
#>   "created": "2026-09-18T07:05:18Z",
#>   "producer": {"shinysnap": "0.1.0", "shiny": "1.14.0", "r": "4.6.1"},
#>   "inputs": {
#>     "dates": {"$type": "Date", "value": ["2024-01-01", "2024-03-01"]},
#>     "method": "b",
#>     "n": 100,
#>     "rate": 0.025,
#>     "weights": [0.5, 0.75]
#>   },
#>   "values": {},
#>   "bindings": {},
#>   "meta": {}
#> }