session {shiny} | R Documentation

## Session object

### Description

Shiny server functions can optionally include `session` as a parameter (e.g. `function(input, output, session)`). The session object is an environment that can be used to access information and functionality relating to the session. The following list describes the items available in the environment; they can be accessed using the `$` operator (for example, `session$clientData$url_search`).

### Value

`allowReconnect(value)`

If `value` is `TRUE` and run in a hosting environment (Shiny Server or Connect) with reconnections enabled, then when the session ends due to the network connection closing, the client will attempt to reconnect to the server. If a reconnection is successful, the browser will send all the current input values to the new session on the server, and the server will recalculate any outputs and send them back to the client. If `value` is `FALSE`, reconnections will be disabled (this is the default state). If `"force"`, then the client browser will always attempt to reconnect. The only reason to use `"force"` is for testing on a local connection (without Shiny Server or Connect).

`clientData`

A `reactiveValues` object that contains information about the client.

- `allowDataUriScheme` is a logical value that indicates whether the browser is able to handle URIs that use the `data:` scheme.

- `pixelratio` reports the "device pixel ratio" from the web browser, or 1 if none is reported. The value is 2 for Apple Retina displays.

- `singletons` - for internal use

- `url_protocol`, `url_hostname`, `url_port`, `url_pathname`, `url_search`, `url_hash_initial` and `url_hash` can be used to get the components of the URL that was requested by the browser to load the Shiny app page. These values are from the browser's perspective, so neither HTTP proxies nor Shiny Server will affect these values. The `url_search` value may be used with `parseQueryString` to access query string parameters.

`clientData` also contains information about each output. `output_outputId_width` and `output_outputId_height` give the dimensions (using `offsetWidth` and `offsetHeight`) of the DOM element that is bound to `outputId`, and `output_outputId_hidden` is a logical that indicates whether the element is hidden. These values may be `NULL` if the output is not bound.

`input` | The session's `input` object (the same as is passed into the Shiny server function as an argument).
`isClosed()` | A function that returns `TRUE` if the client has disconnected.
`ns(id)` | Server-side version of `ns <- NS(id)`. If bare IDs need to be explicitly namespaced for the current module, `session$ns("name")` will return the fully-qualified ID.
`onEnded(callback)` | Synonym for `onSessionEnded`.
`onFlush(func, once=TRUE)` | Registers a function to be called before the next time (if `once=TRUE`) or every time (if `once=FALSE`) Shiny flushes the reactive system. Returns a function that can be called with no arguments to cancel the registration.
`onFlushed(func, once=TRUE)` | Registers a function to be called after the next time (if `once=TRUE`) or every time (if `once=FALSE`) Shiny flushes the reactive system. Returns a function that can be called with no arguments to cancel the registration.
`onSessionEnded(callback)` | Registers a function to be called after the client has disconnected. Returns a function that can be called with no arguments to cancel the registration.
`output` | The session's `output` object (the same as is passed into the Shiny server function as an argument).
`reactlog` | For internal use.

`registerDataObj(name, data, filterFunc)`

Publishes any R object as a URL endpoint that is unique to this session. `name` must be a single element character vector; it will be used to form part of the URL. `filterFunc` must be a function that takes two arguments: `data` (the value that was passed into `registerDataObj`) and `req` (an environment that implements the Rook specification for HTTP requests). `filterFunc` will be called with these values whenever an HTTP request is made to the URL endpoint. The return value of `filterFunc` should be a Rook-style response.

`reload()` | The equivalent of hitting the browser's Reload button. Only works if the session is actually connected.
`request` | An environment that implements the Rook specification for HTTP requests. This is the request that was used to initiate the websocket connection (as opposed to the request that downloaded the web page for the app).
`userData` | An environment for app authors and module/package authors to store whatever session-specific data they want.
`resetBrush(brushId)` | Resets/clears the brush with the given `brushId`, if it exists on any `imageOutput` or `plotOutput` in the app.

`sendCustomMessage(type, message)`

Sends a custom message to the web page. `type` must be a single-element character vector giving the type of message, while `message` can be any jsonlite-encodable value. Custom messages have no meaning to Shiny itself; they are used soley to convey information to custom JavaScript logic in the browser. You can do this by adding JavaScript code to the browser that calls `Shiny.addCustomMessageHandler(type, function(message){...})` as the page loads; the function you provide to `addCustomMessageHandler` will be invoked each time `sendCustomMessage` is called on the server.

`sendBinaryMessage(type, message)` | Similar to `sendCustomMessage`, but the message must be a raw vector and the registration method on the client is `Shiny.addBinaryMessageHandler(type, function(message){...})`. The message argument on the client will be a DataView.

`sendInputMessage(inputId, message)`

Sends a message to an input on the session's client web page; if the input is present and bound on the page at the time the message is received, then the input binding object's `receiveMessage(el, message)` method will be called. `sendInputMessage` should generally not be called directly from Shiny apps, but through friendlier wrapper functions like `updateTextInput`.

`setBookmarkExclude(names)` | Set input names to be excluded from bookmarking.
`getBookmarkExclude()` | Returns the set of input names to be excluded from bookmarking.
`onBookmark(fun)` | Registers a function that will be called just before bookmarking state.
`onBookmarked(fun)` | Registers a function that will be called just after bookmarking state.
`onRestore(fun)` | Registers a function that will be called when a session is restored, before all other reactives, observers, and render functions are run.
`onRestored(fun)` | Registers a function that will be called when a session is restored, after all other reactives, observers, and render functions are run.
`doBookmark()` | Do bookmarking and invoke the onBookmark and onBookmarked callback functions.
`exportTestValues()` | Registers expressions for export in test mode, available at the test snapshot URL.

`getTestSnapshotUrl(input=TRUE, output=TRUE, export=TRUE, format="json")`

Returns a URL for the test snapshots. Only has an effect when the `shiny.testmode` option is set to TRUE. For the input, output, and export arguments, TRUE means to return all of these values. It is also possible to specify by name which values to return by providing a character vector, as in `input=c("x", "y")`. The format can be "rds" or "json".

[Package shiny version 1.0.5 Index]