Session object — session

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".