WebSocket Module

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This XQuery Module contains functions for accessing specific WebSocket functions. This module is mainly useful in the context of WebSockets.

Conventions[edit]

  • The module will be available if the basex-api library is found in the classpath. This is the case if you use one of the complete distributions of BaseX (zip, exe, war).
  • All functions and errors are assigned to the http://basex.org/modules/ws namespace, which is statically bound to the ws prefix.
  • As sessions are side-effecting operations, all functions are flagged as non-deterministic. As a result, some query optimizations will be suppressed.

General Functions[edit]

ws:id[edit]

Signatures ws:id() as xs:string
Summary Returns the ID of the current WebSocket.
Errors not-found: No WebSocket with the specified id exists.

ws:ids[edit]

Signatures ws:ids() as xs:string*
Summary Returns the ids of all currently registered WebSockets.

ws:path[edit]

Signatures ws:path($id as xs:string) as xs:string
Summary Returns the path of the WebSocket with the specified $id.
Errors not-found: No WebSocket with the specified id exists.

ws:close[edit]

Signatures ws:close($id as xs:string) as empty-sequence()
Summary Closes the connection of the WebSocket with the specified $id.
Errors not-found: No WebSocket with the specified id exists.

Sending Data[edit]

ws:send[edit]

Signatures ws:send($message as item(), $ids as xs:string*) as empty-sequence()
Summary Sends a $message to the clients with the specified $ids. Ids that cannot be assigned to clients will be ignored. The message will be handled as follows:
  • Items of type xs:base64Binary and xs:hexBinary will be transmitted as binary messages.
  • Function items (maps, arrays) will be serialized as JSON and transmitted as string messages.
  • All other items will be serialized with the default serialization options and transmitted as string messages.

ws:broadcast[edit]

Signatures ws:broadcast($message as xs:anyAtomicType) as empty-sequence()
Summary Broadcasts a $message to all connected clients except to the caller. Invocations of this convenience function are equivalent to ws:send($message, ws:ids()[. != ws:id()]). See ws:send for more details on the message handling.

ws:emit[edit]

Signatures ws:emit($message as xs:anyAtomicType) as empty-sequence()
Summary Emits a $message to all connected clients. Invocations of this function are equivalent to ws:send($message, ws:ids()). See ws:send for more details on the message handling.

ws:eval[edit]

Signatures ws:eval($query as xs:anyAtomicItem) as xs:string
ws:eval($query as xs:anyAtomicItem, $bindings as map(*)?) as xs:string
ws:eval($query as xs:anyAtomicItem, $bindings as map(*)?, $options as map(*)?) as xs:string
Summary Schedules the evaluation of the supplied $query and returns the result to the calling WebSocket client. The query can be a URI or a string, and variables and context items can be declared via $bindings (see xquery:eval for more details). The following $options can be supplied:
  • base-uri: sets the base-uri property for the query. This URI will be used when resolving relative URIs, such as with fn:doc.
  • id: sets a custom job id. The id must not start with the standard job prefix, and it can only be assigned if no job with the same name exists.

Query scheduling is recommendable if the immediate query execution might be too time consuming and lead to a timeout.

Errors overflow: Query execution is rejected, because too many jobs are queued or being executed.
id: The specified id is invalid or has already been assigned.
Examples
  • Schedule a second query that will notify the client 10 seconds later that a message was processed:
declare
  %ws:message('/tasks', '{$message}')
function local:message($message) {
  ws:eval('prof:sleep(10000), "Your message has been processed."')
};

WebSocket Attributes[edit]

ws:get[edit]

Signatures ws:get($id as xs:string, $name as xs:string) as item()*
ws:get($id as xs:string, $name as xs:string, $default as item()*) as item()*
Summary Returns the value of an attribute with the specified $name from the WebSocket with the specified $id. If the attribute is unknown, an empty sequence or the optionally specified $default value will be returned instead.
Errors not-found: No WebSocket with the specified id exists.

ws:set[edit]

Signatures ws:set($id as xs:string, $name as xs:string, $value as item()*) as empty-sequence()
Summary Returns the specified value of the attribute with the specified $name from the WebSocket with the specified $id.
Errors not-found: No WebSocket with the specified id exists.
set: The supplied value cannot be materialized.

ws:delete[edit]

Signatures ws:delete($id as xs:string, $name as xs:string) as empty-sequence()
Summary Deletes an attribute with the specified $name from the WebSocket with the specified $id.
Errors not-found: No WebSocket with the specified id exists.

Examples[edit]

Example 1[edit]

import module namespace ws = "http://basex.org/modules/ws";

declare
  %ws:connect('/')
function local:connect() as empty-sequence() {
  let $id := ws:id()
  let $message := json:serialize(map {
    'type': 'Connect',
    'id': $id
  })
  return ws:broadcast($message)
};

Explanation:

  • The function has a %ws:connect annotation. It gets called if a client successfully creates a WebSocket connection to the path / (check out WebSockets for further information).
  • A JSON response is generated, which contains the new client id and a Connect string.
  • This response will be sent to all other connected clients.

Example 2[edit]

import module namespace ws = "http://basex.org/modules/ws";

declare
  %ws:message('/', '{$message}')
function local:message(
  $message as xs:string
) as empty-sequence() {
  let $message := json:serialize(map { 'message': $message })
  return ws:emit($message)
};

Explanation:

  • The function has a %ws:message annotation. It gets called if a client sends a new message.
  • A JSON response is generated, which contains the message string.
  • This response will be sent to all connected clients (including the calling client).

Errors[edit]

Code Description
set The supplied value cannot be materialized.
not-found No WebSocket with the specified id exists.

Changelog[edit]

Version 9.2

This module was introduced with Version 9.1.