redis_connection {redux}

Create a Redis connection

Description

Create a Redis connection. This function is designed to be used in other packages, and not directly by end-users. However, it is possible and safe to use. See the hiredis package for the user friendly interface.

Usage

redis_connection(config = redis_config())

Arguments

config

Configuration parameters as generated by redis_config

Details

This function creates a list of functions, appropriately bound to a pointer to a Redis connection. This is designed for package authors to use so without having to ever deal with the actual pointer itself (which cannot be directly manipulated from R anyway).

The returned list has elements, all of which are functions:

config()

The configuration information

reconnect()

Attempt reconnection of a connection that has been closed, through serialisation/deserialisation or through loss of internet connection.

command(cmd)

Run a Redis command. The format of this command will be documented elsewhere.

pipeline(cmds)

Run a pipeline of Redis commands.

subscribe(channel, pattern, callback, envir)

Subscribe to a channel or pattern specifying channels. Here, channel must be a character vector, pattern a logical indicating if channel should be interpreted as a pattern, callback is a function to apply to each received message, returning TRUE when subscription should stop, and envir is the environment in which to evaluate callback. See below.

Subscriptions

The callback function must take a single argument; this will be the received message with named elements type (which will be message), channel (the name of the channel) and value (the message contents). If pattern was TRUE, then an additional element pattern will be present (see the Redis docs). The callback must return TRUE or FALSE; this indicates if the client should continue quit (i.e., TRUE means return control to R, FALSE means keep going).

Because the subscribe function is blocking and returns nothing, so all data collection needs to happen as a side-effect of the callback function.

There is currently no way of interrupting the client while it is waiting for a message.