How to send a WebSocket message from an httpuv server in R without using message callback?

Question

I have set up a simple httpuv WebSocket server which can receive messages from a WebSocket client and echo them back upon receipt.

For example:

library(httpuv)

s <- startServer("0.0.0.0", 8080, 
                 list(
                   onWSOpen = function(ws) {
                     ws$onMessage(function(binary, message) {
                       ws$send(message)
                     })
                   })
)

Is it possible to send messages to that WebSocket client outside of the ws$onMessage callback?

As an example of how I'd imagine the syntax to be structured, I'd like to be able to call: s$ws$send("Hello") and have Hello be sent to the client, without requiring a client message/use of any callback function.

score 0 · Accepted Answer · answered Nov 17 '22 at 02:58

To answer my own question, I have since discovered this is possible using the super assignment operator in R:

library(httpuv)

w <- NULL
s <- startServer("0.0.0.0", 8080, 
                 list(
                   onWSOpen = function(ws) {
                     w <<- ws  # Now, the WebSocket object persists in the global environment

                     ws$onMessage(function(binary, message) {
                       ws$send(message)
                     })
                   })
)

# Wait for client to connect...

w$send("Hello")  # Send message to the client

How to send a WebSocket message from an httpuv server in R without using message callback?

1 Answers1