nrepl-server

Proof of concept nREPL server for something that may end up in babashka. Mostly a port of ogion.

Run

$ clojure -m borkdude.nrepl-server
Starting on port 1667

Connect with your favorite nREPL client:

$ rep -p 1667 '(+ 1 2 3)'
6

Reverse engineering the nREPL protocol

When developing the server, it's useful to inspect messages that are sent back and forth between existing implementations.

E.g., start a lein nREPL server:

$ lein repl
nREPL server started on port 56132 on host 127.0.0.1 - nrepl://127.0.0.1:56132

From CIDER connect with cider-connect and watch the *nrepl-messages* buffer. See the CIDER docs.

With Calva:

And connect to it with the development version of Calva.

To inspect messages, we're going to add some logging to src/nrepl/index.ts:

write(data: any) {
    console.log("write ->", data);
    ...
}

_response(data: any) {
    console.log("response ->", data);
    ...
}

Build Calva (npm install + run build task in VSCode) and run the extension in debug mode (Run > Start Debugging).

Via the command palette, select Calva: connect to a running REPL server outside project.

Behold:

write ->
Object
op
"clone"
session
"2699f4ad-b917-4224-a879-a5bfc8273a57"
id
"4"
response ->
Object
id
"4"
new-session
"310e3c0b-2607-4490-ad14-b1a04cb614d9"
session
"2699f4ad-b917-4224-a879-a5bfc8273a57"
status
Array[1]
0
"done"
write ->
Object
op
"eval"
session
"310e3c0b-2607-4490-ad14-b1a04cb614d9"
code
"(+ 1 1)"
id
"5"
pprint
false
response ->
Object
id
"5"
ns
"user"
session
"310e3c0b-2607-4490-ad14-b1a04cb614d9"
value
"2"
response ->
Object
id
"5"
session
"310e3c0b-2607-4490-ad14-b1a04cb614d9"
status
Array[1]
0
"done"

References

• nrepl-cljs
• ogion