IRC: Chop messages longer than 400 characters

The IRC protocol doesn't permit messages longer than 512 bytes
(https://news.ycombinator.com/item?id=7991049). This includes server,
channel, hostname, etc. information that's also included in the message.

In order to be able to send longer messages, chop them at 400 characters
(https://wholok.com/irc/), which seems like a "reasonable" hard-coded
value.

We already split our messages at newlines, so we need to effectuate a
double split here. First we split at 400 characters because we might
have a line that runs longer than that before encountering a newline. To
do this, we use the `chunksOf` function
(https://wiki.haskell.org/Data.List.Split).

Then, when splitting on newlines, we take the list produced by splitting
at 400 characters, and must split the elements inside that list. This
creates a two-dimensional array. In order to flatten the array, we use
the `concat` function
(https://stackoverflow.com/questions/5994051/is-there-a-function-to-flatten-a-nested-list-of-elements).

1 files changed, 7 insertions, 1 deletions

diff --git a/src/IRC.hs b/src/IRC.hs
index 259772c..1c6a7f5 100644
--- a/src/IRC.hs
+++ b/src/IRC.hs
@@ -66,4 +66,10 @@ privmsgFromPlugin message = do
                 Right r  -> Just $
                     map (\r ->
                             IRC.send $ IRC.Privmsg (channel message) (Right r) )
-                        (T.lines r)
+                        (splitAtNewlines $ splitLongLines r)
+  where
+    -- IRC only permits 512 bytes per line. Use less to allow for protocol
+    -- information that gets sent in addition to the message content.
+    splitLongLines txt = T.chunksOf 400 txt
+
+    splitAtNewlines lst = foldr (\s acc -> (T.lines s) ++ acc) [] lst