ReactionsInfoBot

A long-polling example that handles Telegram's per-user reaction updates and anonymous reaction-count updates. It has no commands and does not respond to ordinary messages.

Behavior

When an identifiable user changes their reactions on a message, the bot:

temporarily adds a ✍ reaction to the original message;
sends that user a private message which externally replies to the reacted message;
lists the user's new reaction set, including ordinary emoji, rendered custom emoji with its custom-emoji ID, a generic label for paid reactions, and fallback information for unknown reaction types;
removes its temporary reaction after the private reply succeeds.

If the user removed all reactions, the private message contains only its heading. Updates where a chat is the reaction actor are not handled by this per-user trigger. Telegram also does not deliver reaction-change updates caused by bots, so the temporary ✍ reaction does not trigger this handler recursively.

For anonymous reaction-count updates, the bot fetches and prints the extended chat plus the raw count update to standard output. It does not send a Telegram message for those updates, which Telegram may deliver after a delay.

If adding ✍ is not allowed, the private-message step is not reached. If the private message fails, the final cleanup is not reached and the bot's temporary reaction can remain on the original message.

Telegram setup, permissions, and privacy

Create a bot with @BotFather and obtain its token.
Add the bot to each group, supergroup, or channel to watch and promote it to administrator. Telegram requires administrator status for both message_reaction and message_reaction_count updates; the long-polling setup explicitly requests these update types.
Enable reactions in the watched chat and allow the ✍ emoji so the bot can apply its temporary marker.
Each user who should receive reports must first open the bot's private chat and press Start. The bot has no /start response, but Telegram otherwise prevents it from initiating a private conversation. Reports also fail if the user blocks the bot.
BotFather privacy mode may remain enabled. It controls group-message delivery, not reaction updates.

The example uses long polling and automatically removes an existing webhook at startup. Run only one update consumer for the token at a time.

Arguments

The first argument is the required bot token. Debug logging is enabled only when the second argument is exactly debug; later occurrences are ignored.

Launch

From the repository root:

./gradlew :ReactionsInfoBot:run --args="<BOT_TOKEN>"

./gradlew :ReactionsInfoBot:run --args="<BOT_TOKEN> debug"