ChatAvatarSetter

This Kotlin/JVM example changes a chat's avatar to the photo sent in that chat. It receives updates by long polling and demonstrates the Telegram Bot API setChatPhoto method with a multipart file upload.

Behavior

There is no command: every photo message received by the bot is a trigger.
The bot downloads the photo, uploads it as sample.jpg, and uses it as the avatar of the same chat.
After a successful update, it replies Done. If setChatPhoto fails, it logs the exception and replies Something went wrong (see logs).
Non-photo messages are ignored. In particular, an image sent as a document is not a photo message.

The implementation does not restrict who may trigger it. In a group or supergroup, any member whose photo message reaches the bot can cause an avatar-change attempt.

Telegram setup and permissions

Create a bot with @BotFather and obtain its token.
Add the bot to the group, supergroup, or channel whose avatar it should manage.
Promote the bot to administrator and grant it the Change chat info permission (can_change_info). It must also be able to send messages in a group or posts in a channel to deliver its status reply.
Send a photo directly in that chat.

Telegram does not allow setChatPhoto to change private-chat photos. The target chat is always taken from the incoming photo message, so a photo sent to the bot privately cannot be used to update another chat.

Arguments

Position	Argument	Required	Description
1	`BOT_TOKEN`	Yes	Bot API token issued by BotFather.

Launch

From the repository root, run:

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

The process continues polling until it is stopped.