The bot handles every content message. It searches the message's text entities for the first plain URL or text-link entity. When one is found, it sends the same text and entities to the same chat seven times:

with link previews disabled;
with a large preview above the text;
with a large preview below the text;
with a small preview above the text;
with a small preview below the text;
with Telegram's default preview size above the text;
with Telegram's default preview size below the text.

The detected URL is selected explicitly for each enabled preview. If the content is not text-bearing or contains no URL entity, the bot replies that only content with a URL is supported. It defines and registers no commands.

Setup and permissions

Create a bot, obtain its token, and keep the token private.
Start a private chat with it, or add it to a chat where previews should be tested.
Ensure Telegram delivers the relevant content messages and the bot may send messages in that chat.

The example uses no administrator-only methods and does not configure a webhook.

Run

From the repository root:

./gradlew :LinkPreviewsBot:run --args="BOT_TOKEN"

The first argument is the required bot token. The optional, case-sensitive second argument debug enables formatted library logging on standard output. Arguments after the second are ignored.

./gradlew :LinkPreviewsBot:run --args="BOT_TOKEN debug"