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Split long Telegram responses into multiple messages #71

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39 changes: 39 additions & 0 deletions plugins/telegram/src/main/java/ai/javaclaw/channels/telegram/TelegramChannel.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
import org.commonmark.parser.Parser;
import org.commonmark.renderer.html.HtmlRenderer;

import java.util.ArrayList;
import java.util.List;

import static java.util.Optional.ofNullable;
Expand All @@ -29,6 +30,8 @@ public class TelegramChannel implements Channel, SpringLongPollingBot, LongPolli

private static final Logger LOGGER = LoggerFactory.getLogger(TelegramChannel.class);

private static final int MAX_MESSAGE_LENGTH = 4000;

private static final Parser MARKDOWN_PARSER = Parser.builder().build();
private static final HtmlRenderer HTML_RENDERER = HtmlRenderer.builder()
.escapeHtml(true)
Expand Down Expand Up @@ -96,6 +99,12 @@ public void sendMessage(String message) {
}

public void sendMessage(long chatId, Integer messageThreadId, String message) {
for (String chunk : splitMessage(message, MAX_MESSAGE_LENGTH)) {

@arefbehboudi arefbehboudi Jul 18, 2026

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Splitting happens on raw markdown, but chunks are HTML-converted after escaping (< → <) and tags (** → ) make the rendered text longer, so a 4000-char chunk can still exceed 4096 and get rejected. Either measure rendered length when chunking

sendSingleMessage(chatId, messageThreadId, chunk);
}
}

private void sendSingleMessage(long chatId, Integer messageThreadId, String message) {
String formattedHtmlMessage = convertMarkdownToTelegramHtml(message);

SendMessage htmlMessage = SendMessage.builder()
Expand Down Expand Up @@ -124,6 +133,36 @@ public void sendMessage(long chatId, Integer messageThreadId, String message) {
}
}

private List<String> splitMessage(String message, int maxLength) {
if (message == null || message.length() <= maxLength) return List.of(message == null ? "" : message);

List<String> chunks = new ArrayList<>();
StringBuilder current = new StringBuilder();

for (String line : message.split("\n", -1)) {
while (line.length() > maxLength) {
flush(chunks, current);
chunks.add(line.substring(0, maxLength));

@arefbehboudi arefbehboudi Jul 18, 2026

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This can split a surrogate pair (emoji) → invalid string, Telegram rejects it. Check Character.isHighSurrogate(line.charAt(maxLength - 1)) and back off by one.

line = line.substring(maxLength);
}
if (!current.isEmpty() && current.length() + 1 + line.length() > maxLength) {
flush(chunks, current);
}
if (!current.isEmpty()) current.append('\n');
current.append(line);
}
flush(chunks, current);

return chunks;
}

private void flush(List<String> chunks, StringBuilder current) {
if (!current.isEmpty()) {
chunks.add(current.toString());
current.setLength(0);
}
}

private String convertMarkdownToTelegramHtml(String markdown) {
if (markdown == null || markdown.isBlank()) return "";

Expand Down
51 changes: 51 additions & 0 deletions plugins/telegram/src/test/java/ai/javaclaw/channels/telegram/TelegramChannelTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
import ai.javaclaw.channels.ChannelRegistry;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.ArgumentCaptor;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.telegram.telegrambots.meta.api.methods.ParseMode;
Expand All @@ -14,11 +15,18 @@
import org.telegram.telegrambots.meta.exceptions.TelegramApiException;
import org.telegram.telegrambots.meta.generics.TelegramClient;

import java.util.List;
import java.util.stream.Collectors;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.mockito.ArgumentMatchers.anyString;
import static org.mockito.ArgumentMatchers.argThat;
import static org.mockito.ArgumentMatchers.eq;
import static org.mockito.Mockito.atLeastOnce;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.never;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyNoInteractions;
import static org.mockito.Mockito.when;
Expand Down Expand Up @@ -229,6 +237,49 @@ void sendMessageFallbacksToSendingRawTextWhenFailingToSendHtml() throws Telegram
));
}

// -----------------------------------------------------------------------
// Long message splitting
// -----------------------------------------------------------------------

@Test
void splitsResponsesLongerThanTelegramLimitIntoMultipleMessages() throws TelegramApiException {
TelegramChannel channel = channel("allowed_user");
String paragraph = "word ".repeat(900); // ~4500 chars, exceeds the 4000-char chunk limit
String longResponse = paragraph + "\n\n" + paragraph;
when(agent.respondTo(anyString(), anyString())).thenReturn(longResponse);

channel.consume(updateFrom("allowed_user", "hello", 42L, null));

ArgumentCaptor<SendMessage> captor = ArgumentCaptor.forClass(SendMessage.class);
verify(telegramClient, atLeastOnce()).execute(captor.capture());

List<SendMessage> sentMessages = captor.getAllValues();
assertTrue(sentMessages.size() > 1, "expected the response to be split into multiple messages");
for (SendMessage msg : sentMessages) {
assertEquals("42", msg.getChatId());
assertTrue(msg.getText().length() <= 4000, "chunk exceeds Telegram's message size limit");
}

String reconstructed = sentMessages.stream()
.map(SendMessage::getText)
.collect(Collectors.joining(" "))
.replaceAll("\\s+", " ")
.trim();
String normalizedOriginal = longResponse.replaceAll("\\s+", " ").trim();
assertEquals(normalizedOriginal, reconstructed);
}

@Test
void doesNotSplitResponsesWithinTelegramLimit() throws TelegramApiException {
TelegramChannel channel = channel("allowed_user");
when(agent.respondTo(anyString(), anyString())).thenReturn("a short response");

channel.consume(updateFrom("allowed_user", "hello", 42L, null));

verify(telegramClient, times(1)).execute(argThat((SendMessage msg) ->
"42".equals(msg.getChatId())));
}

// -----------------------------------------------------------------------
// helpers
// -----------------------------------------------------------------------
Expand Down