fix: use UTF-16 length for Telegram stream consumer message splitting#11170
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freemanconsulting wants to merge 1 commit into
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fix: use UTF-16 length for Telegram stream consumer message splitting#11170freemanconsulting wants to merge 1 commit into
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The stream consumer measured message length using Python's len() (Unicode code points), but Telegram's actual limit is in UTF-16 code units. This caused messages with supplementary characters (emoji, CJK, etc.) to exceed Telegram's 4096-character limit, resulting in truncated messages with formatting artifacts. Changes: - Add message_len_fn property to BasePlatformAdapter (defaults to len) - Override in TelegramAdapter to return utf16_len - Stream consumer uses adapter.message_len_fn for: - safe_limit calculation - overflow detection - truncate_message calls - split point calculation (via _custom_unit_to_cp) - fallback final send chunking Fixes truncated messages with black square artifacts on Telegram when the model generates responses containing multi-byte Unicode characters.
teknium1
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May 10, 2026
New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
Contributor
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Merged via salvage PR #23455 (#23455). Your commit was cherry-picked onto current main with your authorship preserved. During conflict resolution we cleaned up the duplicated try/except+delayed-import dance into a single module-level import + isinstance ternary, dropped the 'if _len_fn is not len' micro-opt guards around _custom_unit_to_cp (the helper short-circuits internally), added an inline comment at the buffer_threshold trigger noting it's intentionally codepoint-based (debounce heuristic, not a platform-limit check), and added two regression tests for the UTF-16 path. Thanks for catching this! |
JZKK720
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May 11, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
rmulligan
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May 11, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
JinyuID
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May 11, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
02356abc
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May 14, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
jsboige
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May 14, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
AlexFoxD
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May 21, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
gweeteve
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Jun 2, 2026
…esearch#11170 New TestUtf16OverflowDetection class covers two scenarios: - test_emoji_text_exceeding_utf16_limit_triggers_overflow_split: feeds 2200 emoji codepoints (4400 UTF-16 units) — under Telegram's codepoint-equivalent limit but over its UTF-16 limit. Asserts truncate_message was called with len_fn=utf16_len, confirming the consumer detected the overflow. - test_codepoint_only_adapter_falls_back_to_len: documents that adapters which don't subclass BasePlatformAdapter (or test MagicMocks) fall back to plain len for backwards compat. The contributor's PR shipped no tests for the UTF-16 path.
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Problem
The stream consumer measured message length using Python's
len()(Unicode code points), but Telegram's actual limit is in UTF-16 code units. This caused messages with supplementary characters (emoji, CJK text, etc.) to exceed Telegram's 4096-character limit, resulting in:editMessageTextcalls that silently fell back to plain textThe
send()method inTelegramAdapteralready correctly usedutf16_lenfortruncate_message, but the streaming path inGatewayStreamConsumerdid not.Solution
Three changes designed for easy adoption by any platform adapter:
BasePlatformAdapter.message_len_fn— new property that returnslenby default. Platforms that measure differently (like Telegram) override this.TelegramAdapter.message_len_fn— returnsutf16_lenso all downstream consumers get correct lengths automatically.GatewayStreamConsumer— usesadapter.message_len_fninstead of barelenfor:_safe_limitcalculationtruncate_messagecalls (passeslen_fn)_custom_unit_to_cp)Testing
message_len_fngetlenbehavior