sgl-project/sglang · error · NotImplementedError

structure_info not used for JSON schema constraints

Error message

structure_info not used for JSON schema constraints

What it means

Raised by JsonArrayParser.structure_info() because JSON-array function-call parsers do not provide a StructureInfo factory; JSON-schema constraints are handled directly by the constraint backends (e.g. xgrammar/outlines) instead. Calling this method on this parser subclass is a programming error, not a runtime data problem.

Source

Thrown at python/sglang/srt/function_call/json_array_parser.py:51

        raise NotImplementedError(
            "Detect and parse not supported for JSON schema constraints."
        )

    def parse_streaming_increment(
        self, new_text: str, tools: List[Tool]
    ) -> StreamingParseResult:
        """
        Streaming incremental parsing with tool validation.
        """
        return super().parse_streaming_increment(new_text, tools)

    def structure_info(self) -> callable:
        """
        Return a function that creates StructureInfo for constrained generation.
        This is not used for JSON schema constraints as they are handled
        by the constraint backends directly.
        """
        raise NotImplementedError("structure_info not used for JSON schema constraints")

View on GitHub (pinned to 0132848349)

Solutions

1. Guard the call with hasattr(parser, 'structure_info') or check parser type before calling
2. Use a parser that implements structure_info (e.g. a structural-tag-based detector) if constrained-generation StructureInfo is required
3. Refactor the call site to only invoke structure_info on parsers that declare it

Example fix

// before
info = parser.structure_info()
// after
if not isinstance(parser, JsonArrayParser):
    info = parser.structure_info()

def has_structure_info(p) -> bool:
    return hasattr(p, "structure_info") and not isinstance(p, JsonArrayParser)

When it happens

Trigger: Calling .structure_info() on a JsonArrayParser instance (or any code path that assumes every FunctionCallParser implements structure_info) while using the JSON array tool-call format.

Common situations: New code that iterates over tool parsers and unconditionally calls structure_info(); switching a server to the json_array parser type while retaining logic written for chat-template/structural-tag parsers like KimiK3.

Related errors

• Kimi K3 uses its model-native structural tag implementation
• /v1/models ${response.status}
• Unsupported msgpack byte ${b}
• This browser does not support gzip stream decoding
• {self._op_label()}: no triton backend

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/f82c79e346123b3f. Report an issue: GitHub.