odysseus-dev/odysseus · error · HTTPException

Invalid JSON

Error message

Invalid JSON

What it means

POST /api/rewrite could not parse the request body as JSON; any exception from request.json() (not just JSONDecodeError) is converted to this 400. The rewrite endpoint expects a JSON body with session_id, original_text, and instruction.

Source

Thrown at routes/chat_routes.py:2487

                restrict_owner=_user is not None,
                include_legacy_owner=False,
            )
        ]

    # ------------------------------------------------------------------ #
    # POST /api/rewrite — lightweight rewrite of last AI message (no tools)
    # ------------------------------------------------------------------ #
    @router.post("/api/rewrite")
    async def rewrite_message(request: Request) -> StreamingResponse:
        """Rewrite the last AI message with an instruction (shorter/simpler/etc).

        Unlike the full chat pipeline, this does NOT run the agent loop or tools.
        It just asks the LLM to rewrite the given text.
        """
        try:
            body = await request.json()
        except Exception:
            raise HTTPException(400, "Invalid JSON")

        session_id = body.get("session_id")
        original_text = body.get("original_text", "")
        instruction = body.get("instruction", "")

        if not session_id or not original_text or not instruction:
            raise HTTPException(400, "session_id, original_text, and instruction are required")

        _verify_session_owner(request, session_id)

        try:
            sess = session_manager.get_session(session_id)
        except (KeyError, SessionNotFoundError):
            raise HTTPException(404, "Session not found")

        messages = [
            {"role": "system", "content": (
                "You are rewriting a previous response. Follow the instruction exactly. "

View on GitHub (pinned to f9235ebbf1)

Solutions

1. Send Content-Type: application/json with a valid JSON body
2. Use JSON.stringify({session_id, original_text, instruction}) in the client
3. Confirm no form-data/multipart wrapper is being applied by the HTTP layer

Example fix

// before
fetch('/api/rewrite', {method:'POST', body: `session_id=${id}&instruction=shorter`})
// after
fetch('/api/rewrite', {method:'POST', headers:{'Content-Type':'application/json'}, body: JSON.stringify({session_id: id, original_text: text, instruction: 'shorter'})})

const body = JSON.stringify({session_id, original_text, instruction});
JSON.parse(body); // sanity round-trip
await fetch('/api/rewrite', {method:'POST', headers:{'Content-Type':'application/json'}, body});

try { await rewrite(...); } catch (e) { if (e.status === 400 && e.message === 'Invalid JSON') { console.error('body serialization bug', lastPayload); } }

When it happens

Trigger: Sending the rewrite request without application/json content type so the body can't be parsed; malformed JSON; empty body; form-encoded data posted to a JSON-only endpoint.

Common situations: Client copy-pasted from the chat_stream form-based flow (which uses multipart form data) into this JSON endpoint; fetch without JSON.stringify; proxies stripping or mangling the body.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Invalid JSON: {e}
• session_id, original_text, and instruction are required
• Invalid JSON
• Expected a JSON object
• text is required

AI-assisted analysis of odysseus-dev/odysseus@f9235ebbf1 (2026-08-14). Data as JSON: /api/errors/2c4987f0eef2768b. Report an issue: GitHub.