What causes "Invalid JSON body" in decolua/9router?

Validate the request body with JSON.parse before sending, or rely on your client's JSON serializer (fetch with JSON.stringify, axios default).

decolua/9router · error

Invalid JSON body

Error message

Invalid JSON body

What it means

The chat endpoint (/v1/chat/completions) could not parse the request body as JSON. handleChat calls request.json() inside a try/catch; any parse failure (SyntaxError) is converted into a 400 response with this message. The gateway requires a well-formed JSON body in one of the supported formats (OpenAI, Claude, Gemini, Responses).

Source

Thrown at src/sse/handlers/chat.js:37

import { augmentModelsWithCapacityAdapter, withCapacityAdapterStripping, getActiveAdapterStrategy } from "open-sse/services/capacityAdapter.js";
import { handleBypassRequest } from "open-sse/utils/bypassHandler.js";
import { HTTP_STATUS } from "open-sse/config/runtimeConfig.js";
import { detectFormatByEndpoint } from "open-sse/translator/formats.js";
import * as log from "../utils/logger.js";
import { updateProviderCredentials, checkAndRefreshToken } from "../services/tokenRefresh.js";
import { getProjectIdForConnection } from "open-sse/services/projectId.js";

/**
 * Handle chat completion request
 * Supports: OpenAI, Claude, Gemini, OpenAI Responses API formats
 * Format detection and translation handled by translator
 */
export async function handleChat(request, clientRawRequest = null) {
  let body;
  try {
    body = await request.json();
  } catch {
    log.warn("CHAT", "Invalid JSON body");
    return errorResponse(HTTP_STATUS.BAD_REQUEST, "Invalid JSON body");
  }

  // Build clientRawRequest for logging (if not provided)
  if (!clientRawRequest) {
    const url = new URL(request.url);
    clientRawRequest = {
      endpoint: url.pathname,
      body,
      headers: Object.fromEntries(request.headers.entries())
    };
  }
  const modelStr = body.model;

  // Request summary is emitted as the unified "▶" line in chatCore (has fmt/thinking/account)

  // Log API key (masked)
  const authHeader = request.headers.get("Authorization");

View on GitHub (pinned to 90b52e06ff)

Solutions

Validate the request body with JSON.parse before sending, or rely on your client's JSON serializer (fetch with JSON.stringify, axios default).
Set Content-Type: application/json and ensure the client actually serializes the object instead of passing a raw string incorrectly.
If using curl, wrap the -d payload in single quotes and check for shell quoting issues; print the exact bytes being sent.
Check for proxies/middleware that may truncate or re-encode the body between client and the 9Router gateway.

Example fix

// before
await fetch(url, { method: 'POST', body: payload }); // payload is an object, sent as '[object Object]'

// after
await fetch(url, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify(payload)
});

Defensive patterns

Strategy: validation

Validate before calling

const payload = JSON.stringify(body);
JSON.parse(payload); // throws before the request if body is not serializable/valid JSON
if (!body || typeof body !== 'object') throw new TypeError('chat body must be an object');

Type guard

function isValidJsonBody(text) {
  try { const v = JSON.parse(text); return v !== null && typeof v === 'object'; }
  catch { return false; }
}

Try / catch

const res = await fetch(url, opts);
if (res.status === 400) {
  const err = await res.json();
  if (err?.error?.message === 'Invalid JSON body') {
    console.error('Payload was not valid JSON:', opts.body);
  }
}

Prevention

Always serialize with JSON.stringify and set Content-Type: application/json.
Round-trip JSON.parse(JSON.stringify(payload)) in tests for hand-built payloads.
Beware shell quoting when using curl with inline JSON.
Check proxies/middleware for body truncation or re-encoding.

When it happens

Trigger: POST to /v1/chat/completions where the raw body is not valid JSON: empty body, trailing garbage, truncated body, or a body with invalid JSON syntax such as unquoted keys, single quotes, or an unclosed brace.

Common situations: Sending the body without a JSON Content-Type while the client serializes incorrectly; curl commands where quotes get mangled by the shell; proxy/intermediary truncating large request bodies; a script posting FormData or plain text instead of JSON; SDK misconfiguration pointing at the gateway with a text payload.

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

AI-assisted analysis of decolua/9router@90b52e06ff (2026-08-30). Data as JSON: /api/errors/9589c8692fd4f675. Report an issue: GitHub.