nodejs/node · error · HttpError

Unexpected json output: %s

Error message

Unexpected json output: %s

What it means

HttpJSONQuery expects Google pRPC-style endpoints, which prefix their JSON body with the XSSI-protection line `)]}'`. If the first line read is anything else, the server returned non-JSON (HTML error/login page, redirect, proxy interstitial) and the call is failed as HttpError 200 with the offending first line in the message.

Source

Thrown at deps/v8/tools/release/roll_bisect.py:85

  response, contents = conn.request(uri=uri, **params)
  contents = contents.decode("utf-8", "replace")
  return StringIO(contents)


def HttpJSONQuery(*args, **params):
  headers = params.setdefault("headers", {})
  headers.setdefault("Accept", "application/json")

  if "body" in params:
    assert (params.get("method", "GET") != "GET")
    if not isinstance(params["body"], str):
      params["body"] = json.dumps(params["body"])
      headers.setdefault("Content-Type", "application/json")

  fh = HttpQuery(*args, **params)
  s = fh.readline()
  if s and s.rstrip() != ")]}'":
    raise HttpError(200, "Unexpected json output: %s" % s)
  s = fh.read()
  if not s:
    return None
  return json.loads(s)


def QueryTryBotsForFailures(change, patchset, timeout=300):
  builds = HttpJSONQuery(
      "https://cr-buildbucket.appspot.com/prpc/buildbucket.v2.Builds/SearchBuilds",
      method="POST",
      body={
          "fields":
              "builds.*.builder,builds.*.id,builds.*.status,builds.*.startTime,builds.*.endTime",
          "predicate": {
              "tags": [{
                  "key": "cq_experimental",
                  "value": "false"
              }],

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Confirm the URL is the correct pRPC endpoint.
2. Re-authenticate / refresh credentials (gcert, luci-auth).
3. Inspect the actual response body (the %s in the message tells you what came back).
4. Rule out proxy/interstitial interference.

try:
    data = HttpJSONQuery(url, method='POST', body=body)
except HttpError as e:
    if e.status == 200 and 'Unexpected json output' in str(e):
        # likely an auth/login page or proxy interstitial
        log.error('endpoint did not return JSON; re-auth or check URL: %s', e)
    raise

When it happens

Trigger: Querying a buildbucket/monorail-style pRPC endpoint whose response does not begin with the `)]}'` prefix.

Common situations: Endpoint moved/deprecated; auth cookie expired so the server returns an HTML login page; corporate proxy returns an interstitial; wrong host/URL.

Related errors

• Retried too often. Giving up. Reason: %s
• 'git %s' failed.
• Couldn't find curent branch.
• Couldn't determine commit position for %s
• The ${key} option is protected, and cannot be retrieved in t

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/84eba837332086f6. Report an issue: GitHub.