Function httpError

Map a non-2xx response to its code, message and details.

• Canonical body (code is an ApiErrorCode, error is a string): code is body.code; message is body.error, plus : <body.message> when present.
• Otherwise (older servers, proxies): code is body.code, else body.error, else http_<status>; message is body.message, else body.error, else HTTP <status> <statusText>.
• details: body.details when present, else the parsed body (or raw text).