bitcoin requires the Content-Length header, but several JSON-RPC libraries do not provide it. When the Content-Length header is absent, bitcoin returns 500 Internal Server Error.
Can you be more specific about which JSON libraries don't provide Content-Length ? It'd be nice to document that.
I guess we should try to support the case where there's no Content-Length parameter. I don't want to rip and replace streams though, even if it has to read one character at a time.
Edit: That is, assuming there actually are any libraries that don't support Content-Length.