def get_http_headers(request_meta):
    """
    Returns HTTP headers send by the downstream caller.

    Transforms keys to normal HTTP header keys.

    >>> get_http_headers({'HTTP_ACCEPT_LANGUAGE': 'xh', 'SPAM': 'spam'})
    {'Accept-Language': 'xh'}

    """
    headers = {k[5:].replace('_', '-').title(): v
               for k, v in request_meta.items()
               if k.startswith('HTTP_')}
    if request_meta.get('CONTENT_TYPE'):
        headers['Content-Type'] = request_meta['CONTENT_TYPE']
    if request_meta.get('CONTENT_LENGTH'):
        headers['Content-Length'] = request_meta['CONTENT_LENGTH']
    # Drop headers added by OpenHIM
    headers.pop('X-Forwarded-For', None)
    headers.pop('X-Forwarded-Host', None)
    headers.pop('X-Openhim-Transactionid', None)
    return headers