Function get_conditional_response

django/utils/cache.py:164–212

(request, etag=None, last_modified=None, response=None)

def get_conditional_response(request, etag=None, last_modified=None, response=None):
    # Only return conditional responses on successful requests.
    if response and not (200 <= response.status_code < 300):
        return response

    # Get HTTP request headers.
    if_match_etags = parse_etags(request.META.get("HTTP_IF_MATCH", ""))
    if_unmodified_since = request.META.get("HTTP_IF_UNMODIFIED_SINCE")
    if_unmodified_since = if_unmodified_since and parse_http_date_safe(
        if_unmodified_since
    )
    if_none_match_etags = parse_etags(request.META.get("HTTP_IF_NONE_MATCH", ""))
    if_modified_since = request.META.get("HTTP_IF_MODIFIED_SINCE")
    if_modified_since = if_modified_since and parse_http_date_safe(if_modified_since)

    # Evaluation of request preconditions below follows RFC 9110 Section
    # 13.2.2.
    # Step 1: Test the If-Match precondition.
    if if_match_etags and not _if_match_passes(etag, if_match_etags):
        return _precondition_failed(request)

    # Step 2: Test the If-Unmodified-Since precondition.
    if (
        not if_match_etags
        and if_unmodified_since
        and not _if_unmodified_since_passes(last_modified, if_unmodified_since)
    ):
        return _precondition_failed(request)

    # Step 3: Test the If-None-Match precondition.
    if if_none_match_etags and not _if_none_match_passes(etag, if_none_match_etags):
        if request.method in ("GET", "HEAD"):
            return _not_modified(request, response)
        else:
            return _precondition_failed(request)

    # Step 4: Test the If-Modified-Since precondition.
    if (
        not if_none_match_etags
        and if_modified_since
        and not _if_modified_since_passes(last_modified, if_modified_since)
        and request.method in ("GET", "HEAD")
    ):
        return _not_modified(request, response)

    # Step 5: Test the If-Range precondition (not supported).
    # Step 6: Return original response since there isn't a conditional
    # response.
    return response


def _if_match_passes(target_etag, etags):