Function ap_send_error_response

modules/http/http_protocol.c:1376–1542

We should have named this send_canned_response, since it is used for any * response that can be generated by the server from the request record. * This includes all 204 (no content), 3xx (redirect), 4xx (client error), * and 5xx (server error) messages that have not been redirected to another * handler via the ErrorDocument feature. */

 * handler via the ErrorDocument feature.
 */
AP_DECLARE(void) ap_send_error_response(request_rec *r, int recursive_error)
{
    int status = r->status;
    int idx = ap_index_of_response(status);
    char *custom_response;
    const char *location = apr_table_get(r->headers_out, "Location");

    /* At this point, we are starting the response over, so we have to reset
     * this value.
     */
    r->eos_sent = 0;

    /* and we need to get rid of any RESOURCE filters that might be lurking
     * around, thinking they are in the middle of the original request
     */

    r->output_filters = r->proto_output_filters;

    ap_run_insert_error_filter(r);

    /* We need to special-case the handling of 204 and 304 responses,
     * since they have specific HTTP requirements and do not include a
     * message body.  Note that being assbackwards here is not an option.
     */
    if (AP_STATUS_IS_HEADER_ONLY(status)) {
        ap_finalize_request_protocol(r);
        return;
    }

    /*
     * It's possible that the Location field might be in r->err_headers_out
     * instead of r->headers_out; use the latter if possible, else the
     * former.
     */
    if (location == NULL) {
        location = apr_table_get(r->err_headers_out, "Location");
    }

    if (!r->assbackwards) {
        apr_table_t *tmp = r->headers_out;

        /* For all HTTP/1.x responses for which we generate the message,
         * we need to avoid inheriting the "normal status" header fields
         * that may have been set by the request handler before the
         * error or redirect, except for Location on external redirects.
         */
        r->headers_out = r->err_headers_out;
        r->err_headers_out = tmp;
        apr_table_clear(r->err_headers_out);

        if (ap_is_HTTP_REDIRECT(status) || (status == HTTP_CREATED)) {
            if ((location != NULL) && *location) {
                apr_table_setn(r->headers_out, "Location", location);
            }
            else {
                location = "";   /* avoids coredump when printing, below */
            }
        }