Embedded perl does not set any request fields needed for conditional requests processing. Further, filter finalization in the not_modified filter can cause segmentation faults due to cleared ctx as in ticket #1786. Before 5fb1e57c758a (1.7.3) the not_modified filter was implicitly disabled for perl responses, as r->headers_out.last_modified_time was -1. This change restores this behaviour by using the explicit r->disable_not_modified flag. Note that this patch doesn't try to address perl module robustness against filter finalization and other errors returned from filter chains. It should be eventually reworked to handle errors instead of ignoring them.
A new directive limit_req_dry_run allows enabling the dry run mode. In this mode requests are neither rejected nor delayed, but reject/delay status is logged as usual.
In case of filter finalization, essential request fields like r->uri, r->args etc could be changed, which affected the cache update subrequest. Also, after filter finalization r->cache could be set to NULL, leading to null pointer dereference in ngx_http_upstream_cache_background_update(). The fix is to create background cache update subrequest before sending the cached response. Since initial introduction in 1aeaae6e9446 (1.11.10) background cache update subrequest was created after sending the cached response because otherwise it blocked the parent request output. In 9552758a786e (1.13.1) background subrequests were introduced to eliminate the delay before sending the final part of the cached response. This also made it possible to create the background cache update subrequest before sending the response. Note that creating the subrequest earlier does not change the fact that in case of filter finalization the background cache update subrequest will likely not have enough time to successfully update the cache entry. Filter finalization leads to the main request termination as soon the current iteration of request processing is complete.
In ngx_http_range_singlepart_body() special buffers where passed unmodified, including ones after the end of the range. As such, if the last buffer of a response was sent separately as a special buffer, two buffers with b->last_buf set were present in the response. In particular, this might result in a duplicate final chunk when using chunked transfer encoding (normally range filter and chunked transfer encoding are not used together, but this may happen if there are trailers in the response). This also likely to cause problems in HTTP/2. Fix is to skip all special buffers after we've sent the last part of the range requested. These special buffers are not meaningful anyway, since we set b->last_buf in the buffer with the last part of the range, and everything is expected to be flushed due to it. Additionally, ngx_http_next_body_filter() is now called even if no buffers are to be passed to it. This ensures that various write events are properly propagated through the filter chain. In particular, this fixes test failures observed with the above change and aio enabled.
Filters are not allowed to change incoming chain links, and should allocate their own links if any modifications are needed. Nevertheless ngx_http_range_singlepart_body() modified incoming chain links in some cases, notably at the end of the requested range. No problems caused by this are currently known, mostly because of limited number of possible modifications and the position of the range body filter in the filter chain. Though this behaviour is clearly incorrect and tests demonstrate that it can at least cause some proxy buffers being lost when using proxy_force_ranges, leading to less effective handling of responses. Fix is to always allocate new chain links in ngx_http_range_singlepart_body(). Links are explicitly freed to ensure constant memory usage with long-lived requests.
If a complex value is expected to be of type size_t, and the compiled value is constant, the constant size_t value is remembered at compile time. The value is accessed through ngx_http_complex_value_size() which either returns the remembered constant or evaluates the expression and parses it as size_t.
Previously only one address was used by the listen directive handler even if host name resolved to multiple addresses. Now a separate listening socket is created for each address.