Cast to intermediate "void *" to lose compiler knowledge about the original
type and pass the warning.  This is not a real fix but rather a workaround.

Found by gcc8.

The fields "uri", "location", and "url" from ngx_http_upstream_conf_t
moved to ngx_http_proxy_loc_conf_t and ngx_http_proxy_vars_t, reflect
this change in create_loc_conf comments.

Previously, only the upstream response body could be accessed with the
NGX_HTTP_SUBREQUEST_IN_MEMORY feature.  Now any response body from a subrequest
can be saved in a memory buffer.  It is available as a single buffer in r->out
and the buffer size is configured by the subrequest_output_buffer_size
directive.

Upstream, proxy and fastcgi code used to handle the old-style feature is
removed.

If the flag space_in_uri is set, the URI in HTTP upstream request is escaped to
convert space to %20.  However this flag is not checked while creating the
default cache key.  This leads to different cache keys for requests
'/foo bar' and '/foo%20bar', while the upstream requests are identical.

Additionally, the change fixes background cache updates when the client URI
contains unescaped space.  Default cache key in a subrequest is always based on
escaped URI, while the main request may not escape it.  As a result, background
cache update subrequest may update a different cache entry.

Previously, the unparsed uri was explicitly allowed to be used only by the main
request.  However the valid_unparsed_uri flag is nonzero only in the main
request, which makes the main request check pointless.

No functional changes.

Previously, each configured header was represented in one of two ways,
depending on whether or not its value included any variables.

If the value didn't include any variables, then it would be represented
as as a single script that contained complete header line with HTTP/1.1
delimiters, i.e.:

     "Header: value\r\n"

But if the value included any variables, then it would be represented
as a series of three scripts: first contained header name and the ": "
delimiter, second evaluated to header value, and third contained only
"\r\n", i.e.:

     "Header: "
     "$value"
     "\r\n"

This commit changes that, so that each configured header is represented
as a series of two scripts: first contains only header name, and second
contains (or evaluates to) only header value, i.e.:

    "Header"
    "$value"

or

    "Header"
    "value"

This not only makes things more consistent, but also allows header name
and value to be accessed separately.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

Previously, an allocation error resulted in uninitialized memory access
when evaluating $upstream_http_ variables.

On a related note, see r->headers_out.headers cleanup work in 0cdee26605f3.

Support for the TLSv1.3 protocol will be introduced in OpenSSL 1.1.1.

This change adds "http_429" parameter to "proxy_next_upstream" for
retrying rate-limited requests, and to "proxy_cache_use_stale" for
serving stale cached responses after being rate-limited.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>