In src/nxt_unit_sptr.h::nxt_unit_sptr_set() we are setting one member of
a union based on another member which cppcheck[0] flags as undefined
behaviour

src/nxt_unit_sptr.h:27:18: error: Overlapping read/write of union is undefined behavior [overlappingWriteUnion]
    sptr->offset = (uint8_t *) ptr - sptr->base;
                 ^

I think this warning is correct as I can't see where we are setting
sptr->base beforehand which I think would make this defined behaviour.

To avoid any doubts take a copy of sptr->base and then use that value in
the above.

[0]: https://cppcheck.sourceforge.io/

No functional changes.

The message tracking is unused since 1d84b9e4b459 commit.

This fixes the issue found by Coverity (CID 376263).

No functional changes.

No functional changes.

No functional changes.

Before Node.js v16.14.0 the "format" value in defaultResolve
was ignored so error was hidden.  For more information see:
https://github.com/nodejs/node/pull/40980

This supports a new variable $request_uri that contains the path
and the query (See RFC 3986, section 3).  Its contents are percent
encoded.  This is useful for example to redirect HTTP to HTTPS:

{
    "return": "301",
    "location": "https://$host$request_uri"
}

When <http://example.com/foo%23bar?baz> is requested, the server
redirects to <https://example.com/foo%23bar?baz>.

===

Testing:

//diff --git a/src/nxt_http_return.c b/src/nxt_http_return.c
//index 82c9156..adeb3a1 100644
//--- a/src/nxt_http_return.c
//+++ b/src/nxt_http_return.c
//@@ -196,6 +196,7 @@ nxt_http_return_send_ready(nxt_task_t *task,
    void *obj, void *data)
//         field->value = ctx->encoded.start;
//         field->value_length = ctx->encoded.length;
//     }
//+    fprintf(stderr, "ALX: target[%1$i]: <%2$.*1$s>\n",
    (int)r->target.length, r->target.start);
//
//     r->state = &nxt_http_return_send_state;
//

{
	"listeners": {
		"*:81": {
			"pass": "routes/ru"
		}
	},

	"routes": {
		"ru": [{
			"action": {
				"return": 301,
				"location": "$request_uri"
			}
		}]
	}
}

$ curl -i http://localhost:81/*foo%2Abar?baz#arg
HTTP/1.1 301 Moved Permanently
Location: /*foo%2Abar?baz
Server: Unit/1.27.0
Date: Mon, 30 May 2022 16:04:30 GMT
Content-Length: 0

$ sudo cat /usr/local/unit.log | grep ALX
ALX: target[15]: </*foo%2Abar?baz>

This supports a new option "index" that configures a custom index
file name to be served when a directory is requested.  This
initial support only allows a single fixed string.  An example:

{
	"share": "/www/data/static/$uri",
	"index": "lookatthis.htm"
}

When <example.com/foo/bar/> is requested,
</www/data/static/foo/bar/lookatthis.html> is served.

Default is "index.html".

===

nxt_conf_validator.c:

Accept "index" as a member of "share", and make sure it's a string.

===

I tried this feature in my own computer, where I tried the
following:

- Setting "index" to "lookatthis.htm", and check that the correct
  file is being served (check both a different name and a
  different extension).
- Not setting "index", and check that <index.html> is being
  served.
- Settind "index" to an array of strings, and check that the
  configuration fails:

{
	"error": "Invalid configuration.",
	"detail": "The \"index\" value must be a string, but not an array."
}