HTTP redirects can use host-relative URLs. See discussion in #1497.

* Use helper functions in staticfiles to redirect.

Previously the browse package invoked staticfiles.Redirect when
redirecting clients who requested a directory but with a Request-URI
that did not contain a trailing '/'. staticfiles.Redirect only used a
relative URI. This change defers the decision of how to format the
Location header value to the helper methods in the staticfiles package.

* Update const URLPathCtxKey in browse package.

* Add the first policy which sends the request to the first available host

* Make the error message clear. As we expect the second not first upstream
host.

* Added Const for CtxKeys

* Move CtxKey Const declarations

* Fixed tests

* fix test

* staticfiles: add Content-Length header (closes #1479)

* make linter happy, rename "Html" in identifiers to "HTML"

systemd README: set mode of caddy.service to 644 instead of 744

* Fixed issue with {path} actually {uri}

* Test added for path rewrite

* add in uri_escaped

* added rewrite_uri and test

* fix broken test.  Just checks for existance of rewrite header

* gitignore

* Use context to store uri value

* ignore .vscode

* tidy up, removal of comments and invalidated tests

* Remove commented out code.

* added comment as requested by lint

* fixed spelling mistake

* clarified code with variable name

* added context for uri and test

* added TODO comment to move consts

* Fixed #1484

Fixed a nil pointer runtime error in newConnHijackerTransport,
where the access to the TLSClientConfig did not check for nil values.

* Minor improvement to UseInsecureTransport

This prevents overwriting a possibly preexisting TLSClientConfig,
even though only a single field should be changed.

* add support for listener middleware

* add proxyprotocol directive

* make caddy.Listener interface required

* Remove tcpKeepAliveListener wrapper from Serve()
This is now done in the Listen() function, along with other potential middleware.

* Fix for missing content-length header when using QUIC

If request.ContentLength is set then it will be used instead of getting
it from request.Header map since quic-go(lucas-clemente/quic-go@bb24be8)
will not store (and pass) the Content-Length header using its header
map.

This fixes a potential issue where FastCGI POST requests body empty when
QUIC is enabled. (#1370)

* Change the data type for fastcgi contentLength to int64

quic-go uses int64 for contentLength

* Fix an error for undeclared variable

* Fix test for fcgiclient

the data type for contentLength

Log certificate location

templates: Set MIME type

* Support realms with basic authentication

* Add test for default basicauth directive in which realm is not specified

* Correct typo: missing space

* Remove 'path' subdirective

This could have just as easily been a tls directive property in the
Caddyfile, but I figure if these challenges are being disabled, it's
because of port availability or process privileges, both of which would
affect all sites served by this process. The names of the flag are long
but descriptive.

I've never needed this but I hear of quite a few people who say they
need this ability, so here it is.

httpserver: Flags to customize HTTP and HTTPS ports (including for ACME challenges)

Adding ServerIP context

If use gzip and templates at the same time, the response body will
be gzipped data. And in this case, the Content-Type header won't be
set by Caddy code. Then Go http package will set "Content-Type" to
wrong value "application/x-gzip" which is determined by response body.
So the header Contenty-Type should be set in templates middleware.

See: https://forum.caddyserver.com/t/reloading-template-files-as-they-change/1483/3?u=matt

The server takes a moment to start; if USR1 is received before the
instance is saved, it would panic because no instances have been saved.
Instead, we just ignore the signal since no config has finished loading.

This commit removes _almost_ all instances of hard-coded ports 80 and
443 strings, and now allows the user to define what the HTTP and HTTPS
ports are by the -http-port and -https-ports flags.

(One instance of "80" is still hard-coded in tls.go because it cannot
import httpserver to get access to the HTTP port variable. I don't
suspect this will be a problem in practice, but one workaround would be
to define an exported variable in the caddytls package and let the
httpserver package set it as well as its own HTTPPort variable.)

The port numbers required by the ACME challenges HTTP-01 and TLS-SNI-01
are hard-coded into the spec as ports 80 and 443 for good reasons,
but the big question is whether they necessarily need to be the HTTP
and HTTPS ports. Although the answer is probably no, they chose those
ports for convenience and widest compatibility/deployability. So this
commit also assumes that the "HTTP port" is necessarily the same port
on which to serve the HTTP-01 challenge, and the "HTTPS port" is
necessarily the same one on which to serve the TLS-SNI-01 challenge. In
other words, changing the HTTP and HTTPS ports also changes the ports
the challenges will be served on.

If you change the HTTP and HTTPS ports, you are responsible for
configuring your system to forward ports 80 and 443 properly.

Closes #918 and closes #1293. Also related: #468.

* feat(request placeholders): adds {?arg}

* test(request placeholders): test query argument extractor {?arg}

* Use RequestURI when redirecting to canonical path.

Caddy may trim a request's URL path when it starts with the path that's
associated with the virtual host. This change uses the path from the request's
RequestURI when performing a redirect.

Fix issue #1327.

* Rename redirurl to redirURL.

* Redirect to the full URL.

The scheme and host from the virtual host's site configuration is used
in order to redirect to the full URL.

* Add comment and remove redundant check.

* Store the original URL path in request context.

By storing the original URL path as a value in the request context,
middlewares can access both it and the sanitized path. The default
default FileServer handler will use the original URL on redirects.

* Replace contextKey type with CtxKey.

In addition to moving the CtxKey definition to the caddy package, this
change updates the CtxKey references in the httpserver, fastcgi, and
basicauth packages.

* httpserver: Fix reference to CtxKey

Timeouts are important for mitigating slowloris, yes. But after a number
of complaints and seeing that default timeouts are a sore point of
confusion, we're disabling them now. However, the code that sets
default timeouts remains intact; the defaults are just the zero value.

While Caddy aims to be secure by default, Caddy also aims to serve a
worldwide audience. Even my own internet here in Utah is poor at times,
with bad WiFi signal, causing some connections to take over 10s to
be established. Many use the Internet while commuting on slower
connection speeds. Latency across country borders is another concern.

As such, disabling default timeouts will serve a greater population of
users than enabling them, as slowloris is easy to mitigate and does
not seem to be reported often (I've only seen it once). It's also very
difficult sometimes to distinguish slowloris from genuine slow networks.
That decision is best left to the site owner for now.

* tls: Refactor TLS config innards with a few minor syntax changes

muststaple -> must_staple
"http2 off" -> "alpn" with list of ALPN values

* Fix typo

* Fix QUIC handler

* Inline struct field assignments

Revert removed method IncrNest

* Disable TLS completely if there is no listener with tls enabled

* Format code

* Revised fileserver Accept-Encoding and ETag

* calculateEtag improved following microbenchmarking

* Push down headers from client

* Push first, serve later

* After review fixes