shorter
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Add an option to the UPnP database plugin to configure which interface
is used by upnp to discover servers.

upnp by default selects the first interface that is not loopback, which
in some cases might not be the desired interface. For example if wanting
to access a DLNA server over a VPN connection.

The "interface" option can now be set to the name of the desired
interface to achieve this.

The default behaviour remains unchanged.

Adds the Interface Name as an argument to the *Init functions to make it
possible to select which interface is used by upnp to detect servers.

Currently "nullptr" is passed in to let the upnp library select an
interface, as before.

These should be equivalent anyway.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

loop is wrong anyway. It's missing a break;
Signed-off-by: Rosen Penev <rosenp@gmail.com>

libnpupnp is a C++ modification of libupnp.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Fixes use-after-free because the temporary goes out of scope.

This fixes compatibility with Plex DLNA.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/851

Found with modernize-use-nodiscard
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Eliminates lots of overhead.

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Introduced in C++17. It replaces gcc's warn_unused_result.

Found with modernize-use-nodiscard.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with performance-move-const-arg
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-equals-default
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with performance-unnecessary-value-param
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Instead of passing tag and group, pass an array of tags.  To support a
nested return value, return a nested std::map of std::maps.  Each key
specifies the tag value, and each value may be another nesting level.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/408

This function implements the "group" feature on top of the
Database::Visit() method.

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Grouping in the "list" command was completely broken from the start,
unlike "count group".  I have no idea what I have been thinking when I
wrote commit ae178c77, but it didn't
make any sense.

This commit is a rewrite of the feature.

For clients to be able to detect this feature, this commit also
increments the protocol version.

That way, each plugin can decide to implement it better.

Prepare to allow more complex expressions.