Add action to add streams via youtube-dl

youtube-dl [0] is a "command-line program to download videos from
YouTube.com" and many other websites, e.g. media libraries of public
broadcasters.

This commit adds a new action to ncmpcpp's playlist view: Pressing 'D',
prompts for the URL of a website.  The input is passed to youtube-dl to
retrieve the URL of the audio stream and available metadata.  If
successful, the URL is added to the MPD playlist.

[0]: https://github.com/ytdl-org/youtube-dl

src/actions.cpp

@@ -25,8 +25,17 @@
 #include <boost/filesystem/operations.hpp>
 #include <boost/locale/conversion.hpp>
 #include <boost/lexical_cast.hpp>
+#include <boost/process/child.hpp>
+#include <boost/process/io.hpp>
+#include <boost/process/pipe.hpp>
+#include <boost/process/search_path.hpp>
+#include <boost/property_tree/exceptions.hpp>
+#include <boost/property_tree/json_parser.hpp>
+#include <boost/property_tree/ptree.hpp>
+#include <boost/property_tree/ptree_fwd.hpp>
 #include <algorithm>
 #include <iostream>
+#include <mpd/tag.h>
 
 #include "actions.h"
 #include "charset.h"
@@ -2746,6 +2755,94 @@ void ShowServerInfo::run()
 	myServerInfo->switchTo();
 }
 
+bool AddYoutubeDLItem::canBeRun()
+{
+	return myScreen == myPlaylist;
+}
+
+void AddYoutubeDLItem::run()
+{
+	using Global::wFooter;
+	namespace bp = boost::process;
+	namespace pt = boost::property_tree;
+
+	std::string url;
+	{
+		Statusbar::ScopedLock slock;
+		Statusbar::put() << "Add via youtube-dl: ";
+		url = wFooter->prompt();
+	}
+
+	// do nothing if no url is given
+	if (url.empty())
+		return;
+
+	// search the youtube-dl executable in the PATH
+	auto ydl_path = bp::search_path("youtube-dl");
+	if (ydl_path.empty()) {
+		Statusbar::ScopedLock slock;
+		Statusbar::put() << "youtube-dl was not found in PATH";
+		return;
+	}
+
+	{
+		Statusbar::ScopedLock slock;
+		Statusbar::put() << "Calling youtube-dl with '" << url << "' ...";
+		wFooter->refresh();
+	}
+
+	// start youtube-dl in a child process
+	// -j: output as JSON, each playlist item on a separate line
+	// -f bestaudio/best: selects the best available audio-only stream, or
+	//                    alternatively the best audio+video stream
+	bp::ipstream output;
+	bp::child child_process(ydl_path, url, "-j", "-f", "bestaudio/best", bp::std_out > output,
+	                        bp::std_err > bp::null);
+
+	// extract the URL and metadata from a ptree object and add
+	auto add_song = [] (const pt::ptree& ptree) {
+		auto download_url = ptree.get<std::string>("url");
+		auto title = ptree.get_optional<std::string>("title");
+		auto artist = ptree.get_optional<std::string>("creator");
+		if (!artist.has_value()) {
+			artist = ptree.get_optional<std::string>("uploader");
+		}
+		auto album = ptree.get_optional<std::string>("album");
+		auto id = Mpd.AddSong(download_url);
+		if (id == -1) {
+			return;
+		}
+		if (title.has_value()) {
+			Mpd.AddTag(id, MPD_TAG_TITLE, *title);
+		}
+		if (artist.has_value()) {
+			Mpd.AddTag(id, MPD_TAG_ARTIST, *artist);
+		}
+		if (album.has_value()) {
+			Mpd.AddTag(id, MPD_TAG_ALBUM, *album);
+		}
+	};
+
+	std::string line;
+	pt::ptree ptree;
+
+	while (std::getline(output, line)) {
+		try {
+			std::istringstream line_stream(line);
+			pt::read_json(line_stream, ptree);
+			add_song(ptree);
+		} catch (pt::ptree_error &e) {
+			Statusbar::ScopedLock slock;
+			Statusbar::put() << "An error occurred while calling youtube-dl or parsing its output";
+			wFooter->refresh();
+		}
+	}
+
+	if (child_process.running()) {
+		child_process.terminate();
+	}
+}
+
 }
 
 namespace {
@@ -2884,6 +2981,7 @@ void populateActions()
 	insert_action(new Actions::ShowVisualizer());
 	insert_action(new Actions::ShowClock());
 	insert_action(new Actions::ShowServerInfo());
+	insert_action(new Actions::AddYoutubeDLItem());
 	for (size_t i = 0; i < AvailableActions.size(); ++i)
 	{
 		if (AvailableActions[i] == nullptr)

src/actions.h

@@ -164,6 +164,7 @@ enum class Type
 	ShowVisualizer,
 	ShowClock,
 	ShowServerInfo,
+	AddYoutubeDLItem,
 	_numberOfActions // needed to dynamically calculate size of action array
 };
 
@@ -1425,6 +1426,15 @@ private:
 	virtual void run() override;
 };
 
+struct AddYoutubeDLItem: BaseAction
+{
+	AddYoutubeDLItem(): BaseAction(Type::AddYoutubeDLItem, "add_youtube-dl_item") { }
+
+private:
+	virtual bool canBeRun() override;
+	virtual void run() override;
+};
+
 }
 
 #endif // NCMPCPP_ACTIONS_H

src/bindings.cpp

@@ -762,6 +762,8 @@ void BindingsConfiguration::generateDefaults()
 		bind(k, Actions::Type::SetSelectedItemsPriority);
 	if (notBound(k = stringToKey("q")))
 		bind(k, Actions::Type::Quit);
+	if (notBound(k = stringToKey("D")))
+		bind(k, Actions::Type::AddYoutubeDLItem);
 }
 
 const Command *BindingsConfiguration::findCommand(const std::string &name)

src/mpdpp.cpp

@@ -567,6 +567,10 @@ int Connection::AddSong(const Song &s, int pos)
 	return AddSong((!s.isFromDatabase() ? "file://" : "") + s.getURI(), pos);
 }
 
+void Connection::AddTag(int id, mpd_tag_type tag, const std::string &value) {
+	mpd_run_add_tag_id(m_connection.get(), id, tag, value.c_str());
+}
+
 bool Connection::Add(const std::string &path)
 {
 	bool result;

src/mpdpp.h

@@ -552,6 +552,7 @@ struct Connection
 	
 	int AddSong(const std::string &, int = -1); // returns id of added song
 	int AddSong(const Song &, int = -1); // returns id of added song
+	void AddTag(int id, mpd_tag_type, const std::string &);
 	bool AddRandomTag(mpd_tag_type, size_t, std::mt19937 &rng);
 	bool AddRandomSongs(size_t number, const std::string &random_exclude_pattern, std::mt19937 &rng);
 	bool Add(const std::string &path);

src/screens/help.cpp

@@ -258,6 +258,7 @@ void write_bindings(NC::Scrollpad &w)
 	key(w, Type::ReversePlaylist, "Reverse range");
 	key(w, Type::JumpToPlayingSong, "Jump to current song");
 	key(w, Type::TogglePlayingSongCentering, "Toggle playing song centering");
+	key(w, Type::AddYoutubeDLItem, "Add items via youtube-dl");
 
 	key_section(w, "Browser");
 	key(w, Type::EnterDirectory, "Enter directory");