SongFilter: new extensible filter syntax

Will allow more complex fitler expression, such as negation (#89).

NEWS

@@ -7,6 +7,7 @@ ver 0.21 (not yet released)
   - "outputs" prints the plugin name
   - "outputset" sets runtime attributes
   - close connection when client sends HTTP request
+  - new filter syntax for "find"/"search" etc.
 * database
   - simple: scan audio formats
 * player

doc/protocol.xml

@@ -208,63 +208,75 @@
 
       <cmdsynopsis>
         <command>find</command>
-        <arg choice="req" rep="repeat">
-          <arg choice="req"><replaceable>TYPE</replaceable></arg>
-          <arg choice="req"><replaceable>VALUE</replaceable></arg>
-        </arg>
+        <arg choice="req" rep="repeat">EXPRESSION</arg>
       </cmdsynopsis>
 
       <para>
-        <varname>TYPE</varname> can
-        be any tag supported by <application>MPD</application>, or one of the special
-        parameters:
+        <varname>EXPRESSION</varname> is a string enclosed in
+        parantheses which can be one of:
       </para>
 
       <itemizedlist>
         <listitem>
           <para>
-            <parameter>any</parameter> checks all tag values
+            "<code>(TAG == 'VALUE')</code>": match a tag value.
           </para>
-        </listitem>
 
-        <listitem>
           <para>
-            <parameter>file</parameter> checks the full path
-            (relative to the music directory)
+            The special tag "<parameter>any</parameter>" checks all
+            tag values.
           </para>
-        </listitem>
 
-        <listitem>
-          <para>
-            <parameter>base</parameter> restricts the search to
-            songs in the given directory (also relative to the
-            music directory)
-          </para>
-        </listitem>
-
-        <listitem>
-          <para>
-            <parameter>modified-since</parameter> compares the
-            file's time stamp with the given value (ISO 8601 or
-            UNIX time stamp)
-          </para>
-        </listitem>
-
-        <listitem>
           <para>
             <parameter>albumartist</parameter> looks for
-            <varname>VALUE</varname> in AlbumArtist and falls back to
-            Artist tags if AlbumArtist does not exist.
+            <varname>VALUE</varname> in <varname>AlbumArtist</varname>
+            and falls back to <varname>Artist</varname> tags if
+            <varname>AlbumArtist</varname> does not exist.
+          </para>
+
+          <para>
+            <varname>VALUE</varname> is what to find.  The
+            <command>find</command> commands specify an exact value
+            and are case-sensitive; the <command>search</command>
+            commands specify a sub string and ignore case.
+          </para>
+        </listitem>
+
+        <listitem>
+          <para>
+            "<code>(file == 'VALUE')</code>": match the full song URI
+            (relative to the music directory).
+          </para>
+        </listitem>
+
+        <listitem>
+          <para>
+            "<code>(base 'VALUE')</code>": restrict the search to
+            songs in the given directory (relative to the music
+            directory).
+          </para>
+        </listitem>
+
+        <listitem>
+          <para>
+            "<code>(modified-since 'VALUE')</code>": compares the
+            file's time stamp with the given value (ISO 8601 or UNIX
+            time stamp).
           </para>
         </listitem>
       </itemizedlist>
 
       <para>
-        <varname>VALUE</varname> is what to find.  The
-        <command>find</command> commands specify an exact value and
-        are case-sensitive; the <command>search</command> commands
-        specify a sub string and ignore case.
+        Prior to MPD 0.21, the syntax looked like this:
       </para>
+
+      <cmdsynopsis>
+        <command>find</command>
+        <arg choice="req" rep="repeat">
+          <arg choice="req"><replaceable>TYPE</replaceable></arg>
+          <arg choice="req"><replaceable>VALUE</replaceable></arg>
+        </arg>
+      </cmdsynopsis>
     </section>
 
     <section id="tags">

src/SongFilter.cxx

@@ -22,10 +22,13 @@
 #include "db/LightSong.hxx"
 #include "DetachedSong.hxx"
 #include "tag/ParseName.hxx"
+#include "util/CharUtil.hxx"
 #include "util/ChronoUtil.hxx"
 #include "util/ConstBuffer.hxx"
+#include "util/RuntimeError.hxx"
 #include "util/StringAPI.hxx"
 #include "util/StringCompare.hxx"
+#include "util/StringStrip.hxx"
 #include "util/StringView.hxx"
 #include "util/ASCII.hxx"
 #include "util/TimeParser.hxx"
@@ -234,6 +237,99 @@ ParseTimeStamp(const char *s)
 	return ParseTimePoint(s, "%FT%TZ");
 }
 
+static constexpr bool
+IsTagNameChar(char ch) noexcept
+{
+	return IsAlphaASCII(ch) || ch == '_';
+}
+
+static const char *
+FirstNonTagNameChar(const char *s) noexcept
+{
+	while (IsTagNameChar(*s))
+		++s;
+	return s;
+}
+
+static auto
+ExpectFilterType(const char *&s)
+{
+	const char *end = FirstNonTagNameChar(s);
+	if (end == s)
+		throw std::runtime_error("Tag name expected");
+
+	const std::string name(s, end);
+	s = StripLeft(end);
+
+	const auto type = locate_parse_type(name.c_str());
+	if (type == TAG_NUM_OF_ITEM_TYPES)
+		throw FormatRuntimeError("Unknown filter type: %s",
+					 name.c_str());
+
+	return type;
+}
+
+static constexpr bool
+IsQuote(char ch) noexcept
+{
+	return ch == '"' || ch == '\'';
+}
+
+static std::string
+ExpectQuoted(const char *&s)
+{
+	const char quote = *s++;
+	if (!IsQuote(quote))
+		throw std::runtime_error("Quoted string expected");
+
+	const char *begin = s;
+	const char *end = strchr(s, quote);
+	if (end == nullptr)
+		throw std::runtime_error("Closing quote not found");
+
+	s = StripLeft(end + 1);
+	return {begin, end};
+}
+
+const char *
+SongFilter::ParseExpression(const char *s, bool fold_case)
+{
+	assert(*s == '(');
+
+	s = StripLeft(s + 1);
+
+	if (*s == '(')
+		throw std::runtime_error("Nested expressions not yet implemented");
+
+	const auto type = ExpectFilterType(s);
+
+	if (type == LOCATE_TAG_MODIFIED_SINCE) {
+		const auto value_s = ExpectQuoted(s);
+		if (*s != ')')
+			throw std::runtime_error("')' expected");
+		items.emplace_back(type, ParseTimeStamp(value_s.c_str()));
+		return StripLeft(s + 1);
+	} else if (type == LOCATE_TAG_BASE_TYPE) {
+		auto value = ExpectQuoted(s);
+		if (*s != ')')
+			throw std::runtime_error("')' expected");
+
+		items.emplace_back(type, std::move(value), fold_case);
+		return StripLeft(s + 1);
+	} else {
+		if (s[0] != '=' || s[1] != '=')
+			throw std::runtime_error("'==' expected");
+
+		s = StripLeft(s + 2);
+		auto value = ExpectQuoted(s);
+		if (*s != ')')
+			throw std::runtime_error("')' expected");
+
+		items.emplace_back(type, std::move(value), fold_case);
+		return StripLeft(s + 1);
+	}
+}
+
 void
 SongFilter::Parse(const char *tag_string, const char *value, bool fold_case)
 {
@@ -262,6 +358,15 @@ SongFilter::Parse(ConstBuffer<const char *> args, bool fold_case)
 		throw std::runtime_error("Incorrect number of filter arguments");
 
 	do {
+		if (*args.front() == '(') {
+			const char *s = args.shift();
+			const char *end = ParseExpression(s, fold_case);
+			if (*end != 0)
+				throw std::runtime_error("Unparsed garbage after expression");
+
+			continue;
+		}
+
 		if (args.size < 2)
 			throw std::runtime_error("Incorrect number of filter arguments");
 

src/SongFilter.hxx

@@ -142,6 +142,8 @@ public:
 	std::string ToExpression() const noexcept;
 
 private:
+	const char *ParseExpression(const char *s, bool fold_case=false);
+
 	gcc_nonnull(2,3)
 	void Parse(const char *tag, const char *value, bool fold_case=false);
 

src/command/AllCommands.cxx

@@ -94,7 +94,7 @@ static constexpr struct command commands[] = {
 	{ "config", PERMISSION_ADMIN, 0, 0, handle_config },
 	{ "consume", PERMISSION_CONTROL, 1, 1, handle_consume },
 #ifdef ENABLE_DATABASE
-	{ "count", PERMISSION_READ, 2, -1, handle_count },
+	{ "count", PERMISSION_READ, 1, -1, handle_count },
 #endif
 	{ "crossfade", PERMISSION_CONTROL, 1, 1, handle_crossfade },
 	{ "currentsong", PERMISSION_READ, 0, 0, handle_currentsong },
@@ -104,8 +104,8 @@ static constexpr struct command commands[] = {
 	{ "disableoutput", PERMISSION_ADMIN, 1, 1, handle_disableoutput },
 	{ "enableoutput", PERMISSION_ADMIN, 1, 1, handle_enableoutput },
 #ifdef ENABLE_DATABASE
-	{ "find", PERMISSION_READ, 2, -1, handle_find },
-	{ "findadd", PERMISSION_ADD, 2, -1, handle_findadd},
+	{ "find", PERMISSION_READ, 1, -1, handle_find },
+	{ "findadd", PERMISSION_ADD, 1, -1, handle_findadd},
 #endif
 	{ "idle", PERMISSION_READ, 0, -1, handle_idle },
 	{ "kill", PERMISSION_ADMIN, -1, -1, handle_kill },
@@ -149,11 +149,11 @@ static constexpr struct command commands[] = {
 	{ "playlistadd", PERMISSION_CONTROL, 2, 2, handle_playlistadd },
 	{ "playlistclear", PERMISSION_CONTROL, 1, 1, handle_playlistclear },
 	{ "playlistdelete", PERMISSION_CONTROL, 2, 2, handle_playlistdelete },
-	{ "playlistfind", PERMISSION_READ, 2, -1, handle_playlistfind },
+	{ "playlistfind", PERMISSION_READ, 1, -1, handle_playlistfind },
 	{ "playlistid", PERMISSION_READ, 0, 1, handle_playlistid },
 	{ "playlistinfo", PERMISSION_READ, 0, 1, handle_playlistinfo },
 	{ "playlistmove", PERMISSION_CONTROL, 3, 3, handle_playlistmove },
-	{ "playlistsearch", PERMISSION_READ, 2, -1, handle_playlistsearch },
+	{ "playlistsearch", PERMISSION_READ, 1, -1, handle_playlistsearch },
 	{ "plchanges", PERMISSION_READ, 1, 2, handle_plchanges },
 	{ "plchangesposid", PERMISSION_READ, 1, 2, handle_plchangesposid },
 	{ "previous", PERMISSION_CONTROL, 0, 0, handle_previous },
@@ -173,9 +173,9 @@ static constexpr struct command commands[] = {
 	{ "rm", PERMISSION_CONTROL, 1, 1, handle_rm },
 	{ "save", PERMISSION_CONTROL, 1, 1, handle_save },
 #ifdef ENABLE_DATABASE
-	{ "search", PERMISSION_READ, 2, -1, handle_search },
-	{ "searchadd", PERMISSION_ADD, 2, -1, handle_searchadd },
-	{ "searchaddpl", PERMISSION_CONTROL, 3, -1, handle_searchaddpl },
+	{ "search", PERMISSION_READ, 1, -1, handle_search },
+	{ "searchadd", PERMISSION_ADD, 1, -1, handle_searchadd },
+	{ "searchaddpl", PERMISSION_CONTROL, 2, -1, handle_searchaddpl },
 #endif
 	{ "seek", PERMISSION_CONTROL, 2, 2, handle_seek },
 	{ "seekcur", PERMISSION_CONTROL, 1, 1, handle_seekcur },