tag/Handler: pass StringView to OnTag() and OnPair()

Eliminates a number of allocations, because callers don't need to copy
the strings to a newly allocated buffer only to null-terminate them.
And most callers don't need to have a null-terminated string.

3 files changed, 44 insertions, 21 deletions

diff --git a/src/tag/Handler.cxx b/src/tag/Handler.cxx
index fb328fda6..9731a7878 100644
--- a/src/tag/Handler.cxx
+++ b/src/tag/Handler.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -21,9 +21,20 @@
 #include "Builder.hxx"
 #include "AudioFormat.hxx"
 #include "util/ASCII.hxx"
-#include "util/StringFormat.hxx"
+#include "util/CharUtil.hxx"
+#include "util/StringView.hxx"
 
-#include <stdlib.h>
+#include <algorithm>
+
+void
+NullTagHandler::OnTag(TagType, StringView) noexcept
+{
+}
+
+void
+NullTagHandler::OnPair(StringView, StringView) noexcept
+{
+}
 
 void
 NullTagHandler::OnAudioFormat(gcc_unused AudioFormat af) noexcept
@@ -36,23 +47,35 @@ AddTagHandler::OnDuration(SongTime duration) noexcept
 	tag.SetDuration(duration);
 }
 
+/**
+ * Skip leading zeroes and a non-decimal suffix.
+ */
+static StringView
+NormalizeDecimal(StringView s)
+{
+	auto start = std::find_if(s.begin(), s.end(),
+				  [](char ch){ return ch != '0'; });
+	auto end = std::find_if(start, s.end(),
+				[](char ch){ return !IsDigitASCII(ch); });
+	return {start, end};
+}
+
 void
-AddTagHandler::OnTag(TagType type, const char *value) noexcept
+AddTagHandler::OnTag(TagType type, StringView value) noexcept
 {
 	if (type == TAG_TRACK || type == TAG_DISC) {
 		/* filter out this extra data and leading zeroes */
-		char *end;
-		unsigned n = strtoul(value, &end, 10);
-		if (value != end)
-			tag.AddItem(type, StringFormat<21>("%u", n));
-	} else
-		tag.AddItem(type, value);
+
+		value = NormalizeDecimal(value);
+	}
+
+	tag.AddItem(type, value);
 }
 
 void
-FullTagHandler::OnPair(const char *name, gcc_unused const char *value) noexcept
+FullTagHandler::OnPair(StringView name, StringView) noexcept
 {
-	if (StringEqualsCaseASCII(name, "cuesheet"))
+	if (name.EqualsIgnoreCase("cuesheet"))
 		tag.SetHasPlaylist(true);
 }
 
diff --git a/src/tag/Handler.hxx b/src/tag/Handler.hxx
index f03ac4af8..4b5118f1b 100644
--- a/src/tag/Handler.hxx
+++ b/src/tag/Handler.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -24,6 +24,7 @@
 #include "Chrono.hxx"
 #include "util/Compiler.h"
 
+struct StringView;
 struct AudioFormat;
 class TagBuilder;
 
@@ -74,13 +75,13 @@ public:
 	 * @param the value of the tag; the pointer will become
 	 * invalid after returning
 	 */
-	virtual void OnTag(TagType type, const char *value) noexcept = 0;
+	virtual void OnTag(TagType type, StringView value) noexcept = 0;
 
 	/**
 	 * A name-value pair has been read.  It is the codec specific
 	 * representation of tags.
 	 */
-	virtual void OnPair(const char *key, const char *value) noexcept = 0;
+	virtual void OnPair(StringView key, StringView value) noexcept = 0;
 
 	/**
 	 * Declare the audio format of a song.
@@ -106,10 +107,8 @@ public:
 		:TagHandler(_want_mask) {}
 
 	void OnDuration(gcc_unused SongTime duration) noexcept override {}
-	void OnTag(gcc_unused TagType type,
-		   gcc_unused const char *value) noexcept override {}
-	void OnPair(gcc_unused const char *key,
-		    gcc_unused const char *value) noexcept override {}
+	void OnTag(TagType type, StringView value) noexcept override;
+	void OnPair(StringView key, StringView value) noexcept override;
 	void OnAudioFormat(AudioFormat af) noexcept override;
 };
 
@@ -130,7 +129,7 @@ public:
 		:AddTagHandler(0, _builder) {}
 
 	void OnDuration(SongTime duration) noexcept override;
-	void OnTag(TagType type, const char *value) noexcept override;
+	void OnTag(TagType type, StringView value) noexcept override;
 };
 
 /**
@@ -154,7 +153,7 @@ public:
 				AudioFormat *_audio_format=nullptr) noexcept
 		:FullTagHandler(0, _builder, _audio_format) {}
 
-	void OnPair(const char *key, const char *value) noexcept override;
+	void OnPair(StringView key, StringView value) noexcept override;
 	void OnAudioFormat(AudioFormat af) noexcept override;
 };
 
diff --git a/src/tag/Id3Scan.cxx b/src/tag/Id3Scan.cxx
index faf98cc00..823e175b5 100644
--- a/src/tag/Id3Scan.cxx
+++ b/src/tag/Id3Scan.cxx
@@ -27,6 +27,7 @@
 #include "util/Alloc.hxx"
 #include "util/ScopeExit.hxx"
 #include "util/StringStrip.hxx"
+#include "util/StringView.hxx"
 #include "Log.hxx"
 
 #include <id3tag.h>