input/buffered: proxy InputStream implementation which caches in a huge buffer

src/input/BufferedInputStream.hxx

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_BUFFERED_INPUT_STREAM_BUFFER_HXX
+#define MPD_BUFFERED_INPUT_STREAM_BUFFER_HXX
+
+#include "check.h"
+#include "InputStream.hxx"
+#include "Ptr.hxx"
+#include "Handler.hxx"
+#include "thread/Thread.hxx"
+#include "thread/Cond.hxx"
+#include "util/SparseBuffer.hxx"
+
+#include <exception>
+
+#include <assert.h>
+
+/**
+ * A "huge" buffer which remembers the (partial) contents of an
+ * #InputStream.  This works only if the #InputStream is a "file", not
+ * a "stream"; see IsEligible() for details.
+ */
+class BufferedInputStream final : public InputStream, InputStreamHandler {
+	InputStreamPtr input;
+
+	Thread thread;
+
+	/**
+	 * This #Cond wakes up the #Thread.  It is used by both the
+	 * "client" thread (to submit commands) and #input's handler
+	 * (to notify new data being available).
+	 */
+	Cond wake_cond;
+
+	/**
+	 * This #Cond wakes up the client upon command completion.
+	 */
+	Cond client_cond;
+
+	SparseBuffer<uint8_t> buffer;
+
+	bool stop = false, seek = false, idle = false;
+
+	offset_type seek_offset;
+
+	std::exception_ptr read_error, seek_error;
+
+	// TODO: make configurable
+	static constexpr offset_type MAX_SIZE = 128 * 1024 * 1024;
+
+public:
+	BufferedInputStream(InputStreamPtr _input);
+	~BufferedInputStream() noexcept override;
+
+	/**
+	 * Check whether the given #InputStream can be used as input
+	 * for this class.
+	 */
+	static bool IsEligible(const InputStream &input) noexcept {
+		assert(input.IsReady());
+
+		return input.IsSeekable() && input.KnownSize() &&
+			input.GetSize() > 0 &&
+			input.GetSize() <= MAX_SIZE;
+	}
+
+	/* virtual methods from class InputStream */
+	void Check() override;
+	/* we don't need to implement Update() because all attributes
+	   have been copied already in our constructor */
+	//void Update() noexcept;
+	void Seek(offset_type offset) override;
+	bool IsEOF() noexcept override;
+	/* we don't support tags */
+	// std::unique_ptr<Tag> ReadTag() override;
+	bool IsAvailable() noexcept override;
+	size_t Read(void *ptr, size_t size) override;
+
+	/* virtual methods from class InputStreamHandler */
+	void OnInputStreamReady() noexcept override {
+		/* this should never be called, because our input must
+		   be "ready" already */
+	}
+
+	void OnInputStreamAvailable() noexcept override {
+		wake_cond.signal();
+	}
+
+private:
+	void RunThread() noexcept;
+};
+
+#endif