input/curl: move code to AsyncInputStream

New base class for other InputStream implementations that run in the
I/O thread.

src/input/AsyncInputStream.hxx

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2003-2014 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_ASYNC_INPUT_STREAM_HXX
+#define MPD_ASYNC_INPUT_STREAM_HXX
+
+#include "InputStream.hxx"
+#include "event/DeferredMonitor.hxx"
+#include "util/CircularBuffer.hxx"
+#include "util/Error.hxx"
+
+/**
+ * Helper class for moving asynchronous (non-blocking) InputStream
+ * implementations to the I/O thread.  Data is being read into a ring
+ * buffer, and that buffer is then consumed by another thread using
+ * the regular #InputStream API.
+ */
+class AsyncInputStream : public InputStream, private DeferredMonitor {
+	enum class SeekState : uint8_t {
+		NONE, SCHEDULED, PENDING
+	};
+
+	CircularBuffer<uint8_t> buffer;
+	const size_t resume_at;
+
+	bool open;
+
+	/**
+	 * Is the connection currently paused?  That happens when the
+	 * buffer was getting too large.  It will be unpaused when the
+	 * buffer is below the threshold again.
+	 */
+	bool paused;
+
+	SeekState seek_state;
+
+	/**
+	 * The #Tag object ready to be requested via
+	 * InputStream::ReadTag().
+	 */
+	Tag *tag;
+
+	offset_type seek_offset;
+
+protected:
+	Error postponed_error;
+
+public:
+	AsyncInputStream(const char *_url,
+			 Mutex &_mutex, Cond &_cond,
+			 void *_buffer, size_t _buffer_size,
+			 size_t _resume_at);
+
+	virtual ~AsyncInputStream();
+
+	/* virtual methods from InputStream */
+	bool Check(Error &error) final;
+	bool IsEOF() final;
+	bool Seek(offset_type new_offset, Error &error) final;
+	Tag *ReadTag() final;
+	bool IsAvailable() final;
+	size_t Read(void *ptr, size_t read_size, Error &error) final;
+
+protected:
+	void SetTag(Tag *_tag);
+
+	void Pause();
+
+	void SetClosed() {
+		open = false;
+	}
+
+	bool IsBufferEmpty() const {
+		return buffer.IsEmpty();
+	}
+
+	gcc_pure
+	size_t GetBufferSpace() const {
+		return buffer.GetSpace();
+	}
+
+	void AppendToBuffer(const void *data, size_t append_size);
+
+	virtual void DoResume() = 0;
+
+	/**
+	 * The actual Seek() implementation.  This virtual method will
+	 * be called from within the I/O thread.  When the operation
+	 * is finished, call SeekDone() to notify the caller.
+	 */
+	virtual void DoSeek(offset_type new_offset) = 0;
+
+	bool IsSeekPending() const {
+		return seek_state == SeekState::PENDING;
+	}
+
+	void SeekDone();
+
+private:
+	void Resume();
+
+	/* virtual methods from DeferredMonitor */
+	void RunDeferred() final;
+};
+
+#endif