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+/*
+ * Copyright (C) 2003-2014 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef FOREIGN_FIFO_BUFFER_HXX
+#define FOREIGN_FIFO_BUFFER_HXX
+
+#include "WritableBuffer.hxx"
+
+#include <utility>
+#include <algorithm>
+
+#include <cstddef>
+
+#include <assert.h>
+
+/**
+ * A first-in-first-out buffer: you can append data at the end, and
+ * read data from the beginning.  This class automatically shifts the
+ * buffer as needed.  It is not thread safe.
+ *
+ * This class does not manage buffer memory.  It will not allocate or
+ * free any memory, it only manages the contents of an existing buffer
+ * given to the constructor.
+ */
+template<typename T>
+class ForeignFifoBuffer {
+public:
+	typedef size_t size_type;
+	typedef WritableBuffer<T> Range;
+	typedef typename Range::pointer_type pointer_type;
+	typedef typename Range::const_pointer_type const_pointer_type;
+
+protected:
+	size_type head, tail, capacity;
+	T *data;
+
+public:
+	explicit constexpr ForeignFifoBuffer(std::nullptr_t n)
+		:head(0), tail(0), capacity(0), data(n) {}
+
+	constexpr ForeignFifoBuffer(T *_data, size_type _capacity)
+		:head(0), tail(0), capacity(_capacity), data(_data) {}
+
+	ForeignFifoBuffer(ForeignFifoBuffer &&src)
+		:head(src.head), tail(src.tail),
+		 capacity(src.capacity), data(src.data) {
+		src.SetNull();
+	}
+
+	ForeignFifoBuffer &operator=(ForeignFifoBuffer &&src) {
+		head = src.head;
+		tail = src.tail;
+		capacity = src.capacity;
+		data = src.data;
+		src.SetNull();
+		return *this;
+	}
+
+	void Swap(ForeignFifoBuffer<T> &other) {
+		std::swap(head, other.head);
+		std::swap(tail, other.tail);
+		std::swap(capacity, other.capacity);
+		std::swap(data, other.data);
+	}
+
+	constexpr bool IsNull() const {
+		return data == nullptr;
+	}
+
+	constexpr bool IsDefined() const {
+		return !IsNull();
+	}
+
+	T *GetBuffer() {
+		return data;
+	}
+
+	constexpr size_type GetCapacity() const {
+		return capacity;
+	}
+
+	void SetNull() {
+		head = tail = 0;
+		capacity = 0;
+		data = nullptr;
+	}
+
+	void SetBuffer(T *_data, size_type _capacity) {
+		assert(_data != nullptr);
+		assert(_capacity > 0);
+
+		head = tail = 0;
+		capacity = _capacity;
+		data = _data;
+	}
+
+	void MoveBuffer(T *new_data, size_type new_capacity) {
+		assert(new_capacity >= tail - head);
+
+		std::move(data + head, data + tail, new_data);
+		data = new_data;
+		capacity = new_capacity;
+		tail -= head;
+		head = 0;
+	}
+
+	void Clear() {
+		head = tail = 0;
+	}
+
+	constexpr bool IsEmpty() const {
+		return head == tail;
+	}
+
+	constexpr bool IsFull() const {
+		return head == 0 && tail == capacity;
+	}
+
+	/**
+	 * Prepares writing.  Returns a buffer range which may be written.
+	 * When you are finished, call append().
+	 */
+	Range Write() {
+		if (IsEmpty())
+			Clear();
+		else if (tail == capacity)
+			Shift();
+
+		return Range(data + tail, capacity - tail);
+	}
+
+	bool WantWrite(size_type n) {
+		if (tail + n <= capacity)
+			/* enough space after the tail */
+			return true;
+
+		const size_type in_use = tail - head;
+		const size_type required_capacity = in_use + n;
+		if (required_capacity > capacity)
+			return false;
+
+		Shift();
+		assert(tail + n <= capacity);
+		return true;
+	}
+
+	/**
+	 * Expands the tail of the buffer, after data has been written to
+	 * the buffer returned by write().
+	 */
+	void Append(size_type n) {
+		assert(tail <= capacity);
+		assert(n <= capacity);
+		assert(tail + n <= capacity);
+
+		tail += n;
+	}
+
+	constexpr size_type GetAvailable() const {
+		return tail - head;
+	}
+
+	/**
+	 * Return a buffer range which may be read.  The buffer pointer is
+	 * writable, to allow modifications while parsing.
+	 */
+	constexpr Range Read() const {
+		return Range(data + head, tail - head);
+	}
+
+	/**
+	 * Marks a chunk as consumed.
+	 */
+	void Consume(size_type n) {
+		assert(tail <= capacity);
+		assert(head <= tail);
+		assert(n <= tail);
+		assert(head + n <= tail);
+
+		head += n;
+	}
+
+	size_type Read(pointer_type p, size_type n) {
+		auto range = Read();
+		if (n > range.size)
+			n = range.size;
+		std::copy_n(range.data, n, p);
+		Consume(n);
+		return n;
+	}
+
+	/**
+	 * Move as much data as possible from the specified buffer.
+	 *
+	 * @return the number of items moved
+	 */
+	size_type MoveFrom(ForeignFifoBuffer<T> &src) {
+		auto r = src.Read();
+		auto w = Write();
+		size_t n = std::min(r.size, w.size);
+
+		std::move(r.data, r.data + n, w.data);
+		Append(n);
+		src.Consume(n);
+		return n;
+	}
+
+protected:
+	void Shift() {
+		if (head == 0)
+			return;
+
+		assert(head <= capacity);
+		assert(tail <= capacity);
+		assert(tail >= head);
+
+		std::move(data + head, data + tail, data);
+
+		tail -= head;
+		head = 0;
+	}
+};
+
+#endif