AK: Move memory streams from LibCore

AK/MemoryStream.h

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/Stream.h>
+#include <AK/Vector.h>
+
+namespace AK {
+
+/// A stream class that allows for reading/writing on a preallocated memory area
+/// using a single read/write head.
+class FixedMemoryStream final : public SeekableStream {
+public:
+    static ErrorOr<NonnullOwnPtr<FixedMemoryStream>> construct(Bytes bytes);
+    static ErrorOr<NonnullOwnPtr<FixedMemoryStream>> construct(ReadonlyBytes bytes);
+
+    virtual bool is_eof() const override;
+    virtual bool is_open() const override;
+    virtual void close() override;
+    virtual ErrorOr<void> truncate(off_t) override;
+    virtual ErrorOr<Bytes> read(Bytes bytes) override;
+
+    virtual ErrorOr<size_t> seek(i64 offset, SeekMode seek_mode = SeekMode::SetPosition) override;
+
+    virtual ErrorOr<size_t> write(ReadonlyBytes bytes) override;
+    virtual ErrorOr<void> write_entire_buffer(ReadonlyBytes bytes) override;
+
+    Bytes bytes();
+    ReadonlyBytes bytes() const;
+    size_t offset() const;
+    size_t remaining() const;
+
+private:
+    explicit FixedMemoryStream(Bytes bytes);
+    explicit FixedMemoryStream(ReadonlyBytes bytes);
+
+    Bytes m_bytes;
+    size_t m_offset { 0 };
+    bool m_writing_enabled { true };
+};
+
+/// A stream class that allows for writing to an automatically allocating memory area
+/// and reading back the written data afterwards.
+class AllocatingMemoryStream final : public Stream {
+public:
+    virtual ErrorOr<Bytes> read(Bytes) override;
+    virtual ErrorOr<size_t> write(ReadonlyBytes) override;
+    virtual ErrorOr<void> discard(size_t) override;
+    virtual bool is_eof() const override;
+    virtual bool is_open() const override;
+    virtual void close() override;
+
+    size_t used_buffer_size() const;
+
+    ErrorOr<Optional<size_t>> offset_of(ReadonlyBytes needle) const;
+
+private:
+    // Note: We set the inline buffer capacity to zero to make moving chunks as efficient as possible.
+    using Chunk = AK::Detail::ByteBuffer<0>;
+    static constexpr size_t chunk_size = 4096;
+
+    ErrorOr<ReadonlyBytes> next_read_range();
+    ErrorOr<Bytes> next_write_range();
+    void cleanup_unused_chunks();
+
+    Vector<Chunk> m_chunks;
+    size_t m_read_offset = 0;
+    size_t m_write_offset = 0;
+};
+
+}
+
+#if USING_AK_GLOBALLY
+using AK::AllocatingMemoryStream;
+using AK::FixedMemoryStream;
+#endif