Add ZeroCopyOutputStream and tidy up

src/ripple/overlay/impl/ZeroCopyStream.h

@@ -0,0 +1,217 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2012, 2013 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef RIPPLE_OVERLAY_ZEROCOPYSTREAM_H_INCLUDED
+#define RIPPLE_OVERLAY_ZEROCOPYSTREAM_H_INCLUDED
+
+#include <google/protobuf/io/zero_copy_stream.h>
+#include <boost/asio/buffer.hpp>
+#include <cstdint>
+
+namespace ripple {
+
+/** Implements ZeroCopyInputStream around a buffer sequence.
+    @tparam Buffers A type meeting the requirements of ConstBufferSequence.
+    @see https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.io.zero_copy_stream
+*/
+template <class Buffers>
+class ZeroCopyInputStream
+    : public ::google::protobuf::io::ZeroCopyInputStream
+{
+private:
+    using iterator = typename Buffers::const_iterator;
+    using const_buffer = boost::asio::const_buffer;
+
+    std::int64_t count_ = 0;
+    iterator last_;
+    iterator first_;    // Where pos_ comes from
+    const_buffer pos_;  // What Next() will return
+
+public:
+    explicit
+    ZeroCopyInputStream (Buffers const& buffers);
+
+    bool
+    Next (const void** data, int* size) override;
+
+    void
+    BackUp (int count) override;
+
+    bool
+    Skip (int count) override;
+
+    std::int64_t
+    ByteCount() const override
+    {
+        return count_;
+    }
+};
+
+//------------------------------------------------------------------------------
+
+template <class Buffers>
+ZeroCopyInputStream<Buffers>::ZeroCopyInputStream (
+        Buffers const& buffers)
+    : last_ (buffers.end())
+    , first_ (buffers.begin())
+    , pos_ ((first_ != last_) ?
+        *first_ : const_buffer(nullptr, 0))
+{
+}
+
+template <class Buffers>
+bool
+ZeroCopyInputStream<Buffers>::Next (
+    const void** data, int* size)
+{
+    *data = boost::asio::buffer_cast<void const*>(pos_);
+    *size = boost::asio::buffer_size(pos_);
+    if (first_ == last_)
+        return false;
+    count_ += *size;
+    pos_ = (++first_ != last_) ? *first_ :
+        const_buffer(nullptr, 0);
+    return true;
+}
+
+template <class Buffers>
+void
+ZeroCopyInputStream<Buffers>::BackUp (int count)
+{
+    --first_;
+    pos_ = *first_ +
+        (boost::asio::buffer_size(*first_) - count);
+    count_ -= count;
+}
+
+template <class Buffers>
+bool
+ZeroCopyInputStream<Buffers>::Skip (int count)
+{
+    if (first_ == last_)
+        return false;
+    while (count > 0)
+    {
+        auto const size =
+            boost::asio::buffer_size(pos_);
+        if (count < size)
+        {
+            pos_ = pos_ + count;
+            count_ += count;
+            return true;
+        }
+        count_ += size;
+        if (++first_ == last_)
+            return false;
+        count -= size;
+        pos_ = *first_;
+    }
+    return true;
+}
+
+//------------------------------------------------------------------------------
+
+/** Implements ZeroCopyOutputStream around a Streambuf.
+    Streambuf matches the public interface defined by boost::asio::streambuf.
+    @tparam Streambuf A type meeting the requirements of Streambuf.
+*/
+template <class Streambuf>
+class ZeroCopyOutputStream
+    : public ::google::protobuf::io::ZeroCopyOutputStream
+{
+private:
+    using buffers_type = typename Streambuf::mutable_buffers_type;
+    using iterator = typename buffers_type::const_iterator;
+    using mutable_buffer = boost::asio::mutable_buffer;
+
+    Streambuf& streambuf_;
+    std::size_t blockSize_;
+    std::size_t count_ = 0;
+    std::size_t commit_ = 0;
+    buffers_type buffers_;
+    iterator pos_;
+
+public:
+    explicit
+    ZeroCopyOutputStream (Streambuf& streambuf,
+        std::size_t blockSize);
+
+    bool
+    Next (void** data, int* size) override;
+
+    void
+    BackUp (int count) override;
+
+    std::int64_t
+    ByteCount() const override
+    {
+        return count_;
+    }
+};
+
+//------------------------------------------------------------------------------
+
+template <class Streambuf>
+ZeroCopyOutputStream<Streambuf>::ZeroCopyOutputStream(
+        Streambuf& streambuf, std::size_t blockSize)
+    : streambuf_ (streambuf)
+    , blockSize_ (blockSize)
+    , buffers_ (streambuf_.prepare(blockSize_))
+    , pos_ (buffers_.begin())
+{
+}
+
+template <class Streambuf>
+bool
+ZeroCopyOutputStream<Streambuf>::Next(
+    void** data, int* size)
+{
+    if (commit_ != 0)
+    {
+        streambuf_.commit(commit_);
+        count_ += commit_;
+    }
+
+    if (pos_ == buffers_.end())
+    {
+        buffers_ = streambuf_.prepare (blockSize_);
+        pos_ = buffers_.begin();
+    }
+
+    *data = boost::asio::buffer_cast<void*>(*pos_);
+    *size = boost::asio::buffer_size(*pos_);
+    commit_ = *size;
+    ++pos_;
+    return true;
+}
+
+template <class Streambuf>
+void
+ZeroCopyOutputStream<Streambuf>::BackUp (int count)
+{
+    assert(count <= commit_);
+    auto const n = commit_ - count;
+    streambuf_.commit(n);
+    count_ += n;
+    commit_ = 0;
+}
+
+} // ripple
+
+#endif