Add ref-counted buffer byte_slice. Currently used for sending TCP data.

contrib/epee/src/byte_slice.cpp

@@ -0,0 +1,209 @@
+// Copyright (c) 2019, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. 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.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// 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 COPYRIGHT HOLDER 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.
+
+#include <atomic>
+#include <cstdlib>
+#include <cstring>
+#include <limits>
+#include <stdexcept>
+#include <utility>
+
+#include "byte_slice.h"
+
+namespace epee
+{
+  struct byte_slice_data
+  {
+    byte_slice_data() noexcept
+      : ref_count(1)
+    {}
+
+    virtual ~byte_slice_data() noexcept
+    {}
+
+    std::atomic<std::size_t> ref_count;
+  };
+
+  void release_byte_slice::operator()(byte_slice_data* ptr) const noexcept
+  {
+    if (ptr && --(ptr->ref_count) == 0)
+    {
+      ptr->~byte_slice_data();
+      free(ptr);
+    }
+  }
+
+  namespace
+  {
+    template<typename T>
+    struct adapted_byte_slice final : byte_slice_data
+    {
+      explicit adapted_byte_slice(T&& buffer)
+        : byte_slice_data(), buffer(std::move(buffer))
+      {}
+
+      virtual ~adapted_byte_slice() noexcept final override
+      {}
+
+      const T buffer;
+    };
+
+    // bytes "follow" this structure in memory slab
+    struct raw_byte_slice final : byte_slice_data
+    {
+      raw_byte_slice() noexcept
+        : byte_slice_data()
+      {}
+
+      virtual ~raw_byte_slice() noexcept final override
+      {}
+    };
+
+    /* This technique is not-standard, but allows for the reference count and
+       memory for the bytes (when given a list of spans) to be allocated in a
+       single call. In that situation, the dynamic sized bytes are after/behind
+       the raw_byte_slice class. The C runtime has to track the number of bytes
+       allocated regardless, so free'ing is relatively easy. */
+
+    template<typename T, typename... U>
+    std::unique_ptr<T, release_byte_slice> allocate_slice(std::size_t extra_bytes, U&&... args)
+    {
+      if (std::numeric_limits<std::size_t>::max() - sizeof(T) < extra_bytes)
+        throw std::bad_alloc{};
+
+      void* const ptr = malloc(sizeof(T) + extra_bytes);
+      if (ptr == nullptr)
+        throw std::bad_alloc{};
+
+      try
+      {
+        new (ptr) T{std::forward<U>(args)...};
+      }
+      catch (...)
+      {
+        free(ptr);
+        throw;
+      }
+      return std::unique_ptr<T, release_byte_slice>{reinterpret_cast<T*>(ptr)};
+    }
+  } // anonymous
+
+  byte_slice::byte_slice(byte_slice_data* storage, span<const std::uint8_t> portion) noexcept
+    : storage_(storage), portion_(portion)
+  {
+    if (storage_)
+      ++(storage_->ref_count);
+  }
+
+  template<typename T>
+  byte_slice::byte_slice(const adapt_buffer, T&& buffer)
+    : storage_(nullptr), portion_(to_byte_span(to_span(buffer)))
+  {
+    if (!buffer.empty())
+      storage_ = allocate_slice<adapted_byte_slice<T>>(0, std::move(buffer));
+  }
+
+  byte_slice::byte_slice(std::initializer_list<span<const std::uint8_t>> sources)
+    : byte_slice()
+  {
+    std::size_t space_needed = 0;
+    for (const auto source : sources)
+      space_needed += source.size();
+
+    if (space_needed)
+    {
+      auto storage = allocate_slice<raw_byte_slice>(space_needed);
+      span<std::uint8_t> out{reinterpret_cast<std::uint8_t*>(storage.get() + 1), space_needed};
+      portion_ = {out.data(), out.size()};
+
+      for (const auto source : sources)
+      {
+        std::memcpy(out.data(), source.data(), source.size());
+        if (out.remove_prefix(source.size()) < source.size())
+          throw std::bad_alloc{}; // size_t overflow on space_needed
+      }
+      storage_ = std::move(storage);
+    }
+  }
+
+  byte_slice::byte_slice(std::string&& buffer)
+    : byte_slice(adapt_buffer{}, std::move(buffer))
+  {}
+
+  byte_slice::byte_slice(std::vector<std::uint8_t>&& buffer)
+    : byte_slice(adapt_buffer{}, std::move(buffer))
+  {}
+
+  byte_slice::byte_slice(byte_slice&& source) noexcept
+    : storage_(std::move(source.storage_)), portion_(source.portion_)
+  {
+    source.portion_ = epee::span<const std::uint8_t>{};
+  }
+
+  byte_slice& byte_slice::operator=(byte_slice&& source) noexcept
+  {
+    storage_ = std::move(source.storage_);
+    portion_ = source.portion_;
+    if (source.storage_ == nullptr)
+      source.portion_ = epee::span<const std::uint8_t>{};
+
+    return *this;
+  }
+
+  std::size_t byte_slice::remove_prefix(std::size_t max_bytes) noexcept
+  {
+    max_bytes = portion_.remove_prefix(max_bytes);
+    if (portion_.empty())
+      storage_ = nullptr;
+    return max_bytes;
+  }
+
+  byte_slice byte_slice::take_slice(const std::size_t max_bytes) noexcept
+  {
+    byte_slice out{};
+    std::uint8_t const* const ptr = data();
+    out.portion_ = {ptr, portion_.remove_prefix(max_bytes)};
+
+    if (portion_.empty())
+      out.storage_ = std::move(storage_); // no atomic inc/dec
+    else
+      out = {storage_.get(), out.portion_};
+
+    return out;
+  }
+
+  byte_slice byte_slice::get_slice(const std::size_t begin, const std::size_t end) const
+  {
+    if (end < begin || portion_.size() < end)
+      throw std::out_of_range{"bad slice range"};
+
+    if (begin == end)
+      return {};
+    return {storage_.get(), {portion_.begin() + begin, end - begin}};
+  }
+} // epee