epee: better network buffer data structure

avoids pointless allocs and memcpy

contrib/epee/src/buffer.cpp

@@ -0,0 +1,97 @@
+// Copyright (c) 2018, 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 <string.h>
+#include "net/buffer.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "net.buffer"
+
+namespace epee
+{
+namespace net_utils
+{
+
+void buffer::append(const void *data, size_t sz)
+{
+  const size_t capacity = storage.capacity();
+  const size_t avail = capacity - storage.size();
+
+  CHECK_AND_ASSERT_THROW_MES(storage.size() < std::numeric_limits<size_t>::max() - sz, "Too much data to append");
+
+  // decide when to move
+  if (sz > avail)
+  {
+    // we have to reallocate or move
+    const bool move = size() + sz <= capacity;
+    if (move)
+    {
+      const size_t bytes = storage.size() - offset;
+      NET_BUFFER_LOG("appending " << sz << " from " << size() << " by moving " << bytes << " from offset " << offset << " first (forced)");
+      memmove(storage.data(), storage.data() + offset, bytes);
+      storage.resize(bytes);
+      offset = 0;
+    }
+    else
+    {
+      NET_BUFFER_LOG("appending " << sz << " from " << size() << " by reallocating");
+      std::vector<uint8_t> new_storage;
+      size_t reserve = (((size() + sz) * 3 / 2) + 4095) & ~4095;
+      new_storage.reserve(reserve);
+      new_storage.resize(size());
+      memcpy(new_storage.data(), storage.data() + offset, storage.size() - offset);
+      offset = 0;
+      std::swap(storage, new_storage);
+    }
+  }
+  else
+  {
+    // we have space already
+    if (size() <= 4096 && offset > 4096 * 16 && offset >= capacity / 2)
+    {
+      // we have little to move, and we're far enough into the buffer that it's probably a win to move anyway
+      const size_t pos = storage.size() - offset;
+      NET_BUFFER_LOG("appending " << sz << " from " << size() << " by moving " << pos << " from offset " << offset << " first (unforced)");
+      memmove(storage.data(), storage.data() + offset, storage.size() - offset);
+      storage.resize(pos);
+      offset = 0;
+    }
+    else
+    {
+      NET_BUFFER_LOG("appending " << sz << " from " << size() << " by writing to existing capacity");
+    }
+  }
+
+  // add the new data
+  storage.insert(storage.end(), (const uint8_t*)data, (const uint8_t*)data + sz);
+
+  NET_BUFFER_LOG("storage now " << offset << "/" << storage.size() << "/" << storage.capacity());
+}
+
+}
+}