epee: better network buffer data structure

avoids pointless allocs and memcpy

contrib/epee/include/net/buffer.h

@@ -0,0 +1,62 @@
+// 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.
+
+#pragma once
+
+#include <vector>
+#include "misc_log_ex.h"
+#include "span.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "net.buffer"
+
+//#define NET_BUFFER_LOG(x) MDEBUG(x)
+#define NET_BUFFER_LOG(x) ((void)0)
+
+namespace epee
+{
+namespace net_utils
+{
+class buffer
+{
+public:
+  buffer(size_t reserve = 0): offset(0) { storage.reserve(reserve); }
+
+  void append(const void *data, size_t sz);
+  void erase(size_t sz) { NET_BUFFER_LOG("erasing " << sz << "/" << size()); CHECK_AND_ASSERT_THROW_MES(offset + sz <= storage.size(), "erase: sz too large"); offset += sz; if (offset == storage.size()) { storage.resize(0); offset = 0; } }
+  epee::span<const uint8_t> span(size_t sz) const { CHECK_AND_ASSERT_THROW_MES(sz <= size(), "span is too large"); return epee::span<const uint8_t>(storage.data() + offset, sz); }
+  // carve must keep the data in scope till next call, other API calls (such as append, erase) can invalidate the carved buffer
+  epee::span<const uint8_t> carve(size_t sz) { CHECK_AND_ASSERT_THROW_MES(sz <= size(), "span is too large"); offset += sz; return epee::span<const uint8_t>(storage.data() + offset - sz, sz); }
+  size_t size() const { return storage.size() - offset; }
+
+private:
+  std::vector<uint8_t> storage;
+  size_t offset;
+};
+}
+}