Adding initial support for broadcasting transactions over Tor

- Support for ".onion" in --add-exclusive-node and --add-peer
  - Add --anonymizing-proxy for outbound Tor connections
  - Add --anonymous-inbounds for inbound Tor connections
  - Support for sharing ".onion" addresses over Tor connections
  - Support for broadcasting transactions received over RPC exclusively
    over Tor (else broadcast over public IP when Tor not enabled).

src/net/error.cpp

@@ -0,0 +1,92 @@
+// 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 "error.h"
+
+#include <string>
+
+namespace
+{
+    struct net_category : std::error_category
+    {
+        net_category() noexcept
+          : std::error_category()
+        {}
+
+        const char* name() const noexcept override
+        {
+            return "net::error_category";
+        }
+
+        std::string message(int value) const override
+        {
+            switch (net::error(value))
+            {
+            case net::error::expected_tld:
+                return "Expected top-level domain";
+            case net::error::invalid_host:
+                return "Host value is not valid";
+            case net::error::invalid_i2p_address:
+                return "Invalid I2P address";
+            case net::error::invalid_port:
+                return "Invalid port value (expected 0-65535)";
+            case net::error::invalid_tor_address:
+                return "Invalid Tor address";
+            case net::error::unsupported_address:
+                return "Network address not supported";
+            default:
+                break;
+            }
+
+            return "Unknown net::error";
+        }
+
+        std::error_condition default_error_condition(int value) const noexcept override
+        {
+            switch (net::error(value))
+            {
+            case net::error::invalid_port:
+                return std::errc::result_out_of_range;
+            case net::error::expected_tld:
+            case net::error::invalid_tor_address:
+            default:
+                break;
+            }
+            return std::error_condition{value, *this};
+        }
+    };
+} // anonymous
+
+namespace net
+{
+    std::error_category const& error_category() noexcept
+    {
+        static const net_category instance{};
+        return instance;
+    }
+}