core: include a dummy encrypted payment id when no payment is used

For better transaction uniformity, even though this wastes space.

src/net/string.cpp

@@ -0,0 +1,34 @@
+
+
+#include "string.h"
+
+#include "net/tor_address.h"
+#include "string_tools.h"
+
+namespace net
+{
+    expect<epee::net_utils::network_address>
+    get_network_address(const boost::string_ref address, const std::uint16_t default_port)
+    {
+        const boost::string_ref host = address.substr(0, address.rfind(':'));
+
+        if (host.empty())
+            return make_error_code(net::error::kInvalidHost);
+        if (host.ends_with(".onion"))
+            return tor_address::make(address, default_port);
+        if (host.ends_with(".i2p"))
+            return make_error_code(net::error::kInvalidI2PAddress); // not yet implemented (prevent public DNS lookup)
+
+        std::uint16_t port = default_port;
+        if (host.size() < address.size())
+        {
+            if (!epee::string_tools::get_xtype_from_string(port, std::string{address.substr(host.size() + 1)}))
+                return make_error_code(net::error::kInvalidPort);
+        }
+
+        std::uint32_t ip = 0;
+        if (epee::string_tools::get_ip_int32_from_string(ip, std::string{host}))
+            return {epee::net_utils::ipv4_network_address{ip, port}};
+        return make_error_code(net::error::kUnsupportedAddress);
+    }
+}