Allow wallet2.h to run in WebAssembly

- Add abstract_http_client.h which http_client.h extends.
- Replace simple_http_client with abstract_http_client in wallet2,
message_store, message_transporter, and node_rpc_proxy.
- Import and export wallet data in wallet2.
- Use #if defined __EMSCRIPTEN__ directives to skip incompatible code.

contrib/epee/include/net/abstract_http_client.h

@@ -0,0 +1,87 @@
+// Copyright (c) 2006-2013, Andrey N. Sabelnikov, www.sabelnikov.net
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * 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.
+// * Neither the name of the Andrey N. Sabelnikov 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 OWNER  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 <string>
+#include <boost/optional/optional.hpp>
+#include "http_auth.h"
+#include "net/net_ssl.h"
+
+namespace epee
+{
+namespace net_utils
+{
+  inline const char* get_hex_vals()
+  {
+    static constexpr const char hexVals[16] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
+    return hexVals;
+  }
+
+  inline const char* get_unsave_chars()
+  {
+    //static constexpr char unsave_chars[] = "\"<>%\\^[]`+$,@:;/!#?=&";
+    static constexpr const char unsave_chars[] = "\"<>%\\^[]`+$,@:;!#&";
+    return unsave_chars;
+  }
+
+  bool is_unsafe(unsigned char compare_char);
+  std::string dec_to_hex(char num, int radix);
+  int get_index(const char *s, char c);
+  std::string hex_to_dec_2bytes(const char *s);
+  std::string convert(char val);
+  std::string conver_to_url_format(const std::string& uri);
+  std::string convert_from_url_format(const std::string& uri);
+  std::string convert_to_url_format_force_all(const std::string& uri);
+
+namespace http
+{
+  class abstract_http_client
+  {
+  public:
+    abstract_http_client() {}
+    virtual ~abstract_http_client() {}
+    bool set_server(const std::string& address, boost::optional<login> user, ssl_options_t ssl_options = ssl_support_t::e_ssl_support_autodetect);
+    virtual void set_server(std::string host, std::string port, boost::optional<login> user, ssl_options_t ssl_options = ssl_support_t::e_ssl_support_autodetect) = 0;
+    virtual void set_auto_connect(bool auto_connect) = 0;
+    virtual bool connect(std::chrono::milliseconds timeout) = 0;
+    virtual bool disconnect() = 0;
+    virtual bool is_connected(bool *ssl = NULL) = 0;
+    virtual bool invoke(const boost::string_ref uri, const boost::string_ref method, const std::string& body, std::chrono::milliseconds timeout, const http_response_info** ppresponse_info = NULL, const fields_list& additional_params = fields_list()) = 0;
+    virtual bool invoke_get(const boost::string_ref uri, std::chrono::milliseconds timeout, const std::string& body = std::string(), const http_response_info** ppresponse_info = NULL, const fields_list& additional_params = fields_list()) = 0;
+    virtual bool invoke_post(const boost::string_ref uri, const std::string& body, std::chrono::milliseconds timeout, const http_response_info** ppresponse_info = NULL, const fields_list& additional_params = fields_list()) = 0;
+    virtual uint64_t get_bytes_sent() const = 0;
+    virtual uint64_t get_bytes_received() const = 0;
+  };
+
+  class http_client_factory
+  {
+  public:
+    virtual ~http_client_factory() {}
+    virtual std::unique_ptr<abstract_http_client> create() = 0;
+  };
+}
+}
+}