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/src/abstract_http_client.cpp

@@ -0,0 +1,142 @@
+#include "net/abstract_http_client.h"
+#include "net/http_base.h"
+#include "net/net_parse_helpers.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "net.http"
+
+namespace epee
+{
+namespace net_utils
+{
+  //----------------------------------------------------------------------------------------------------
+  bool is_unsafe(unsigned char compare_char)
+  {
+    if(compare_char <= 32 || compare_char >= 123)
+      return true;
+
+    const char* punsave = get_unsave_chars();
+
+    for(int ichar_pos = 0; 0!=punsave[ichar_pos] ;ichar_pos++)
+      if(compare_char == punsave[ichar_pos])
+        return true;
+
+    return false;
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string dec_to_hex(char num, int radix)
+  {
+    int temp=0;
+    std::string csTmp;
+    int num_char;
+
+    num_char = (int) num;
+    if (num_char < 0)
+      num_char = 256 + num_char;
+
+    while (num_char >= radix)
+    {
+      temp = num_char % radix;
+      num_char = (int)floor((float)num_char / (float)radix);
+      csTmp = get_hex_vals()[temp];
+    }
+
+    csTmp += get_hex_vals()[num_char];
+
+    if(csTmp.size() < 2)
+    {
+      csTmp += '0';
+    }
+
+    std::reverse(csTmp.begin(), csTmp.end());
+    //_mbsrev((unsigned char*)csTmp.data());
+
+    return csTmp;
+  }
+  //----------------------------------------------------------------------------------------------------
+  int get_index(const char *s, char c)
+  {
+    const char *ptr = (const char*)memchr(s, c, 16);
+    return ptr ? ptr-s : -1;
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string hex_to_dec_2bytes(const char *s)
+  {
+    const char *hex = get_hex_vals();
+    int i0 = get_index(hex, toupper(s[0]));
+    int i1 = get_index(hex, toupper(s[1]));
+    if (i0 < 0 || i1 < 0)
+      return std::string("%") + std::string(1, s[0]) + std::string(1, s[1]);
+    return std::string(1, i0 * 16 | i1);
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string convert(char val)
+  {
+    std::string csRet;
+    csRet += "%";
+    csRet += dec_to_hex(val, 16);
+    return  csRet;
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string conver_to_url_format(const std::string& uri)
+  {
+
+    std::string result;
+
+    for(size_t i = 0; i!= uri.size(); i++)
+    {
+      if(is_unsafe(uri[i]))
+        result += convert(uri[i]);
+      else
+        result += uri[i];
+
+    }
+
+    return result;
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string convert_from_url_format(const std::string& uri)
+  {
+
+    std::string result;
+
+    for(size_t i = 0; i!= uri.size(); i++)
+    {
+      if(uri[i] == '%' && i + 2 < uri.size())
+      {
+        result += hex_to_dec_2bytes(uri.c_str() + i + 1);
+        i += 2;
+      }
+      else
+        result += uri[i];
+
+    }
+
+    return result;
+  }
+  //----------------------------------------------------------------------------------------------------
+  std::string convert_to_url_format_force_all(const std::string& uri)
+  {
+    std::string result;
+
+    for(size_t i = 0; i!= uri.size(); i++)
+    {
+        result += convert(uri[i]);
+    }
+    return result;
+  }
+
+namespace http
+{
+  //----------------------------------------------------------------------------------------------------
+  bool epee::net_utils::http::abstract_http_client::set_server(const std::string& address, boost::optional<login> user, ssl_options_t ssl_options)
+  {
+    http::url_content parsed{};
+    const bool r = parse_url(address, parsed);
+    CHECK_AND_ASSERT_MES(r, false, "failed to parse url: " << address);
+    set_server(std::move(parsed.host), std::to_string(parsed.port), std::move(user), std::move(ssl_options));
+    return true;
+  }
+}
+}
+}