Decode strings returned by ExecuteScript()

ExecuteScript returns strings as fully
quoted JSON strings so they have to be decoded
to a binary string.

include/wx/private/json.h

@@ -0,0 +1,89 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/private/json.h
+// Purpose:     Helper functions to handle JSON data
+// Author:      Tobias Taschner
+// Created:     2020-01-17
+// Copyright:   (c) 2020 wxWidgets development team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PRIVATE_JSON_H_
+#define _WX_PRIVATE_JSON_H_
+
+namespace wxJSON
+{
+
+// Decode a string literal including escape sequences
+// If the input is not quoted string it will be returned as the input
+wxString DecodeString(const wxString& str)
+{
+    if (!str.starts_with('"') || !str.ends_with('"'))
+        return str;
+
+    wxString result;
+    const wxWCharBuffer buf = str.wc_str();
+    const wchar_t* end = buf.data() + buf.length() - 1;
+    for (const wchar_t* ch = buf.data() + 1; ch < end; ++ch)
+    {
+        if (*ch == '\\')
+        {
+            switch (*(++ch))
+            {
+            case 'b':
+                result.append('\b');
+                break;
+            case 'n':
+                result.append('\n');
+                break;
+            case 'r':
+                result.append('\r');
+                break;
+            case 't':
+                result.append('\t');
+                break;
+            case 'v':
+                result.append('\v');
+                break;
+            case '\'':
+                result.append('\'');
+                break;
+            case '"':
+                result.append('"');
+                break;
+            case '\\':
+                result.append('\\');
+                break;
+            case 'u':
+                if (wxIsxdigit(ch[1]) && wxIsxdigit(ch[2]) &&
+                    wxIsxdigit(ch[3]) && wxIsxdigit(ch[4]))
+                {
+                    wxUChar uchar = wxHexToDec(wxString(&ch[3], 2)) |
+                        wxHexToDec(wxString(&ch[1], 2)) >> 8;
+                    result.append(uchar);
+                    ch += 4;
+                }
+                break;
+            case 'x':
+                if (wxIsxdigit(ch[1]) && wxIsxdigit(ch[2]))
+                {
+                    wxChar hchar = wxHexToDec(wxString(&ch[1], 2));
+                    result.append(hchar);
+                    ch += 2;
+                }
+                break;
+
+            default:
+                result.append(*ch);
+                break;
+            }
+        }
+        else
+            result.append(*ch);
+    }
+
+    return result;
+}
+
+} // namespace JSON
+
+#endif // _WX_PRIVATE_JSON_H_