json_settings.cpp

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/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2020 Jon Evans <[email protected]>
 * Copyright (C) 2020-2022 KiCad Developers, see AUTHORS.txt for contributors.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
#include <algorithm>
#include <fstream>
#include <iomanip>
#include <utility>
#include <sstream>
 
#include <locale_io.h>
#include <gal/color4d.h>
#include <settings/json_settings.h>
#include <settings/json_settings_internals.h>
#include <settings/nested_settings.h>
#include <settings/parameters.h>
#include <wx/config.h>
#include <wx/debug.h>
#include <wx/fileconf.h>
#include <wx/filename.h>
#include <wx/log.h>
#include <wx/stdstream.h>
#include <wx/wfstream.h>
 
const wxChar* const traceSettings = wxT( "KICAD_SETTINGS" );
 
 
nlohmann::json::json_pointer JSON_SETTINGS_INTERNALS::PointerFromString( std::string aPath )
{
 std::replace( aPath.begin(), aPath.end(), '.', '/' );
 aPath.insert( 0, "/" );
 
 nlohmann::json::json_pointer p;
 
 try
 {
 p = nlohmann::json::json_pointer( aPath );
 }
 catch( ... )
 {
 wxASSERT_MSG( false, wxT( "Invalid pointer path in PointerFromString!" ) );
 }
 
 return p;
}
 
 
JSON_SETTINGS::JSON_SETTINGS( const wxString& aFilename, SETTINGS_LOC aLocation,
 int aSchemaVersion, bool aCreateIfMissing, bool aCreateIfDefault,
 bool aWriteFile ) :
 m_filename( aFilename ),
 m_legacy_filename( "" ),
 m_location( aLocation ),
 m_createIfMissing( aCreateIfMissing ),
 m_createIfDefault( aCreateIfDefault ),
 m_writeFile( aWriteFile ),
 m_deleteLegacyAfterMigration( true ),
 m_resetParamsIfMissing( true ),
 m_schemaVersion( aSchemaVersion ),
 m_manager( nullptr )
{
 m_internals = std::make_unique<JSON_SETTINGS_INTERNALS>();
 
 try
 {
 m_internals->SetFromString( "meta.filename", GetFullFilename() );
 }
 catch( ... )
 {
 wxLogTrace( traceSettings, wxT( "Error: Could not create filename field for %s" ),
 GetFullFilename() );
 }
 
 
 m_params.emplace_back(
 new PARAM<int>( "meta.version", &m_schemaVersion, m_schemaVersion, true ) );
}
 
 
JSON_SETTINGS::~JSON_SETTINGS()
{
 for( auto param: m_params )
 delete param;
 
 m_params.clear();
}
 
 
wxString JSON_SETTINGS::GetFullFilename() const
{
 return wxString( m_filename + "." + getFileExt() );
}
 
 
nlohmann::json& JSON_SETTINGS::At( const std::string& aPath )
{
 return m_internals->At( aPath );
}
 
 
bool JSON_SETTINGS::Contains( const std::string& aPath ) const
{
 return m_internals->contains( JSON_SETTINGS_INTERNALS::PointerFromString( aPath ) );
}
 
 
JSON_SETTINGS_INTERNALS* JSON_SETTINGS::Internals()
{
 return m_internals.get();
}
 
 
void JSON_SETTINGS::Load()
{
 for( auto param : m_params )
 {
 try
 {
 param->Load( this, m_resetParamsIfMissing );
 }
 catch( ... )
 {
 // Skip unreadable parameters in file
 wxLogTrace( traceSettings, wxT( "param '%s' load err" ), param->GetJsonPath().c_str() );
 }
 }
}
 
 
bool JSON_SETTINGS::LoadFromFile( const wxString& aDirectory )
{
 // First, load all params to default values
 m_internals->clear();
 Load();
 
 bool success = true;
 bool migrated = false;
 bool legacy_migrated = false;
 
 LOCALE_IO locale;
 
 auto migrateFromLegacy = [&] ( wxFileName& aPath ) {
 // Backup and restore during migration so that the original can be mutated if convenient
 bool backed_up = false;
 wxFileName temp;
 
 if( aPath.IsDirWritable() )
 {
 temp.AssignTempFileName( aPath.GetFullPath() );
 
 if( !wxCopyFile( aPath.GetFullPath(), temp.GetFullPath() ) )
 {
 wxLogTrace( traceSettings, wxT( "%s: could not create temp file for migration" ),
 GetFullFilename() );
 }
 else
 backed_up = true;
 }
 
 // Silence popups if legacy file is read-only
 wxLogNull doNotLog;
 
 wxConfigBase::DontCreateOnDemand();
 auto cfg = std::make_unique<wxFileConfig>( wxT( "" ), wxT( "" ), aPath.GetFullPath() );
 
 // If migrate fails or is not implemented, fall back to built-in defaults that were
 // already loaded above
 if( !MigrateFromLegacy( cfg.get() ) )
 {
 success = false;
 wxLogTrace( traceSettings,
 wxT( "%s: migrated; not all settings were found in legacy file" ),
 GetFullFilename() );
 }
 else
 {
 success = true;
 wxLogTrace( traceSettings, wxT( "%s: migrated from legacy format" ), GetFullFilename() );
 }
 
 if( backed_up )
 {
 cfg.reset();
 
 if( !wxCopyFile( temp.GetFullPath(), aPath.GetFullPath() ) )
 {
 wxLogTrace( traceSettings,
 wxT( "migrate; copy temp file %s to %s failed" ),
 temp.GetFullPath(), aPath.GetFullPath() );
 }
 
 if( !wxRemoveFile( temp.GetFullPath() ) )
 {
 wxLogTrace( traceSettings,
 wxT( "migrate; failed to remove temp file %s" ),
 temp.GetFullPath() );
 }
 }
 
 // Either way, we want to clean up the old file afterwards
 legacy_migrated = true;
 };
 
 wxFileName path;
 
 if( aDirectory.empty() )
 {
 path.Assign( m_filename );
 path.SetExt( getFileExt() );
 }
 else
 {
 wxString dir( aDirectory );
 path.Assign( dir, m_filename, getFileExt() );
 }
 
 if( !path.Exists() )
 {
 // Case 1: legacy migration, no .json extension yet
 path.SetExt( getLegacyFileExt() );
 
 if( path.Exists() )
 {
 migrateFromLegacy( path );
 }
 // Case 2: legacy filename is different from new one
 else if( !m_legacy_filename.empty() )
 {
 path.SetName( m_legacy_filename );
 
 if( path.Exists() )
 migrateFromLegacy( path );
 }
 else
 {
 success = false;
 }
 }
 else
 {
 if( !path.IsFileWritable() )
 m_writeFile = false;
 
 try
 {
 wxFFileInputStream fp( path.GetFullPath(), wxT( "rt" ) );
 wxStdInputStream fstream( fp );
 
 if( fp.IsOk() )
 {
 *static_cast<nlohmann::json*>( m_internals.get() ) =
 nlohmann::json::parse( fstream, nullptr,
 /* allow_exceptions = */ true,
 /* ignore_comments = */ true );
 
 // If parse succeeds, check if schema migration is required
 int filever = -1;
 
 try
 {
 filever = m_internals->Get<int>( "meta.version" );
 }
 catch( ... )
 {
 wxLogTrace( traceSettings, wxT( "%s: file version could not be read!" ),
 GetFullFilename() );
 success = false;
 }
 
 if( filever >= 0 && filever < m_schemaVersion )
 {
 wxLogTrace( traceSettings, wxT( "%s: attempting migration from version %d to %d" ),
 GetFullFilename(), filever, m_schemaVersion );
 
 if( Migrate() )
 {
 migrated = true;
 }
 else
 {
 wxLogTrace( traceSettings, wxT( "%s: migration failed!" ), GetFullFilename() );
 }
 }
 else if( filever > m_schemaVersion )
 {
 wxLogTrace( traceSettings,
 wxT( "%s: warning: file version %d is newer than latest (%d)" ),
 GetFullFilename(), filever, m_schemaVersion );
 }
 }
 else
 {
 wxLogTrace( traceSettings, wxT( "%s exists but can't be opened for read" ),
 GetFullFilename() );
 }
 }
 catch( nlohmann::json::parse_error& error )
 {
 success = false;
 wxLogTrace( traceSettings, wxT( "Json parse error reading %s: %s" ),
 path.GetFullPath(), error.what() );
 wxLogTrace( traceSettings, wxT( "Attempting migration in case file is in legacy format" ) );
 migrateFromLegacy( path );
 }
 }
 
 // Now that we have new data in the JSON structure, load the params again
 Load();
 
 // And finally load any nested settings
 for( auto settings : m_nested_settings )
 settings->LoadFromFile();
 
 wxLogTrace( traceSettings, wxT( "Loaded <%s> with schema %d" ), GetFullFilename(), m_schemaVersion );
 
 // If we migrated, clean up the legacy file (with no extension)
 if( m_writeFile && ( legacy_migrated || migrated ) )
 {
 if( legacy_migrated && m_deleteLegacyAfterMigration && !wxRemoveFile( path.GetFullPath() ) )
 {
 wxLogTrace( traceSettings, wxT( "Warning: could not remove legacy file %s" ),
 path.GetFullPath() );
 }
 
 // And write-out immediately so that we don't lose data if the program later crashes.
 if( m_deleteLegacyAfterMigration )
 SaveToFile( aDirectory, true );
 }
 
 return success;
}
 
 
bool JSON_SETTINGS::Store()
{
 bool modified = false;
 
 for( auto param : m_params )
 {
 modified |= !param->MatchesFile( this );
 param->Store( this );
 }
 
 return modified;
}
 
 
void JSON_SETTINGS::ResetToDefaults()
{
 for( auto param : m_params )
 param->SetDefault();
}
 
 
bool JSON_SETTINGS::SaveToFile( const wxString& aDirectory, bool aForce )
{
 if( !m_writeFile )
 return false;
 
 // Default PROJECT won't have a filename set
 if( m_filename.IsEmpty() )
 return false;
 
 wxFileName path;
 
 if( aDirectory.empty() )
 {
 path.Assign( m_filename );
 path.SetExt( getFileExt() );
 }
 else
 {
 wxString dir( aDirectory );
 path.Assign( dir, m_filename, getFileExt() );
 }
 
 if( !m_createIfMissing && !path.FileExists() )
 {
 wxLogTrace( traceSettings,
 wxT( "File for %s doesn't exist and m_createIfMissing == false; not saving" ),
 GetFullFilename() );
 return false;
 }
 
 // Ensure the path exists, and create it if not.
 if( !path.DirExists() && !path.Mkdir() )
 {
 wxLogTrace( traceSettings, wxT( "Warning: could not create path %s, can't save %s" ),
 path.GetPath(), GetFullFilename() );
 return false;
 }
 
 if( ( path.FileExists() && !path.IsFileWritable() ) ||
 ( !path.FileExists() && !path.IsDirWritable() ) )
 {
 wxLogTrace( traceSettings, wxT( "File for %s is read-only; not saving" ), GetFullFilename() );
 return false;
 }
 
 bool modified = false;
 
 for( auto settings : m_nested_settings )
 modified |= settings->SaveToFile();
 
 modified |= Store();
 
 if( !modified && !aForce && path.FileExists() )
 {
 wxLogTrace( traceSettings, wxT( "%s contents not modified, skipping save" ), GetFullFilename() );
 return false;
 }
 else if( !modified && !aForce && !m_createIfDefault )
 {
 wxLogTrace( traceSettings,
 wxT( "%s contents still default and m_createIfDefault == false; not saving" ),
 GetFullFilename() );
 return false;
 }
 
 wxLogTrace( traceSettings, wxT( "Saving %s" ), GetFullFilename() );
 
 LOCALE_IO dummy;
 bool success = true;
 
 try
 {
 std::stringstream buffer;
 buffer << std::setw( 2 ) << *m_internals << std::endl;
 
 wxFFileOutputStream fileStream( path.GetFullPath(), "wb" );
 
 if( !fileStream.IsOk()
 || !fileStream.WriteAll( buffer.str().c_str(), buffer.str().size() ) )
 {
 wxLogTrace( traceSettings, wxT( "Warning: could not save %s" ), GetFullFilename() );
 success = false;
 }
 }
 catch( nlohmann::json::exception& error )
 {
 wxLogTrace( traceSettings, wxT( "Catch error: could not save %s. Json error %s" ),
 GetFullFilename(), error.what() );
 success = false;
 }
 catch( ... )
 {
 wxLogTrace( traceSettings, wxT( "Error: could not save %s." ) );
 success = false;
 }
 
 return success;
}
 
 
const std::string JSON_SETTINGS::FormatAsString() const
{
 LOCALE_IO dummy;
 
 std::stringstream buffer;
 buffer << std::setw( 2 ) << *m_internals << std::endl;
 
 return buffer.str();
}
 
 
bool JSON_SETTINGS::LoadFromRawFile( const wxString& aPath )
{
 try
 {
 wxFFileInputStream fp( aPath, wxT( "rt" ) );
 wxStdInputStream fstream( fp );
 
 if( fp.IsOk() )
 {
 *static_cast<nlohmann::json*>( m_internals.get() ) =
 nlohmann::json::parse( fstream, nullptr,
 /* allow_exceptions = */ true,
 /* ignore_comments = */ true );
 }
 else
 {
 return false;
 }
 }
 catch( nlohmann::json::parse_error& error )
 {
 wxLogTrace( traceSettings, wxT( "Json parse error reading %s: %s" ), aPath, error.what() );
 
 return false;
 }
 
 // Now that we have new data in the JSON structure, load the params again
 Load();
 return true;
}
 
 
std::optional<nlohmann::json> JSON_SETTINGS::GetJson( const std::string& aPath ) const
{
 nlohmann::json::json_pointer ptr = m_internals->PointerFromString( aPath );
 
 if( m_internals->contains( ptr ) )
 {
 try
 {
 return std::optional<nlohmann::json>{ m_internals->at( ptr ) };
 }
 catch( ... )
 {
 }
 }
 
 return std::optional<nlohmann::json>{};
}
 
 
template<typename ValueType>
std::optional<ValueType> JSON_SETTINGS::Get( const std::string& aPath ) const
{
 if( std::optional<nlohmann::json> ret = GetJson( aPath ) )
 {
 try
 {
 return ret->get<ValueType>();
 }
 catch( ... )
 {
 }
 }
 
 return std::nullopt;
}
 
 
// Instantiate all required templates here to allow reducing scope of json.hpp
template std::optional<bool> JSON_SETTINGS::Get<bool>( const std::string& aPath ) const;
template std::optional<double> JSON_SETTINGS::Get<double>( const std::string& aPath ) const;
template std::optional<float> JSON_SETTINGS::Get<float>( const std::string& aPath ) const;
template std::optional<int> JSON_SETTINGS::Get<int>( const std::string& aPath ) const;
template std::optional<unsigned int> JSON_SETTINGS::Get<unsigned int>( const std::string& aPath ) const;
template std::optional<unsigned long long> JSON_SETTINGS::Get<unsigned long long>( const std::string& aPath ) const;
template std::optional<std::string> JSON_SETTINGS::Get<std::string>( const std::string& aPath ) const;
template std::optional<nlohmann::json> JSON_SETTINGS::Get<nlohmann::json>( const std::string& aPath ) const;
template std::optional<KIGFX::COLOR4D> JSON_SETTINGS::Get<KIGFX::COLOR4D>( const std::string& aPath ) const;
 
 
template<typename ValueType>
void JSON_SETTINGS::Set( const std::string& aPath, ValueType aVal )
{
 m_internals->SetFromString( aPath, aVal );
}
 
 
// Instantiate all required templates here to allow reducing scope of json.hpp
template void JSON_SETTINGS::Set<bool>( const std::string& aPath, bool aValue );
template void JSON_SETTINGS::Set<double>( const std::string& aPath, double aValue );
template void JSON_SETTINGS::Set<float>( const std::string& aPath, float aValue );
template void JSON_SETTINGS::Set<int>( const std::string& aPath, int aValue );
template void JSON_SETTINGS::Set<unsigned int>( const std::string& aPath, unsigned int aValue );
template void JSON_SETTINGS::Set<unsigned long long>( const std::string& aPath, unsigned long long aValue );
template void JSON_SETTINGS::Set<const char*>( const std::string& aPath, const char* aValue );
template void JSON_SETTINGS::Set<std::string>( const std::string& aPath, std::string aValue );
template void JSON_SETTINGS::Set<nlohmann::json>( const std::string& aPath, nlohmann::json aValue );
template void JSON_SETTINGS::Set<KIGFX::COLOR4D>( const std::string& aPath, KIGFX::COLOR4D aValue );
 
 
void JSON_SETTINGS::registerMigration( int aOldSchemaVersion, int aNewSchemaVersion,
 std::function<bool()> aMigrator )
{
 wxASSERT( aNewSchemaVersion > aOldSchemaVersion );
 wxASSERT( aNewSchemaVersion <= m_schemaVersion );
 m_migrators[aOldSchemaVersion] = std::make_pair( aNewSchemaVersion, aMigrator );
}
 
 
bool JSON_SETTINGS::Migrate()
{
 int filever = m_internals->Get<int>( "meta.version" );
 
 while( filever < m_schemaVersion )
 {
 if( !m_migrators.count( filever ) )
 {
 wxLogTrace( traceSettings, wxT( "Migrator missing for %s version %d!" ),
 typeid( *this ).name(), filever );
 return false;
 }
 
 std::pair<int, std::function<bool()>> pair = m_migrators.at( filever );
 
 if( pair.second() )
 {
 wxLogTrace( traceSettings, wxT( "Migrated %s from %d to %d" ), typeid( *this ).name(),
 filever, pair.first );
 filever = pair.first;
 m_internals->At( "meta.version" ) = filever;
 }
 else
 {
 wxLogTrace( traceSettings, wxT( "Migration failed for %s from %d to %d" ),
 typeid( *this ).name(), filever, pair.first );
 return false;
 }
 }
 
 return true;
}
 
 
bool JSON_SETTINGS::MigrateFromLegacy( wxConfigBase* aLegacyConfig )
{
 wxLogTrace( traceSettings,
 wxT( "MigrateFromLegacy() not implemented for %s" ), typeid( *this ).name() );
 return false;
}
 
 
bool JSON_SETTINGS::SetIfPresent( const nlohmann::json& aObj, const std::string& aPath,
 wxString& aTarget )
{
 nlohmann::json::json_pointer ptr = JSON_SETTINGS_INTERNALS::PointerFromString( aPath );
 
 if( aObj.contains( ptr ) && aObj.at( ptr ).is_string() )
 {
 aTarget = aObj.at( ptr ).get<wxString>();
 return true;
 }
 
 return false;
}
 
 
bool JSON_SETTINGS::SetIfPresent( const nlohmann::json& aObj, const std::string& aPath,
 bool& aTarget )
{
 nlohmann::json::json_pointer ptr = JSON_SETTINGS_INTERNALS::PointerFromString( aPath );
 
 if( aObj.contains( ptr ) && aObj.at( ptr ).is_boolean() )
 {
 aTarget = aObj.at( ptr ).get<bool>();
 return true;
 }
 
 return false;
}
 
 
bool JSON_SETTINGS::SetIfPresent( const nlohmann::json& aObj, const std::string& aPath,
 int& aTarget )
{
 nlohmann::json::json_pointer ptr = JSON_SETTINGS_INTERNALS::PointerFromString( aPath );
 
 if( aObj.contains( ptr ) && aObj.at( ptr ).is_number_integer() )
 {
 aTarget = aObj.at( ptr ).get<int>();
 return true;
 }
 
 return false;
}
 
 
bool JSON_SETTINGS::SetIfPresent( const nlohmann::json& aObj, const std::string& aPath,
 unsigned int& aTarget )
{
 nlohmann::json::json_pointer ptr = JSON_SETTINGS_INTERNALS::PointerFromString( aPath );
 
 if( aObj.contains( ptr ) && aObj.at( ptr ).is_number_unsigned() )
 {
 aTarget = aObj.at( ptr ).get<unsigned int>();
 return true;
 }
 
 return false;
}
 
 
template<typename ValueType>
bool JSON_SETTINGS::fromLegacy( wxConfigBase* aConfig, const std::string& aKey,
 const std::string& aDest )
{
 ValueType val;
 
 if( aConfig->Read( aKey, &val ) )
 {
 try
 {
 ( *m_internals )[aDest] = val;
 }
 catch( ... )
 {
 wxASSERT_MSG( false, wxT( "Could not write value in fromLegacy!" ) );
 return false;
 }
 
 return true;
 }
 
 return false;
}
 
 
// Explicitly declare these because we only support a few types anyway, and it means we can keep
// wxConfig detail out of the header file
template bool JSON_SETTINGS::fromLegacy<int>( wxConfigBase*, const std::string&,
 const std::string& );
 
template bool JSON_SETTINGS::fromLegacy<double>( wxConfigBase*, const std::string&,
 const std::string& );
 
template bool JSON_SETTINGS::fromLegacy<bool>( wxConfigBase*, const std::string&,
 const std::string& );
 
 
bool JSON_SETTINGS::fromLegacyString( wxConfigBase* aConfig, const std::string& aKey,
 const std::string& aDest )
{
 wxString str;
 
 if( aConfig->Read( aKey, &str ) )
 {
 try
 {
 ( *m_internals )[aDest] = str.ToUTF8();
 }
 catch( ... )
 {
 wxASSERT_MSG( false, wxT( "Could not write value in fromLegacyString!" ) );
 return false;
 }
 
 return true;
 }
 
 return false;
}
 
 
bool JSON_SETTINGS::fromLegacyColor( wxConfigBase* aConfig, const std::string& aKey,
 const std::string& aDest )
{
 wxString str;
 
 if( aConfig->Read( aKey, &str ) )
 {
 KIGFX::COLOR4D color;
 color.SetFromWxString( str );
 
 try
 {
 nlohmann::json js = nlohmann::json::array( { color.r, color.g, color.b, color.a } );
 ( *m_internals )[aDest] = js;
 }
 catch( ... )
 {
 wxASSERT_MSG( false, wxT( "Could not write value in fromLegacyColor!" ) );
 return false;
 }
 
 return true;
 }
 
 return false;
}
 
 
void JSON_SETTINGS::AddNestedSettings( NESTED_SETTINGS* aSettings )
{
 wxLogTrace( traceSettings, wxT( "AddNestedSettings %s" ), aSettings->GetFilename() );
 m_nested_settings.push_back( aSettings );
}
 
 
void JSON_SETTINGS::ReleaseNestedSettings( NESTED_SETTINGS* aSettings )
{
 if( !aSettings || !m_manager )
 return;
 
 auto it = std::find_if( m_nested_settings.begin(), m_nested_settings.end(),
 [&aSettings]( const JSON_SETTINGS* aPtr ) {
 return aPtr == aSettings;
 } );
 
 if( it != m_nested_settings.end() )
 {
 wxLogTrace( traceSettings, wxT( "Flush and release %s" ), ( *it )->GetFilename() );
 ( *it )->SaveToFile();
 m_nested_settings.erase( it );
 }
 
 aSettings->SetParent( nullptr );
}
 
 
// Specializations to allow conversion between wxString and std::string via JSON_SETTINGS API
 
template<> std::optional<wxString> JSON_SETTINGS::Get( const std::string& aPath ) const
{
 if( std::optional<nlohmann::json> opt_json = GetJson( aPath ) )
 return wxString( opt_json->get<std::string>().c_str(), wxConvUTF8 );
 
 return std::nullopt;
}
 
 
template<> void JSON_SETTINGS::Set<wxString>( const std::string& aPath, wxString aVal )
{
 ( *m_internals )[aPath] = aVal.ToUTF8();
}
 
// Specializations to allow directly reading/writing wxStrings from JSON
 
void to_json( nlohmann::json& aJson, const wxString& aString )
{
 aJson = aString.ToUTF8();
}
 
 
void from_json( const nlohmann::json& aJson, wxString& aString )
{
 aString = wxString( aJson.get<std::string>().c_str(), wxConvUTF8 );
}
 
 
template<typename ResultType>
ResultType JSON_SETTINGS::fetchOrDefault( const nlohmann::json& aJson, const std::string& aKey,
 ResultType aDefault )
{
 ResultType ret = aDefault;
 
 try
 {
 if( aJson.contains( aKey ) )
 ret = aJson.at( aKey ).get<ResultType>();
 }
 catch( ... )
 {
 }
 
 return ret;
}
 
 
template std::string JSON_SETTINGS::fetchOrDefault( const nlohmann::json& aJson,
 const std::string& aKey, std::string aDefault );
 
template bool JSON_SETTINGS::fetchOrDefault( const nlohmann::json& aJson, const std::string& aKey,
 bool aDefault );