VFSSvc.cpp

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/***********************************************************************************\
* (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
*                                                                                   *
* This software is distributed under the terms of the Apache version 2 licence,     *
* copied verbatim in the file "LICENSE".                                            *
*                                                                                   *
* In applying this licence, CERN does not waive the privileges and immunities       *
* granted to it by virtue of its status as an Intergovernmental Organization        *
* or submit itself to any jurisdiction.                                             *
\***********************************************************************************/
#include "VFSSvc.h"
 
#include "GaudiKernel/IAlgTool.h"
#include "GaudiKernel/IToolSvc.h"
#include "GaudiKernel/MsgStream.h"
 
DECLARE_COMPONENT( VFSSvc )
 
//------------------------------------------------------------------------------
StatusCode VFSSvc::initialize() {
  StatusCode sc = Service::initialize();
  if ( sc.isFailure() ) return sc;
 
  m_toolSvc = serviceLocator()->service( "ToolSvc" );
  if ( !m_toolSvc ) {
    error() << "Cannot locate ToolSvc" << endmsg;
    return StatusCode::FAILURE;
  }
 
  IAlgTool* tool;
  for ( const auto& i : m_urlHandlersNames ) {
    // retrieve the tool and the pointer to the interface
    sc = m_toolSvc->retrieve( i, IAlgTool::interfaceID(), tool, nullptr, true );
    if ( sc.isFailure() ) {
      error() << "Cannot get tool " << i << endmsg;
      return sc;
    }
    m_acquiredTools.push_back( tool ); // this is one tool that we will have to release
    auto hndlr = SmartIF<IFileAccess>( tool );
    if ( !hndlr ) {
      error() << i << " does not implement IFileAccess" << endmsg;
      return StatusCode::FAILURE;
    }
    // We do not need to increase the reference count for the IFileAccess interface
    // because we hold the tool by its IAlgTool interface.
    // loop over the list of supported protocols and add them to the map (for quick access)
    for ( const auto& prot : hndlr->protocols() ) m_urlHandlers[prot].emplace_back( hndlr.get() );
  }
 
  // Now let's check if we can handle the fallback protocol
  if ( m_urlHandlers.find( m_fallBackProtocol ) == m_urlHandlers.end() ) {
    error() << "No handler specified for fallback protocol prefix " << m_fallBackProtocol.value() << endmsg;
    return StatusCode::FAILURE;
  }
 
  // Note: the list of handled protocols will be filled only if requested
 
  return sc;
}
//------------------------------------------------------------------------------
StatusCode VFSSvc::finalize() {
  m_urlHandlers.clear(); // clear the map
  m_protocols.clear();
 
  if ( m_toolSvc ) {
    // release the acquired tools (from the last acquired one)
    while ( !m_acquiredTools.empty() ) {
      m_toolSvc->releaseTool( m_acquiredTools.back() ).ignore();
      m_acquiredTools.pop_back();
    }
    m_toolSvc.reset(); // release the tool service
  }
  return Service::finalize();
}
//------------------------------------------------------------------------------
std::unique_ptr<std::istream> VFSSvc::open( const std::string& url ) {
  // get the url prefix endpos
  auto pos = url.find( "://" );
 
  if ( std::string::npos == pos ) {
    // no url prefix, try fallback protocol
    return VFSSvc::open( m_fallBackProtocol + "://" + url );
  }
 
  const std::string url_prefix( url, 0, pos );
  const auto        handlers = m_urlHandlers.find( url_prefix );
  if ( handlers == m_urlHandlers.end() ) {
    // if we do not have a handler for the URL prefix,
    // use the fall back one
    return VFSSvc::open( m_fallBackProtocol + url.substr( pos ) );
  }
 
  std::unique_ptr<std::istream> out; // this might help RVO
  // try the hendlers for the protocol one after the other until one succeds
  for ( auto hndlr : handlers->second ) {
    out = hndlr->open( url );
    if ( out ) break;
  }
  return out;
}
//------------------------------------------------------------------------------
namespace {
  constexpr struct select1st_t {
    template <typename S, typename T>
    const S& operator()( const std::pair<S, T>& x ) const {
      return x.first;
    }
  } select1st{};
} // namespace
 
const std::vector<std::string>& VFSSvc::protocols() const {
  if ( m_protocols.empty() ) {
    // prepare the list of handled protocols
    std::transform( m_urlHandlers.begin(), m_urlHandlers.end(),
                    std::back_inserter( const_cast<VFSSvc*>( this )->m_protocols ), select1st );
  }
  return m_protocols;
}