IIIF.cc

/*

    IIIF Request Command Handler Class Member Function

    Copyright (C) 2014-2024 Ruven Pillay

    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 2 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, write to the Free Software Foundation,
    Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
*/

#include <algorithm>
#include <sstream>
#include <cmath>
#include <cstdlib>
#include "Task.h"
#include "Tokenizer.h"
#include "Transforms.h"
#include "URL.h"

// Define several IIIF strings
#define IIIF_SYNTAX "IIIF syntax is {identifier}/{region}/{size}/{rotation}/{quality}{.format}"

// The canonical IIIF protocol URI
#define IIIF_PROTOCOL "http://iiif.io/api/image"

// The context is the protocol plus API version
#define IIIF_CONTEXT IIIF_PROTOCOL "/%d/context.json"

// IIIF compliance level
#ifdef HAVE_PNG
#define IIIF_PROFILE "level2"
#else
#define IIIF_PROFILE "level1"
#endif


using namespace std;


// Need to initialize static members
unsigned int IIIF::version;
string IIIF::delimiter = "";
string IIIF::extra_info = "";


// The request is in the form {identifier}/{region}/{size}/{rotation}/{quality}{.format}
//     eg. filename.tif/full/full/0/native.jpg
// or in the form {identifier}/info.json
//    eg. filename.jp2/info.json

void IIIF::run( Session* session, const string& src )
{

  if ( session->loglevel >= 3 ) *(session->logfile) << "IIIF handler reached" << endl;

  // Time this command
  if ( session->loglevel >= 2 ) command_timer.start();

  // Various string variables
  string suffix, filename, params;

  // First filter and decode our URL
  URL url( src );
  string argument = url.decode();

  if ( session->loglevel >= 1 ){
    if ( url.warning().length() > 0 ) *(session->logfile) << "IIIF :: " << url.warning() << endl;
    if ( session->loglevel >= 5 ){
      *(session->logfile) << "IIIF :: URL decoded to " << argument << endl;
    }
  }

  // Check if there is slash in argument and if it is not last / first character, extract identifier and suffix
  size_t lastSlashPos = argument.find_last_of("/");
  if ( lastSlashPos != string::npos ){

    suffix = argument.substr( lastSlashPos + 1, string::npos );

    // If we have an info command, file name must be everything
    if ( suffix.substr(0, 4) == "info" ){
      filename = argument.substr(0, lastSlashPos);
    }
    else{
      size_t positionTmp = lastSlashPos;
      for ( int i = 0; i < 3; i++ ){
        positionTmp = argument.find_last_of("/", positionTmp - 1);
        if ( positionTmp == string::npos ){
          throw invalid_argument( "IIIF: Not enough parameters" );
        }
      }
      filename = argument.substr(0, positionTmp);
      params = argument.substr(positionTmp + 1, string::npos);
    }
  }
  else{
    // No parameters, so redirect to info request
    string id;
    string host = session->headers["BASE_URL"];
    if ( host.length() > 0 ){
      id = host + (session->headers["QUERY_STRING"]).substr(5, string::npos);
    }
    else{
      string request_uri = session->headers["REQUEST_URI"];
      request_uri.erase( request_uri.length() - suffix.length(), string::npos );
      id = "//" + session->headers["HTTP_HOST"] + request_uri;
    }
    string header = string( "Status: 303 See Other\r\n" )
                    + "Location: " + id + "/info.json\r\n"
                    + "Server: iipsrv/" + VERSION + "\r\n"
                    + "X-Powered-By: IIPImage\r\n"
                    + "\r\n";
    session->out->putStr( header.c_str(), (int) header.size() );
    session->response->setImageSent();
    if ( session->loglevel >= 2 ){
      *(session->logfile) << "IIIF :: Sending HTTP 303 See Other : " << id + "/info.json" << endl;
    }
    return;
  }

  // Re-usable string position variable
  size_t pos;

  // Extract any meta-identifier in the file name that may refer to a page within an image stack or multi-page image
  // These consist of a semi-colon and a page or stack index of the form <image>;<index> For example: image.tif;3
  if( IIIF::delimiter.size() && ( (pos=filename.rfind(IIIF::delimiter)) != string::npos ) ){
    int page = atoi( filename.substr(pos+1).c_str() );
    session->view->xangle = page;
    filename = filename.substr(0,pos);
    if ( session->loglevel >= 3 ){
      *(session->logfile) << "IIIF :: Requested stack or page index: " << page << endl;
    }
  }

  // Check whether requested image exists
  FIF fif;
  fif.run( session, filename );

  // Reload our filename
  filename = (*session->image)->getImagePath();

  // Get the information about image, that can be shown in info.json
  unsigned int requested_width;
  unsigned int requested_height;
  unsigned int width = (*session->image)->getImageWidth();
  unsigned int height = (*session->image)->getImageHeight();
  unsigned tw = (*session->image)->getTileWidth();
  unsigned th = (*session->image)->getTileHeight();
  unsigned numResolutions = (*session->image)->getNumResolutions();

  session->view->setImageSize( width, height );
  session->view->setMaxResolutions( numResolutions );

  // Set a default IIIF version
  int iiif_version = IIIF::version;

  // Check whether the client has requested a specific IIIF version within the HTTP Accept header
  //  - first look for the protocol prefix
  pos = session->headers["HTTP_ACCEPT"].find( IIIF_PROTOCOL );
  if( pos != string::npos ){
    // The Accept header should contain a versioned context string of the form http://iiif.io/api/image/3/context.json
    string profile = session->headers["HTTP_ACCEPT"].substr( pos, string(IIIF_PROTOCOL).size()+15 );
    // Make sure the string is correctly terminated
    if( profile.substr( string(IIIF_PROTOCOL).size()+2 ) == "/context.json" ){
      int v;
      if( sscanf( profile.c_str(), IIIF_CONTEXT, &v ) == 1 ){
        // Set cache control to private if user request is not for the default version
        if( v != (int)iiif_version ) session->response->setCacheControl( "private" );
        iiif_version = v;
        if ( session->loglevel >= 2 ) *(session->logfile) << "IIIF :: User request for IIIF version " << iiif_version << endl;
      }
    }
  }

  // PARSE INPUT PARAMETERS

  // info.json
  if ( suffix == "info.json" ){

    // Our string buffer
    stringstream infoStringStream;

    // Generate our @id - use our BASE_URL environment variable if we are
    //  behind a web server rewrite function
    string id;
    string host = session->headers["BASE_URL"];
    if ( host.length() > 0 ){
      string query = (session->headers["QUERY_STRING"]);
      query = query.substr( 5, query.length() - suffix.length() - 6 );
      id = host + query;
    }
    else{

      string request_uri = session->headers["REQUEST_URI"];
      string scheme = session->headers["HTTPS"].empty() ? "http://" : "https://";

      if (request_uri.empty()){
        throw invalid_argument( "IIIF: REQUEST_URI was not set in FastCGI request, so the ID parameter cannot be set." );
      }

      request_uri.erase( request_uri.length() - suffix.length() - 1, string::npos );
      id = scheme + session->headers["HTTP_HOST"] + request_uri;
    }

    // Decode and escape any URL-encoded characters from our file name for JSON
    URL json(id);
    string escapedFilename = json.escape();
    string iiif_id = session->headers["HTTP_X_IIIF_ID"].empty() ? escapedFilename : session->headers["HTTP_X_IIIF_ID"];

    if ( session->loglevel >= 5 ){
      *(session->logfile) << "IIIF :: ID is set to " << iiif_id << endl;
    }

    // Set the context URL string
    char iiif_context[48];
    snprintf( iiif_context, 48, IIIF_CONTEXT, iiif_version );

    // Get rights field if set either in image metadata or globally
    string rights = (*session->image)->metadata["rights"];
    if( rights.empty() ) rights = session->headers["COPYRIGHT"];


    infoStringStream << "{" << endl
                     << "  \"@context\" : \"" << iiif_context << "\"," << endl
                     << "  \"protocol\" : \"" << IIIF_PROTOCOL << "\"," << endl
                     << "  \"width\" : " << width << "," << endl
                     << "  \"height\" : " << height << "," << endl
                     << "  \"sizes\" : [" << endl
                     << "     { \"width\" : " << (*session->image)->image_widths[numResolutions - 1]
                     << ", \"height\" : " << (*session->image)->image_heights[numResolutions - 1] << " }";


    // Need to keep track of maximum allowable image export sizes
    unsigned int max = session->view->getMaxSize();

    for ( int i = numResolutions - 2; i > 0; i-- ){
      unsigned int w = (*session->image)->image_widths[i];
      unsigned int h = (*session->image)->image_heights[i];
      infoStringStream << "," << endl
		       << "     { \"width\" : " << w << ", \"height\" : " << h << " }";
    }

    infoStringStream << endl << "  ]," << endl
                     << "  \"tiles\" : [" << endl
                     << "     { \"width\" : " << tw << ", \"height\" : " << th
                     << ", \"scaleFactors\" : [ 1"; // Scale 1 is original image

    for( unsigned int i = 1; i < numResolutions; i++ ){
      infoStringStream << ", " << (int)( width / (*session->image)->image_widths[i] );
    }

    infoStringStream << " ] }" << endl
                     << "  ]," << endl;


    // Profile for IIIF version 3 and above
    if( iiif_version >= 3 ){
      infoStringStream << "  \"id\" : \"" << iiif_id << "\"," << endl
		       << "  \"type\": \"ImageService3\"," << endl
		       << "  \"profile\" : \"" << IIIF_PROFILE << "\"," << endl
		       << "  \"maxWidth\" : " << max << "," << endl
		       << "  \"maxHeight\" : " << max << "," << endl
		       << "  \"extraQualities\": [\"color\",\"gray\",\"bitonal\"]," << endl
#ifdef HAVE_WEBP
		       << "  \"extraFormats\": [\"webp\"]," << endl
#endif
		       << "  \"extraFeatures\": [\"regionByPct\",\"sizeByForcedWh\",\"sizeByWh\",\"sizeAboveFull\",\"sizeUpscaling\",\"rotationBy90s\",\"mirroring\"]";

      if( !rights.empty() ){
	infoStringStream << "," << endl
			 << "  \"rights\": \"" << rights << "\"";
      }

    }
    // Profile for IIIF versions 1 and 2
    else {
      infoStringStream << "  \"@id\" : \"" << iiif_id << "\"," << endl
		       << "  \"profile\" : [" << endl
		       << "     \"" << IIIF_PROTOCOL << "/" << iiif_version << "/" << IIIF_PROFILE << ".json\"," << endl
		       << "     { \"formats\" : [ \"jpg\", \"png\", \"webp\" ]," << endl
		       << "       \"qualities\" : [\"native\",\"color\",\"gray\",\"bitonal\"]," << endl
		       << "       \"supports\" : [\"regionByPct\",\"regionSquare\",\"sizeByForcedWh\",\"sizeByWh\",\"sizeAboveFull\",\"sizeUpscaling\",\"rotationBy90s\",\"mirroring\"]," << endl
		       << "       \"maxWidth\" : " << max << "," << endl
		       << "       \"maxHeight\" : " << max << "\n     }" << endl
		       << "  ]";

      if( !rights.empty() ){
	infoStringStream << "," << endl
			 << "  \"license\": \"" << rights << "\"";
      }
    }

    // Add any extra info fields
    if( IIIF::extra_info.size() > 0 ){
      infoStringStream << "," << endl
		       << "  " << IIIF::extra_info;
    }

    // Add physical dimensions service if DPI resolution exists
    if( (*session->image)->dpi_x ){
      infoStringStream << "," << endl
		       << "  \"service\": [" << endl
		       << "    {" << endl
		       << "      \"@context\": \"http://iiif.io/api/annex/services/physdim/1/context.json\"," << endl
		       << "      \"profile\": \"http://iiif.io/api/annex/services/physdim\"," << endl
		       << "      \"physicalScale\": " << 1.0/(*session->image)->dpi_x << "," << endl
		       << "      \"physicalUnits\": " << ( ((*session->image)->dpi_units==1) ? "\"in\"" : "\"cm\"" ) << endl
		       << "    }" << endl
		       << "  ]" << endl;
    }

    // Add final closing brackets
    infoStringStream << endl << "}";

    // Now output the HTTP header and info text
    string mime = string("application/ld+json;profile=\"") + iiif_context + "\"";
    stringstream header;
    header << session->response->createHTTPHeader( mime, (*session->image)->getTimestamp() )
	   << infoStringStream.str();

    session->out->putStr( header.str().c_str(), (int) header.tellp() );
    session->response->setImageSent();

    // Because of our ability to serve different versions and because of possible content-negotiation
    // do not cache any info.json files via Memcached
    session->response->setCachability( false );

    return;

  }
  // Parse image request - anything other than info requests are considered image requests
  else{

    // IIIF requests are / separated with no CGI style '&' separators
    Tokenizer izer( params, "/" );

    // Keep track of the number of parameters than have been given
    int numOfTokens = 0;

    // Our region parameters (always between 0 and 1)
    float region[4] = {0.0, 0.0, 1.0, 1.0};

    // Region Parameter: { "full"; "square"; "x,y,w,h"; "pct:x,y,w,h" }
    if ( izer.hasMoreTokens() ){

      // Get our region string and convert to lower case if necessary
      string regionString = izer.nextToken();
      transform( regionString.begin(), regionString.end(), regionString.begin(), ::tolower );

      // Export request for full image
      if ( regionString == "full" ){
	// Do nothing - region array already initialized
      }
      // Square region export using centered crop - avaialble in IIIF version 3
      else if (regionString == "square" ){
        if ( height > width ){
	  region[3] = (float)width / (float)height;
	  region[1] = (1.0-region[3]) / 2.0;
        }
	else if ( width > height ){
	  region[2] = (float)height / (float)width;
	  region[0] = (1.0-region[2]) / 2.0;
        }
	// No need for default else clause if image is already perfectly square
      }

      // Export request for region from image
      else{

        // Check for pct (%) and strip it from the beginning
        bool isPCT = false;
        if ( regionString.substr(0, 4) == "pct:" ){
          isPCT = true;
          // Strip this from our string
          regionString.erase( 0, 4 );
        }

        // Extract x,y,w,h tokenizing on ","
        Tokenizer regionIzer(regionString, ",");
        int n = 0;

        // Extract our region values
        while ( regionIzer.hasMoreTokens() && n < 4 ){
          region[n++] = atof( regionIzer.nextToken().c_str() );
        }

        // Define our denominators as our session view expects a ratio, not pixel values
        float wd = (float) width;
        float hd = (float) height;

        if( isPCT ){
	  wd = 100.0;
	  hd = 100.0;
        }

	region[0] = region[0] / wd;
	region[1] = region[1] / hd;
	region[2] = region[2] / wd;
	region[3] = region[3] / hd;

	// Sanity check of region sizes
	if( region[0] + region[2] > 1.0 ) region[2] = 1.0 - region[0];
	if( region[1] + region[3] > 1.0 ) region[3] = 1.0 - region[1];

        // Incorrect region request
        if ( region[2] <= 0.0 || region[3] <= 0.0 || regionIzer.hasMoreTokens() || n < 4 ){
          throw invalid_argument( "IIIF: incorrect region format: " + regionString );
        }

      } // end of else - end of parsing x,y,w,h

      // Update our view with our region values
      session->view->setViewLeft( region[0] );
      session->view->setViewTop( region[1] );
      session->view->setViewWidth( region[2] );
      session->view->setViewHeight( region[3] );

      numOfTokens++;

      if ( session->loglevel > 4 ){
        *(session->logfile) << "IIIF :: Requested Region (x, y, w. h): " << round( region[0] * width ) << ", " << round( region[1] * height )
			    << ", " << round( region[2] * width ) << ", " << round( region[3] * height ) << " (ratios: "
			    << region[0] << ", " << region[1] << ", " << region[2] << ", " << region[3] << ")" << endl;
      }

    }

    // Size Parameter: { "full/max"; "w,"; ",h"; "pct:n"; "w,h"; "!w,h" }
    // Note that "full" will be deprecated in favour of "max" in version 3.0
    if ( izer.hasMoreTokens() ){

      string sizeString = izer.nextToken();
      transform( sizeString.begin(), sizeString.end(), sizeString.begin(), ::tolower );

      // Calculate the width and height of our region at full resolution
      requested_width = region[2] * width;   // view->getViewWidth not trustworthy yet (no resolution set)
      requested_height = region[3] * height;

      // Calculate ratio - use region float array directly to avoid rounding errors
      float ratio = (region[2] * width) / (region[3] * height);

      unsigned int max_size = session->view->getMaxSize();

      // ^ request prefix (upscaling) - remove ^ symbol and continue usual parsing
      if( iiif_version >= 3 ){
	if ( sizeString.substr(0, 1) == "^" ) sizeString.erase(0, 1);
	else session->view->allow_upscaling = false;
      }

      // "full" or "max" request
      if ( sizeString == "full" || sizeString == "max" ){
        // No need to do anything
      }

      // "pct:n" request
      else if ( sizeString.substr(0, 4) == "pct:" ){

        float scale;
        istringstream i( sizeString.substr( sizeString.find_first_of(":") + 1, string::npos ) );
        if ( !(i >> scale) ) throw invalid_argument( "invalid size" );

        requested_width = round( requested_width * scale / 100.0 );
        requested_height = round( requested_height * scale / 100.0 );
      }

      // "w,h", "w,", ",h", "!w,h" requests
      else{

        // !w,h request (do not break aspect ratio) - remove the !, store the info and continue usual parsing
        if ( sizeString.substr(0, 1) == "!" ) sizeString.erase(0, 1);
        // Otherwise tell our view it can break aspect ratio
        else session->view->maintain_aspect = false;

        size_t pos = sizeString.find_first_of(",");

        // If no comma, size is invalid
        if ( pos == string::npos ){
          throw invalid_argument( "invalid size: no comma found" );
        }

        // If comma is at the beginning, we have a ",height" request
        else if ( pos == 0 ){
          istringstream i( sizeString.substr( 1, string::npos ) );
          if ( !(i >> requested_height) ) throw invalid_argument( "invalid height" );
	  requested_width = round( (float)requested_height * ratio );
	  // Maintain aspect ratio in this case
 	  session->view->maintain_aspect = true;
        }

        // If comma is not at the beginning, we must have a "width,height" or "width," request
        // Test first for the "width," request
        else if ( pos == sizeString.length() - 1 ){
          istringstream i( sizeString.substr( 0, string::npos - 1 ) );
          if ( !(i >> requested_width ) ) throw invalid_argument( "invalid width" );
	  requested_height = round( (float)requested_width / ratio );
	  // Maintain aspect ratio in this case
 	  session->view->maintain_aspect = true;
        }

        // Remaining case is "width,height"
        else{
          istringstream i( sizeString.substr( 0, pos ) );
          if ( !(i >> requested_width) ) throw invalid_argument( "invalid width" );
          i.clear();
          i.str( sizeString.substr( pos + 1, string::npos ) );
          if ( !(i >> requested_height) ) throw invalid_argument( "invalid height" );
        }
      }


      if ( requested_width <= 0 || requested_height <= 0 ){
        throw invalid_argument( "IIIF: invalid size: requested width or height < 0" );
      }

      // Check for malformed upscaling request
      if( iiif_version >= 3 ){
	if( session->view->allow_upscaling == false &&
	    ( requested_width > width || requested_height > height ) ){
	  throw invalid_argument( "IIIF: upscaling should be prefixed with ^" );
	}
      }

      // Limit our requested size to the maximum allowable size if necessary
      if( requested_width > max_size || requested_height > max_size ){
	if( ratio > 1.0 ){
	  requested_width = max_size;
	  requested_height = session->view->maintain_aspect ? round(max_size*ratio) : max_size;
	}
	else{
	  requested_height = max_size;
	  requested_width = session->view->maintain_aspect ? round(max_size/ratio) : max_size;
	}
      }

      session->view->setRequestWidth( requested_width );
      session->view->setRequestHeight( requested_height );

      numOfTokens++;

      if ( session->loglevel >= 4 ){
        *(session->logfile) << "IIIF :: Requested Size: " << requested_width << "x" << requested_height << endl;
      }

    }

    // Rotation Parameter
    if ( izer.hasMoreTokens() ){

      string rotationString = izer.nextToken();

      // Flip requests (IIIF 2.0 API)
      if ( rotationString.substr(0, 1) == "!" ){
        session->view->flip = 1;
        rotationString.erase(0, 1);
      }

      // Convert our string to a float
      float rotation = 0;
      istringstream i( rotationString );
      if ( !(i >> rotation) ) throw invalid_argument( "IIIF: invalid rotation" );


      // Check if converted value is supported
      if (!( rotation == 0 || rotation == 90 || rotation == 180 || rotation == 270 || rotation == 360 )){
        throw invalid_argument( "IIIF: currently implemented rotation angles are 0, 90, 180 and 270 degrees" );
      }

      // Set rotation - watch for a '!180' request, which is simply a vertical flip
      if ( rotation == 180 && session->view->flip == 1 ) session->view->flip = 2;
      else session->view->setRotation( rotation );

      numOfTokens++;

      if ( session->loglevel >= 4 ){
        *(session->logfile) << "IIIF :: Requested Rotation: " << rotation << " degrees";
        if ( session->view->flip != 0 ) *(session->logfile) << " with horizontal flip";
        *(session->logfile) << endl;
      }

    }

    // Quality and Format Parameters
    if ( izer.hasMoreTokens() ){
      string format = "jpg";
      string quality = izer.nextToken();
      transform( quality.begin(), quality.end(), quality.begin(), ::tolower );

      // Strip off any query suffixes that use the ? character
      // For example versioning such as ../default.jpg?t=23421232
      size_t pos = quality.find_first_of("?");
      if ( pos != string::npos ) quality = quality.substr( 0, pos );

      // Check for a format specifier
      pos = quality.find_last_of(".");

      // Get requested output format: JPEG, PNG and WebP are currently supported
      if ( pos != string::npos ){
        format = quality.substr( pos + 1, string::npos );
        quality.erase( pos, string::npos );

	if( format == "jpg" ) session->view->output_format = ImageEncoding::JPEG;
#ifdef HAVE_PNG
	else if( format == "png" ) session->view->output_format = ImageEncoding::PNG;
#endif
#ifdef HAVE_WEBP
	else if( format == "webp" ) session->view->output_format = ImageEncoding::WEBP;
#endif
	else throw invalid_argument( "IIIF :: unsupported output format" );
      }


      // Quality
      if ( quality == "native" || quality == "color" || quality == "default" ){
        // Do nothing
      }
      else if ( quality == "grey" || quality == "gray" ){
        session->view->colorspace = ColorSpace::GREYSCALE;
      }
      else if ( quality == "bitonal" ){
        session->view->colorspace = ColorSpace::BINARY;
      }
      else{
        throw invalid_argument( "unsupported quality parameter - must be one of native, color or grey" );
      }

      numOfTokens++;

      if ( session->loglevel >= 4 ){
        *(session->logfile) << "IIIF :: Requested Quality: " << quality << " with format: " << format << endl;
      }
    }

    // Too many parameters
    if ( izer.hasMoreTokens() ){
      throw invalid_argument( "IIIF: Query has too many parameters. " IIIF_SYNTAX );
    }

    // Not enough parameters
    if ( numOfTokens < 4 ){
      throw invalid_argument( "IIIF: Query has too few parameters. " IIIF_SYNTAX );
    }

  }
  // End of parsing input parameters


  // Get most suitable resolution and recalculate width and height of region in this resolution
  int requested_res = session->view->getResolution();
  unsigned int im_width = (*session->image)->image_widths[numResolutions - requested_res - 1];
  unsigned int im_height = (*session->image)->image_heights[numResolutions - requested_res - 1];


  // Write info about request to log
  if ( session->loglevel >= 3 ){
    if ( suffix == "info.json" ){
      *(session->logfile) << "IIIF :: " << suffix << " request for " << (*session->image)->getImagePath() << endl;
    }
    else{
      *(session->logfile) << "IIIF :: image request for " << (*session->image)->getImagePath()
                          << " with arguments: scaled region: " << session->view->getViewLeft() << "," << session->view->getViewTop() << ","
                          << session->view->getViewWidth() << "," << session->view->getViewHeight()
                          << "; size: " << requested_width << "x" << requested_height
                          << "; rotation: " << session->view->getRotation()
                          << "; mirroring: " << session->view->flip
                          << endl;
    }
  }


  unsigned int view_left, view_top;
  if ( session->view->viewPortSet() ){
    // Set the absolute viewport size and extract the co-ordinates
    view_left = session->view->getViewLeft();
    view_top = session->view->getViewTop();
  }
  else{
    view_left = 0;
    view_top = 0;
  }


  // For edge tiles, adjust the tile width and height accordingly so that we can detect pure tile requests
  unsigned int vtw = tw;
  unsigned int vth = th;
  if( (width%tw > 0) && (view_left == im_width - (im_width%tw)) ) vtw = im_width%tw;
  if( (height%th > 0) && (view_top == im_height - (im_height%th)) ) vth = im_height%th;


  // Determine whether this is a request for an individual tile which, therefore, coincides exactly with our tile boundaries
  if( ( session->view->maintain_aspect && (requested_res > 0) &&
	(view_left % tw == 0) && (view_top % th == 0) &&                            // Left / top boundaries align with tile positions
	(requested_width == vtw) && (requested_height == vth) &&                    // Request is for exact tile dimensions
	(session->view->getViewWidth() == vtw) && (session->view->getViewHeight() == vth) ) ||  // View size should also be identical to tile dimensions
      // For smallest resolution, image size can be given as equal or less than tile size or exactly equal to tile size
      ( ( session->view->maintain_aspect && (requested_res == 0) ) &&
	( ( ((unsigned int) requested_width == im_width) && ((unsigned int) requested_height == im_height)) ||
	  ( ((unsigned int) requested_width == tw) && ((unsigned int) requested_height == th)) ) )
      ){

    // Get the width and height for last row and column tiles
    unsigned int rem_x = im_width % tw;

    // Calculate the number of tiles in each direction
    unsigned int ntlx = (im_width / tw) + (rem_x == 0 ? 0 : 1);

    // Calculate tile index
    unsigned int i = view_left / tw;
    unsigned int j = view_top / th;
    unsigned int tile = (j * ntlx) + i;

    // Simply pass this on to our JTL send command
    JTL jtl;
    jtl.send( session, requested_res, tile );

  }
  else{
    // Otherwise do a CVT style region request
    CVT cvt;
    cvt.send( session );
  }

  // Total IIIF response time
  if ( session->loglevel >= 2 ){
    *(session->logfile) << "IIIF :: Total command time " << command_timer.getTime() << " microseconds" << endl;
  }

}