PrFTZoneHandler - Check array bounds before access

No index checking was applied before accessing the zone array.

In dd4hep builds this actually leads to out-of-bounds access due to some issues with the zone ID being larger than I presume was expected.

This will lead to exceptions being thrown in the dd4hep builds until that numbering is fixed, but this should be viewed as an improvement over out of bounds writing to random memory locations…

@lohenry FYI

Pr/PrKernel/include/PrKernel/PrFTZoneHandler.h

@@ -15,6 +15,8 @@
 #include "FTDet/DeFTDetector.h"
 #include "Kernel/DetectorSegment.h"
 #include "PrKernel/PrHitZone.h"
+#include <cassert>
+#include <stdexcept>
 
 namespace FTZoneCache {
 
@@ -31,32 +33,35 @@ namespace FTZoneCache {
     PrFTZoneHandler( DeFT const& ftDet ) {
 #ifdef USE_DD4HEP
       auto func = [this]( const DeFTLayer& layer ) {
-        int id = layer.layerID();
+        const auto id = layer.layerID();
         // fixme
         DetectorSegment seg( 0, layer.globalZ(), layer.dxdy(), layer.dzdy(), 0., 0. );
-        float           xmax = 0.5f * layer.sizeX();
-        float           ymax = 0.5f * layer.sizeY();
+        const auto      xmax = 0.5f * layer.sizeX();
+        const auto      ymax = 0.5f * layer.sizeY();
         // The setGeometry defines the z at y=0, the dxDy and the dzDy, as well as the isX properties of the zone.
         // This is important, since these are used in the following.
         // They are set once for each zone in this method.
-        this->MakeZone( 2 * id + 1, seg, -xmax, xmax, -25.f, ymax ); // Small overlap (25 mm) for stereo layers
-        this->MakeZone( 2 * id, seg, -xmax, xmax, -ymax, 25.f );     // Small overlap (25 mm) for stereo layers
+        const bool ok =
+            ( this->MakeZone( 2 * id + 1, seg, -xmax, xmax, -25.f, ymax ) && // Small overlap (25 mm) for stereo layers
+              this->MakeZone( 2 * id, seg, -xmax, xmax, -ymax, 25.f ) );     // Small overlap (25 mm) for stereo layers
+        if ( !ok ) { throw std::runtime_error( "Failed to create DeFT Zones for ID = " + std::to_string( id ) ); }
       };
       ftDet.applyToAllLayers( func );
 #else
       for ( auto station : ftDet.stations() ) {
         for ( auto layer : station->layers() ) {
-          int id = 4 * ( station->stationID() - 1 ) + layer->layerID();
-
+          const auto      id = 4 * ( station->stationID() - 1 ) + layer->layerID();
           DetectorSegment seg( 0, layer->globalZ(), layer->dxdy(), layer->dzdy(), 0., 0. );
-          float           xmax = 0.5f * layer->sizeX();
-          float           ymax = 0.5f * layer->sizeY();
-
+          const auto      xmax = 0.5f * layer->sizeX();
+          const auto      ymax = 0.5f * layer->sizeY();
           // The setGeometry defines the z at y=0, the dxDy and the dzDy, as well as the isX properties of the zone.
           // This is important, since these are used in the following.
           // They are set once for each zone in this method.
-          this->MakeZone( 2 * id + 1, seg, -xmax, xmax, -25.f, ymax ); // Small overlap (25 mm) for stereo layers
-          this->MakeZone( 2 * id, seg, -xmax, xmax, -ymax, 25.f );     // Small overlap (25 mm) for stereo layers
+          const bool ok =
+              ( this->MakeZone( 2 * id + 1, seg, -xmax, xmax, -25.f, ymax ) && // Small overlap (25 mm) for stereo
+                                                                               // layers
+                this->MakeZone( 2 * id, seg, -xmax, xmax, -ymax, 25.f ) ); // Small overlap (25 mm) for stereo layers
+          if ( !ok ) { throw std::runtime_error( "Failed to create DeFT Zones for ID = " + std::to_string( id ) ); }
         }
       }
 #endif
@@ -64,10 +69,20 @@ namespace FTZoneCache {
     /// Standard constructor
     PrFTZoneHandler() = default;
 
-    void MakeZone( unsigned int n, DetectorSegment& seg, float xMin, float xMax, float yMin, float yMax ) {
-      m_zones[n].setZone( n, seg, xMin, xMax, yMin, yMax );
+    bool MakeZone( unsigned int n, DetectorSegment& seg, float xMin, float xMax, float yMin, float yMax ) {
+      if ( n < m_zones.size() ) {
+        m_zones[n].setZone( n, seg, xMin, xMax, yMin, yMax );
+        return true;
+      } else {
+        return false;
+      }
+    }
+    const PrHitZone& zone( unsigned int n ) const {
+      if ( n >= m_zones.size() ) {
+        throw std::runtime_error( "Zone index " + std::to_string( n ) + " is out-of-range" );
+      }
+      return m_zones[n];
     }
-    const PrHitZone& zone( unsigned int n ) const { return m_zones[n]; }
 
     template <PrHitZone::Side SIDE>
     static int getXZone( int layer ) {
@@ -112,7 +127,6 @@ namespace FTZoneCache {
     std::array<float, PrFTInfo::NFTZones> zoneDxDy{std::numeric_limits<float>::signaling_NaN()};
     std::array<float, PrFTInfo::NFTZones> zoneDzDy{std::numeric_limits<float>::signaling_NaN()};
     std::array<float, PrFTInfo::NFTZones> zoneZPos{std::numeric_limits<float>::signaling_NaN()};
-    ZoneCache() = default; // Needed by DD4hep even if unused !
     ZoneCache( const DeFT& ftDet ) : handler( ftDet ) {
       for ( int i{0}; i < PrFTInfo::NFTLayers; ++i ) {
         zoneZPos[2 * i]     = handler.zone( 2 * i ).z();