Scan server: Enforce loop limits

services/scan-server/.classpath

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <classpath>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
+    <classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/5"/>
 	<classpathentry kind="src" output="target/classes" path="src/main/java"/>
 	<classpathentry kind="src" path="src/main/resources"/>
 	<classpathentry kind="src" path="src/test/java"/>
-	<classpathentry combineaccessrules="false" kind="src" path="/phoebus-target"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/core-framework"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/core-util"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/core-pv"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/core-pv-ca"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/core-pv-pva"/>
-        <classpathentry combineaccessrules="false" kind="src" path="/core-vtype"/>
+	<classpathentry combineaccessrules="false" kind="src" path="/core-vtype"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/app-scan-model"/>
-	<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/5"/>
+	<classpathentry combineaccessrules="false" kind="src" path="/phoebus-target"/>
 	<classpathentry kind="output" path="target/classes"/>
 </classpath>

services/scan-server/src/main/java/org/csstudio/scan/server/command/LoopCommandImpl.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2011-2018 Oak Ridge National Laboratory.
+ * Copyright (c) 2011-2026 Oak Ridge National Laboratory.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -111,15 +111,20 @@ public String[] getDeviceNames(final MacroContext macros) throws Exception
         return device_names.toArray(new String[device_names.size()]);
     }
 
-    private double getLoopStart()
+    /** @return Lower loop limit */
+    double getLoopStart()
     {
         return Math.min(command.getStart(), command.getEnd());
     }
-    private double getLoopEnd()
+
+    /** @return Upper loop limit */
+    double getLoopEnd()
     {
         return Math.max(command.getStart(), command.getEnd());
     }
-    private double getLoopStep()
+
+    /** @return Loop step, might toggle direction */
+    double getLoopStep()
     {
         final double step  = direction * command.getStepSize();
         // Revert direction for next iteration of the complete loop?
@@ -128,10 +133,27 @@ private double getLoopStep()
         return step;
     }
 
-    public int getNumSteps() {
+    /** @return Number of loop steps */
+    int getNumSteps()
+    {
         return (int)Math.ceil(Math.abs(((command.getEnd() - command.getStart()) / command.getStepSize()))) + 1;
     }
 
+    /** @param start Start value, might be upper or lower limit
+     *  @param step Loop step value, positive or negative
+     *  @param i Loop index
+     *  @return Loop value
+     */
+    double computeStep(double start, double step, int i)
+    {
+        // Compute loop value, but limit to upper or lower
+        // end depending on step direction
+        if (step >= 0)
+            return Math.min(start + i * step, getLoopEnd());
+        else
+            return Math.max(start + i * step, getLoopStart());
+    }
+
     /** {@inheritDoc} */
     @Override
     public void simulate(final SimulationContext context) throws Exception
@@ -143,7 +165,7 @@ public void simulate(final SimulationContext context) throws Exception
         double start = step < 0 ? getLoopEnd() : getLoopStart();
         int num_steps = getNumSteps();
         for (int i = 0; i < num_steps; i++)
-            simulateStep(context, device, start + i * step);
+            simulateStep(context, device, computeStep(start, step, i));
     }
 
     /** Simulate one step in the loop iteration
@@ -211,7 +233,7 @@ public void execute(final ScanContext context) throws Exception
         int num_steps = getNumSteps();
 
         for (int i = 0; i < num_steps; i++)
-            executeStep(context, device, condition, readback, start + i * step);
+            executeStep(context, device, condition, readback, computeStep(start, step, i));
     }
 
     /** Execute one step of the loop

services/scan-server/src/test/java/org/csstudio/scan/server/command/LoopTest.java

@@ -0,0 +1,122 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Oak Ridge National Laboratory.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * The scan engine idea is based on the "ScanEngine" developed
+ * by the Software Services Group (SSG),  Advanced Photon Source,
+ * Argonne National Laboratory,
+ * Copyright (c) 2011 , UChicago Argonne, LLC.
+ *
+ * This implementation, however, contains no SSG "ScanEngine" source code
+ * and is not endorsed by the SSG authors.
+ ******************************************************************************/
+package org.csstudio.scan.server.command;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+
+import org.csstudio.scan.command.LoopCommand;
+import org.junit.jupiter.api.Test;
+
+/** JUnit test for loop */
+public class LoopTest
+{
+    @Test
+    void testNormalLoop() throws Exception
+    {
+        LoopCommand cmd = new LoopCommand("loc://x(0)", 1.0, 10.0, 0.5, List.of());
+        LoopCommandImpl impl = new LoopCommandImpl(cmd);
+
+        System.out.println(cmd);
+
+        double step = impl.getLoopStep();
+        double start = step < 0 ? impl.getLoopEnd() : impl.getLoopStart();
+        int num_steps = impl.getNumSteps();
+
+        double last = Double.NaN;
+        for (int i = 0; i < num_steps; i++)
+        {
+            last = impl.computeStep(start, step, i);
+            System.out.println(last);
+        }
+        assertEquals(10.0, last);
+    }
+
+    @Test
+    void testUpwardsLoop() throws Exception
+    {
+        LoopCommand cmd = new LoopCommand("loc://x(0)", 1.0, 1.1, 5.0, List.of());
+        LoopCommandImpl impl = new LoopCommandImpl(cmd);
+
+        System.out.println(cmd);
+
+        double step = impl.getLoopStep();
+        double start = step < 0 ? impl.getLoopEnd() : impl.getLoopStart();
+        int num_steps = impl.getNumSteps();
+
+        double last = Double.NaN;
+        for (int i = 0; i < num_steps; i++)
+        {
+            last = impl.computeStep(start, step, i);
+            System.out.println(last);
+        }
+        assertEquals(1.1, last);
+    }
+
+    @Test
+    void testDownwardsLoop() throws Exception
+    {
+        LoopCommand cmd = new LoopCommand("loc://x(0)", 1.1, 1.0, -5.0, List.of());
+        LoopCommandImpl impl = new LoopCommandImpl(cmd);
+
+        System.out.println(cmd);
+
+        double step = impl.getLoopStep();
+        double start = step < 0 ? impl.getLoopEnd() : impl.getLoopStart();
+        int num_steps = impl.getNumSteps();
+
+        double last = Double.NaN;
+        for (int i = 0; i < num_steps; i++)
+        {
+            last = impl.computeStep(start, step, i);
+            System.out.println(last);
+        }
+        assertEquals(1.0, last);
+    }
+
+    @Test
+    void testTogglingLoop() throws Exception
+    {
+        LoopCommand cmd = new LoopCommand("loc://x(0)", 1.0, 1.1, -5.0, List.of());
+        LoopCommandImpl impl = new LoopCommandImpl(cmd);
+
+        System.out.println(cmd);
+
+        double step = impl.getLoopStep();
+        double start = step < 0 ? impl.getLoopEnd() : impl.getLoopStart();
+        int num_steps = impl.getNumSteps();
+
+        double last = Double.NaN;
+        for (int i = 0; i < num_steps; i++)
+        {
+            last = impl.computeStep(start, step, i);
+            System.out.println(last);
+        }
+        assertEquals(1.0, last);
+
+        // Run loop again, expect toggled direction
+        step = impl.getLoopStep();
+        start = step < 0 ? impl.getLoopEnd() : impl.getLoopStart();
+        num_steps = impl.getNumSteps();
+        for (int i = 0; i < num_steps; i++)
+        {
+            last = impl.computeStep(start, step, i);
+            System.out.println(last);
+        }
+        assertEquals(1.1, last);
+    }
+}