Fix ExpressionInfoValueRenderer.renderAsFailedStringComparison overflow

The length check in renderAsFailedStringComparison did overflow, so we
need to cast it to long first. Also add some more info when the
OOM protection kicks in. Furthermore, decrease the the memory limit from
1mb to 50kb. And add some specs for tryReduceStringSizes.

spock-core/src/main/java/org/spockframework/runtime/ExpressionInfoValueRenderer.java

@@ -18,12 +18,11 @@
 import org.spockframework.runtime.condition.EditDistance;
 import org.spockframework.runtime.condition.EditPathRenderer;
 import org.spockframework.runtime.model.ExpressionInfo;
-import org.spockframework.runtime.GroovyRuntimeUtil;
-import org.spockframework.util.ObjectUtil;
 import org.spockframework.util.Nullable;
+import org.spockframework.util.ObjectUtil;
 
 public class ExpressionInfoValueRenderer {
-  public static final long MAX_EDIT_DISTANCE_MEMORY = 1024*1024;
+  public static final long MAX_EDIT_DISTANCE_MEMORY = 50 * 1024;
   private final ExpressionInfo expr;
 
   private ExpressionInfoValueRenderer(ExpressionInfo expr) {
@@ -88,13 +87,13 @@ private String javaLangObjectToString(Object value) {
   private String doRenderValue(ExpressionInfo expr) {
     String result = renderAsFailedStringComparison(expr);
     if (result != null) return result;
-    
+
     result = renderAsFailedEqualityComparison(expr);
     if (result != null) return result;
-    
+
     return GroovyRuntimeUtil.toString(expr.getValue());
   }
-  
+
   private String renderAsFailedStringComparison(ExpressionInfo expr) {
     if (!(Boolean.FALSE.equals(expr.getValue()))) return null;
     if (!expr.isEqualityComparison(String.class, GString.class)) return null;
@@ -103,7 +102,7 @@ private String renderAsFailedStringComparison(ExpressionInfo expr) {
     String str1 = expr.getChildren().get(0).getValue().toString();
     String str2 = expr.getChildren().get(1).getValue().toString();
 
-    if (str1.length() * str2.length() > MAX_EDIT_DISTANCE_MEMORY) {
+    if (((long)str1.length()) * str2.length() > MAX_EDIT_DISTANCE_MEMORY) {
       return tryReduceStringSizes(str1, str2);
     } else {
       return createAndRenderEditDistance(str1, str2);
@@ -137,7 +136,7 @@ private String tryReduceStringSizes(String str1, String str2) {
         end1 = Math.min(str1.length(), end1 + 10);
         end2 = Math.min(str2.length(), end2 + 10);
       }
-      return createAndRenderEditDistance(str1.substring(commonStart, end1), str2.substring(commonStart, end2));
+      return createAndRenderEditDistance(str1, str2, commonStart, end1, end2);
     }
   }
 
@@ -148,6 +147,16 @@ private String createAndRenderEditDistance(String str1, String str2) {
       new EditPathRenderer().render(str1, str2, dist.calculatePath()));
   }
 
+  private String createAndRenderEditDistance(String str1, String str2, int commonStart, int end1, int end2) {
+    String sub1 = str1.substring(commonStart, end1);
+    String sub2 = str2.substring(commonStart, end2);
+    EditDistance dist = new EditDistance(sub1, sub2);
+    return String.format("false\n%d difference%s (%d%% similarity) (comparing subset start: %d, end1: %d, end2: %d)\n%s",
+      dist.getDistance(), dist.getDistance() == 1 ? "" : "s", dist.getSimilarityInPercent(),
+      commonStart, end1, end2,
+      new EditPathRenderer().render(sub1, sub2, dist.calculatePath()));
+  }
+
   private String renderAsFailedEqualityComparison(ExpressionInfo expr) {
     if (!(Boolean.FALSE.equals(expr.getValue()))) return null;
     if (!expr.isEqualityComparison()) return null;

spock-specs/src/test/groovy/org/spockframework/smoke/condition/ConditionRenderingSpec.groovy

@@ -16,9 +16,8 @@
 
 package org.spockframework.smoke.condition
 
-import org.spockframework.runtime.ConditionNotSatisfiedError
 import org.spockframework.runtime.Condition
-
+import org.spockframework.runtime.ConditionNotSatisfiedError
 import spock.lang.Specification
 
 /**
@@ -41,4 +40,16 @@ abstract class ConditionRenderingSpec extends Specification {
 
     assert false, "condition should have failed but didn't"
   }
-}
+
+  void renderedConditionContains(Closure condition, String... contents) {
+    try {
+      condition()
+    } catch (ConditionNotSatisfiedError e) {
+      String rendering = e.condition.rendering.trim()
+      contents.each { assert rendering.contains(it)}
+      return
+    }
+
+    assert false, "condition should have failed but didn't"
+  }
+}

spock-specs/src/test/groovy/org/spockframework/smoke/condition/StringComparisonRendering.groovy

@@ -16,6 +16,7 @@
 
 package org.spockframework.smoke.condition
 
+import org.spockframework.runtime.ExpressionInfoValueRenderer
 import spock.lang.Issue
 
 class StringComparisonRendering extends ConditionRenderingSpec {
@@ -78,4 +79,96 @@ null == "foo"
       assert ("the quick" == "the quick") instanceof String
     }
   }
+  @Issue("https://github.com/spockframework/spock/issues/121")
+  def "large String comparision does not cause OOM-Error, difference at start"() {
+    StringBuilder sb = largeStringBuilder()
+    String a = sb.toString()
+    sb.setCharAt(0, 'b'  as char)
+    String b = sb.toString()
+
+    expect:
+    renderedConditionContains({
+      assert a == b
+    },
+      "1 difference (90% similarity) (comparing subset start: 0, end1: 11, end2: 11)",
+      "(a)aaaaaaaaaa",
+      "(b)aaaaaaaaaa"
+    )
+  }
+
+  @Issue("https://github.com/spockframework/spock/issues/121")
+  def "large String comparision does not cause OOM-Error, difference in the middle"() {
+    StringBuilder sb = largeStringBuilder()
+    String a = sb.toString()
+    sb.setCharAt(sb.length() / 2 as int, 'b'  as char)
+    String b = sb.toString()
+
+    expect:
+    renderedConditionContains({
+      assert a == b
+    },
+      "1 difference (95% similarity) (comparing subset start: 12789, end1: 12811, end2: 12811)",
+      "aaaaaaaaaaa(a)aaaaaaaaaa",
+      "aaaaaaaaaaa(b)aaaaaaaaaa"
+    )
+  }
+
+  @Issue("https://github.com/spockframework/spock/issues/121")
+  def "large String comparision does not cause OOM-Error, difference at end"() {
+    StringBuilder sb = largeStringBuilder()
+    String a = sb.toString()
+    sb.setCharAt(sb.length()-1, 'b'  as char)
+    String b = sb.toString()
+
+    expect:
+    renderedConditionContains({
+      assert a == b
+    },
+      "1 difference (91% similarity) (comparing subset start: 25588, end1: 25600, end2: 25600)",
+      "aaaaaaaaaaa(a)",
+      "aaaaaaaaaaa(b)")
+  }
+
+
+
+  @Issue("https://github.com/spockframework/spock/issues/121")
+  def "large String comparision does not cause OOM-Error, difference at start and  end"() {
+    StringBuilder sb = largeStringBuilder()
+    String a = sb.toString()
+    sb.setCharAt(0, 'b'  as char)
+    sb.setCharAt(sb.length()-1, 'b'  as char)
+    String b = sb.toString()
+
+    expect:
+    renderedConditionContains({
+      assert a == b
+    },
+      "false",
+      "Strings too large to calculate edit distance.")
+  }
+
+
+  @Issue("https://github.com/spockframework/spock/issues/121")
+  def "large String comparision does not cause OOM-Error, complete difference"() {
+    String a = largeStringBuilder()
+    String b = largeStringBuilder("bbbbbbbbbbbbbbbb")
+
+
+    expect:
+    renderedConditionContains({
+      assert a == b
+    },
+      "false",
+      "Strings too large to calculate edit distance.")
+  }
+
+  private StringBuilder largeStringBuilder(CharSequence source = "aaaaaaaaaaaaaaaa") {
+    int length = ExpressionInfoValueRenderer.MAX_EDIT_DISTANCE_MEMORY / 2
+    def sb = new StringBuilder(length + 10)
+    int cslength = source.length()
+    for (int i = 0; i < length; i += cslength) {
+      sb.append(source, 0, Math.min(length - i, cslength))
+    }
+    return sb
+  }
 }