Merge first part of #4848 (actual fix to "type pollution") (#4862)

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -425,6 +425,8 @@ Jonas Konrad (yawkat@github)
   * Contributed fix for #3655: `ObjectMapper` default heap consumption increased significantly
     from 2.13.x to 2.14.0
    (2.14.1)
+  * Contributed fix for #4848: Avoid type pollution in `StringCollectionDeserializer`
+   (2.18.3)
 
 Jirka Kremser (Jiri-Kremser@github)
   * Suggested #924: SequenceWriter.writeAll() could accept Iterable

release-notes/VERSION-2.x

@@ -12,6 +12,8 @@ Project: jackson-databind
  (fix by Joo-Hyuk K)
 #4844: Fix wrapped array hanlding wrt `null` by `StdDeserializer`
  (fix by Stanislav S)
+#4848: Avoid type pollution in `StringCollectionDeserializer`
+ (contributed by Jonas K)
 #4860: `ConstructorDetector.USE_PROPERTIES_BASED` does not work with
   multiple constructors since 2.18
  (reported by Tomáš P)

src/main/java/com/fasterxml/jackson/databind/deser/std/StringCollectionDeserializer.java

@@ -1,12 +1,12 @@
 package com.fasterxml.jackson.databind.deser.std;
 
 import java.io.IOException;
-import java.util.Collection;
-import java.util.Objects;
+import java.util.*;
 
 import com.fasterxml.jackson.annotation.JsonFormat;
 
-import com.fasterxml.jackson.core.*;
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonToken;
 
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
@@ -171,16 +171,15 @@ public ValueInstantiator getValueInstantiator() {
     /**********************************************************
      */
 
-    @SuppressWarnings("unchecked")
     @Override
     public Collection<String> deserialize(JsonParser p, DeserializationContext ctxt)
         throws IOException
     {
         if (_delegateDeserializer != null) {
-            return (Collection<String>) _valueInstantiator.createUsingDelegate(ctxt,
-                    _delegateDeserializer.deserialize(p, ctxt));
+            return castToCollection(_valueInstantiator.createUsingDelegate(ctxt,
+                    _delegateDeserializer.deserialize(p, ctxt)));
         }
-        final Collection<String> result = (Collection<String>) _valueInstantiator.createUsingDefault(ctxt);
+        final Collection<String> result = castToCollection(_valueInstantiator.createUsingDefault(ctxt));
         return deserialize(p, ctxt, result);
     }
 
@@ -273,7 +272,6 @@ public Object deserializeWithType(JsonParser p, DeserializationContext ctxt,
      * throw an exception, or try to handle value as if member of implicit
      * array, depending on configuration.
      */
-    @SuppressWarnings("unchecked")
     private final Collection<String> handleNonArray(JsonParser p, DeserializationContext ctxt,
             Collection<String> result) throws IOException
     {
@@ -285,7 +283,7 @@ private final Collection<String> handleNonArray(JsonParser p, DeserializationCon
             if (p.hasToken(JsonToken.VALUE_STRING)) {
                 return _deserializeFromString(p, ctxt);
             }
-            return (Collection<String>) ctxt.handleUnexpectedToken(_containerType, p);
+            return castToCollection(ctxt.handleUnexpectedToken(_containerType, p));
         }
         // Strings are one of "native" (intrinsic) types, so there's never type deserializer involved
         JsonDeserializer<String> valueDes = _valueDeserializer;
@@ -307,15 +305,15 @@ private final Collection<String> handleNonArray(JsonParser p, DeserializationCon
                     final CoercionAction act = ctxt.findCoercionAction(logicalType(), handledType(),
                             CoercionInputShape.EmptyString);
                     if (act != CoercionAction.Fail) {
-                        return (Collection<String>) _deserializeFromEmptyString(p, ctxt, act, handledType(),
-                                "empty String (\"\")");
+                        return castToCollection(_deserializeFromEmptyString(p, ctxt, act, handledType(),
+                                "empty String (\"\")"));
                     }
                 } else if (_isBlank(textValue)) {
                     final CoercionAction act = ctxt.findCoercionFromBlankString(logicalType(), handledType(),
                             CoercionAction.Fail);
                     if (act != CoercionAction.Fail) {
-                        return (Collection<String>) _deserializeFromEmptyString(p, ctxt, act, handledType(),
-                                "blank String (all whitespace)");
+                        return castToCollection(_deserializeFromEmptyString(p, ctxt, act, handledType(),
+                                "blank String (all whitespace)"));
                     }
                 }
                 // if coercion failed, we can still add it to a list
@@ -330,4 +328,24 @@ private final Collection<String> handleNonArray(JsonParser p, DeserializationCon
         result.add(value);
         return result;
     }
+
+    // Used to avoid type pollution: see
+    //   https://micronaut-projects.github.io/micronaut-test/latest/guide/#typePollution
+    // for details
+    //
+    // @since 2.18
+    @SuppressWarnings("unchecked")
+    private static Collection<String> castToCollection(Object o) {
+        if (o != null) {
+            // fast path for specific classes to avoid type pollution:
+            // https://micronaut-projects.github.io/micronaut-test/latest/guide/#typePollution
+            if (o.getClass() == ArrayList.class) {
+                return (ArrayList<String>) o;
+            }
+            if (o.getClass() == HashSet.class) {
+                return (HashSet<String>) o;
+            }
+        }
+        return (Collection<String>) o;
+    }
 }