When masking, replace all regex matches in string values

Previously, the whole field value had to match the regex in order to be masked.
Now, each regex match within a string value will be replaced.

Fixes #400

Author: philsttr

README.md

@@ -1452,6 +1452,9 @@ for the path string format and more examples.  But in general:
 
 Specific values to be masked can be specified in several ways, as seen in the following example:
 
+When using regexes to identify strings to mask, all matches within each string field value will be replaced.
+If you want to match the full string field value, then use the beginning of line (`^`) and end of line (`$`) markers.
+
 ```xml
 <encoder class="net.logstash.logback.encoder.LogstashEncoder">
   <jsonGeneratorDecorator class="net.logstash.logback.mask.MaskingJsonGeneratorDecorator">
@@ -1462,9 +1465,9 @@ Specific values to be masked can be specified in several ways, as seen in the fo
     -->
     <defaultMask>****</defaultMask>
 
-    <!-- Values to mask added via <value> will use the  default mask string -->
+    <!-- Values to mask added via <value> will use the default mask string -->
     <value>^foo$</value>
-    <value>^bar$</value>
+    <value>bar</value>
 
     <!-- Multiple values can be specified as a comma separated string in the <values> element. -->
     <values>^baz$,^blah$</values>

src/main/java/net/logstash/logback/mask/RegexValueMasker.java

@@ -41,17 +41,20 @@ public RegexValueMasker(String regex, Object mask) {
      */
     public RegexValueMasker(Pattern pattern, Object mask) {
         this.pattern = Objects.requireNonNull(pattern, "pattern must not be null");
-        this.mask = Objects.requireNonNull(mask, "rmask must not be null");
+        this.mask = Objects.requireNonNull(mask, "mask must not be null");
     }
 
     @Override
     public Object mask(JsonStreamContext context, Object o) {
         if (o instanceof CharSequence) {
             Matcher matcher = pattern.matcher((CharSequence) o);
-            if (matcher.matches()) {
-                return mask instanceof String
-                        ? matcher.replaceAll((String) mask)
-                        : mask;
+            if (mask instanceof String) {
+                String replaced = matcher.replaceAll((String) mask);
+                if (replaced != o) {
+                    return replaced;
+                }
+            } else if (matcher.matches()) {
+                return mask;
             }
         }
         return null;

src/test/java/net/logstash/logback/mask/MaskingJsonGeneratorDecoratorTest.java

@@ -175,8 +175,8 @@ public void configuration() throws IOException {
                 "{\"fieldA\":\"****\",\"fieldB\":\"****\",\"fieldC\":\"****\",\"fieldD\":\"****\",\"fieldE\":\"[masked]\",\"fieldF\":\"****\",\"testfield\":\"[maskedtestfield]\"}",
                 masks);
         test(
-                "{\"field0\":\"value0\",\"field1\":\"value1\",\"field2\":\"value2\",\"field3\":\"value3\",\"field-Z\":\"value-Z\",\"field4\":\"value4\",\"field5\":\"testvalue\",\"field6\":\"value6\"}",
-                "{\"field0\":\"****\",\"field1\":\"****\",\"field2\":\"****\",\"field3\":\"****\",\"field-Z\":\"value-masked\",\"field4\":\"value4\",\"field5\":\"[maskedtestvalue]\",\"field6\":\"****\"}",
+                "{\"field0\":\"value0\",\"field1\":\"value1\",\"field2\":\"value2\",\"field3\":\"value3\",\"field-Z\":\"value-Z\",\"field4\":\"value4\",\"field5\":\"testvalue\",\"field6\":\"value6\",\"field7\":\"nestedvalue1-nestedvalue1\"}",
+                "{\"field0\":\"****\",\"field1\":\"****\",\"field2\":\"****\",\"field3\":\"****\",\"field-Z\":\"value-masked\",\"field4\":\"value4\",\"field5\":\"[maskedtestvalue]\",\"field6\":\"****\",\"field7\":\"****-****\"}",
                 masks);
     }
 

src/test/java/net/logstash/logback/mask/RegexValueMaskerTest.java

@@ -0,0 +1,39 @@
+package net.logstash.logback.mask;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.node.NullNode;
+
+class RegexValueMaskerTest {
+
+    @Test
+    void regexMatchesFullString() {
+        RegexValueMasker masker = new RegexValueMasker("^test$", "****");
+        assertThat(masker.mask(null, "test")).isEqualTo("****");
+        assertThat(masker.mask(null, "testtest")).isNull();
+    }
+
+    @Test
+    void regexMatchesPartialString() {
+        RegexValueMasker masker = new RegexValueMasker("test", "****");
+        assertThat(masker.mask(null, "test")).isEqualTo("****");
+        assertThat(masker.mask(null, "test-test")).isEqualTo("****-****");
+        assertThat(masker.mask(null, "foo")).isNull();
+    }
+
+    @Test
+    void nullMask() {
+        RegexValueMasker masker = new RegexValueMasker("test", NullNode.instance);
+        assertThat(masker.mask(null, "test")).isEqualTo(NullNode.instance);
+        assertThat(masker.mask(null, "test-test")).isNull();
+    }
+
+    @Test
+    void nonString() {
+        RegexValueMasker masker = new RegexValueMasker("test", "****");
+        assertThat(masker.mask(null, 1)).isNull();
+    }
+
+}

src/test/resources/net/logstash/logback/mask/MaskingJsonGeneratorDecoratorTest-masks.xml

@@ -19,6 +19,7 @@
                 <value>^value0$</value>
                 <value>^value1$</value>
                 <values>^value2$,^value3$</values>
+                <value>nestedvalue1</value>
                 <valueMask>
                     <value>^(value-).*$</value>
                     <mask>$1masked</mask>