Merge pull request #62 from tkowalcz/56-patterns-in-labels

56 patterns in labels

core/src/main/java/pl/tkowalcz/tjahzi/LabelSerializer.java

@@ -32,19 +32,25 @@ public class LabelSerializer {
         return this;
     }
 
-    public void startAppendingLabelValue() {
+    public LabelSerializer startAppendingLabelValue() {
         lastSizePosition = cursor;
         cursor += Integer.BYTES;
+
+        return this;
     }
 
-    public void appendPartialLabelValue(String value) {
-        cursor += buffer.putStringWithoutLengthAscii(cursor, value);
+    public LabelSerializer appendPartialLabelValue(CharSequence value) {
+        cursor += buffer.putStringWithoutLengthAscii(cursor, value.toString());
+
+        return this;
     }
 
-    public void finishAppendingLabelValue() {
+    public LabelSerializer finishAppendingLabelValue() {
         buffer.putInt(
                 lastSizePosition,
                 cursor - lastSizePosition - Integer.BYTES);
+
+        return this;
     }
 
     public LabelSerializer appendLabel(String key, String value) {

core/src/test/java/pl/tkowalcz/tjahzi/LabelSerializerTest.java

@@ -64,20 +64,19 @@ class LabelSerializerTest {
         // When
         serializer.appendLabel("Foo", "Bar");
 
-        serializer.appendLabelName("Aliens");
-        serializer.startAppendingLabelValue();
-        serializer.appendPartialLabelValue("Kang");
-        serializer.appendPartialLabelValue("Kodos");
-        serializer.appendPartialLabelValue("Johnson");
-        serializer.finishAppendingLabelValue();
-
-        serializer.appendLabelName("Omicronians");
-        serializer.startAppendingLabelValue();
-        serializer.appendPartialLabelValue("Lrrr");
-        serializer.appendPartialLabelValue("RULER OF THE PLANET OMICRON PERSEI EIGHT");
-        serializer.finishAppendingLabelValue();
-
-        serializer.appendLabel("Popplers", "Problem");
+        serializer
+                .appendLabelName("Aliens")
+                    .startAppendingLabelValue()
+                        .appendPartialLabelValue("Kang")
+                        .appendPartialLabelValue("Kodos")
+                        .appendPartialLabelValue("Johnson")
+                    .finishAppendingLabelValue()
+                .appendLabelName("Omicronians")
+                    .startAppendingLabelValue()
+                        .appendPartialLabelValue("Lrrr")
+                        .appendPartialLabelValue("RULER OF THE PLANET OMICRON PERSEI EIGHT")
+                    .finishAppendingLabelValue()
+                .appendLabel("Popplers", "Problem");
 
         // Then
         assertThat(serializer.getLabelsCount()).isEqualTo(4);

log4j2-appender/README.md

@@ -30,6 +30,7 @@ Log4j2 appender seemed like a good first.
 1. Include minimal appender configuration:
 
 ```xml
+
 <Loki name="loki-appender">
     <host>${sys:loki.host}</host>
     <port>${sys:loki.port}</port>
@@ -45,6 +46,7 @@ Log4j2 appender seemed like a good first.
 1. Reference the appender from inside one of your logger definitions:
 
 ```xml
+
 <Root level="INFO">
     <AppenderRef ref="Loki"/>
 </Root>
@@ -59,6 +61,7 @@ will configure the appender to call to URL: `http://loki.mydomain.com:3100/loki/
 ### Grafana Cloud configuration
 
 Tjahzi can send logs to Grafana Cloud. It needs two things to be configured:
+
 - Set port number to `443` which switches HTTP client into HTTPS mode.
 - Specify `username` and `password` for HTTP basic authentication that Grafana uses.
 
@@ -66,6 +69,7 @@ Password is your "Grafana.com API Key" and can be generated in "Grafana datasour
 is just for illustrative purposes.
 
 ```xml
+
 <Loki name="loki-appender">
     <!-- example host -->
     <host>logs-prod-us-central1.grafana.net</host>
@@ -115,12 +119,27 @@ attribute of configuration so that the appender can be found.
 Contents of the properties
 are [automatically interpolated by Log4j2](https://logging.apache.org/log4j/log4j-2.2/manual/configuration.html#PropertySubstitution)
 . All environment, system etc. variable references will be replaced by their values during initialization of the
-appender. The exception is context/MDC (`${ctx:foo}`) value lookup as it make sense only during runtime.
+appender. The exception to this rule is context/MDC (`${ctx:foo}`) value lookup - it is performed for each message at
+runtime (allocation free).
 
 NOTE: This process could have been executed for every lookup type at runtime (for each log message). This approach was
 deemed too expensive. If you need a mechanism to replace a variable (other than context/MDC) after logging system
 initialization I would love to hear your use case - please file an issue.
 
+## Patterns in Labels
+
+Alternative way of specifying label contents is via pattern attribute:
+
+```xml
+
+<Label name="server" pattern="%C{1.}"/>
+```
+
+This pattern is compatible with
+Log4j [pattern layout](https://logging.apache.org/log4j/2.x/manual/layouts.html#PatternLayout). In fact, we reuse lgo4j
+internal classes for this implementation. It is generally efficient and allocation free as
+per [documentation](https://logging.apache.org/log4j/log4j-2.12.1/manual/garbagefree.html#PatternLayout).
+
 ## Details
 
 Let's go through the example config above and analyze configuration options (**Note: Tags are case-insensitive**).
@@ -154,6 +173,13 @@ when [running Loki in multi-tenant mode](https://grafana.com/docs/loki/latest/op
 Specify additional labels attached to each log line sent via this appender instance. See also note
 about [label naming](https://github.com/tkowalcz/tjahzi/wiki/Label-naming).
 
+You can use value attribute to specify static text. You can use `${}` variable substitution inside that text and Tjahzi
+will resolve variables once at startup. If the varaible is a context/MDC lookup it will be resolved dynamically for each
+log line.
+
+This tag also supports `pattern` attribute where you can use pattern layout expressions that will be resolved at
+runtime.
+
 #### LogLevelLabel (optional)
 
 If defined then log level label of configured name will be added to each line sent to Loki. It will contain Log4j log

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/LokiAppenderBuilder.java

@@ -122,7 +122,12 @@ public class LokiAppenderBuilder<B extends LokiAppenderBuilder<B>> extends Abstr
             );
         }
 
-        LabelFactory labelFactory = new LabelFactory(logLevelLabel, labels);
+        LabelFactory labelFactory = new LabelFactory(
+                getConfiguration(),
+                logLevelLabel,
+                labels
+        );
+
         LabelsDescriptor labelsDescriptor = labelFactory.convertLabelsDroppingInvalid();
         logLevelLabel = labelsDescriptor.getLogLevelLabel();
 

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/AggregateLabelPrinter.java

@@ -18,7 +18,7 @@ public class AggregateLabelPrinter implements LabelPrinter {
     }
 
     @Override
-    public void append(LogEvent event, Consumer<String> appendable) {
+    public void append(LogEvent event, Consumer<CharSequence> appendable) {
         for (LabelPrinter node : nodes) {
             node.append(event, appendable);
         }

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/Label.java

@@ -7,37 +7,69 @@ import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
 import org.apache.logging.log4j.core.config.plugins.PluginFactory;
 import org.apache.logging.log4j.core.config.plugins.PluginValue;
 import org.apache.logging.log4j.status.StatusLogger;
-import pl.tkowalcz.tjahzi.log4j2.Property;
 
 import java.util.regex.Pattern;
 
 @Plugin(name = "label", category = Node.CATEGORY, printObject = true)
-public class Label extends Property {
+public class Label {
 
     private static final Logger LOGGER = StatusLogger.getLogger();
 
     private static final Pattern LABEL_NAME_PATTER = Pattern.compile("[a-zA-Z_][a-zA-Z0-9_]*");
 
-    private Label(String name, String value) {
-        super(name, value);
+    private final String name;
+    private final String value;
+    private final String pattern;
+
+    private Label(String name, String value, String pattern) {
+        this.name = name;
+        this.value = value;
+        this.pattern = pattern;
     }
 
     @PluginFactory
     public static Label createLabel(
             @PluginAttribute("name") String name,
-            @PluginValue("value") String value) {
+            @PluginValue("value") String value,
+            @PluginValue("pattern") String pattern
+    ) {
         if (name == null) {
             LOGGER.error("Property name cannot be null");
         }
 
-        return new Label(name, value);
+        if (pattern == null && value == null) {
+            LOGGER.error("Property must have pattern or value specified");
+        }
+
+        return new Label(name, value, pattern);
     }
 
     public boolean hasValidName() {
         return hasValidName(getName());
     }
 
+    public String getName() {
+        return name;
+    }
+
+    public String getPattern() {
+        return pattern;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
     public static boolean hasValidName(String label) {
         return LABEL_NAME_PATTER.matcher(label).matches();
     }
+
+    @Override
+    public String toString() {
+        return "Label{" +
+                "name='" + name + '\'' +
+                ", pattern='" + pattern + '\'' +
+                ", value='" + value + '\'' +
+                '}';
+    }
 }

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/LabelFactory.java

@@ -1,6 +1,9 @@
 package pl.tkowalcz.tjahzi.log4j2.labels;
 
 import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.layout.PatternLayout;
+import org.apache.logging.log4j.core.pattern.PatternParser;
 import org.apache.logging.log4j.status.StatusLogger;
 import pl.tkowalcz.tjahzi.github.GitHubDocs;
 
@@ -22,9 +25,13 @@ public class LabelFactory {
     private final String logLevelLabel;
     private final Label[] labels;
 
-    public LabelFactory(String logLevelLabel, Label... labels) {
+    private final PatternParser patternParser;
+
+    public LabelFactory(Configuration configuration, String logLevelLabel, Label... labels) {
         this.logLevelLabel = logLevelLabel;
         this.labels = labels;
+
+        this.patternParser = new PatternParser(configuration, PatternLayout.KEY, null);
     }
 
     public LabelsDescriptor convertLabelsDroppingInvalid() {
@@ -95,11 +102,19 @@ public class LabelFactory {
                 )
                 .collect(toMap(
                         Label::getName,
-                        LabelPrinterFactory::parse,
+                        this::toLabelOrLog4jPattern,
                         (original, duplicate) -> duplicate)
                 );
     }
 
+    private LabelPrinter toLabelOrLog4jPattern(Label label) {
+        if (label.getPattern() != null) {
+            return Log4jAdapterLabelPrinter.of(patternParser.parse(label.getPattern()));
+        }
+
+        return LabelPrinterFactory.parse(label);
+    }
+
     private static String validateLogLevelLabel(
             String logLevelLabel,
             Map<String, ?> staticLabels,

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/LabelPrinter.java

@@ -7,7 +7,7 @@ import java.util.function.Consumer;
 
 public interface LabelPrinter {
 
-    void append(LogEvent event, Consumer<String> appendable);
+    void append(LogEvent event, Consumer<CharSequence> appendable);
 
     default boolean isStatic() {
         return false;

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/Literal.java

@@ -22,7 +22,7 @@ public class Literal implements LabelPrinter {
     }
 
     @Override
-    public void append(LogEvent event, Consumer<String> appendable) {
+    public void append(LogEvent event, Consumer<CharSequence> appendable) {
         appendable.accept(contents);
     }
 }

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/Log4jAdapterLabelPrinter.java

@@ -0,0 +1,53 @@
+package pl.tkowalcz.tjahzi.log4j2.labels;
+
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.pattern.LiteralPatternConverter;
+import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;
+import org.apache.logging.log4j.core.pattern.PatternFormatter;
+
+import java.util.List;
+import java.util.function.Consumer;
+
+@SuppressWarnings("ForLoopReplaceableByForEach")
+public class Log4jAdapterLabelPrinter implements LabelPrinter {
+
+    private final StringBuilder outputBuffer = new StringBuilder();
+    private final List<PatternFormatter> formatters;
+
+    public Log4jAdapterLabelPrinter(List<PatternFormatter> formatters) {
+        this.formatters = formatters;
+    }
+
+    @Override
+    public void append(LogEvent event, Consumer<CharSequence> appendable) {
+        outputBuffer.setLength(0);
+
+        for (int i = 0; i < formatters.size(); i++) {
+            formatters.get(i).format(event, outputBuffer);
+        }
+
+        appendable.accept(outputBuffer);
+    }
+
+    @Override
+    public boolean isStatic() {
+        for (int i = 0; i < formatters.size(); i++) {
+            LogEventPatternConverter converter = formatters.get(i).getConverter();
+
+            if (!(converter instanceof LiteralPatternConverter)) {
+                return false;
+            }
+
+            if (((LiteralPatternConverter) converter).getLiteral().contains("$")) {
+                return false;
+            }
+
+        }
+
+        return true;
+    }
+
+    public static Log4jAdapterLabelPrinter of(List<PatternFormatter> parse) {
+        return new Log4jAdapterLabelPrinter(parse);
+    }
+}

log4j2-appender/src/main/java/pl/tkowalcz/tjahzi/log4j2/labels/MDCLookup.java

@@ -19,7 +19,7 @@ public class MDCLookup implements LabelPrinter {
     }
 
     @Override
-    public void append(LogEvent event, Consumer<String> appendable) {
+    public void append(LogEvent event, Consumer<CharSequence> appendable) {
         Object value = event.getContextData().getValue(variableName);
         if (value != null) {
             appendable.accept(value.toString());

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/LabelFactoryTest.java

@@ -1,6 +1,9 @@
 package pl.tkowalcz.tjahzi.log4j2.labels;
 
+import org.apache.logging.log4j.core.config.NullConfiguration;
+import org.apache.logging.log4j.core.config.xml.XmlConfiguration;
 import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
 
 import java.util.Map;
 
@@ -11,11 +14,12 @@ class LabelFactoryTest {
     @Test
     void shouldRemoveDuplicatedLabels() {
         // Given
-        Label thisIsADuplicateAndShouldBeDropped = Label.createLabel("ip", "127.0.0.1");
-        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34");
-        Label thisTooShouldStay = Label.createLabel("hostname", "hostname");
+        Label thisIsADuplicateAndShouldBeDropped = Label.createLabel("ip", "127.0.0.1", null);
+        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34", null);
+        Label thisTooShouldStay = Label.createLabel("hostname", "hostname", null);
 
         LabelFactory labelFactory = new LabelFactory(
+                new NullConfiguration(),
                 "log_level",
                 thisIsADuplicateAndShouldBeDropped,
                 thisShouldStay,
@@ -36,17 +40,22 @@ class LabelFactoryTest {
     @Test
     void shouldIdentifyDynamicLabels() {
         // Given
-        Label thisIsAStaticLabel = Label.createLabel("ip", "127.0.0.1");
-        Label thisIsAlsoAStaticLabel = Label.createLabel("region", "us-east-1");
-        Label thisIsADynamicLabel = Label.createLabel("tenant", "${ctx:tenant}");
-        Label thisIsAnotherDynamicLabel = Label.createLabel("tenant", "foo_${ctx:baz}_bar");
+        Label thisIsAStaticLabel = Label.createLabel("ip", "127.0.0.1", null);
+        Label thisIsAlsoAStaticLabel = Label.createLabel("region", "us-east-1", null);
+        Label thisIsADynamicLabel = Label.createLabel("tenant", "${ctx:tenant}", null);
+        Label thisIsAnotherDynamicLabel = Label.createLabel("tenant", "foo_${ctx:baz}_bar", null);
+        Label thisIsAStaticPatternLabel = Label.createLabel("AZ", null, "us-east-1a");
+        Label thisIsADynamicPatternLabel = Label.createLabel("iam_role", null, "${iam}");
 
         LabelFactory labelFactory = new LabelFactory(
+                new NullConfiguration(),
                 "log_level",
                 thisIsAStaticLabel,
                 thisIsAlsoAStaticLabel,
                 thisIsADynamicLabel,
-                thisIsAnotherDynamicLabel
+                thisIsAnotherDynamicLabel,
+                thisIsAStaticPatternLabel,
+                thisIsADynamicPatternLabel
         );
 
         // When
@@ -56,24 +65,27 @@ class LabelFactoryTest {
         assertThat(actual.getStaticLabels())
                 .containsOnly(
                         asEntry(thisIsAStaticLabel),
-                        asEntry(thisIsAlsoAStaticLabel)
+                        asEntry(thisIsAlsoAStaticLabel),
+                        asEntryUsingPattern(thisIsAStaticPatternLabel)
                 );
 
         assertThat(actual.getDynamicLabels().keySet())
                 .containsOnly(
                         thisIsADynamicLabel.getName(),
-                        thisIsAnotherDynamicLabel.getName()
+                        thisIsAnotherDynamicLabel.getName(),
+                        thisIsADynamicPatternLabel.getName()
                 );
     }
 
     @Test
     void shouldSkipLabelsWithInvalidName() {
         // Given
-        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34");
-        Label thisShouldStayToo = Label.createLabel("region", "coruscant-west-2");
-        Label invalidNameShouldBeDropped = Label.createLabel("host-name", "hostname");
+        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34", null);
+        Label thisShouldStayToo = Label.createLabel("region", "coruscant-west-2", null);
+        Label invalidNameShouldBeDropped = Label.createLabel("host-name", "hostname", null);
 
         LabelFactory labelFactory = new LabelFactory(
+                new NullConfiguration(),
                 "log_level",
                 thisShouldStayToo,
                 thisShouldStay,
@@ -93,10 +105,11 @@ class LabelFactoryTest {
     @Test
     void shouldAcceptNullLogLevel() {
         // Given
-        Label label1 = Label.createLabel("ip", "10.0.2.34");
-        Label label2 = Label.createLabel("region", "coruscant-west-2");
+        Label label1 = Label.createLabel("ip", "10.0.2.34", null);
+        Label label2 = Label.createLabel("region", "coruscant-west-2", null);
 
         LabelFactory labelFactory = new LabelFactory(
+                new NullConfiguration(),
                 null,
                 label2,
                 label1
@@ -117,10 +130,11 @@ class LabelFactoryTest {
         // Given
         String logLevelLabel = "log_level";
 
-        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34");
-        Label thisShouldBeRemovedDueToConflict = Label.createLabel(logLevelLabel, "coruscant-west-2");
+        Label thisShouldStay = Label.createLabel("ip", "10.0.2.34", null);
+        Label thisShouldBeRemovedDueToConflict = Label.createLabel(logLevelLabel, "coruscant-west-2", null);
 
         LabelFactory labelFactory = new LabelFactory(
+                Mockito.mock(XmlConfiguration.class),
                 logLevelLabel,
                 thisShouldBeRemovedDueToConflict,
                 thisShouldStay
@@ -142,7 +156,7 @@ class LabelFactoryTest {
         // Given
         String logLevelLabel = "log-level";
 
-        LabelFactory labelFactory = new LabelFactory(logLevelLabel);
+        LabelFactory labelFactory = new LabelFactory(null, logLevelLabel);
 
         // When
         LabelsDescriptor actual = labelFactory.convertLabelsDroppingInvalid();
@@ -155,7 +169,7 @@ class LabelFactoryTest {
     void shouldHandleDisabledLogLevelLabel() {
         // Given
         String logLevelLabel = null;
-        LabelFactory labelFactory = new LabelFactory(logLevelLabel);
+        LabelFactory labelFactory = new LabelFactory(null, logLevelLabel);
 
         // When
         LabelsDescriptor actual = labelFactory.convertLabelsDroppingInvalid();
@@ -167,4 +181,8 @@ class LabelFactoryTest {
     public Map.Entry<String, String> asEntry(Label label) {
         return Map.entry(label.getName(), label.getValue());
     }
+
+    public Map.Entry<String, String> asEntryUsingPattern(Label label) {
+        return Map.entry(label.getName(), label.getPattern());
+    }
 }

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/LabelTest.java

@@ -9,9 +9,9 @@ class LabelTest {
     @Test
     void shouldValidateNamePattern() {
         // Given
-        Label correctLabel = Label.createLabel("aaa_bbb_ccc", "fobar");
-        Label tooShortLabel = Label.createLabel("", "foobar");
-        Label labelWithInvalidChars = Label.createLabel("log-level", "foobar");
+        Label correctLabel = Label.createLabel("aaa_bbb_ccc", "fobar", null);
+        Label tooShortLabel = Label.createLabel("", "foobar", null);
+        Label labelWithInvalidChars = Label.createLabel("log-level", "foobar", null);
 
         // When & Then
         assertThat(correctLabel.hasValidName()).isTrue();

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/LabelsContextSubstitutionTest.java

@@ -55,7 +55,7 @@ class LabelsContextSubstitutionTest {
         Logger logger = LogManager.getLogger(LabelsContextSubstitutionTest.class);
 
         // When
-        MDC.put("object", "bust_ticket");
+        MDC.put("object", "bus_ticket");
         MDC.put("owner", "wally");
         logger.info("Test1");
 
@@ -90,7 +90,7 @@ class LabelsContextSubstitutionTest {
                             .body("status", equalTo("success"))
                             .body("data.result.size()", equalTo(3))
                             .body("data.result.stream.server", everyItem(equalTo("127.0.0.1")))
-                            .body("data.result.stream.object", contains("prefix_", "prefix_bust_ticket", "prefix_comb"))
+                            .body("data.result.stream.object", contains("prefix_", "prefix_bus_ticket", "prefix_comb"))
                             .body("data.result.stream.owner", contains("_suffix", "wally_suffix", "jennifer_suffix"))
                             .body("data.result.stream.default_value_test", contains("use_this_if_missing", "use_this_if_missing", "use_this_if_missing"))
                             .body("data.result.values",

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/Log4jAdapterLabelPrinterTest.java

@@ -0,0 +1,124 @@
+package pl.tkowalcz.tjahzi.log4j2.labels;
+
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.core.config.NullConfiguration;
+import org.apache.logging.log4j.core.impl.JdkMapAdapterStringMap;
+import org.apache.logging.log4j.core.impl.MutableLogEvent;
+import org.apache.logging.log4j.core.layout.PatternLayout;
+import org.apache.logging.log4j.core.pattern.PatternFormatter;
+import org.apache.logging.log4j.core.pattern.PatternParser;
+import org.apache.logging.log4j.message.SimpleMessage;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class Log4jAdapterLabelPrinterTest {
+
+    @Test
+    void shouldHandleEmptyListOfFormatters() {
+        // Given
+        Log4jAdapterLabelPrinter printer = new Log4jAdapterLabelPrinter(List.of());
+
+        MutableLogEvent event = new MutableLogEvent();
+        StringBuilder builder = new StringBuilder();
+
+        // When
+        printer.append(event, builder::append);
+
+        // Then
+        assertThat(builder).isEmpty();
+    }
+
+    @Test
+    void shouldInvokeFormatters() {
+        // Given
+        PatternParser patternParser = new PatternParser(null, PatternLayout.KEY, null);
+        List<PatternFormatter> patternFormatters = patternParser.parse("%mdc{tid} %5p %c{1} - %m");
+
+        Log4jAdapterLabelPrinter printer = new Log4jAdapterLabelPrinter(patternFormatters);
+
+        Map<String, String> mdcMap = Map.of(
+                "tid", "req-43tnfwenb"
+        );
+
+        MutableLogEvent event = new MutableLogEvent();
+        event.setContextData(new JdkMapAdapterStringMap(mdcMap));
+        event.setLoggerName(getClass().getName());
+        event.setMessage(new SimpleMessage("Test"));
+        event.setLevel(Level.ERROR);
+        event.setLoggerFqcn(getClass().getCanonicalName());
+
+        StringBuilder builder = new StringBuilder();
+
+        // When
+        printer.append(event, builder::append);
+
+        // Then
+        assertThat(builder.toString()).isEqualTo("req-43tnfwenb ERROR Log4jAdapterLabelPrinterTest - Test");
+    }
+
+    @Test
+    void shouldSubstituteEnvVariables() {
+        // Given
+        System.setProperty("server", "127.0.0.1");
+
+        PatternParser patternParser = new PatternParser(
+                new NullConfiguration(),
+                PatternLayout.KEY,
+                null
+        );
+        List<PatternFormatter> patternFormatters = patternParser.parse("${sys:server} %5p %c{1} - %m");
+
+        Log4jAdapterLabelPrinter printer = new Log4jAdapterLabelPrinter(patternFormatters);
+
+        MutableLogEvent event = new MutableLogEvent();
+        event.setLoggerName(getClass().getName());
+        event.setMessage(new SimpleMessage("Test"));
+        event.setLevel(Level.ERROR);
+        event.setLoggerFqcn(getClass().getCanonicalName());
+
+        StringBuilder builder = new StringBuilder();
+
+        // When
+        printer.append(event, builder::append);
+
+        // Then
+        assertThat(builder.toString()).isEqualTo("127.0.0.1 ERROR Log4jAdapterLabelPrinterTest - Test");
+    }
+
+    private static Stream<Arguments> shouldCorrectlyIdentifyStaticPattern() {
+        return Stream.of(
+                Arguments.of("Empty", "", true),
+                Arguments.of("Literal value", "literal value", true),
+                Arguments.of("Literal value with variable", "Literal & variable: ${server}", false),
+                Arguments.of("Contains pattern", "With pattern %c{1}", false)
+        );
+    }
+
+    @ParameterizedTest(name = "{0}")
+    @MethodSource
+    void shouldCorrectlyIdentifyStaticPattern(String name, String pattern, boolean isStatic) {
+        // Given
+        PatternParser patternParser = new PatternParser(
+                new NullConfiguration(),
+                PatternLayout.KEY,
+                null
+        );
+
+        List<PatternFormatter> patternFormatters = patternParser.parse(pattern);
+        Log4jAdapterLabelPrinter labelPrinter = Log4jAdapterLabelPrinter.of(patternFormatters);
+
+        // When
+        boolean actual = labelPrinter.isStatic();
+
+        // Then
+        assertThat(actual).isEqualTo(isStatic);
+    }
+}

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/Log4jPatternsInLabelsTest.java

@@ -0,0 +1,102 @@
+package pl.tkowalcz.tjahzi.log4j2.labels;
+
+import io.restassured.RestAssured;
+import io.restassured.http.ContentType;
+import io.restassured.parsing.Parser;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.awaitility.Awaitility;
+import org.awaitility.Durations;
+import org.junit.jupiter.api.Test;
+import org.slf4j.MDC;
+import org.testcontainers.containers.BindMode;
+import org.testcontainers.containers.GenericContainer;
+import org.testcontainers.containers.wait.strategy.Wait;
+import org.testcontainers.junit.jupiter.Container;
+import org.testcontainers.junit.jupiter.Testcontainers;
+
+import java.net.URI;
+
+import static io.restassured.RestAssured.given;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.hasItems;
+import static org.hamcrest.core.Every.everyItem;
+
+@Testcontainers
+class Log4jPatternsInLabelsTest {
+
+    @Container
+    public GenericContainer loki = new GenericContainer("grafana/loki:latest")
+            .withCommand("-config.file=/etc/loki-config.yaml")
+            .withClasspathResourceMapping(
+                    "loki-config.yaml",
+                    "/etc/loki-config.yaml",
+                    BindMode.READ_ONLY
+            )
+            .waitingFor(
+                    Wait
+                            .forHttp("/ready")
+                            .forPort(3100)
+            )
+            .withExposedPorts(3100);
+
+    @Test
+    void shouldSendData() throws Exception {
+        // Given
+        System.setProperty("loki.host", loki.getHost());
+        System.setProperty("loki.port", loki.getFirstMappedPort().toString());
+
+        URI uri = getClass()
+                .getClassLoader()
+                .getResource("log4j-patterns-in-labels-configuration.xml")
+                .toURI();
+
+        ((org.apache.logging.log4j.core.LoggerContext) LogManager.getContext(false))
+                .setConfigLocation(uri);
+
+        Logger logger = LogManager.getLogger(Log4jPatternsInLabelsTest.class);
+
+        // When
+        MDC.put("tid", "req-230rq9ubou");
+        logger.info("Test1");
+
+        MDC.clear();
+        logger.info("Test2");
+
+        // Then
+        RestAssured.port = loki.getFirstMappedPort();
+        RestAssured.baseURI = "http://" + loki.getHost();
+        RestAssured.registerParser("text/plain", Parser.JSON);
+
+        Awaitility
+                .await()
+                .atMost(Durations.TEN_SECONDS)
+                .pollInterval(Durations.ONE_SECOND)
+                .ignoreExceptions()
+                .untilAsserted(() -> {
+                    given()
+                            .contentType(ContentType.URLENC)
+                            .urlEncodingEnabled(false)
+                            .formParam("query=%7Bserver%3D%22127.0.0.1%22%7D")
+                            .when()
+                            .get("/loki/api/v1/query_range")
+                            .then()
+                            .log()
+                            .all()
+                            .statusCode(200)
+                            .body("status", equalTo("success"))
+                            .body("data.result.size()", equalTo(2))
+                            .body("data.result.stream.server", everyItem(equalTo("127.0.0.1")))
+                            .body("data.result.stream.class_pattern", everyItem(equalTo("p.t.t.l.l.Log4jPatternsInLabelsTest")))
+                            .body("data.result.stream.sequence_number", contains("2", "1"))
+                            .body("data.result.stream.mdc_tid", contains("", "req-230rq9ubou"))
+                            .body("data.result.values",
+                                    hasItems(
+                                            hasItems(hasItems("Log4jPatternsInLabelsTest - Test2")),
+                                            hasItems(hasItems("Log4jPatternsInLabelsTest - Test1"))
+                                    )
+                            );
+                });
+    }
+}

log4j2-appender/src/test/java/pl/tkowalcz/tjahzi/log4j2/labels/LogLevelLabelConfigurationTest.java

@@ -37,7 +37,7 @@ class LogLevelLabelConfigurationTest {
             .withExposedPorts(3100);
 
     @Test
-    void shouldWorkWIthNoLogLevelConfigured() throws Exception {
+    void shouldWorkWithNoLogLevelConfigured() throws Exception {
         // Given
         System.setProperty("loki.host", loki.getHost());
         System.setProperty("loki.port", loki.getFirstMappedPort().toString());

log4j2-appender/src/test/resources/labels-context-substitution-test-configuration.xml

@@ -17,6 +17,8 @@
             </PatternLayout>
 
             <Header name="server" value="127.0.0.1"/>
+
+            <Label name="server" value="127.0.0.1"/>
             <Label name="server" value="127.0.0.1"/>
             <Label name="object" value="prefix_${ctx:object}"/>
             <Label name="owner" value="${ctx:owner}_suffix"/>

log4j2-appender/src/test/resources/log4j-patterns-in-labels-configuration.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration packages="pl.tkowalcz.tjahzi.log4j2">
+    <Loggers>
+        <Root level="INFO">
+            <AppenderRef ref="Loki"/>
+        </Root>
+    </Loggers>
+
+    <appenders>
+        <Loki name="Loki">
+            <host>${sys:loki.host}</host>
+            <port>${sys:loki.port}</port>
+
+            <ThresholdFilter level="ALL"/>
+            <PatternLayout>
+                <Pattern>%c{1} - %m</Pattern>
+            </PatternLayout>
+
+            <Header name="server" value="127.0.0.1"/>
+
+            <Label name="server" pattern="127.0.0.1"/>
+            <Label name="class_pattern" pattern="%C{1.}"/>
+            <Label name="sequence_number" pattern="%sn"/>
+            <Label name="mdc_tid" pattern="%mdc{tid}"/>
+        </Loki>
+    </appenders>
+</configuration>