Optimized forEach loop into counted loop to avoid allocation. Added d…

…ocumentation of MDC lookups.
tkowalcz · Jul 20, 2021 · 40149bc · 40149bc
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diff --git a/logback-appender/README.md b/logback-appender/README.md
@@ -53,7 +53,8 @@ On top of the `Core` component that sends logs to Loki this project gives you Lo
 
 ### Note on Loki HTTP endpoint and host/port configuration
 
-Tjahzi sends `POST` requests to `/loki/api/v1/push` HTTP endpoint. Specifying e.g. `<host>loki.mydomain.com</host><port>3100</port>`
+Tjahzi sends `POST` requests to `/loki/api/v1/push` HTTP endpoint. Specifying
+e.g. `<host>loki.mydomain.com</host><port>3100</port>`
 will configure the appender to call to URL: `http://loki.mydomain.com:3100/loki/api/v1/push`.
 
 ## Custom pattern layout and decreasing allocations
@@ -116,6 +117,47 @@ Contents of the properties are automatically interpolated by Logback (
 see [here](http://logback.qos.ch/manual/configuration.html#variableSubstitution)). All environment, system etc. variable
 references will be replaced by their values during initialization of the appender.
 
+### MDC support
+
+MDC is supported via `mdcLogLabel` tag. It will dynamically extract MDC value associated with its content and will turn
+it into a label.
+
+<details>
+    <summary>Click to expand example</summary>
+
+```xml
+<configuration debug="true">
+    <appender name="Loki" class="pl.tkowalcz.tjahzi.logback.LokiAppender">
+        <host>${loki.host}</host>
+        <port>${loki.port}</port>
+
+        <efficientLayout>
+            <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
+        </efficientLayout>
+
+        <label>
+            <name>server</name>
+            <value>127.0.0.1</value>
+        </label>
+
+        <!-- MDC -->
+        <mdcLogLabel>
+            trace_id
+        </mdcLogLabel>
+
+       <!-- MDC -->
+        <mdcLogLabel>
+            span_id
+        </mdcLogLabel>
+    </appender>
+
+    <root level="debug">
+        <appender-ref ref="Loki"/>
+    </root>
+</configuration>
+```
+</details>
+
 ## Details
 
 Let's go through the example config above and analyze configuration options (**Note: Tags are case-insensitive**).

diff --git a/logback-appender/src/main/java/pl/tkowalcz/tjahzi/logback/LokiAppender.java b/logback-appender/src/main/java/pl/tkowalcz/tjahzi/logback/LokiAppender.java
@@ -26,6 +26,7 @@ public class LokiAppender extends LokiAppenderConfigurator {
     private TjahziLogger logger;
     private String logLevelLabel;
     private List<String> mdcLogLabels;
+
     private MutableMonitoringModuleWrapper monitoringModuleWrapper;
 
     public EfficientPatternLayout getEfficientLayout() {
@@ -80,13 +81,16 @@ private void appendLogLabel(LabelSerializer labelSerializer, String logLevel) {
         }
     }
 
+    @SuppressWarnings("ForLoopReplaceableByForEach") // Allocator goes brrrr
     private void appendMdcLogLabels(LabelSerializer serializer,
                                     Map<String, String> mdcPropertyMap) {
-        mdcLogLabels.forEach(mdcLogLabel -> {
+        for (int i = 0; i < mdcLogLabels.size(); i++) {
+            String mdcLogLabel = mdcLogLabels.get(i);
+
             if (mdcPropertyMap.containsKey(mdcLogLabel)) {
                 serializer.appendLabel(mdcLogLabel, mdcPropertyMap.get(mdcLogLabel));
             }
-        });
+        }
     }
 
     @Override