Implement custom Logback JSON encoder

src/main/java/app/quickcase/sdk/spring/logging/logback/JsonEncoder.java

@@ -0,0 +1,323 @@
+package app.quickcase.sdk.spring.logging.logback;
+
+import java.util.Collection;
+import java.util.Map;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.classic.spi.IThrowableProxy;
+import ch.qos.logback.classic.spi.StackTraceElementProxy;
+import ch.qos.logback.core.CoreConstants;
+import ch.qos.logback.core.encoder.EncoderBase;
+
+import static ch.qos.logback.core.CoreConstants.NULL_STR;
+import static ch.qos.logback.core.encoder.JsonEscapeUtil.jsonEscapeString;
+import static java.util.stream.Collectors.toMap;
+
+/**
+ * A take on {@link ch.qos.logback.classic.encoder.JsonEncoder} simplified and with different opinions:
+ * <ul>
+ *     <li>Serialise `formattedMessage` as `message` with raw message and arguments dropped</li>
+ *     <li>Serialise key/value pairs as object `kvp`, not list: keys should not be duplicated or they will be overridden</li>
+ *     <li>Serialise stacktrace as `exception` instead of `throwable`</li>
+ *     <li>Empty lists/maps are implicitly hidden instead of being serialised as `null`</li>
+ * </ul>
+ */
+public class JsonEncoder extends EncoderBase<ILoggingEvent> {
+    static int DEFAULT_SIZE = 1024;
+    static int DEFAULT_SIZE_WITH_THROWABLE = DEFAULT_SIZE * 8;
+
+    static byte[] EMPTY_BYTES = new byte[0];
+
+    protected static final String TIMESTAMP_ATTR_NAME = "timestamp";
+    protected static final String LEVEL_ATTR_NAME = "level";
+    protected static final String LOGGER_ATTR_NAME = "loggerName";
+    protected static final String THREAD_NAME_ATTR_NAME = "threadName";
+    protected static final String MARKERS_ATTR_NAME = "markers";
+    protected static final String MDC_ATTR_NAME = "mdc";
+    protected static final String MESSAGE_ATTR_NAME = "message";
+    protected static final String KEY_VALUE_PAIRS_ATTR_NAME = "kvp";
+    protected static final String THROWABLE_ATTR_NAME = "exception";
+
+    protected static final String CYCLIC_THROWABLE_ATTR_NAME = "cyclic";
+    protected static final String CAUSE_ATTR_NAME = "cause";
+    protected static final String SUPPRESSED_ATTR_NAME = "suppressed";
+    protected static final String COMMON_FRAMES_COUNT_ATTR_NAME = "commonFramesCount";
+
+    protected static final String CLASS_NAME_ATTR_NAME = "className";
+    protected static final String METHOD_NAME_ATTR_NAME = "methodName";
+    protected static final String FILE_NAME_ATTR_NAME = "fileName";
+    protected static final String LINE_NUMBER_ATTR_NAME = "lineNumber";
+
+    protected static final String STEP_ARRAY_NAME_ATTRIBUTE = "stepArray";
+
+    protected static final char OPEN_OBJ = '{';
+    protected static final char CLOSE_OBJ = '}';
+    protected static final char OPEN_ARRAY = '[';
+    protected static final char CLOSE_ARRAY = ']';
+
+    protected static final char QUOTE = '"';
+    protected static final char SP = ' ';
+    protected static final String QUOTE_COL = "\":";
+    protected static final char VALUE_SEPARATOR = ',';
+
+    @Override
+    public byte[] headerBytes() {
+        return EMPTY_BYTES;
+    }
+
+    @Override
+    public byte[] encode(ILoggingEvent event) {
+        final int initialCapacity = event.getThrowableProxy() == null ? DEFAULT_SIZE : DEFAULT_SIZE_WITH_THROWABLE;
+        StringBuilder sb = new StringBuilder(initialCapacity);
+
+        sb.append(OPEN_OBJ);
+
+        // Timestamp
+        appenderMemberWithLongValue(sb, TIMESTAMP_ATTR_NAME, event.getTimeStamp());
+
+        // Level
+        sb.append(VALUE_SEPARATOR);
+        String levelStr = event.getLevel() != null ? event.getLevel().levelStr : NULL_STR;
+        appenderMember(sb, LEVEL_ATTR_NAME, levelStr);
+
+        // Thread
+        sb.append(VALUE_SEPARATOR);
+        appenderMember(sb, THREAD_NAME_ATTR_NAME, jsonEscape(event.getThreadName()));
+
+        // Logger
+        sb.append(VALUE_SEPARATOR);
+        appenderMember(sb, LOGGER_ATTR_NAME, event.getLoggerName());
+
+        // Markers
+        appendMarkers(sb, event);
+
+        // MDC
+        appendMDC(sb, event);
+
+        // Message
+        sb.append(VALUE_SEPARATOR);
+        appenderMember(sb, MESSAGE_ATTR_NAME, jsonEscape(event.getFormattedMessage()));
+
+        // Key/value pairs
+        appendKeyValuePairs(sb, event);
+
+        // Throwable
+        appendException(sb, event);
+
+        sb.append(CLOSE_OBJ);
+        sb.append(CoreConstants.JSON_LINE_SEPARATOR);
+
+        return sb.toString().getBytes(CoreConstants.UTF_8_CHARSET);
+    }
+
+    @Override
+    public byte[] footerBytes() {
+        return EMPTY_BYTES;
+    }
+
+    private void appenderMember(StringBuilder sb, String key, String value) {
+        sb.append(QUOTE).append(key).append(QUOTE_COL).append(QUOTE).append(value).append(QUOTE);
+    }
+
+    private void appenderMemberWithIntValue(StringBuilder sb, String key, int value) {
+        sb.append(QUOTE).append(key).append(QUOTE_COL).append(value);
+    }
+
+    private void appenderMemberWithLongValue(StringBuilder sb, String key, long value) {
+        sb.append(QUOTE).append(key).append(QUOTE_COL).append(value);
+    }
+
+    private void appendMarkers(StringBuilder sb, ILoggingEvent event) {
+        var markerList = event.getMarkerList();
+
+        if (isEmptyCollection(markerList))
+            return;
+
+        sb.append(VALUE_SEPARATOR);
+        sb.append(QUOTE).append(MARKERS_ATTR_NAME).append(QUOTE_COL).append(SP).append(OPEN_ARRAY);
+        final int len = markerList.size();
+        for (int i = 0; i < len; i++) {
+            if (i != 0)
+                sb.append(VALUE_SEPARATOR);
+            sb.append(QUOTE).append(jsonEscapedToString(markerList.get(i))).append(QUOTE);
+
+        }
+        sb.append(CLOSE_ARRAY);
+    }
+
+    private void appendMDC(StringBuilder sb, ILoggingEvent event) {
+        var mdc = event.getMDCPropertyMap();
+
+        if (isEmptyMap(mdc))
+            return;
+
+        sb.append(VALUE_SEPARATOR);
+        appendMap(sb, MDC_ATTR_NAME, mdc);
+    }
+
+    private void appendKeyValuePairs(StringBuilder sb, ILoggingEvent event) {
+        var kvpList = event.getKeyValuePairs();
+
+        if (isEmptyCollection(kvpList))
+            return;
+
+        sb.append(VALUE_SEPARATOR);
+        appendMap(sb, KEY_VALUE_PAIRS_ATTR_NAME, kvpList.stream().collect(toMap(kvp -> kvp.key, kvp -> kvp.value)));
+    }
+
+    private void appendException(StringBuilder sb, ILoggingEvent event) {
+        var itp = event.getThrowableProxy();
+
+        if (itp == null)
+            return;
+
+        appendThrowableProxy(sb, THROWABLE_ATTR_NAME, itp, true);
+    }
+
+    private void appendThrowableProxy(StringBuilder sb, String attributeName, IThrowableProxy itp) {
+        appendThrowableProxy(sb, attributeName, itp, true);
+    }
+
+    private void appendThrowableProxy(StringBuilder sb, String attributeName, IThrowableProxy itp, boolean appendValueSeparator) {
+
+        if (appendValueSeparator)
+            sb.append(VALUE_SEPARATOR);
+
+        // in the nominal case, attributeName != null. However, attributeName will be null for suppressed
+        // IThrowableProxy array, in which case no attribute name is needed
+        if (attributeName != null) {
+            sb.append(QUOTE).append(attributeName).append(QUOTE_COL);
+            if (itp == null) {
+                sb.append(NULL_STR);
+                return;
+            }
+        }
+
+        sb.append(OPEN_OBJ);
+
+        appenderMember(sb, CLASS_NAME_ATTR_NAME, nullSafeStr(itp.getClassName()));
+
+        sb.append(VALUE_SEPARATOR);
+        appenderMember(sb, MESSAGE_ATTR_NAME, jsonEscape(itp.getMessage()));
+
+        if (itp.isCyclic()) {
+            sb.append(VALUE_SEPARATOR);
+            appenderMember(sb, CYCLIC_THROWABLE_ATTR_NAME, jsonEscape("true"));
+        }
+
+        sb.append(VALUE_SEPARATOR);
+        appendSTEPArray(sb, itp.getStackTraceElementProxyArray(), itp.getCommonFrames());
+
+        if (itp.getCommonFrames() != 0) {
+            sb.append(VALUE_SEPARATOR);
+            appenderMemberWithIntValue(sb, COMMON_FRAMES_COUNT_ATTR_NAME, itp.getCommonFrames());
+        }
+
+        IThrowableProxy cause = itp.getCause();
+        if (cause != null) {
+            appendThrowableProxy(sb, CAUSE_ATTR_NAME, cause);
+        }
+
+        IThrowableProxy[] suppressedArray = itp.getSuppressed();
+        if (suppressedArray != null && suppressedArray.length != 0) {
+            sb.append(VALUE_SEPARATOR);
+            sb.append(QUOTE).append(SUPPRESSED_ATTR_NAME).append(QUOTE_COL);
+            sb.append(OPEN_ARRAY);
+
+            boolean first = true;
+            for (IThrowableProxy suppressedITP : suppressedArray) {
+                appendThrowableProxy(sb, null, suppressedITP, !first);
+                if (first)
+                    first = false;
+            }
+            sb.append(CLOSE_ARRAY);
+        }
+
+        sb.append(CLOSE_OBJ);
+
+    }
+
+    private void appendSTEPArray(StringBuilder sb, StackTraceElementProxy[] stepArray, int commonFrames) {
+        sb.append(QUOTE).append(STEP_ARRAY_NAME_ATTRIBUTE).append(QUOTE_COL).append(OPEN_ARRAY);
+
+        int len = stepArray != null ? stepArray.length : 0;
+
+        if (commonFrames >= len) {
+            commonFrames = 0;
+        }
+
+        for (int i = 0; i < len - commonFrames; i++) {
+            if (i != 0)
+                sb.append(VALUE_SEPARATOR);
+
+            StackTraceElementProxy step = stepArray[i];
+
+            sb.append(OPEN_OBJ);
+            StackTraceElement ste = step.getStackTraceElement();
+
+            appenderMember(sb, CLASS_NAME_ATTR_NAME, nullSafeStr(ste.getClassName()));
+            sb.append(VALUE_SEPARATOR);
+
+            appenderMember(sb, METHOD_NAME_ATTR_NAME, nullSafeStr(ste.getMethodName()));
+            sb.append(VALUE_SEPARATOR);
+
+            appenderMember(sb, FILE_NAME_ATTR_NAME, nullSafeStr(ste.getFileName()));
+            sb.append(VALUE_SEPARATOR);
+
+            appenderMemberWithIntValue(sb, LINE_NUMBER_ATTR_NAME, ste.getLineNumber());
+            sb.append(CLOSE_OBJ);
+
+        }
+
+        sb.append(CLOSE_ARRAY);
+    }
+
+    private void appendMap(StringBuilder sb, String attrName, Map<String, ?> map) {
+        sb.append(QUOTE).append(attrName).append(QUOTE_COL).append(SP);
+
+        if (map == null) {
+            sb.append(NULL_STR);
+            return;
+        }
+
+        sb.append(OPEN_OBJ);
+
+        boolean addComma = false;
+        var entries = map.entrySet();
+        for (var entry : entries) {
+            if (addComma) {
+                sb.append(VALUE_SEPARATOR);
+            }
+            addComma = true;
+            appenderMember(sb, jsonEscapedToString(entry.getKey()), jsonEscapedToString(entry.getValue()));
+        }
+
+        sb.append(CLOSE_OBJ);
+    }
+
+    private String jsonEscapedToString(Object o) {
+        if (o == null)
+            return NULL_STR;
+        return jsonEscapeString(o.toString());
+    }
+
+    private String nullSafeStr(String s) {
+        if (s == null)
+            return NULL_STR;
+        return s;
+    }
+
+    private String jsonEscape(String s) {
+        if (s == null)
+            return NULL_STR;
+        return jsonEscapeString(s);
+    }
+
+    private boolean isEmptyMap(Map map) {
+        return map == null || map.isEmpty();
+    }
+
+    private boolean isEmptyCollection(Collection collection) {
+        return collection == null || collection.isEmpty();
+    }
+}

src/main/resources/console-json-appender.xml

@@ -10,13 +10,6 @@ initialization performed by Boot
         <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
             <level>${CONSOLE_LOG_THRESHOLD}</level>
         </filter>
-        <encoder class="ch.qos.logback.classic.encoder.JsonEncoder">
-            <withSequenceNumber>false</withSequenceNumber>
-            <withNanoseconds>false</withNanoseconds>
-            <withContext>false</withContext>
-            <withMessage>false</withMessage>
-            <withArguments>false</withArguments>
-            <withFormattedMessage>true</withFormattedMessage>
-        </encoder>
+        <encoder class="app.quickcase.sdk.spring.logging.logback.JsonEncoder" />
     </appender>
 </included>