Rename slf4j ref impl, add constants

Change-Id: Ib3f24c3aa4974ac8c87fa969613192e884674f00
Issue-ID: LOG-115
Signed-off-by: Luke Parker <lparker@amdocs.com>

3 files changed, 896 insertions, 0 deletions

diff --git a/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogAdapter.java b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogAdapter.java
new file mode 100644
index 0000000..50693cb
--- /dev/null
+++ b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogAdapter.java
@@ -0,0 +1,611 @@
+/**
+ * ============LICENSE_START=======================================================
+ * org.onap.logging
+ * ================================================================================
+ * Copyright © 2018 Amdocs
+ * All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.logging.ref.slf4j;
+
+import java.time.LocalDateTime;
+import java.util.UUID;
+
+import javax.servlet.http.HttpServletRequest;
+
+import org.slf4j.Logger;
+import org.slf4j.MDC;
+import org.slf4j.Marker;
+import org.slf4j.event.Level;
+
+/**
+ * Extensible adapter for cheaply meeting ONAP logging obligations using
+ * an SLF4J facade.
+ *
+ * <p>This can be used with any SLF4J-compatible logging provider, with
+ * appropriate provider configuration.</p>
+ *
+ * <p>The basics are that:
+ * <ul>
+ *     <li>{@link #entering} sets all MDCs.</li>
+ *     <li>{@link #exiting} unsets all MDCs *and* logs response information.</li>
+ *     <li>{@link #invoke} logs and returns a UUID to passed during invocation,
+ *     and optionally sets these for you on your downstream request by way of
+ *     an adapter.</li>
+ *     <li>Call {@link #getServiceDescriptor()} and its setters to set service-related MDCs.</li>
+ *     <li>Call {@link #getResponseDescriptor()} and its setters to set response-related MDCs.</li>
+ * </ul>
+ * </p>
+ *
+ * <p>Minimal usage is:
+ * <ol>
+ *     <li>#entering(RequestAdapter)</li>
+ *     <li>#invoke, #invoke, ...</li>
+ *     <li>#getResponse + setters (or #setResponse)</li>
+ *     <li>#exiting</li>
+ * </ol>
+ * </p>
+ *
+ * <p> ... if you're happy for service information to be automatically derived as follows:
+ * <ul>
+ *     <li><tt>ServiceName</tt> - from <tt>HttpServletRequest#getRequestURI()</tt></li>
+ *     <li><tt>InstanceUUID</tt> - classloader-scope UUID.</li>
+ * </ul>
+ * </p>
+ *
+ * <p>... and if those defaults don't suit, then you can override using properties on
+ * {@link #getServiceDescriptor()}, or by injecting your own adapter using
+ * {@link #setServiceDescriptor(ServiceDescriptor)}, or by overriding
+ * a <tt>protected</tt> methods like{@link #setEnteringMDCs}.</p>
+ *
+ * <p>For everything else:
+ * <ul>
+ *     <li>The underlying SLF4J {@link Logger} can be retrieved using {@link #unwrap}.
+ *     Use this or create your own using the usual SLF4J factor.</li>
+ *     <li>Set whatever MDCs you like.</li>
+ *     <li>Log whatever else you like.</li>
+ * </ul>
+ * </p>
+ */
+public class ONAPLogAdapter {
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Constants.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /** String constant for messages <tt>ENTERING</tt>, <tt>EXITING</tt>, etc. */
+    private static final String EMPTY_MESSAGE = "";
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Fields.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /** Automatic UUID, overrideable per adapter or per invocation. */
+    private static UUID sInstanceUUID = UUID.randomUUID();
+
+    /** Logger delegate. */
+    private Logger mLogger;
+
+    /** Overrideable descriptor for the service doing the logging. */
+    private ServiceDescriptor mServiceDescriptor = new ServiceDescriptor();
+
+    /** Overrideable descriptor for the response returned by the service doing the logging. */
+    private ResponseDescriptor mResponseDescriptor = new ResponseDescriptor();
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Constructors.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Construct adapter.
+     *
+     * @param logger non-null logger.
+     */
+    public ONAPLogAdapter(final Logger logger) {
+        this.mLogger = checkNotNull(logger);
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Public methods.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Get logger.
+     *
+     * @return unwrapped logger.
+     */
+    public Logger unwrap() {
+        return this.mLogger;
+    }
+
+    /**
+     * Report <tt>ENTERING</tt> marker.
+     *
+     * @param request non-null incoming request (wrapper).
+     * @return this.
+     */
+    public ONAPLogAdapter entering(final RequestAdapter request) {
+
+        checkNotNull(request);
+
+        // Default the service name.
+
+        this.setEnteringMDCs(request);
+        this.mLogger.info(ONAPLogConstants.Markers.ENTRY, EMPTY_MESSAGE);
+
+        return this;
+    }
+
+    /**
+     * Report <tt>ENTERING</tt> marker.
+     *
+     * @param request non-null incoming request.
+     * @return this.
+     */
+    public ONAPLogAdapter entering(final HttpServletRequest request) {
+        return this.entering(new HttpServletRequestAdapter(checkNotNull(request)));
+    }
+
+    /**
+     * Report <tt>EXITING</tt> marker.
+     *
+     * @return this.
+     */
+    public ONAPLogAdapter exiting() {
+        try {
+            this.mResponseDescriptor.setMDCs();
+            this.mLogger.info(ONAPLogConstants.Markers.EXIT, EMPTY_MESSAGE);
+        }
+        finally {
+            MDC.clear();
+        }
+        return this;
+    }
+
+    /**
+     * Report pending invocation with <tt>INVOKE</tt> marker.
+     *
+     * <p>If you call this variant, then YOU are assuming responsibility for
+     * setting the requisite ONAP headers.</p>
+     *
+     * @param sync whether synchronous.
+     * @return invocation ID to be passed with invocation.
+     */
+    public UUID invoke(final ONAPLogConstants.InvocationMode sync) {
+
+        final UUID invocationID = UUID.randomUUID();
+
+        // Derive SYNC/ASYNC marker.
+
+        final Marker marker = (sync == null) ? ONAPLogConstants.Markers.INVOKE : sync.getMarker();
+
+        // Log INVOKE*, with the invocationID as the message body.
+        // (We didn't really want this kind of behavior in the standard,
+        // but is it worse than new, single-message MDC?)
+
+        this.mLogger.info(marker, "{}", invocationID);
+        return invocationID;
+    }
+
+    /**
+     * Report pending invocation with <tt>INVOKE</tt> marker,
+     * setting standard ONAP logging headers automatically.
+     *
+     * @param builder request builder, for setting headers.
+     * @param sync whether synchronous, nullable.
+     * @return invocation ID to be passed with invocation.
+     */
+    public UUID invoke(final RequestBuilder builder,
+                       final ONAPLogConstants.InvocationMode sync) {
+
+        // Sync can be defaulted. Builder cannot.
+
+        checkNotNull(builder);
+
+        // Log INVOKE, and retain invocation ID for header + return.
+
+        final UUID invocationID = this.invoke(sync);
+
+        // Set standard HTTP headers on (southbound request) builder.
+
+        builder.setHeader(ONAPLogConstants.Headers.REQUEST_ID,
+                defaultToEmpty(MDC.get(ONAPLogConstants.MDCs.REQUEST_ID)));
+        builder.setHeader(ONAPLogConstants.Headers.INVOCATION_ID,
+                defaultToEmpty(invocationID));
+        builder.setHeader(ONAPLogConstants.Headers.PARTNER_NAME,
+                defaultToEmpty(MDC.get(ONAPLogConstants.MDCs.PARTNER_NAME)));
+
+        return invocationID;
+    }
+
+    /**
+     * Report vanilla <tt>INVOKE</tt> marker.
+     *
+     * @param builder builder for downstream requests, if you want the
+     *                standard ONAP headers to be added automatically.
+     * @return invocation ID to be passed with invocation.
+     */
+    public UUID invoke(final RequestBuilder builder) {
+        return this.invoke(builder, (ONAPLogConstants.InvocationMode)null);
+    }
+
+    /**
+     * Get descriptor, for overriding service details.
+     * @return non-null descriptor.
+     */
+    public ServiceDescriptor getServiceDescriptor() {
+        return checkNotNull(this.mServiceDescriptor);
+    }
+
+    /**
+     * Override {@link ServiceDescriptor}.
+     * @param d non-null override.
+     * @return this.
+     */
+    public ONAPLogAdapter setServiceDescriptor(final ServiceDescriptor d) {
+        this.mServiceDescriptor = checkNotNull(d);
+        return this;
+    }
+
+    /**
+     * Get descriptor, for setting response details.
+     * @return non-null descriptor.
+     */
+    public ResponseDescriptor getResponseDescriptor() {
+        return checkNotNull(this.mResponseDescriptor);
+    }
+
+    /**
+     * Override {@link ResponseDescriptor}.
+     * @param d non-null override.
+     * @return this.
+     */
+    public ONAPLogAdapter setResponseDescriptor(final ResponseDescriptor d) {
+        this.mResponseDescriptor = checkNotNull(d);
+        return this;
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Protected methods.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Set MDCs that persist for the duration of an invocation.
+     *
+     * <p>It would be better to roll this into {@link #entering}, like
+     * with {@link #exiting}. Then it would be easier to do, but it
+     * would mean more work. </p>
+     *
+     * @param request incoming HTTP request.
+     * @return this.
+     */
+    protected ONAPLogAdapter setEnteringMDCs(final RequestAdapter<?> request) {
+
+        // Extract MDC values from standard HTTP headers.
+
+        final String requestID = defaultToUUID(request.getHeader(ONAPLogConstants.Headers.REQUEST_ID));
+        final String invocationID = defaultToUUID(request.getHeader(ONAPLogConstants.Headers.INVOCATION_ID));
+        final String partnerName = defaultToEmpty(request.getHeader(ONAPLogConstants.Headers.PARTNER_NAME));
+
+        // Set standard MDCs. Override this entire method if you want to set
+        // others, OR set them BEFORE or AFTER the invocation of #entering,
+        // depending on where you need them to appear, OR extend the
+        // ServiceDescriptor to add them.
+
+        MDC.put(ONAPLogConstants.MDCs.INVOKE_TIMESTAMP, LocalDateTime.now().toString());
+        MDC.put(ONAPLogConstants.MDCs.REQUEST_ID, requestID);
+        MDC.put(ONAPLogConstants.MDCs.INVOCATION_ID, invocationID);
+        MDC.put(ONAPLogConstants.MDCs.PARTNER_NAME, partnerName);
+        MDC.put(ONAPLogConstants.MDCs.CLIENT_IP_ADDRESS, defaultToEmpty(request.getClientAddress()));
+        MDC.put(ONAPLogConstants.MDCs.SERVER_FQDN, defaultToEmpty(request.getServerAddress()));
+
+        // Delegate to the service adapter, for service-related DMCs.
+
+        this.mServiceDescriptor.setMDCs();
+
+        // Default the service name to the requestURI, in the event that
+        // no value has been provided.
+
+        if (MDC.get(ONAPLogConstants.MDCs.SERVICE_NAME) == null) {
+            MDC.put(ONAPLogConstants.MDCs.SERVICE_NAME, request.getRequestURI());
+        }
+
+        return this;
+    }
+
+    /**
+     * Dependency-free nullcheck.
+     *
+     * @param in to be checked.
+     * @param <T> argument (and return) type.
+     * @return input arg.
+     */
+    protected static <T> T checkNotNull(final T in) {
+        if (in == null) {
+            throw new NullPointerException();
+        }
+        return in;
+    }
+
+    /**
+     * Dependency-free string default.
+     *
+     * @param in to be filtered.
+     * @return input string or null.
+     */
+    protected static String defaultToEmpty(final Object in) {
+        if (in == null) {
+            return "";
+        }
+        return in.toString();
+    }
+
+    /**
+     * Dependency-free string default.
+     *
+     * @param in to be filtered.
+     * @return input string or null.
+     */
+    protected static String defaultToUUID(final String in) {
+        if (in == null) {
+            return UUID.randomUUID().toString();
+        }
+        return in;
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Inner classes.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Extensible descriptor for reporting service details.
+     *
+     * <p>In most cases extension isn't required. </p>
+     */
+    public static class ServiceDescriptor {
+
+        /** <tt>ServiceName</tt>. */
+        protected String mName;
+
+        /** <tt>InstanceUUID</tt>. */
+        protected String mUUID = sInstanceUUID.toString();
+
+        /**
+         * Set name.
+         * @param name <tt>ServiceName</tt>.
+         * @return this.
+         */
+        public ServiceDescriptor setServiceName(final String name) {
+            this.mName = name;
+            return this;
+        }
+
+        /**
+         * Set name.
+         * @param uuid <tt>InstanceUUID</tt>.
+         * @return this.
+         */
+        public ServiceDescriptor setServiceUUID(final String uuid) {
+            this.mUUID = uuid;
+            return this;
+        }
+
+        /**
+         * Set MDCs. Once set they remain set until everything is cleared.
+         */
+        protected void setMDCs() {
+            MDC.put(ONAPLogConstants.MDCs.SERVICE_NAME, defaultToEmpty(this.mName));
+            MDC.put(ONAPLogConstants.MDCs.INSTANCE_UUID, defaultToEmpty(this.mUUID));
+        }
+    }
+
+    /**
+     * Response is different in that response MDCs are normally only
+     * reported once, for a single log message. (But there's no method
+     * for clearing them, because this is only expected to be called
+     * during <tt>#exiting</tt>.)
+     */
+    public static class ResponseDescriptor {
+
+        /** Response errorcode. */
+        protected String mCode;
+
+        /** Response description. */
+        protected String mDescription;
+
+        /** Response severity. */
+        protected Level mSeverity;
+
+        /** Response status, of {<tt>COMPLETED</tt>, <tt>ERROR</tt>}. */
+        protected ONAPLogConstants.ResponseStatus mStatus;
+
+        /**
+         * Setter.
+         *
+         * @param code response (error) code.
+         * @return this.
+         */
+        public ResponseDescriptor setResponseCode(final String code) {
+            this.mCode = code;
+            return this;
+        }
+
+        /**
+         * Setter.
+         *
+         * @param description response description.
+         * @return this.
+         */
+        public ResponseDescriptor setResponseDescription(final String description) {
+            this.mDescription = description;
+            return this;
+        }
+
+        /**
+         * Setter.
+         *
+         * @param severity response outcome severity.
+         * @return this.
+         */
+        public ResponseDescriptor setResponseSeverity(final Level severity) {
+            this.mSeverity = severity;
+            return this;
+        }
+
+        /**
+         * Setter.
+         *
+         * @param status response overall status.
+         * @return this.
+         */
+        public ResponseDescriptor setResponseStatus(final ONAPLogConstants.ResponseStatus status) {
+            this.mStatus = status;
+            return this;
+        }
+
+        /**
+         * Overrideable method to set MDCs based on property values.
+         */
+        protected void setMDCs() {
+            MDC.put(ONAPLogConstants.MDCs.RESPONSE_CODE, defaultToEmpty(this.mCode));
+            MDC.put(ONAPLogConstants.MDCs.RESPONSE_DESCRIPTION, defaultToEmpty(this.mDescription));
+            MDC.put(ONAPLogConstants.MDCs.RESPONSE_SEVERITY, defaultToEmpty(this.mSeverity));
+            MDC.put(ONAPLogConstants.MDCs.RESPONSE_STATUS_CODE, defaultToEmpty(this.mStatus));
+        }
+    }
+
+    /**
+     * Adapter for reading information from an incoming HTTP request.
+     *
+     * <p>Incoming is generally easy, because in most cases you'll be able to
+     * get your hands on the <tt>HttpServletRequest</tt>.</p>
+     *
+     * <p>Perhaps should be generalized to refer to constants instead of
+     * requiring the implementation of specific methods.</p>
+     *
+     * @param <T> type, for chaining.
+     */
+    public interface RequestAdapter<T extends RequestAdapter> {
+
+        /**
+         * Get header by name.
+         * @param name header name.
+         * @return header value, or null.
+         */
+        String getHeader(String name);
+
+        /**
+         * Get client address.
+         * @return address, if available.
+         */
+        String getClientAddress();
+
+        /**
+         * Get server address.
+         * @return address, if available.
+         */
+        String getServerAddress();
+
+        /**
+         * Get default service name, from service URI.
+         * @return service name default.
+         */
+        String getRequestURI();
+    }
+
+    /**
+     * Default {@link RequestBuilder} impl for {@link HttpServletRequest}, which
+     * will should available for most incoming REST requests.
+     */
+    public static class HttpServletRequestAdapter implements RequestAdapter<HttpServletRequestAdapter> {
+
+        /** Wrapped HTTP request. */
+        private final HttpServletRequest mRequest;
+
+        /**
+         * Construct adapter for HTTP request.
+         * @param request to be wrapped;
+         */
+        public HttpServletRequestAdapter(final HttpServletRequest request) {
+            this.mRequest = checkNotNull(request);
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public String getHeader(final String name) {
+            return this.mRequest.getHeader(name);
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public String getClientAddress() {
+            return this.mRequest.getRemoteAddr();
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public String getServerAddress() {
+            return this.mRequest.getServerName();
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public String getRequestURI() {
+            return this.mRequest.getRequestURI();
+        }
+    }
+
+    /**
+     * Header builder, which (unlike {@link RequestAdapter} will tend to
+     * vary a lot from caller to caller, since they each get to choose their
+     * own REST (or HTTP, or whatever) client APIs.
+     *
+     * <p>No default implementation, because there's no HTTP client that's
+     * sufficiently ubiquitous to warrant incurring a mandatory dependency.</p>
+     *
+     * @param <T> type, for chaining.
+     */
+    public interface RequestBuilder<T extends RequestBuilder> {
+
+        /**
+         * Set HTTP header.
+         * @param name header name.
+         * @param value header value.
+         * @return this.
+         */
+        T setHeader(String name, String value);
+    }
+}
diff --git a/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogConstants.java b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogConstants.java
new file mode 100644
index 0000000..744f99f
--- /dev/null
+++ b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/ONAPLogConstants.java
@@ -0,0 +1,253 @@
+/**
+ * ============LICENSE_START=======================================================
+ * org.onap.logging
+ * ================================================================================
+ * Copyright © 2018 Amdocs
+ * All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.logging.ref.slf4j;
+
+import org.slf4j.Marker;
+import org.slf4j.MarkerFactory;
+
+/**
+ * Constants for standard ONAP headers, MDCs, etc.
+ *
+ * <p>See <tt>package-info.java</tt>.</p>
+ */
+public final class ONAPLogConstants {
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Constructors.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Hide and forbid construction.
+     */
+    private ONAPLogConstants() {
+        throw new UnsupportedOperationException();
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Inner classes.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Marker constants.
+     */
+    public static final class Markers {
+
+        /** Marker reporting invocation. */
+        public static final Marker INVOKE = MarkerFactory.getMarker("INVOKE");
+
+        /** Marker reporting synchronous invocation. */
+        public static final Marker INVOKE_SYNCHRONOUS = build("INVOKE", "SYNCHRONOUS");
+
+        /** Marker reporting asynchronous invocation. */
+        public static final Marker INVOKE_ASYNCHRONOUS = build("INVOKE", "ASYNCHRONOUS");
+
+        /** Marker reporting entry into a component. */
+        public static final Marker ENTRY = MarkerFactory.getMarker("ENTRY");
+
+        /** Marker reporting exit from a component. */
+        public static final Marker EXIT = MarkerFactory.getMarker("EXIT");
+
+        /**
+         * Build nested, detached marker.
+         * @param m1 top token.
+         * @param m2 sub-token.
+         * @return detached Marker.
+         */
+        private static Marker build(final String m1, final String m2) {
+            final Marker marker = MarkerFactory.getDetachedMarker(m1);
+            marker.add(MarkerFactory.getDetachedMarker(m2));
+            return marker;
+        }
+
+        /**
+         * Hide and forbid construction.
+         */
+        private Markers() {
+            throw new UnsupportedOperationException();
+        }
+    }
+
+    /**
+     * MDC name constants.
+     */
+    public static final class MDCs {
+
+        // Tracing. ////////////////////////////////////////////////////////////
+
+        /** MDC correlating messages for an invocation. */
+        public static final String INVOCATION_ID = "InvocationID";
+
+        /** MDC correlating messages for a logical transaction. */
+        public static final String REQUEST_ID = "RequestID";
+
+        /** MDC recording calling service. */
+        public static final String PARTNER_NAME = "PartnerName";
+
+        /** MDC recording current service. */
+        public static final String SERVICE_NAME = "ServiceName";
+
+        /** MDC recording target service. */
+        public static final String TARGET_SERVICE_NAME = "TargetServiceName";
+
+        /** MDC recording current service instance. */
+        public static final String INSTANCE_UUID = "InstanceUUID";
+
+        // Network. ////////////////////////////////////////////////////////////
+
+        /** MDC recording caller address. */
+        public static final String CLIENT_IP_ADDRESS = "ClientIPAddress";
+
+        /** MDC recording server address. */
+        public static final String SERVER_FQDN = "ServerFQDN";
+
+        /**
+         * MDC recording timestamp at the start of the current request,
+         * with the same scope as {@link #REQUEST_ID}.
+         *
+         * <p>Open issues:
+         * <ul>
+         *     <ul>Easily confused with {@link #INVOKE_TIMESTAMP}.</ul>
+         *     <ul>No mechanism for propagation between components, e.g. via HTTP headers.</ul>
+         *     <ul>Whatever mechanism we define, it's going to be costly.</ul>
+         * </ul>
+         * </p>
+         * */
+        public static final String ENTRY_TIMESTAMP = "EntryTimestamp";
+
+        /** MDC recording timestamp at the start of the current invocation. */
+        public static final String INVOKE_TIMESTAMP = "InvokeTimestamp";
+
+        // Outcomes. ///////////////////////////////////////////////////////////
+
+        /** MDC reporting outcome code. */
+        public static final String RESPONSE_CODE = "ResponseCode";
+
+        /** MDC reporting outcome description. */
+        public static final String RESPONSE_DESCRIPTION = "ResponseDescription";
+
+        /** MDC reporting outcome error level. */
+        public static final String RESPONSE_SEVERITY = "Severity";
+
+        /** MDC reporting outcome error level. */
+        public static final String RESPONSE_STATUS_CODE = "StatusCode";
+
+        // Unsorted. ///////////////////////////////////////////////////////////
+
+        /**
+         * Hide and forbid construction.
+         */
+        private MDCs() {
+            throw new UnsupportedOperationException();
+        }
+    }
+
+    /**
+     * Header name constants.
+     */
+    public static final class Headers {
+
+        /** HTTP <tt>X-ONAP-RequestID</tt> header. */
+        public static final String REQUEST_ID = "X-ONAP-RequestID";
+
+        /** HTTP <tt>X-ONAP-InvocationID</tt> header. */
+        public static final String INVOCATION_ID = "X-ONAP-InvocationID";
+
+        /** HTTP <tt>X-ONAP-PartnerName</tt> header. */
+        public static final String PARTNER_NAME = "X-ONAP-PartnerName";
+
+        /**
+         * Hide and forbid construction.
+         */
+        private Headers() {
+            throw new UnsupportedOperationException();
+        }
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Enums.
+    //
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Response success or not, for setting <tt>StatusCode</tt>.
+     */
+    public enum ResponseStatus {
+
+        /** Success. */
+        COMPLETED,
+
+        /** Not. */
+        ERROR,
+    }
+
+    /**
+     * Synchronous or asynchronous execution, for setting invocation marker.
+     */
+    public enum InvocationMode {
+
+        /** Synchronous, blocking. */
+        SYNCHRONOUS("SYNCHRONOUS", Markers.INVOKE_SYNCHRONOUS),
+
+        /** Asynchronous, non-blocking. */
+        ASYNCHRONOUS("ASYNCHRONOUS", Markers.INVOKE_ASYNCHRONOUS);
+
+        /** Enum value. */
+        private String mString;
+
+        /** Corresponding marker. */
+        private Marker mMarker;
+
+        /**
+         * Construct enum.
+         *
+         * @param s enum value.
+         * @param m corresponding Marker.
+         */
+        InvocationMode(final String s, final Marker m) {
+            this.mString = s;
+            this.mMarker = m;
+        }
+
+        /**
+         * Get Marker for enum.
+         *
+         * @return Marker.
+         */
+        public Marker getMarker() {
+            return this.mMarker;
+        }
+
+        /**
+         * {@inheritDoc}
+         */
+        @Override
+        public String toString() {
+            return this.mString;
+        }
+    }
+
+}
diff --git a/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/package-info.java b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/package-info.java
new file mode 100644
index 0000000..d9a6247
--- /dev/null
+++ b/reference/logging-slf4j/src/main/java/org/onap/logging/ref/slf4j/package-info.java
@@ -0,0 +1,32 @@
+/**
+ * ============LICENSE_START=======================================================
+ * org.onap.logging
+ * ================================================================================
+ * Copyright © 2018 Amdocs
+ * All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.logging.ref.slf4j;
+
+/**
+ * <p>Code in here has potential application outside this reference
+ * example, and accordingly:
+ * <ul>
+ *     <li>Packaged in <tt>common</tt>.</li>
+ *     <li>Has minimal dependencies.</li>
+ * </ul>
+ * </p>
+ */
\ No newline at end of file