When registering a config file, automatically register a health check…

… that reflects whether the current config value can be read

guice/common/src/main/java/com/peterphi/std/guice/common/GuiceModule.java

@@ -1,5 +1,6 @@
 package com.peterphi.std.guice.common;
 
+import com.codahale.metrics.health.HealthCheckRegistry;
 import com.google.inject.AbstractModule;
 import com.google.inject.Module;
 import com.peterphi.std.guice.common.serviceprops.composite.GuiceConfig;
@@ -51,7 +52,8 @@ protected <T> JAXBResourceProvider<T> bindConfigFile(final Class<T> type, final
 	 */
 	protected <T> JAXBResourceProvider<T> bindConfigFile(final Class<T> type, final String propertyName, Consumer<T> onLoad)
 	{
-		final JAXBResourceProvider<T> provider = new JAXBResourceProvider<T>(super.getProvider(JAXBResourceFactory.class),
+		final JAXBResourceProvider<T> provider = new JAXBResourceProvider<T>(getProvider(JAXBResourceFactory.class),
+		                                                                     getProvider(HealthCheckRegistry.class),
 		                                                                     propertyName,
 		                                                                     type,
 		                                                                     onLoad);

guice/common/src/main/java/com/peterphi/std/guice/common/serviceprops/jaxbref/JAXBResourceFactory.java

@@ -33,6 +33,7 @@ public JAXBResourceFactory(GuiceConfig config, JAXBSerialiserFactory factory)
 	 * @param name
 	 * 		the name of the property
 	 * @param <T>
+	 * @throws RuntimeException if a value cannot be retrieved
 	 *
 	 * @return
 	 */
@@ -42,7 +43,7 @@ public synchronized <T> T get(Class<T> clazz, final String name)
 
 		if (cached == null)
 		{
-			cached = new JAXBNamedResourceFactory<T>(this.config, this.factory, name, clazz);
+			cached = makeFactory(clazz, name);
 			cachedReferences.put(name, cached);
 		}
 
@@ -69,7 +70,7 @@ public synchronized <T> T get(Class<T> clazz, final String name, T defaultValue)
 
 		if (cached == null)
 		{
-			cached = new JAXBNamedResourceFactory<T>(this.config, this.factory, name, clazz);
+			cached = makeFactory(clazz, name);
 			cachedReferences.put(name, cached);
 		}
 
@@ -83,11 +84,16 @@ public synchronized <T> T get(Class<T> clazz, final String name, T defaultValue)
 	 * @param clazz
 	 * @param name
 	 * @param <T>
-	 *
 	 * @return
 	 */
 	public <T> T getOnce(final Class<T> clazz, final String name)
 	{
-		return new JAXBNamedResourceFactory<T>(this.config, this.factory, name, clazz).get();
+		return makeFactory(clazz, name).get();
+	}
+
+
+	private <T> JAXBNamedResourceFactory<T> makeFactory(final Class<T> clazz, final String name)
+	{
+		return new JAXBNamedResourceFactory<T>(this.config, this.factory, name, clazz);
 	}
 }

guice/common/src/main/java/com/peterphi/std/guice/common/serviceprops/jaxbref/JAXBResourceProvider.java

@@ -1,5 +1,7 @@
 package com.peterphi.std.guice.common.serviceprops.jaxbref;
 
+import com.codahale.metrics.health.HealthCheck;
+import com.codahale.metrics.health.HealthCheckRegistry;
 import com.google.inject.Provider;
 import com.peterphi.std.threading.Timeout;
 
@@ -8,6 +10,7 @@
 public class JAXBResourceProvider<T> implements Provider<T>
 {
 	private final Provider<JAXBResourceFactory> resourceFactoryProvider;
+	private final Provider<HealthCheckRegistry> healthCheckRegistryProvider;
 	private final String propertyName;
 	private final Class<T> clazz;
 	private final Consumer<T> onLoadMethod;
@@ -17,13 +20,17 @@ public class JAXBResourceProvider<T> implements Provider<T>
 	private volatile T value;
 	private volatile long cacheExpires = Integer.MIN_VALUE;
 
+	private boolean hasRegisteredHealthCheck = false;
+
 
 	public JAXBResourceProvider(final Provider<JAXBResourceFactory> resourceFactoryProvider,
+	                            final Provider<HealthCheckRegistry> healthCheckRegistryProvider,
 	                            final String propertyName,
 	                            final Class<T> clazz,
 	                            final Consumer<T> onLoadMethod)
 	{
 		this.resourceFactoryProvider = resourceFactoryProvider;
+		this.healthCheckRegistryProvider = healthCheckRegistryProvider;
 		this.propertyName = propertyName;
 		this.clazz = clazz;
 		this.onLoadMethod = onLoadMethod;
@@ -55,6 +62,14 @@ public synchronized T get()
 				return obj;
 		}
 
+		final T obj = load(now);
+
+		return obj;
+	}
+
+
+	private synchronized T load(final long now)
+	{
 		// Cannot use cache, must recompute
 		final T obj = deserialise();
 
@@ -64,13 +79,43 @@ public synchronized T get()
 			this.value = obj;
 			this.cacheExpires = now + cacheValidity.getMilliseconds();
 		}
-
 		return obj;
 	}
 
-	private T deserialise()
+
+	private synchronized T deserialise()
 	{
-		final T obj = resourceFactoryProvider.get().getOnce(clazz, propertyName);
+		final JAXBResourceFactory provider = resourceFactoryProvider.get();
+
+		if (!hasRegisteredHealthCheck)
+		{
+			// Make sure we only register (or try to register) once
+			hasRegisteredHealthCheck = true;
+
+			// N.B. manually constructing a name of the form used by AbstractHealthCheck (which is not available in this module) so errors appear with the appropriate severity
+			healthCheckRegistryProvider.get().register("COMPROMISED:ConfigFile." + propertyName, new HealthCheck()
+			{
+				@Override
+				protected Result check() throws Exception
+				{
+					try
+					{
+						// Try to reload the live value on disk
+						// We call this because we want the actual value, not the last successfully loaded value
+						// N.B. this will also populate the cache on successful load
+						load(System.currentTimeMillis());
+
+						return Result.healthy();
+					}
+					catch (Throwable t)
+					{
+						return Result.unhealthy(t);
+					}
+				}
+			});
+		}
+
+		final T obj = provider.getOnce(clazz, propertyName);
 
 		if (onLoadMethod != null)
 			onLoadMethod.accept(obj);