Improves error messages around talking to Druid

CHANGELOG.md

@@ -14,6 +14,13 @@ Current
 
 ### Changed:
 
+- [Improves error messages when querying Druid goes wrong](https:://github.com/yahoo/fili/pull/61)
+    - The `ResponseException` now includes a message that prints the `ResponseException`'s internal state 
+        (i.e. the druid query and response code) using the error messages 
+        `ErrorMessageFormat::FAILED_TO_SEND_QUERY_TO_DRUID` and `ErrorMessageFormat::ERROR_FROM_DRUID`
+    - The druid query and status code, reason and response body are now logged at the error level in the 
+      failure and error callbacks in `AsyncDruidWebServiceImpl`  
+
 - [Fili now supports custom Druid query types](https://github.com/yahoo/fili/pull/57)
     * `QueryType` has been turned into an interface, backed by an enum `DefaultQueryType`.
         - The default implementations of `DruidResponseParser` `DruidQueryBuilder`, `WeightEvaluationQuery` and

fili-core/src/main/java/com/yahoo/bard/webservice/async/ResponseException.java

@@ -64,13 +64,42 @@ public ResponseException(
             DruidQuery<?> druidQuery,
             Throwable cause
     ) {
+        super(buildMessage(reason, description, statusCode, druidQuery, cause));
         this.statusCode = statusCode;
         this.reason = reason;
         this.description = description;
         this.druidQuery = druidQuery;
         this.cause = cause;
     }
 
+    /**
+     * Builds a message for this exception that is basically a straightforward serialization of its interesting state.
+     *
+     * @param reason  The reason for the error
+     * @param description  A description of the error
+     * @param statusCode  The status code received from Druid
+     * @param druidQuery  The druid query that triggered the invalid response
+     * @param cause  The cause of this exception, if any
+     *
+     * @return A Stringification of the parameters to serve as this exception's message
+     */
+    private static String buildMessage(
+            String reason,
+            String description,
+            int statusCode,
+            DruidQuery<?> druidQuery,
+            Throwable cause
+    ) {
+        return String.format(
+                "Reason: %s, Description: %s, statusCode: %d, druid query: %s, cause: %s",
+                reason,
+                description,
+                statusCode,
+                druidQuery,
+                cause
+        );
+    }
+
     public String getReason() {
         return reason;
     }

fili-core/src/main/java/com/yahoo/bard/webservice/web/ErrorMessageFormat.java

@@ -165,6 +165,11 @@ public enum ErrorMessageFormat implements MessageFormatter {
     INVALID_ASYNC_AFTER( "Invalid 'asyncAfter' parameter: '%s'. 'asyncAfter' must be either 'never' or an integer number of milliseconds."),
 
     FILTER_JOBFIELD_UNDEFINED("Filter field '%s' does not exist. The possible fields to filter on are '%s'"),
+
+    FAILED_TO_SEND_QUERY_TO_DRUID("Failed to retrieve data.", "Failed to send the query %s to Druid."),
+
+    ERROR_FROM_DRUID("Failed to retrieve data.", "Received %s with status code %s for reason %s when sending %s to Druid"),
+
     ;
     // CHECKSTYLE:ON
 

fili-core/src/main/java/com/yahoo/bard/webservice/web/responseprocessors/MappingResponseProcessor.java

@@ -11,6 +11,10 @@
 import com.yahoo.bard.webservice.druid.model.query.DruidAggregationQuery;
 import com.yahoo.bard.webservice.async.ResponseException;
 import com.yahoo.bard.webservice.web.DataApiRequest;
+import com.yahoo.bard.webservice.web.ErrorMessageFormat;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import rx.subjects.Subject;
 
@@ -27,6 +31,7 @@
  * Response Processor which will perform result set mapping.
  */
 public abstract class MappingResponseProcessor implements ResponseProcessor {
+    private static final Logger LOG = LoggerFactory.getLogger(MappingResponseProcessor.class);
 
     protected final DataApiRequest apiRequest;
     protected final ResponseContext responseContext;
@@ -102,6 +107,7 @@ public HttpErrorCallback getStandardError(
         return new HttpErrorCallback() {
             @Override
             public void invoke(int statusCode, String reason, String responseBody) {
+                LOG.error(ErrorMessageFormat.ERROR_FROM_DRUID.logFormat(responseBody, statusCode, reason, druidQuery));
                 responseEmitter.onError(new ResponseException(statusCode, reason, responseBody, druidQuery));
             }
         };
@@ -122,6 +128,7 @@ public FailureCallback getStandardFailure(
         return new FailureCallback() {
             @Override
             public void invoke(Throwable error) {
+                LOG.error(ErrorMessageFormat.FAILED_TO_SEND_QUERY_TO_DRUID.logFormat(druidQuery), error);
                 responseEmitter.onError(new ResponseException(Status.INTERNAL_SERVER_ERROR, druidQuery, error));
             }
         };

fili-core/src/test/groovy/com/yahoo/bard/webservice/web/responseprocessors/ResultSetResponseProcessorSpec.groovy

@@ -241,7 +241,6 @@ class ResultSetResponseProcessorSpec extends Specification {
         entity.contains("message1234")
     }
 
-
     def "Test error callback"() {
         setup:
         def resultSetResponseProcessor = new ResultSetResponseProcessor(