Mark the callback as optional

Without callback, it is impossible to unit-test the backbeat
routes, as we run async code and do not yet support promises.

Issue: CLDSRV-591

Author: williamlardier

lib/routes/routeBackbeat.js

@@ -1310,38 +1310,37 @@ const indexingSchema = joi.array().items(indexEntrySchema).min(1);
 
 function respondToRequest(err, response, log, callback) {
     responseJSONBody(err, null, response, log);
-    return callback(err);
+    // The callback is optional, as it is only used for testing purposes
+    // but value may be set to non-undefined or null due to the arsenal
+    // routes implementation
+    if (callback && typeof callback === 'function') {
+        return callback(err);
+    }
+    return undefined;
 }
 
 function routeIndexingAPIs(request, response, userInfo, log, callback) {
     const route = backbeatRoutes[request.method][request.resourceType];
 
     if (!['GET', 'POST'].includes(request.method)) {
-        responseJSONBody(errors.MethodNotAllowed, null, response, log);
-        return callback(errors.MethodNotAllowed);
+        return respondToRequest(errors.MethodNotAllowed, response, log, callback);
     }
 
     if (request.method === 'GET') {
-        return route(request, response, userInfo, log, err => {
-            if (err) {
-                responseJSONBody(err, null, response, log);
-            }
-            return callback(err);
-        });
+        return route(request, response, userInfo, log, err =>
+            respondToRequest(err, response, log, callback));
     }
 
     const op = request.query.operation;
 
     if (!op || typeof route[op] !== 'function') {
         log.error('Invalid operataion parameter', { operation: op });
-        responseJSONBody(errors.BadRequest, null, response, log);
-        return callback(errors.BadRequest);
+        return respondToRequest(errors.BadRequest, response, log, callback);
     }
 
     return _getRequestPayload(request, (err, payload) => {
         if (err) {
-            responseJSONBody(err, null, response, log);
-            return callback(err);
+            return respondToRequest(err, response, log, callback);
         }
 
         let parsedIndex;
@@ -1350,16 +1349,11 @@ function routeIndexingAPIs(request, response, userInfo, log, callback) {
             parsedIndex = joi.attempt(JSON.parse(payload), indexingSchema, 'invalid payload');
         } catch (err) {
             log.error('Unable to parse index request body', { error: err });
-            responseJSONBody(errors.BadRequest, null, response, log);
-            return callback(errors.BadRequest);
+            return respondToRequest(errors.BadRequest, response, log, callback);
         }
 
-        return route[op](parsedIndex, request, response, userInfo, log, err => {
-            if (err) {
-                responseJSONBody(err, null, response, log);
-            }
-            return callback(err);
-        });
+        return route[op](parsedIndex, request, response, userInfo, log, err =>
+            respondToRequest(err, response, log, callback));
     });
 }
 
@@ -1477,10 +1471,11 @@ function routeBackbeat(clientIP, request, response, log, callback) {
             resourceType: request.resourceType,
             query: request.query,
         });
-        responseJSONBody(errors.MethodNotAllowed, null, response, log);
-        return callback(errors.MethodNotAllowed);
+        return respondToRequest(errors.MethodNotAllowed, response, log, callback);
     }
 
+    const isObjectRequest = _isObjectRequest(request);
+
     return async.waterfall([
         next => auth.server.doAuth(
             request, log, (err, userInfo, authorizationResults, streamingV4Params, infos) => {
@@ -1501,7 +1496,7 @@ function routeBackbeat(clientIP, request, response, log, callback) {
                 next(err, userInfo)),
         (userInfo, next) => {
             // TODO: understand why non-object requests (batchdelete) were not authenticated
-            if (!_isObjectRequest(request)) {
+            if (!isObjectRequest) {
                 if (userInfo.getCanonicalID() === constants.publicId) {
                     log.debug(`unauthenticated access to backbeat ${request.resourceType} routes`, {
                         method: request.method,
@@ -1543,6 +1538,10 @@ function routeBackbeat(clientIP, request, response, log, callback) {
             return standardMetadataValidateBucketAndObj(mdValParams, request.actionImplicitDenies, log, next);
         },
         (bucketInfo, objMd, next) => {
+            // Function was already called
+            if (!isObjectRequest) {
+                return next();
+            }
             if (!useMultipleBackend) {
                 return backbeatRoutes[request.method][request.resourceType](
                     request, response, bucketInfo, objMd, log, next);

tests/unit/routeBackbeat.js

@@ -23,8 +23,6 @@ const testBucket = {
     namespace,
     headers: {
         'host': `${bucketName}.s3.amazonaws.com`,
-        // set versioning
-
     },
     url: `/${bucketName}`,
     actionImplicitDenies: false,
@@ -47,7 +45,6 @@ describe('routeBackbeat', () => {
     let response;
 
     beforeEach(() => {
-        // Mock backbeatRoutes
         sinon.stub(backbeatRoutes, 'PUT').returns({
             data: sinon.stub(),
             metadata: sinon.stub(),
@@ -86,7 +83,6 @@ describe('routeBackbeat', () => {
             index: sinon.stub(),
         });
 
-        // Mock request and response
         request = new DummyRequest(
             {
                 method: 'GET',
@@ -131,7 +127,6 @@ describe('routeBackbeat', () => {
             target: `${bucketName}/${objectName}`,
             operation: null,
             versionId: false,
-            // not sending any body here, so expect error
             expect: errors.MalformedPOSTRequest,
         },
         {