added 2 transformers to help representing ObjectId as strings

very useful for angularjs that removes all properties whose name start with $, due to issue 1463 angular/angular.js#1463
removed old angularjs workaround

src/main/java/org/restheart/hal/metadata/RepresentationTransformer.java

@@ -149,12 +149,14 @@ private static RepresentationTransformer getSingleFromJson(DBObject props) throw
 
         String name = (String) _name;
 
+        DBObject args;
+
         if (_args == null || !(_args instanceof DBObject)) {
-            throw new InvalidMetadataException((_args == null ? "missing '" : "invalid '") + RT_ARGS_ELEMENT_NAME + "' element. it must be an Object");
+            args = null;
+        } else {
+            args = (DBObject) _args;
         }
 
-        DBObject args = (DBObject) _args;
-
         return new RepresentationTransformer(phase, scope, name, args);
     }
 }

src/main/java/org/restheart/hal/metadata/singletons/OidsAsStringsTransformer.java

@@ -0,0 +1,59 @@
+/*
+ * RESTHeart - the data REST API server
+ * Copyright (C) SoftInstigate Srl
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.restheart.hal.metadata.singletons;
+
+import com.mongodb.DBObject;
+import io.undertow.server.HttpServerExchange;
+import org.bson.types.ObjectId;
+import org.restheart.handlers.RequestContext;
+
+/**
+ *
+ * @author Andrea Di Cesare <andrea@softinstigate.com>
+ *
+ * On RESPONSE phase this transformer replaces ObjectId with strings.
+ *
+ * <br>Example, document { "_id": {"$oid": "553f59d2e4b041ceaac64e33" }, a: 1 } 
+ * <br>GET -> { "_id": "553f59d2e4b041ceaac64e33", a:1 } 
+ *
+ */
+public class OidsAsStringsTransformer implements Transformer {
+    /**
+     *
+     * @param exchange
+     * @param context
+     * @param contentToTransform
+     * @param args
+     */
+    @Override
+    public void tranform(final HttpServerExchange exchange, final RequestContext context, DBObject contentToTransform, final DBObject args) {
+        _transform(contentToTransform);
+    }
+
+    private void _transform(DBObject data) {
+        data.keySet().stream().forEach(key -> {
+            Object value = data.get(key);
+
+            if (value instanceof DBObject) {
+                _transform((DBObject)value);
+            } else if (value instanceof ObjectId) {
+                data.put(key, ((ObjectId)value).toString());
+            }
+        });
+    }
+}

src/main/java/org/restheart/hal/metadata/singletons/ValidOidsStringsAsOidsTransformer.java

@@ -0,0 +1,106 @@
+/*
+ * RESTHeart - the data REST API server
+ * Copyright (C) SoftInstigate Srl
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.restheart.hal.metadata.singletons;
+
+import com.mongodb.BasicDBList;
+import com.mongodb.DBObject;
+import io.undertow.server.HttpServerExchange;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.regex.Pattern;
+import org.bson.types.ObjectId;
+import org.restheart.handlers.RequestContext;
+
+/**
+ *
+ * @author Andrea Di Cesare <andrea@softinstigate.com>
+ *
+ * On REQUEST phase This transformer replaces strings that are valid ObjectIds
+ * with ObjectIds.
+ *
+ * <br>Example:
+ * <br>POST( { "_id": "553f59d2e4b041ceaac64e33", a:2 } -> { "_id": {"$oid":
+ * "553f59d2e4b041ceaac64e33" }, a: 1 }
+ *
+ */
+public class ValidOidsStringsAsOidsTransformer implements Transformer {
+    /**
+     *
+     * @param exchange
+     * @param context
+     * @param contentToTransform
+     * @param args names of properties to tranform eventually (if value is valid
+     * ObjectId) as an array of strings (["_id", "prop2"]
+     */
+    @Override
+    public void tranform(final HttpServerExchange exchange, final RequestContext context, DBObject contentToTransform, final DBObject args) {
+        // this set contains the names of the properties to transform eventually
+        Set<String> propertiesToTransform = new HashSet<>();
+
+        if (args instanceof BasicDBList) {
+            BasicDBList _ids = (BasicDBList) args;
+
+            _ids.forEach(propertyName -> {
+                if (propertyName instanceof String) {
+                    propertiesToTransform.add((String) propertyName);
+
+                } else {
+                    context.addWarning("element in the args list is not a string: " + propertyName);
+                }
+            });
+
+        } else {
+            context.addWarning("transformer wrong definition: args property must be an arrary of string (properties names).");
+        }
+
+        _transform(contentToTransform, propertiesToTransform);
+    }
+
+    private void _transform(DBObject data, Set<String> propertiesNames) {
+        data.keySet().stream().forEach(key -> {
+            Object value = data.get(key);
+
+            if (shouldTransform(key, propertiesNames)) {
+                if (value instanceof String && ObjectId.isValid((String) value)) {
+                    data.put(key, new ObjectId((String) value));
+                }
+            }
+
+            if (value instanceof DBObject) {
+                _transform((DBObject) value, propertiesNames);
+            }
+        });
+    }
+
+    /**
+     * @param key the name of the property to transform (in case of patch can
+     * also use the dot notation)
+     * @param propertiesToTransform the set of properties names to tranform if
+     * their value is a valid ObjectId
+     * @return true if the property should be transformed
+     */
+    private boolean shouldTransform(String key, Set<String> propertiesToTransform) {
+        if (key.contains(".")) {
+            String keyTokens[] = key.split(Pattern.quote("."));
+
+            key = keyTokens[keyTokens.length - 1];
+        } 
+
+        return propertiesToTransform.contains(key);
+    }
+}

src/main/java/org/restheart/handlers/injectors/BodyInjectorHandler.java

@@ -103,7 +103,7 @@ public void handleRequest(HttpServerExchange exchange, RequestContext context) t
         DBObject content;
 
         if (isNotFormData(contentTypes)) { // json or hal+json
-            final String contentString = workaroundAngularJSIssue1463(ChannelReader.read(exchange.getRequestChannel()));
+            final String contentString = ChannelReader.read(exchange.getRequestChannel());
 
             try {
                 content = (DBObject) JSON.parse(contentString);
@@ -174,28 +174,6 @@ public void handleRequest(HttpServerExchange exchange, RequestContext context) t
         getNext().handleRequest(exchange, context);
     }
 
-    /**
-     * need this to workaroung angularjs issue
-     * https://github.com/angular/angular.js/issues/1463
-     * 
-     * TODO: allow enabling the workaround via configuration option
-     *
-     * @param content
-     * @return
-     */
-    private static String workaroundAngularJSIssue1463(String contentString) {
-        if (contentString == null)
-            return null;
-
-        String ret = contentString.replaceAll("\"€oid\" *:", "\"\\$oid\" :");
-
-        if (!ret.equals(contentString)) {
-            LOGGER.debug("Replaced €oid alias with $oid in message body. This is to workaround angularjs issue 1463 (https://github.com/angular/angular.js/issues/1463)");
-        }
-
-        return ret;
-    }
-
     /**
      *
      * @param contentTypes