Add RocksDb/GeoDb Iterator interface

Summary:
This diff is a first step towards an iterator based interface for the
SearchRadial method which replaces a vector of GeoObjects with an
iterator for GeoObjects. This diff works by just wrapping the iterator
for the encapsulated vector of GeoObjects. A future diff could extend
this approach by defining an interator in terms of the underlying
iteration in SearchRadial which would then remove the need to have
an in-memory representation for all the matching GeoObjects.
Fixes T8421387

Test Plan:
The existing tests have been modified to work with the new
interface.

Reviewers: IslamAbdelRahman, kradhakrishnan, dhruba, igor

Reviewed By: igor

Subscribers: igor, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D50031

include/rocksdb/utilities/geo_db.h

@@ -59,6 +59,16 @@ class GeoObject {
   }
 };
 
+class GeoIterator {
+ public:
+  GeoIterator() = default;
+  virtual ~GeoIterator() {}
+  virtual void Next() = 0;
+  virtual bool Valid() const = 0;
+  virtual const GeoObject& geo_object() = 0;
+  virtual Status status() const = 0;
+};
+
 //
 // Stack your DB with GeoDB to be able to get geo-spatial support
 //
@@ -91,14 +101,13 @@ class GeoDB : public StackableDB {
   // Delete the specified object
   virtual Status Remove(const Slice& id) = 0;
 
-  // Returns a list of all items within a circular radius from the
+  // Returns an iterator for the items within a circular radius from the
   // specified gps location. If 'number_of_values' is specified,
-  // then this call returns at most that many number of objects.
+  // then the iterator is capped to that number of objects.
   // The radius is specified in 'meters'.
-  virtual Status SearchRadial(const GeoPosition& pos,
+  virtual GeoIterator* SearchRadial(const GeoPosition& pos,
-                              double radius,
+                                    double radius,
-                              std::vector<GeoObject>* values,
+                                    int number_of_values = INT_MAX) = 0;
-                              int number_of_values = INT_MAX) = 0;
 };
 
 }  // namespace rocksdb

utilities/geodb/geodb_impl.cc

@@ -159,15 +159,63 @@ Status GeoDBImpl::Remove(const Slice& id) {
   return db_->Write(woptions_, &batch);
 }
 
-Status GeoDBImpl::SearchRadial(const GeoPosition& pos,
+class GeoIteratorImpl : public GeoIterator {
+ private:
+  std::vector<GeoObject> values_;
+  std::vector<GeoObject>::iterator iter_;
+ public:
+  explicit GeoIteratorImpl(std::vector<GeoObject> values)
+    : values_(std::move(values)) {
+    iter_ = values_.begin();
+  }
+  virtual void Next() override;
+  virtual bool Valid() const override;
+  virtual const GeoObject& geo_object() override;
+  virtual Status status() const override;
+};
+
+class GeoErrorIterator : public GeoIterator {
+ private:
+  Status status_;
+ public:
+  explicit GeoErrorIterator(Status s) : status_(s) {}
+  virtual void Next() override {};
+  virtual bool Valid() const override { return false; }
+  virtual const GeoObject& geo_object() override {
+    GeoObject* g = new GeoObject();
+    return *g;
+  }
+  virtual Status status() const override { return status_; }
+};
+
+void GeoIteratorImpl::Next() {
+  assert(Valid());
+  iter_++;
+}
+
+bool GeoIteratorImpl::Valid() const {
+  return iter_ != values_.end();
+}
+
+const GeoObject& GeoIteratorImpl::geo_object() {
+  assert(Valid());
+  return *iter_;
+}
+
+Status GeoIteratorImpl::status() const {
+  return Status::OK();
+}
+
+GeoIterator* GeoDBImpl::SearchRadial(const GeoPosition& pos,
   double radius,
-  std::vector<GeoObject>* values,
   int number_of_values) {
+  std::vector<GeoObject> values;
+
   // Gather all bounding quadkeys
   std::vector<std::string> qids;
   Status s = searchQuadIds(pos, radius, &qids);
   if (!s.ok()) {
-    return s;
+    return new GeoErrorIterator(s);
   }
 
   // create an iterator
@@ -200,7 +248,7 @@ Status GeoDBImpl::SearchRadial(const GeoPosition& pos,
       if (res.first == qid.end()) {
         GeoPosition obj_pos(atof(parts[3].c_str()), atof(parts[4].c_str()));
         GeoObject obj(obj_pos, parts[4], iter->value().ToString());
-        values->push_back(obj);
+        values.push_back(obj);
         number_of_values--;
       } else {
         break;
@@ -208,7 +256,7 @@ Status GeoDBImpl::SearchRadial(const GeoPosition& pos,
     }
   }
   delete iter;
-  return Status::OK();
+  return new GeoIteratorImpl(std::move(values));
 }
 
 std::string GeoDBImpl::MakeKey1(const GeoPosition& pos, Slice id,

utilities/geodb/geodb_impl.h

@@ -46,9 +46,8 @@ class GeoDBImpl : public GeoDB {
 
   // Returns a list of all items within a circular radius from the
   // specified gps location
-  virtual Status SearchRadial(const GeoPosition& pos, double radius,
+  virtual GeoIterator* SearchRadial(const GeoPosition& pos, double radius,
-                              std::vector<GeoObject>* values,
+                                    int number_of_values) override;
-                              int number_of_values) override;
 
  private:
   DB* db_;

utilities/geodb/geodb_test.cc

@@ -103,17 +103,21 @@ TEST_F(GeoDBTest, Search) {
   // search all objects centered at 46 degree latitude with
   // a radius of 200 kilometers. We should find the one object that
   // we inserted earlier.
-  std::vector<GeoObject> values;
+  GeoIterator* iter = getdb()->SearchRadial(GeoPosition(46, 46), 200000);
-  status = getdb()->SearchRadial(GeoPosition(46, 46), 200000, &values);
   ASSERT_TRUE(status.ok());
-  ASSERT_EQ(values.size(), 1U);
+  ASSERT_EQ(iter->geo_object().value, "midvalue1");
+  uint size = 0;
+  while (iter->Valid()) {
+    size++;
+    iter->Next();
+  }
+  ASSERT_EQ(size, 1U);
 
   // search all objects centered at 46 degree latitude with
   // a radius of 2 kilometers. There should be none.
-  values.clear();
+  iter = getdb()->SearchRadial(GeoPosition(46, 46), 2);
-  status = getdb()->SearchRadial(GeoPosition(46, 46), 2, &values);
   ASSERT_TRUE(status.ok());
-  ASSERT_EQ(values.size(), 0U);
+  ASSERT_FALSE(iter->Valid());
 }
 
 }  // namespace rocksdb