[core] *TileMonitor => *TileSource

21 files changed, 309 insertions, 240 deletions

diff --git a/src/mbgl/annotation/annotation_manager.cpp b/src/mbgl/annotation/annotation_manager.cpp
index e332850357..22cdf313bf 100644
--- a/src/mbgl/annotation/annotation_manager.cpp
+++ b/src/mbgl/annotation/annotation_manager.cpp
@@ -5,6 +5,7 @@
 #include <mbgl/annotation/fill_annotation_impl.hpp>
 #include <mbgl/annotation/style_sourced_annotation_impl.hpp>
 #include <mbgl/style/source.hpp>
+#include <mbgl/tile/annotation_tile_source.hpp>
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/layers/symbol_layer.hpp>
 #include <mbgl/style/layers/symbol_layer_impl.hpp>
@@ -139,12 +140,12 @@ void AnnotationManager::updateStyle(Style& style) {
     }
 }
 
-void AnnotationManager::addTileMonitor(AnnotationTileMonitor& monitor) {
+void AnnotationManager::addTileSource(AnnotationTileSource& monitor) {
     monitors.insert(&monitor);
     monitor.update(getTile(monitor.tileID.canonical));
 }
 
-void AnnotationManager::removeTileMonitor(AnnotationTileMonitor& monitor) {
+void AnnotationManager::removeTileSource(AnnotationTileSource& monitor) {
     monitors.erase(&monitor);
 }
 
diff --git a/src/mbgl/annotation/annotation_manager.hpp b/src/mbgl/annotation/annotation_manager.hpp
index 73907e10c8..6f2700ab70 100644
--- a/src/mbgl/annotation/annotation_manager.hpp
+++ b/src/mbgl/annotation/annotation_manager.hpp
@@ -15,7 +15,7 @@
 namespace mbgl {
 
 class AnnotationTile;
-class AnnotationTileMonitor;
+class AnnotationTileSource;
 class SymbolAnnotationImpl;
 class ShapeAnnotationImpl;
 
@@ -41,8 +41,8 @@ public:
 
     void updateStyle(style::Style&);
 
-    void addTileMonitor(AnnotationTileMonitor&);
-    void removeTileMonitor(AnnotationTileMonitor&);
+    void addTileSource(AnnotationTileSource&);
+    void removeTileSource(AnnotationTileSource&);
 
     static const std::string SourceID;
     static const std::string PointLayerID;
@@ -65,7 +65,7 @@ private:
     SymbolAnnotationMap symbolAnnotations;
     ShapeAnnotationMap shapeAnnotations;
     std::vector<std::string> obsoleteShapeAnnotationLayers;
-    std::set<AnnotationTileMonitor*> monitors;
+    std::set<AnnotationTileSource*> monitors;
 
     SpriteStore spriteStore;
     SpriteAtlas spriteAtlas;
diff --git a/src/mbgl/annotation/annotation_tile.cpp b/src/mbgl/annotation/annotation_tile.cpp
index ba4b69108c..dd2afca127 100644
--- a/src/mbgl/annotation/annotation_tile.cpp
+++ b/src/mbgl/annotation/annotation_tile.cpp
@@ -32,23 +32,4 @@ util::ptr<GeometryTileLayer> AnnotationTile::getLayer(const std::string& name) c
     return nullptr;
 }
 
-AnnotationTileMonitor::AnnotationTileMonitor(const OverscaledTileID& tileID_, AnnotationManager& annotationManager_)
-    : tileID(tileID_),
-      annotationManager(annotationManager_) {
-}
-
-AnnotationTileMonitor::~AnnotationTileMonitor() {
-    annotationManager.removeTileMonitor(*this);
-}
-
-std::unique_ptr<AsyncRequest> AnnotationTileMonitor::monitorTile(const GeometryTileMonitor::Callback& callback_) {
-    callback = callback_;
-    annotationManager.addTileMonitor(*this);
-    return nullptr;
-}
-
-void AnnotationTileMonitor::update(std::unique_ptr<GeometryTile> tile) {
-    callback(nullptr, std::move(tile), {}, {});
-}
-
 } // namespace mbgl
diff --git a/src/mbgl/annotation/annotation_tile.hpp b/src/mbgl/annotation/annotation_tile.hpp
index d607d563d4..8e8d76286e 100644
--- a/src/mbgl/annotation/annotation_tile.hpp
+++ b/src/mbgl/annotation/annotation_tile.hpp
@@ -1,10 +1,6 @@
 #pragma once
 
 #include <mbgl/tile/geometry_tile.hpp>
-#include <mbgl/tile/tile_id.hpp>
-
-#include <map>
-#include <unordered_map>
 
 namespace mbgl {
 
@@ -40,24 +36,7 @@ class AnnotationTile : public GeometryTile {
 public:
     util::ptr<GeometryTileLayer> getLayer(const std::string&) const override;
 
-    std::map<std::string, util::ptr<AnnotationTileLayer>> layers;
-};
-
-class AnnotationManager;
-
-class AnnotationTileMonitor : public GeometryTileMonitor {
-public:
-    AnnotationTileMonitor(const OverscaledTileID&, AnnotationManager&);
-    ~AnnotationTileMonitor();
-
-    void update(std::unique_ptr<GeometryTile>);
-    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileMonitor::Callback&) override;
-
-    OverscaledTileID tileID;
-
-private:
-    AnnotationManager& annotationManager;
-    GeometryTileMonitor::Callback callback;
+    std::unordered_map<std::string, util::ptr<AnnotationTileLayer>> layers;
 };
 
 } // namespace mbgl
diff --git a/src/mbgl/annotation/symbol_annotation_impl.cpp b/src/mbgl/annotation/symbol_annotation_impl.cpp
index 44a89576bb..9859f6b032 100644
--- a/src/mbgl/annotation/symbol_annotation_impl.cpp
+++ b/src/mbgl/annotation/symbol_annotation_impl.cpp
@@ -1,5 +1,6 @@
 #include <mbgl/annotation/symbol_annotation_impl.hpp>
 #include <mbgl/annotation/annotation_tile.hpp>
+#include <mbgl/tile/tile_id.hpp>
 #include <mbgl/math/clamp.hpp>
 
 namespace mbgl {
diff --git a/src/mbgl/style/source.cpp b/src/mbgl/style/source.cpp
index 8e5973f412..701fc2c8cc 100644
--- a/src/mbgl/style/source.cpp
+++ b/src/mbgl/style/source.cpp
@@ -22,6 +22,10 @@
 #include <mbgl/util/string.hpp>
 #include <mbgl/util/tile_cover.hpp>
 
+#include <mbgl/tile/vector_tile_source.hpp>
+#include <mbgl/tile/geojson_tile_source.hpp>
+#include <mbgl/tile/annotation_tile_source.hpp>
+
 #include <mbgl/tile/vector_tile_data.hpp>
 #include <mbgl/tile/raster_tile_data.hpp>
 #include <mbgl/style/parser.hpp>
@@ -202,14 +206,14 @@ std::unique_ptr<TileData> Source::createTile(const OverscaledTileID& overscaledT
                                                 tileset->tiles.at(0), parameters.texturePool,
                                                 parameters.worker, parameters.fileSource, callback);
     } else {
-        std::unique_ptr<GeometryTileMonitor> monitor;
+        std::unique_ptr<GeometryTileSource> monitor;
 
         if (type == SourceType::Vector) {
-            monitor = std::make_unique<VectorTileMonitor>(overscaledTileID, parameters.pixelRatio, tileset->tiles.at(0), parameters.fileSource);
+            monitor = std::make_unique<VectorTileSource>(overscaledTileID, parameters.pixelRatio, tileset->tiles.at(0), parameters.fileSource);
         } else if (type == SourceType::Annotations) {
-            monitor = std::make_unique<AnnotationTileMonitor>(overscaledTileID, parameters.annotationManager);
+            monitor = std::make_unique<AnnotationTileSource>(overscaledTileID, parameters.annotationManager);
         } else if (type == SourceType::GeoJSON) {
-            monitor = std::make_unique<GeoJSONTileMonitor>(geojsonvt.get(), overscaledTileID);
+            monitor = std::make_unique<GeoJSONTileSource>(geojsonvt.get(), overscaledTileID);
         } else {
             Log::Warning(Event::Style, "Source type '%s' is not implemented", SourceTypeClass(type).c_str());
             return nullptr;
diff --git a/src/mbgl/tile/annotation_tile_source.cpp b/src/mbgl/tile/annotation_tile_source.cpp
new file mode 100644
index 0000000000..a89b62f66f
--- /dev/null
+++ b/src/mbgl/tile/annotation_tile_source.cpp
@@ -0,0 +1,28 @@
+#include <mbgl/tile/annotation_tile_source.hpp>
+#include <mbgl/tile/geometry_tile.hpp>
+#include <mbgl/annotation/annotation_manager.hpp>
+#include <mbgl/util/async_request.hpp>
+
+namespace mbgl {
+
+AnnotationTileSource::AnnotationTileSource(const OverscaledTileID& tileID_,
+                                             AnnotationManager& annotationManager_)
+    : tileID(tileID_), annotationManager(annotationManager_) {
+}
+
+AnnotationTileSource::~AnnotationTileSource() {
+    annotationManager.removeTileSource(*this);
+}
+
+std::unique_ptr<AsyncRequest>
+AnnotationTileSource::monitorTile(const GeometryTileSource::Callback& callback_) {
+    callback = callback_;
+    annotationManager.addTileSource(*this);
+    return nullptr;
+}
+
+void AnnotationTileSource::update(std::unique_ptr<GeometryTile> tile) {
+    callback(nullptr, std::move(tile), {}, {});
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/annotation_tile_source.hpp b/src/mbgl/tile/annotation_tile_source.hpp
new file mode 100644
index 0000000000..8626791e1a
--- /dev/null
+++ b/src/mbgl/tile/annotation_tile_source.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <mbgl/tile/tile_source.hpp>
+#include <mbgl/tile/tile_id.hpp>
+
+#include <memory>
+
+namespace mbgl {
+
+class AnnotationManager;
+
+class AnnotationTileSource : public GeometryTileSource {
+public:
+    AnnotationTileSource(const OverscaledTileID&, AnnotationManager&);
+    ~AnnotationTileSource();
+
+    void update(std::unique_ptr<GeometryTile>);
+    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileSource::Callback&) override;
+
+    OverscaledTileID tileID;
+
+private:
+    AnnotationManager& annotationManager;
+    GeometryTileSource::Callback callback;
+};
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/geojson_tile.cpp b/src/mbgl/tile/geojson_tile.cpp
index 90147ffd87..ec399d6e5a 100644
--- a/src/mbgl/tile/geojson_tile.cpp
+++ b/src/mbgl/tile/geojson_tile.cpp
@@ -1,6 +1,4 @@
 #include <mbgl/tile/geojson_tile.hpp>
-#include <mbgl/storage/file_source.hpp>
-#include <mapbox/geojsonvt.hpp>
 
 namespace mbgl {
 
@@ -45,97 +43,4 @@ util::ptr<GeometryTileLayer> GeoJSONTile::getLayer(const std::string&) const {
     return layer;
 }
 
-// Converts the geojsonvt::Tile to a a GeoJSONTile. They have a differing internal structure.
-std::unique_ptr<GeoJSONTile> convertTile(const mapbox::geojsonvt::Tile& tile) {
-    std::shared_ptr<GeoJSONTileLayer> layer;
-
-    if (tile) {
-        std::vector<std::shared_ptr<const GeoJSONTileFeature>> features;
-        GeometryCoordinates line;
-
-        for (auto& feature : tile.features) {
-            const FeatureType featureType =
-                (feature.type == mapbox::geojsonvt::TileFeatureType::Point
-                     ? FeatureType::Point
-                     : (feature.type == mapbox::geojsonvt::TileFeatureType::LineString
-                            ? FeatureType::LineString
-                            : (feature.type == mapbox::geojsonvt::TileFeatureType::Polygon
-                                   ? FeatureType::Polygon
-                                   : FeatureType::Unknown)));
-            if (featureType == FeatureType::Unknown) {
-                continue;
-            }
-
-            GeometryCollection geometry;
-
-            // Flatten the geometry; GeoJSONVT distinguishes between a Points array and Rings array
-            // (Points = GeoJSON types Point, MultiPoint, LineString)
-            // (Rings = GeoJSON types MultiLineString, Polygon, MultiPolygon)
-            // However, in Mapbox GL, we use one structure for both types, and just have one outer
-            // element for Points.
-            if (feature.tileGeometry.is<mapbox::geojsonvt::TilePoints>()) {
-                line.clear();
-                for (auto& point : feature.tileGeometry.get<mapbox::geojsonvt::TilePoints>()) {
-                    line.emplace_back(point.x, point.y);
-                }
-                geometry.emplace_back(std::move(line));
-            } else if (feature.tileGeometry.is<mapbox::geojsonvt::TileRings>()) {
-                for (auto& ring : feature.tileGeometry.get<mapbox::geojsonvt::TileRings>()) {
-                    line.clear();
-                    for (auto& point : ring) {
-                        line.emplace_back(point.x, point.y);
-                    }
-                    geometry.emplace_back(std::move(line));
-                }
-            }
-
-            // https://github.com/mapbox/geojson-vt-cpp/issues/44
-            if (featureType == FeatureType::Polygon) {
-                geometry = fixupPolygons(geometry);
-            }
-
-            Feature::property_map properties { feature.tags.begin(), feature.tags.end() };
-
-            features.emplace_back(std::make_shared<GeoJSONTileFeature>(
-                featureType, std::move(geometry), std::move(properties)));
-        }
-
-        layer = std::make_unique<GeoJSONTileLayer>(std::move(features));
-    }
-
-    return std::make_unique<GeoJSONTile>(layer);
-}
-
-GeoJSONTileMonitor::GeoJSONTileMonitor(mapbox::geojsonvt::GeoJSONVT* geojsonvt_,
-                                       const OverscaledTileID& id)
-    : tileID(id), geojsonvt(geojsonvt_) {
-}
-
-GeoJSONTileMonitor::~GeoJSONTileMonitor() = default;
-
-// A monitor can have its GeoJSONVT object swapped out (e.g. when loading a new GeoJSON file).
-// In that case, we're sending new notifications to all observers.
-void GeoJSONTileMonitor::setGeoJSONVT(mapbox::geojsonvt::GeoJSONVT* vt) {
-    // Don't duplicate notifications in case of nil changes.
-    if (geojsonvt != vt) {
-        geojsonvt = vt;
-        update();
-    }
-}
-
-void GeoJSONTileMonitor::update() {
-    if (geojsonvt) {
-        auto tile = convertTile(
-            geojsonvt->getTile(tileID.canonical.z, tileID.canonical.x, tileID.canonical.y));
-        callback(nullptr, std::move(tile), {}, {});
-    }
-}
-
-std::unique_ptr<AsyncRequest>
-GeoJSONTileMonitor::monitorTile(const GeometryTileMonitor::Callback& cb) {
-    callback = cb;
-    update();
-    return nullptr;
-}
-
 } // namespace mbgl
diff --git a/src/mbgl/tile/geojson_tile.hpp b/src/mbgl/tile/geojson_tile.hpp
index 04ecbc9a24..99698e9058 100644
--- a/src/mbgl/tile/geojson_tile.hpp
+++ b/src/mbgl/tile/geojson_tile.hpp
@@ -1,15 +1,6 @@
 #pragma once
 
 #include <mbgl/tile/geometry_tile.hpp>
-#include <mbgl/tile/tile_id.hpp>
-
-#include <unordered_map>
-
-namespace mapbox {
-namespace geojsonvt {
-class GeoJSONVT;
-} // namespace geojsonvt
-} // namespace mapbox
 
 namespace mbgl {
 
@@ -52,24 +43,4 @@ private:
     const std::shared_ptr<GeoJSONTileLayer> layer;
 };
 
-class GeoJSONTileMonitor : public GeometryTileMonitor {
-public:
-    GeoJSONTileMonitor(mapbox::geojsonvt::GeoJSONVT*, const OverscaledTileID&);
-    virtual ~GeoJSONTileMonitor();
-
-    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileMonitor::Callback&) override;
-
-    void setGeoJSONVT(mapbox::geojsonvt::GeoJSONVT*);
-
-private:
-    void update();
-
-public:
-    const OverscaledTileID tileID;
-
-private:
-    mapbox::geojsonvt::GeoJSONVT* geojsonvt = nullptr;
-    GeometryTileMonitor::Callback callback;
-};
-
 } // namespace mbgl
diff --git a/src/mbgl/tile/geojson_tile_source.cpp b/src/mbgl/tile/geojson_tile_source.cpp
new file mode 100644
index 0000000000..824df4bd49
--- /dev/null
+++ b/src/mbgl/tile/geojson_tile_source.cpp
@@ -0,0 +1,103 @@
+#include <mbgl/tile/geojson_tile_source.hpp>
+#include <mbgl/tile/geojson_tile.hpp>
+
+#include <mbgl/util/async_request.hpp>
+
+#include <mapbox/geojsonvt.hpp>
+
+namespace mbgl {
+
+GeoJSONTileSource::GeoJSONTileSource(mapbox::geojsonvt::GeoJSONVT* geojsonvt_,
+                                     const OverscaledTileID& id)
+    : tileID(id), geojsonvt(geojsonvt_) {
+}
+
+GeoJSONTileSource::~GeoJSONTileSource() = default;
+
+// A monitor can have its GeoJSONVT object swapped out (e.g. when loading a new GeoJSON file).
+// In that case, we're sending new notifications to all observers.
+void GeoJSONTileSource::setGeoJSONVT(mapbox::geojsonvt::GeoJSONVT* vt) {
+    // Don't duplicate notifications in case of nil changes.
+    if (geojsonvt != vt) {
+        geojsonvt = vt;
+        update();
+    }
+}
+
+// Converts the geojsonvt::Tile to a a GeoJSONTile. They have a differing internal structure.
+std::unique_ptr<GeoJSONTile> convertTile(const mapbox::geojsonvt::Tile& tile) {
+    std::shared_ptr<GeoJSONTileLayer> layer;
+
+    if (tile) {
+        std::vector<std::shared_ptr<const GeoJSONTileFeature>> features;
+        GeometryCoordinates line;
+
+        for (auto& feature : tile.features) {
+            const FeatureType featureType =
+                (feature.type == mapbox::geojsonvt::TileFeatureType::Point
+                     ? FeatureType::Point
+                     : (feature.type == mapbox::geojsonvt::TileFeatureType::LineString
+                            ? FeatureType::LineString
+                            : (feature.type == mapbox::geojsonvt::TileFeatureType::Polygon
+                                   ? FeatureType::Polygon
+                                   : FeatureType::Unknown)));
+            if (featureType == FeatureType::Unknown) {
+                continue;
+            }
+
+            GeometryCollection geometry;
+
+            // Flatten the geometry; GeoJSONVT distinguishes between a Points array and Rings array
+            // (Points = GeoJSON types Point, MultiPoint, LineString)
+            // (Rings = GeoJSON types MultiLineString, Polygon, MultiPolygon)
+            // However, in Mapbox GL, we use one structure for both types, and just have one outer
+            // element for Points.
+            if (feature.tileGeometry.is<mapbox::geojsonvt::TilePoints>()) {
+                line.clear();
+                for (auto& point : feature.tileGeometry.get<mapbox::geojsonvt::TilePoints>()) {
+                    line.emplace_back(point.x, point.y);
+                }
+                geometry.emplace_back(std::move(line));
+            } else if (feature.tileGeometry.is<mapbox::geojsonvt::TileRings>()) {
+                for (auto& ring : feature.tileGeometry.get<mapbox::geojsonvt::TileRings>()) {
+                    line.clear();
+                    for (auto& point : ring) {
+                        line.emplace_back(point.x, point.y);
+                    }
+                    geometry.emplace_back(std::move(line));
+                }
+            }
+
+            // https://github.com/mapbox/geojson-vt-cpp/issues/44
+            if (featureType == FeatureType::Polygon) {
+                geometry = fixupPolygons(geometry);
+            }
+
+            Feature::property_map properties{ feature.tags.begin(), feature.tags.end() };
+
+            features.emplace_back(std::make_shared<GeoJSONTileFeature>(
+                featureType, std::move(geometry), std::move(properties)));
+        }
+
+        layer = std::make_unique<GeoJSONTileLayer>(std::move(features));
+    }
+
+    return std::make_unique<GeoJSONTile>(layer);
+}
+
+void GeoJSONTileSource::update() {
+    if (geojsonvt) {
+        auto tile = convertTile(
+            geojsonvt->getTile(tileID.canonical.z, tileID.canonical.x, tileID.canonical.y));
+        callback(nullptr, std::move(tile), {}, {});
+    }
+}
+
+std::unique_ptr<AsyncRequest>
+GeoJSONTileSource::monitorTile(const GeometryTileSource::Callback& cb) {
+    callback = cb;
+    update();
+    return nullptr;
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/geojson_tile_source.hpp b/src/mbgl/tile/geojson_tile_source.hpp
new file mode 100644
index 0000000000..d37f3cf617
--- /dev/null
+++ b/src/mbgl/tile/geojson_tile_source.hpp
@@ -0,0 +1,37 @@
+#pragma once
+
+#include <mbgl/tile/tile_source.hpp>
+#include <mbgl/tile/geometry_tile.hpp>
+#include <mbgl/tile/tile_id.hpp>
+
+#include <unordered_map>
+
+namespace mapbox {
+namespace geojsonvt {
+class GeoJSONVT;
+} // namespace geojsonvt
+} // namespace mapbox
+
+namespace mbgl {
+
+class GeoJSONTileSource : public GeometryTileSource {
+public:
+    GeoJSONTileSource(mapbox::geojsonvt::GeoJSONVT*, const OverscaledTileID&);
+    virtual ~GeoJSONTileSource();
+
+    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileSource::Callback&) override;
+
+    void setGeoJSONVT(mapbox::geojsonvt::GeoJSONVT*);
+
+private:
+    void update();
+
+public:
+    const OverscaledTileID tileID;
+
+private:
+    mapbox::geojsonvt::GeoJSONVT* geojsonvt = nullptr;
+    GeometryTileSource::Callback callback;
+};
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/geometry_tile.hpp b/src/mbgl/tile/geometry_tile.hpp
index 6904c922ba..80d6d6031d 100644
--- a/src/mbgl/tile/geometry_tile.hpp
+++ b/src/mbgl/tile/geometry_tile.hpp
@@ -67,27 +67,6 @@ public:
     virtual util::ptr<GeometryTileLayer> getLayer(const std::string&) const = 0;
 };
 
-class AsyncRequest;
-
-class GeometryTileMonitor : private util::noncopyable {
-public:
-    virtual ~GeometryTileMonitor() = default;
-
-    using Callback = std::function<void (std::exception_ptr,
-                                         std::unique_ptr<GeometryTile>,
-                                         optional<Timestamp> modified,
-                                         optional<Timestamp> expires)>;
-    /*
-     * Monitor the tile held by this object for changes. When the tile is loaded for the first time,
-     * or updates, the callback is executed. If an error occurs, the first parameter will be set.
-     * Otherwise it will be null. If there is no data for the requested tile, the second parameter
-     * will be null.
-     *
-     * To cease monitoring, release the returned Request.
-     */
-    virtual std::unique_ptr<AsyncRequest> monitorTile(const Callback&) = 0;
-};
-
 // classifies an array of rings into polygons with outer rings and holes
 std::vector<GeometryCollection> classifyRings(const GeometryCollection&);
 
diff --git a/src/mbgl/tile/tile_source.cpp b/src/mbgl/tile/tile_source.cpp
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/src/mbgl/tile/tile_source.cpp
diff --git a/src/mbgl/tile/tile_source.hpp b/src/mbgl/tile/tile_source.hpp
new file mode 100644
index 0000000000..bbfd08eaf7
--- /dev/null
+++ b/src/mbgl/tile/tile_source.hpp
@@ -0,0 +1,34 @@
+#pragma once
+
+#include <mbgl/util/noncopyable.hpp>
+#include <mbgl/util/optional.hpp>
+#include <mbgl/util/chrono.hpp>
+
+#include <memory>
+#include <functional>
+
+namespace mbgl {
+
+class GeometryTile;
+class AsyncRequest;
+
+class GeometryTileSource : private util::noncopyable {
+public:
+    virtual ~GeometryTileSource() = default;
+
+    using Callback = std::function<void (std::exception_ptr,
+                                         std::unique_ptr<GeometryTile>,
+                                         optional<Timestamp> modified,
+                                         optional<Timestamp> expires)>;
+    /*
+     * Monitor the tile held by this object for changes. When the tile is loaded for the first time,
+     * or updates, the callback is executed. If an error occurs, the first parameter will be set.
+     * Otherwise it will be null. If there is no data for the requested tile, the second parameter
+     * will be null.
+     *
+     * To cease monitoring, release the returned Request.
+     */
+    virtual std::unique_ptr<AsyncRequest> monitorTile(const Callback&) = 0;
+};
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/vector_tile.cpp b/src/mbgl/tile/vector_tile.cpp
index 5126d0ce83..0a59bafecd 100644
--- a/src/mbgl/tile/vector_tile.cpp
+++ b/src/mbgl/tile/vector_tile.cpp
@@ -220,28 +220,4 @@ std::string VectorTileLayer::getName() const {
     return name;
 }
 
-VectorTileMonitor::VectorTileMonitor(const OverscaledTileID& tileID_, float pixelRatio_,
-                                     const std::string& urlTemplate_, FileSource& fileSource_)
-    : tileID(tileID_),
-      pixelRatio(pixelRatio_),
-      urlTemplate(urlTemplate_),
-      fileSource(fileSource_) {
-}
-
-std::unique_ptr<AsyncRequest> VectorTileMonitor::monitorTile(const GeometryTileMonitor::Callback& callback) {
-    const Resource resource = Resource::tile(urlTemplate, pixelRatio, tileID.canonical.x,
-                                             tileID.canonical.y, tileID.canonical.z);
-    return fileSource.request(resource, [callback, this](Response res) {
-        if (res.error) {
-            callback(std::make_exception_ptr(std::runtime_error(res.error->message)), nullptr, res.modified, res.expires);
-        } else if (res.notModified) {
-            return;
-        } else if (res.noContent) {
-            callback(nullptr, nullptr, res.modified, res.expires);
-        } else {
-            callback(nullptr, std::make_unique<VectorTile>(res.data), res.modified, res.expires);
-        }
-    });
-}
-
 } // namespace mbgl
diff --git a/src/mbgl/tile/vector_tile.hpp b/src/mbgl/tile/vector_tile.hpp
index 9e81f0ec8c..636cd233ab 100644
--- a/src/mbgl/tile/vector_tile.hpp
+++ b/src/mbgl/tile/vector_tile.hpp
@@ -66,20 +66,4 @@ private:
     mutable std::map<std::string, util::ptr<GeometryTileLayer>> layers;
 };
 
-class TileID;
-class FileSource;
-
-class VectorTileMonitor : public GeometryTileMonitor {
-public:
-    VectorTileMonitor(const OverscaledTileID&, float pixelRatio, const std::string& urlTemplate, FileSource&);
-
-    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileMonitor::Callback&) override;
-
-private:
-    OverscaledTileID tileID;
-    float pixelRatio;
-    std::string urlTemplate;
-    FileSource& fileSource;
-};
-
 } // namespace mbgl
diff --git a/src/mbgl/tile/vector_tile_data.cpp b/src/mbgl/tile/vector_tile_data.cpp
index 1ab2566a25..b23efb4273 100644
--- a/src/mbgl/tile/vector_tile_data.cpp
+++ b/src/mbgl/tile/vector_tile_data.cpp
@@ -1,4 +1,5 @@
 #include <mbgl/tile/vector_tile_data.hpp>
+#include <mbgl/tile/tile_source.hpp>
 #include <mbgl/tile/geometry_tile.hpp>
 #include <mbgl/style/layer_impl.hpp>
 #include <mbgl/util/worker.hpp>
@@ -12,7 +13,7 @@
 namespace mbgl {
 
 VectorTileData::VectorTileData(const OverscaledTileID& id_,
-                               std::unique_ptr<GeometryTileMonitor> monitor_,
+                               std::unique_ptr<GeometryTileSource> monitor_,
                                std::string sourceID,
                                style::Style& style_,
                                const MapMode mode_,
diff --git a/src/mbgl/tile/vector_tile_data.hpp b/src/mbgl/tile/vector_tile_data.hpp
index df2a23fda6..e7ff5fbcc6 100644
--- a/src/mbgl/tile/vector_tile_data.hpp
+++ b/src/mbgl/tile/vector_tile_data.hpp
@@ -12,7 +12,7 @@
 namespace mbgl {
 
 class AsyncRequest;
-class GeometryTileMonitor;
+class GeometryTileSource;
 class FeatureIndex;
 
 namespace style {
@@ -22,7 +22,7 @@ class Style;
 class VectorTileData : public TileData {
 public:
     VectorTileData(const OverscaledTileID&,
-                   std::unique_ptr<GeometryTileMonitor> monitor,
+                   std::unique_ptr<GeometryTileSource> monitor,
                    std::string sourceID,
                    style::Style&,
                    const MapMode,
@@ -50,7 +50,7 @@ private:
     Worker& worker;
     TileWorker tileWorker;
 
-    std::unique_ptr<GeometryTileMonitor> monitor;
+    std::unique_ptr<GeometryTileSource> monitor;
     std::unique_ptr<AsyncRequest> tileRequest;
     std::unique_ptr<AsyncRequest> workRequest;
 
diff --git a/src/mbgl/tile/vector_tile_source.cpp b/src/mbgl/tile/vector_tile_source.cpp
new file mode 100644
index 0000000000..9563fb7bee
--- /dev/null
+++ b/src/mbgl/tile/vector_tile_source.cpp
@@ -0,0 +1,32 @@
+#include <mbgl/tile/vector_tile_source.hpp>
+#include <mbgl/tile/vector_tile.hpp>
+#include <mbgl/storage/file_source.hpp>
+
+namespace mbgl {
+
+VectorTileSource::VectorTileSource(const OverscaledTileID& tileID_,
+                                   float pixelRatio_,
+                                   const std::string& urlTemplate_,
+                                   FileSource& fileSource_)
+    : tileID(tileID_), pixelRatio(pixelRatio_), urlTemplate(urlTemplate_), fileSource(fileSource_) {
+}
+
+std::unique_ptr<AsyncRequest>
+VectorTileSource::monitorTile(const GeometryTileSource::Callback& callback) {
+    const Resource resource = Resource::tile(urlTemplate, pixelRatio, tileID.canonical.x,
+                                             tileID.canonical.y, tileID.canonical.z);
+    return fileSource.request(resource, [callback, this](Response res) {
+        if (res.error) {
+            callback(std::make_exception_ptr(std::runtime_error(res.error->message)), nullptr,
+                     res.modified, res.expires);
+        } else if (res.notModified) {
+            return;
+        } else if (res.noContent) {
+            callback(nullptr, nullptr, res.modified, res.expires);
+        } else {
+            callback(nullptr, std::make_unique<VectorTile>(res.data), res.modified, res.expires);
+        }
+    });
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/tile/vector_tile_source.hpp b/src/mbgl/tile/vector_tile_source.hpp
new file mode 100644
index 0000000000..03b6be6c79
--- /dev/null
+++ b/src/mbgl/tile/vector_tile_source.hpp
@@ -0,0 +1,26 @@
+#pragma once
+
+#include <mbgl/tile/tile_source.hpp>
+#include <mbgl/tile/tile_id.hpp>
+
+namespace mbgl {
+
+class FileSource;
+
+class VectorTileSource : public GeometryTileSource {
+public:
+    VectorTileSource(const OverscaledTileID&,
+                     float pixelRatio,
+                     const std::string& urlTemplate,
+                     FileSource&);
+
+    std::unique_ptr<AsyncRequest> monitorTile(const GeometryTileSource::Callback&) override;
+
+private:
+    OverscaledTileID tileID;
+    float pixelRatio;
+    std::string urlTemplate;
+    FileSource& fileSource;
+};
+
+} // namespace mbgl