[core] introduce Blob for compressed and uncompressed dataupstream/blob

- Blob is a wrapper type for a shared_ptr<const string> that has accessor functions for getting compressed and uncompressed data
- Moved util::writeFile, util::readFile, util::compress, util::uncompress, decodeImage, and encodePNG to the Blob interface
- Added Blob support to Request and file sources
- Added Blob support to VectorTile objects
- Added support for gzip decoding to util::uncompress
- We're no longer compressing WebP, PNG, and JPEG data when storing in the OfflineDatabase
- Android's HTTPRequest returns compressed Blobs by default

One caveat is that our previous decompress function didn't support gzip, so once users upgrade to this version, their offline cache may contain both zlib-compressed data and gzip-compressed data, but older versions won't be able to decompress gzip data. On the other hand, we don't support downgrading SDKs anyway, so this shouldn't be a problem. To be on the safe side, we could bump the user_version of the SQLite DB.

7 files changed, 19 insertions, 15 deletions

diff --git a/src/mbgl/style/sources/geojson_source.cpp b/src/mbgl/style/sources/geojson_source.cpp
index 4e3478322d..48308ccbc3 100644
--- a/src/mbgl/style/sources/geojson_source.cpp
+++ b/src/mbgl/style/sources/geojson_source.cpp
@@ -61,7 +61,8 @@ void GeoJSONSource::loadDescription(FileSource& fileSource) {
                 *this, std::make_exception_ptr(std::runtime_error("unexpectedly empty GeoJSON")));
         } else {
             conversion::Error error;
-            optional<GeoJSON> geoJSON = conversion::convertJSON<GeoJSON>(*res.data, error);
+            optional<GeoJSON> geoJSON =
+                conversion::convertJSON<GeoJSON>(*res.data.uncompressedData(), error);
             if (!geoJSON) {
                 Log::Error(Event::ParseStyle, "Failed to parse GeoJSON data: %s",
                            error.message.c_str());
diff --git a/src/mbgl/style/sources/image_source.cpp b/src/mbgl/style/sources/image_source.cpp
index fa268da0ef..5be1b54410 100644
--- a/src/mbgl/style/sources/image_source.cpp
+++ b/src/mbgl/style/sources/image_source.cpp
@@ -70,7 +70,7 @@ void ImageSource::loadDescription(FileSource& fileSource) {
             observer->onSourceError(*this, std::make_exception_ptr(std::runtime_error("unexpectedly empty image url")));
         } else {
             try {
-                baseImpl = makeMutable<Impl>(impl(), decodeImage(*res.data));
+                baseImpl = makeMutable<Impl>(impl(), decodeImage(res.data));
             } catch (...) {
                 observer->onSourceError(*this, std::current_exception());
             }
diff --git a/src/mbgl/style/sources/raster_source.cpp b/src/mbgl/style/sources/raster_source.cpp
index 53f29d660b..c3c47567aa 100644
--- a/src/mbgl/style/sources/raster_source.cpp
+++ b/src/mbgl/style/sources/raster_source.cpp
@@ -57,7 +57,7 @@ void RasterSource::loadDescription(FileSource& fileSource) {
             observer->onSourceError(*this, std::make_exception_ptr(std::runtime_error("unexpectedly empty TileJSON")));
         } else {
             conversion::Error error;
-            optional<Tileset> tileset = conversion::convertJSON<Tileset>(*res.data, error);
+            optional<Tileset> tileset = conversion::convertJSON<Tileset>(*res.data.uncompressedData(), error);
             if (!tileset) {
                 observer->onSourceError(*this, std::make_exception_ptr(std::runtime_error(error.message)));
                 return;
diff --git a/src/mbgl/style/sources/vector_source.cpp b/src/mbgl/style/sources/vector_source.cpp
index ccdd453c75..d88622f1b8 100644
--- a/src/mbgl/style/sources/vector_source.cpp
+++ b/src/mbgl/style/sources/vector_source.cpp
@@ -54,7 +54,8 @@ void VectorSource::loadDescription(FileSource& fileSource) {
             observer->onSourceError(*this, std::make_exception_ptr(std::runtime_error("unexpectedly empty TileJSON")));
         } else {
             conversion::Error error;
-            optional<Tileset> tileset = conversion::convertJSON<Tileset>(*res.data, error);
+            optional<Tileset> tileset =
+                conversion::convertJSON<Tileset>(*res.data.uncompressedData(), error);
             if (!tileset) {
                 observer->onSourceError(*this, std::make_exception_ptr(std::runtime_error(error.message)));
                 return;
diff --git a/src/mbgl/style/style.cpp b/src/mbgl/style/style.cpp
index bd8631fc52..82f421ecdf 100644
--- a/src/mbgl/style/style.cpp
+++ b/src/mbgl/style/style.cpp
@@ -14,7 +14,7 @@ Style::Style(Scheduler& scheduler, FileSource& fileSource, float pixelRatio)
 
 Style::~Style() = default;
 
-void Style::loadJSON(const std::string& json) {
+void Style::loadJSON(Blob json) {
     impl->loadJSON(json);
 }
 
@@ -22,7 +22,7 @@ void Style::loadURL(const std::string& url) {
     impl->loadURL(url);
 }
 
-std::string Style::getJSON() const {
+Blob Style::getJSON() const {
     return impl->getJSON();
 }
 
diff --git a/src/mbgl/style/style_impl.cpp b/src/mbgl/style/style_impl.cpp
index d330b3120a..a952ccb8c2 100644
--- a/src/mbgl/style/style_impl.cpp
+++ b/src/mbgl/style/style_impl.cpp
@@ -39,7 +39,7 @@ Style::Impl::Impl(Scheduler& scheduler_, FileSource& fileSource_, float pixelRat
 
 Style::Impl::~Impl() = default;
 
-void Style::Impl::loadJSON(const std::string& json_) {
+void Style::Impl::loadJSON(Blob json_) {
     lastError = nullptr;
     observer->onStyleLoading();
 
@@ -73,15 +73,17 @@ void Style::Impl::loadURL(const std::string& url_) {
         } else if (res.notModified || res.noContent) {
             return;
         } else {
-            parse(*res.data);
+            parse(res.data);
         }
     });
 }
 
-void Style::Impl::parse(const std::string& json_) {
+void Style::Impl::parse(Blob json_) {
     Parser parser;
 
-    if (auto error = parser.parse(json_)) {
+    const auto data = json_.uncompressedData();
+
+    if (auto error = parser.parse(*data)) {
         std::string message = "Failed to parse style: " + util::toString(error);
         Log::Error(Event::ParseStyle, message.c_str());
         observer->onStyleError(std::make_exception_ptr(util::StyleParseException(message)));
@@ -124,7 +126,7 @@ void Style::Impl::parse(const std::string& json_) {
     observer->onStyleLoaded();
 }
 
-std::string Style::Impl::getJSON() const {
+Blob Style::Impl::getJSON() const {
     return json;
 }
 
diff --git a/src/mbgl/style/style_impl.hpp b/src/mbgl/style/style_impl.hpp
index 3dc222bfad..9dc2704391 100644
--- a/src/mbgl/style/style_impl.hpp
+++ b/src/mbgl/style/style_impl.hpp
@@ -41,10 +41,10 @@ public:
     Impl(Scheduler&, FileSource&, float pixelRatio);
     ~Impl() override;
 
-    void loadJSON(const std::string&);
+    void loadJSON(Blob);
     void loadURL(const std::string&);
 
-    std::string getJSON() const;
+    Blob getJSON() const;
     std::string getURL() const;
 
     void setObserver(Observer*);
@@ -96,13 +96,13 @@ public:
     bool spriteLoaded = false;
 
 private:
-    void parse(const std::string&);
+    void parse(Blob);
 
     Scheduler& scheduler;
     FileSource& fileSource;
 
     std::string url;
-    std::string json;
+    Blob json;
 
     std::unique_ptr<AsyncRequest> styleRequest;
     std::unique_ptr<SpriteLoader> spriteLoader;