[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.

2 files changed, 4 insertions, 6 deletions

diff --git a/platform/node/src/node_map.cpp b/platform/node/src/node_map.cpp
index ac14df0228..a4f6f6a9de 100644
--- a/platform/node/src/node_map.cpp
+++ b/platform/node/src/node_map.cpp
@@ -214,8 +214,8 @@ void NodeMap::Load(const Nan::FunctionCallbackInfo<v8::Value>& info) {
     }
 
     try {
-        nodeMap->map->getStyle().loadJSON(style);
-    } catch (const std::exception &ex) {
+        nodeMap->map->getStyle().loadJSON(mbgl::Blob{ std::move(style), false });
+    } catch (const std::exception& ex) {
         return Nan::ThrowError(ex.what());
     }
 
diff --git a/platform/node/src/node_request.cpp b/platform/node/src/node_request.cpp
index de16710f78..7b2b57fd1f 100644
--- a/platform/node/src/node_request.cpp
+++ b/platform/node/src/node_request.cpp
@@ -99,10 +99,8 @@ void NodeRequest::HandleCallback(const Nan::FunctionCallbackInfo<v8::Value>& inf
         if (Nan::Has(res, Nan::New("data").ToLocalChecked()).FromJust()) {
             auto data = Nan::Get(res, Nan::New("data").ToLocalChecked()).ToLocalChecked();
             if (node::Buffer::HasInstance(data)) {
-                response.data = std::make_shared<std::string>(
-                    node::Buffer::Data(data),
-                    node::Buffer::Length(data)
-                );
+                response.data = { std::string{ node::Buffer::Data(data), node::Buffer::Length(data), },
+                                  false };
             } else {
                 return Nan::ThrowTypeError("Response data must be a Buffer");
             }