[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.

1 files changed, 6 insertions, 5 deletions

diff --git a/platform/qt/src/qt_image.cpp b/platform/qt/src/qt_image.cpp
index a5c92514c1..ff45b02ef1 100644
--- a/platform/qt/src/qt_image.cpp
+++ b/platform/qt/src/qt_image.cpp
@@ -6,7 +6,7 @@
 
 namespace mbgl {
 
-std::string encodePNG(const PremultipliedImage& pre) {
+Blob encodePNG(const PremultipliedImage& pre) {
     QImage image(pre.data.get(), pre.size.width, pre.size.height,
         QImage::Format_ARGB32_Premultiplied);
 
@@ -16,7 +16,7 @@ std::string encodePNG(const PremultipliedImage& pre) {
     buffer.open(QIODevice::WriteOnly);
     image.rgbSwapped().save(&buffer, "PNG");
 
-    return std::string(array.constData(), array.size());
+    return { std::string(array.constData(), array.size()), false };
 }
 
 #if !defined(QT_IMAGE_DECODERS)
@@ -24,9 +24,10 @@ PremultipliedImage decodeJPEG(const uint8_t*, size_t);
 PremultipliedImage decodeWebP(const uint8_t*, size_t);
 #endif
 
-PremultipliedImage decodeImage(const std::string& string) {
-    const uint8_t* data = reinterpret_cast<const uint8_t*>(string.data());
-    const size_t size = string.size();
+PremultipliedImage decodeImage(Blob blob) {
+    const auto uncompressed = blob.uncompressedData();
+    const uint8_t* data = reinterpret_cast<const uint8_t*>(uncompressed->data());
+    const size_t size = uncompressed->size();
 
 #if !defined(QT_IMAGE_DECODERS)
     if (size >= 12) {