1 files changed, 81 insertions, 0 deletions
diff --git a/src/base/istream_ref_data_source.cc b/src/base/istream_ref_data_source.cc
new file mode 100644
index 0000000..5e3d126
--- /dev/null
+++ b/src/base/istream_ref_data_source.cc
@@ -0,0 +1,81 @@
+#include "image_io/base/istream_ref_data_source.h"
+
+#include "image_io/base/data_destination.h"
+#include "image_io/base/data_segment.h"
+
+namespace photos_editing_formats {
+namespace image_io {
+
+void IStreamRefDataSource::Reset() {
+  istream_ref_.clear();
+  istream_ref_.seekg(0);
+  current_data_segment_.reset();
+}
+
+std::shared_ptr<DataSegment> IStreamRefDataSource::GetDataSegment(
+    size_t begin, size_t min_size) {
+  if (current_data_segment_ && current_data_segment_->Contains(begin)) {
+    return current_data_segment_;
+  }
+  current_data_segment_ = Read(begin, min_size);
+  return current_data_segment_;
+}
+
+DataSource::TransferDataResult IStreamRefDataSource::TransferData(
+    const DataRange &data_range, size_t best_size,
+    DataDestination *data_destination) {
+  bool data_transferred = false;
+  DataDestination::TransferStatus status = DataDestination::kTransferDone;
+  if (data_destination && data_range.IsValid()) {
+    size_t min_size = std::min(data_range.GetLength(), best_size);
+    if (current_data_segment_ &&
+        current_data_segment_->GetLength() >= min_size &&
+        current_data_segment_->GetDataRange().Contains(data_range)) {
+      status = data_destination->Transfer(data_range, *current_data_segment_);
+      data_transferred = true;
+    } else {
+      istream_ref_.clear();
+      size_t chunk_size = min_size;
+      for (size_t begin = data_range.GetBegin(); begin < data_range.GetEnd();
+           begin += chunk_size) {
+        size_t segment_length = 0;
+        size_t end = std::min(data_range.GetEnd(), begin + chunk_size);
+        std::shared_ptr<DataSegment> data_segment = Read(begin, end - begin);
+        if (data_segment) {
+          segment_length = data_segment->GetLength();
+          if (segment_length) {
+            status = data_destination->Transfer(data_segment->GetDataRange(),
+                                                *data_segment);
+            data_transferred = true;
+          }
+        }
+        if (status != DataDestination::kTransferOk || segment_length == 0) {
+          break;
+        }
+      }
+    }
+  }
+  if (data_transferred) {
+    return status == DataDestination::kTransferError ? kTransferDataError
+                                                     : kTransferDataSuccess;
+  } else {
+    return data_destination ? kTransferDataNone : kTransferDataError;
+  }
+}
+
+std::shared_ptr<DataSegment> IStreamRefDataSource::Read(size_t begin,
+                                                        size_t count) {
+  std::shared_ptr<DataSegment> shared_data_segment;
+  istream_ref_.seekg(begin);
+  if (istream_ref_.rdstate() == std::ios_base::goodbit) {
+    Byte *buffer = new Byte[count];
+    istream_ref_.read(reinterpret_cast<char *>(buffer), count);
+    size_t bytes_read = istream_ref_.gcount();
+    shared_data_segment =
+        DataSegment::Create(DataRange(begin, begin + bytes_read), buffer);
+  }
+  return shared_data_segment;
+}
+
+}  // namespace image_io
+}  // namespace photos_editing_formats