blob_builder_from_stream.h | Explore in Territory

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef STORAGE_BROWSER_BLOB_BLOB_BUILDER_FROM_STREAM_H_
#define STORAGE_BROWSER_BLOB_BLOB_BUILDER_FROM_STREAM_H_

#include "base/component_export.h"
#include "base/containers/queue.h"
#include "mojo/public/cpp/system/data_pipe.h"
#include "mojo/public/cpp/system/simple_watcher.h"
#include "storage/browser/blob/blob_data_handle.h"
#include "storage/browser/blob/shareable_blob_data_item.h"
#include "third_party/blink/public/mojom/blob/blob_registry.mojom.h"

namespace storage {

// This class can be used to create a blob from a stream source, when it is not
// known in advance how large the blob is going to be. The actual blob won't be
// created until all the data is received. This class deals with memory
// management and quota allocation for the new blob, and makes sure we have
// enough available blob quota for the blob being constructed.
//
// This class will allocate space from the BlobMemoryController as data is
// received. If more data is received than we can allocate space for we abort
// the creation of the blob, free up all space already allocated and return an
// error.
//
// The high-level strategy for how this class allocated space is that it stores
// the first several KB of a blob in memory, and switches to files on disk if
// the blob grows bigger than a certain size (assuming paging to disk is
// enabled, otherwise the entire blob of course has to be stored in memory).
// Space is allocated in chunks, before data is received for that chunk. If the
// end of the stream is reached before a chunk is filled up, the chunk (and its
// space allocation) is shrunk to match the actual size of the data in it.
//
// Generally this class tries avoid evicting other blobs that are already in
// memory to disk. So if there is no more room in-memory so store the blob being
// built we might switch to disk before the normal trigger size is reached.
//
// Finally you can pass an |length_hint| to the constructor. If this is done,
// the size is used for an initial space allocation, and if the size is too
// large to fit in memory anyway, the entire blob will be stored on disk.
//
// If this needs to be destroyed before building has finished, you should make
// sure to call Abort() before destroying the instance. No blob will be created
// in that case.
class COMPONENT_EXPORT(STORAGE_BROWSER) BlobBuilderFromStream { … };

}  // namespace storage

#endif  // STORAGE_BROWSER_BLOB_BLOB_BUILDER_FROM_STREAM_H_
chromium/storage/browser/blob/blob_builder_from_stream.h
