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//
//
// Copyright 2018 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//
#ifndef GRPCPP_SUPPORT_PROTO_BUFFER_WRITER_H
#define GRPCPP_SUPPORT_PROTO_BUFFER_WRITER_H
#include <type_traits>
#include <grpc/byte_buffer.h>
#include <grpc/impl/grpc_types.h>
#include <grpc/slice.h>
#include <grpc/slice_buffer.h>
#include <grpc/support/log.h>
#include <grpcpp/impl/codegen/config_protobuf.h>
#include <grpcpp/impl/serialization_traits.h>
#include <grpcpp/support/byte_buffer.h>
#include <grpcpp/support/status.h>
/// This header provides an object that writes bytes directly into a
/// grpc::ByteBuffer, via the ZeroCopyOutputStream interface
namespace grpc {
// Forward declaration for testing use only
namespace internal {
class ProtoBufferWriterPeer;
} // namespace internal
const int kProtoBufferWriterMaxBufferLength = 1024 * 1024;
/// This is a specialization of the protobuf class ZeroCopyOutputStream.
/// The principle is to give the proto layer one buffer of bytes at a time
/// that it can use to serialize the next portion of the message, with the
/// option to "backup" if more buffer is given than required at the last buffer.
///
/// Read more about ZeroCopyOutputStream interface here:
/// https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.io.zero_copy_stream#ZeroCopyOutputStream
class ProtoBufferWriter : public grpc::protobuf::io::ZeroCopyOutputStream {
public:
/// Constructor for this derived class
///
/// \param[out] byte_buffer A pointer to the grpc::ByteBuffer created
/// \param block_size How big are the chunks to allocate at a time
/// \param total_size How many total bytes are required for this proto
ProtoBufferWriter(ByteBuffer* byte_buffer, int block_size, int total_size)
: block_size_(block_size),
total_size_(total_size),
byte_count_(0),
have_backup_(false) {
GPR_ASSERT(!byte_buffer->Valid());
/// Create an empty raw byte buffer and look at its underlying slice buffer
grpc_byte_buffer* bp = grpc_raw_byte_buffer_create(nullptr, 0);
byte_buffer->set_buffer(bp);
slice_buffer_ = &bp->data.raw.slice_buffer;
}
~ProtoBufferWriter() override {
if (have_backup_) {
grpc_slice_unref(backup_slice_);
}
}
/// Give the proto library the next buffer of bytes and its size. It is
/// safe for the caller to write from data[0, size - 1].
bool Next(void** data, int* size) override {
// Protobuf should not ask for more memory than total_size_.
GPR_ASSERT(byte_count_ < total_size_);
// 1. Use the remaining backup slice if we have one
// 2. Otherwise allocate a slice, up to the remaining length needed
// or our maximum allocation size
// 3. Provide the slice start and size available
// 4. Add the slice being returned to the slice buffer
size_t remain = static_cast<size_t>(total_size_ - byte_count_);
if (have_backup_) {
/// If we have a backup slice, we should use it first
slice_ = backup_slice_;
have_backup_ = false;
if (GRPC_SLICE_LENGTH(slice_) > remain) {
GRPC_SLICE_SET_LENGTH(slice_, remain);
}
} else {
// When less than a whole block is needed, only allocate that much.
// But make sure the allocated slice is not inlined.
size_t allocate_length =
remain > static_cast<size_t>(block_size_) ? block_size_ : remain;
slice_ = grpc_slice_malloc(allocate_length > GRPC_SLICE_INLINED_SIZE
? allocate_length
: GRPC_SLICE_INLINED_SIZE + 1);
}
*data = GRPC_SLICE_START_PTR(slice_);
// On win x64, int is only 32bit
GPR_ASSERT(GRPC_SLICE_LENGTH(slice_) <= INT_MAX);
byte_count_ += * size = static_cast<int>(GRPC_SLICE_LENGTH(slice_));
// Using grpc_slice_buffer_add could modify slice_ and merge it with the
// previous slice. Therefore, use grpc_slice_buffer_add_indexed method to
// ensure the slice gets added at a separate index. It can then be kept
// around and popped later in the BackUp function.
grpc_slice_buffer_add_indexed(slice_buffer_, slice_);
return true;
}
/// Backup by \a count bytes because Next returned more bytes than needed
/// (only used in the last buffer). \a count must be less than or equal too
/// the last buffer returned from next.
void BackUp(int count) override {
// count == 0 is invoked by ZeroCopyOutputStream users indicating that any
// potential buffer obtained through a previous call to Next() is final.
// ZeroCopyOutputStream implementations such as streaming output can use
// these calls to flush any temporary buffer and flush the output. The logic
// below is not robust against count == 0 invocations, so directly return.
if (count == 0) return;
/// 1. Remove the partially-used last slice from the slice buffer
/// 2. Split it into the needed (if any) and unneeded part
/// 3. Add the needed part back to the slice buffer
/// 4. Mark that we still have the remaining part (for later use/unref)
GPR_ASSERT(count <= static_cast<int>(GRPC_SLICE_LENGTH(slice_)));
grpc_slice_buffer_pop(slice_buffer_);
if (static_cast<size_t>(count) == GRPC_SLICE_LENGTH(slice_)) {
backup_slice_ = slice_;
} else {
backup_slice_ =
grpc_slice_split_tail(&slice_, GRPC_SLICE_LENGTH(slice_) - count);
grpc_slice_buffer_add(slice_buffer_, slice_);
}
// It's dangerous to keep an inlined grpc_slice as the backup slice, since
// on a following Next() call, a reference will be returned to this slice
// via GRPC_SLICE_START_PTR, which will not be an address held by
// slice_buffer_.
have_backup_ = backup_slice_.refcount != nullptr;
byte_count_ -= count;
}
/// Returns the total number of bytes written since this object was created.
int64_t ByteCount() const override { return byte_count_; }
// These protected members are needed to support internal optimizations.
// they expose internal bits of grpc core that are NOT stable. If you have
// a use case needs to use one of these functions, please send an email to
// https://groups.google.com/forum/#!forum/grpc-io.
protected:
grpc_slice_buffer* slice_buffer() { return slice_buffer_; }
void set_byte_count(int64_t byte_count) { byte_count_ = byte_count; }
private:
// friend for testing purposes only
friend class internal::ProtoBufferWriterPeer;
const int block_size_; ///< size to alloc for each new \a grpc_slice needed
const int total_size_; ///< byte size of proto being serialized
int64_t byte_count_; ///< bytes written since this object was created
grpc_slice_buffer*
slice_buffer_; ///< internal buffer of slices holding the serialized data
bool have_backup_; ///< if we are holding a backup slice or not
grpc_slice backup_slice_; ///< holds space we can still write to, if the
///< caller has called BackUp
grpc_slice slice_; ///< current slice passed back to the caller
};
} // namespace grpc
#endif // GRPCPP_SUPPORT_PROTO_BUFFER_WRITER_H
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