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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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.
*/
#include <nvram/messages/message_codec.h>
namespace nvram {
namespace proto {
MessageEncoderBase::MessageEncoderBase(const void* object,
const FieldDescriptor* descriptors,
size_t num_descriptors)
: object_(object),
descriptors_(descriptors),
num_descriptors_(num_descriptors) {}
bool MessageEncoderBase::Encode(const void* object,
ProtoWriter* writer,
const FieldDescriptor* descriptors,
size_t num_descriptors) {
MessageEncoderBase encoder(object, descriptors, num_descriptors);
return encoder.Encode(writer);
}
size_t MessageEncoderBase::GetSize() {
CountingOutputStreamBuffer counting_stream;
ProtoWriter writer(&counting_stream);
return EncodeData(&writer) ? counting_stream.bytes_written() : 0;
}
bool MessageEncoderBase::Encode(ProtoWriter* writer) {
// We need to compute the total size of all struct fields up front in order to
// write a length delimiter that designates the end of the encoded nested
// message. Note that computing the size of |object| requires a second
// |EncodeData()| call in addition to the one that actually encodes the data.
// When handling nested message structures, each level triggers its own size
// computation, which are redundant with those performed by the levels above.
//
// For now, we just accept this inefficiency in the interest of keeping things
// simple and correct. If this ever becomes a performance problem for deeply
// nested structs here are some options:
// * Reserve bytes in |writer| for the encoded size. Once |Encode()|
// completes, it is known how many bytes were required, at which point the
// size field can be updated. The drawback with this solution is that
// varint encoding is variable length, so we'd have to write a degenerated
// varint that may occupy more bytes than actually required.
// * Cache encoded sizes in the struct. This is the solution implemented in
// the regular protobuf implementation. This is relatively straightforward,
// but at the expense of holding data in struct that doesn't really belong
// there.
// * Make a first pass over the struct tree, compute sizes and cache them in
// some auxiliary data structure held in the encoder. This is probably the
// cleanest solution, but comes at the expense of having to thread the size
// cache data structure through the encoding logic.
return writer->WriteLengthHeader(GetSize()) && EncodeData(writer);
}
bool MessageEncoderBase::EncodeData(ProtoWriter* writer) {
for (size_t i = 0; i < num_descriptors_; ++i) {
const FieldDescriptor& desc = descriptors_[i];
writer->set_field_number(desc.field_number);
if (!desc.encode_function(object_, writer)) {
return false;
}
}
return true;
}
MessageDecoderBase::MessageDecoderBase(void* object,
const FieldDescriptor* descriptors,
size_t num_descriptors)
: object_(object),
descriptors_(descriptors),
num_descriptors_(num_descriptors) {}
bool MessageDecoderBase::Decode(void* object,
ProtoReader* reader,
const FieldDescriptor* descriptors,
size_t num_descriptors) {
MessageDecoderBase decoder(object, descriptors, num_descriptors);
return decoder.Decode(reader);
}
bool MessageDecoderBase::Decode(ProtoReader* reader) {
NestedInputStreamBuffer nested_stream_buffer(reader->stream_buffer(),
reader->field_size());
ProtoReader nested_reader(&nested_stream_buffer);
return DecodeData(&nested_reader) && nested_reader.Done();
}
bool MessageDecoderBase::DecodeData(ProtoReader* reader) {
while (!reader->Done()) {
if (!reader->ReadWireTag()) {
return false;
}
const FieldDescriptor* desc = FindDescriptor(reader);
if (desc) {
if (!desc->decode_function(object_, reader)) {
return false;
}
} else {
// Unknown field number or wire type mismatch. Skip field data.
if (!reader->SkipField()) {
return false;
}
}
}
return true;
}
const FieldDescriptor* MessageDecoderBase::FindDescriptor(
ProtoReader* reader) const {
for (size_t i = 0; i < num_descriptors_; ++i) {
const FieldDescriptor& desc = descriptors_[i];
if (reader->field_number() == desc.field_number &&
reader->wire_type() == desc.wire_type) {
return &desc;
}
}
return nullptr;
}
} // namespace nvram
} // namespace proto
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