src/dawn/wire/ChunkedCommandHandler.cpp

// Copyright 2020 The Dawn & Tint Authors
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#include "dawn/wire/ChunkedCommandHandler.h"

#include <algorithm>
#include <cstring>
#include <utility>

#include "dawn/common/Alloc.h"

namespace dawn::wire {

ChunkedCommandHandler::ChunkedCommandHandler() = default;

ChunkedCommandHandler::~ChunkedCommandHandler() = default;

const volatile char* ChunkedCommandHandler::HandleCommands(const volatile char* commands,
                                                           size_t size) {
    if (mChunkedCommandRemainingSize > 0) {
        // If there is a chunked command in flight, append the command data.
        // We append at most |mChunkedCommandRemainingSize| which is enough to finish the
        // in-flight chunked command, and then pass the rest along to a second call to
        // |HandleCommandsImpl|.
        size_t chunkSize = std::min(size, mChunkedCommandRemainingSize);

        memcpy(mChunkedCommandData.get() + mChunkedCommandPutOffset,
               const_cast<const char*>(commands), chunkSize);
        mChunkedCommandPutOffset += chunkSize;
        mChunkedCommandRemainingSize -= chunkSize;

        commands += chunkSize;
        size -= chunkSize;

        if (mChunkedCommandRemainingSize == 0) {
            // Once the chunked command is complete, pass the data to the command handler
            // implemenation.
            auto chunkedCommandData = std::move(mChunkedCommandData);
            if (HandleCommandsImpl(chunkedCommandData.get(), mChunkedCommandPutOffset) == nullptr) {
                // |HandleCommandsImpl| returns nullptr on error. Forward any errors
                // out.
                return nullptr;
            }
        }
    }

    return HandleCommandsImpl(commands, size);
}

ChunkedCommandHandler::ChunkedCommandsResult ChunkedCommandHandler::BeginChunkedCommandData(
    const volatile char* commands,
    size_t commandSize,
    size_t initialSize) {
    DAWN_ASSERT(!mChunkedCommandData);

    // Reserve space for all the command data we're expecting, and copy the initial data
    // to the start of the memory.
    mChunkedCommandData.reset(AllocNoThrow<char>(commandSize));
    if (!mChunkedCommandData) {
        return ChunkedCommandsResult::Error;
    }

    memcpy(mChunkedCommandData.get(), const_cast<const char*>(commands), initialSize);
    mChunkedCommandPutOffset = initialSize;
    mChunkedCommandRemainingSize = commandSize - initialSize;

    return ChunkedCommandsResult::Consumed;
}

}  // namespace dawn::wire