zstd_streambuf.cpp

/*******************************************************************************
 * Copyright 2026 MINRES Technologies GmbH
 *
 * 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 "zstd_streambuf.h"
 
util::zstd_streambuf::zstd_streambuf(const std::string& path)
: file_(fopen(path.c_str(), "rb"))
, buffer_(64 * 1024)
, inbuf_(64 * 1024) {
    if(!file_)
        throw std::runtime_error("fopen failed");
 
    dctx_ = ZSTD_createDCtx();
    if(!dctx_)
        throw std::runtime_error("ZSTD_createDCtx failed");
 
    setg(buffer_.data(), buffer_.data(), buffer_.data());
}
 
util::zstd_streambuf::~zstd_streambuf() {
    if(dctx_)
        ZSTD_freeDCtx(dctx_);
 
    if(file_)
        fclose(file_);
}
 
auto util::zstd_streambuf::underflow() -> int_type {
    size_t inSize = fread(inbuf_.data(), 1, inbuf_.size(), file_);
    if(inSize == 0)
        return traits_type::eof();
 
    size_t outSize = ZSTD_decompressDCtx(dctx_, buffer_.data(), buffer_.size(), inbuf_.data(), inSize);
    if(ZSTD_isError(outSize))
        return traits_type::eof();
 
    setg(buffer_.data(), buffer_.data(), buffer_.data() + outSize);
    return traits_type::to_int_type(*gptr());
}