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// Copyright 2025 Huawei Cloud Computing Technology Co., Ltd.
//
// 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 "src/utils/cpp/incremental_reader.hpp"
#include <cstdint>
#include <exception>
#include <string_view>
#include "fmt/core.h"
#include "src/utils/cpp/in_place_visitor.hpp"
namespace {
void DisposeFile(gsl::owner<std::FILE*> file) noexcept {
if (file == nullptr) {
return;
}
std::fclose(file);
}
} // namespace
auto IncrementalReader::FromFile(std::size_t chunk_size,
std::filesystem::path const& path) noexcept
-> expected<IncrementalReader, std::string> {
if (chunk_size == 0) {
return unexpected<std::string>{
"IncrementalReader: the chunk size cannot be 0"};
}
try {
// Ensure this is a file:
if (not std::filesystem::is_regular_file(path)) {
return unexpected{fmt::format(
"IncrementalReader: not a file :\n {} ", path.string())};
}
// Open file for reading:
static constexpr std::string_view kReadBinary = "rb";
auto file = std::shared_ptr<std::FILE>{
std::fopen(path.c_str(), kReadBinary.data()), ::DisposeFile};
if (file == nullptr) {
return unexpected{
fmt::format("IncrementalReader: failed to open the file:\n{}",
path.string())};
}
std::size_t const content_size = std::filesystem::file_size(path);
return IncrementalReader{chunk_size,
content_size,
std::move(file),
/*buffer=*/std::string(chunk_size, '\0')};
} catch (std::exception const& e) {
return unexpected{fmt::format(
"IncrementalReader: While processing {}\ngot an exception: {}",
path.string(),
e.what())};
} catch (...) {
return unexpected{fmt::format(
"IncrementalReader: While processing {}\ngot an unknown exception",
path.string())};
}
}
auto IncrementalReader::ReadChunk(std::size_t offset) const noexcept
-> expected<std::string_view, std::string> {
using Result = expected<std::string_view, std::string>;
InPlaceVisitor const visitor{
[this, offset](FileSource const& file) -> Result {
return ReadFromFile(file, offset);
},
};
try {
return std::visit(visitor, content_);
} catch (std::exception const& e) {
return unexpected{fmt::format(
"IncrementalReader: ReadChunk got an exception:\n{}", e.what())};
} catch (...) {
return unexpected<std::string>{
"IncrementalReader: ReadChunk got an unknown exception"};
}
}
auto IncrementalReader::ReadFromFile(FileSource const& file, std::size_t offset)
const -> expected<std::string_view, std::string> {
if (file == nullptr) {
return unexpected<std::string>{
"IncrementalReader: ReadFromFile: got corrupted file"};
}
if (std::fseek(file.get(), gsl::narrow<std::int64_t>(offset), SEEK_SET) !=
0) {
return unexpected<std::string>{
"IncrementalReader: ReadFromFile: failed to set offset"};
}
std::size_t read = 0;
while (std::feof(file.get()) == 0 and std::ferror(file.get()) == 0 and
read < buffer_.size()) {
read += std::fread(
&buffer_[read], sizeof(char), buffer_.size() - read, file.get());
}
if (std::ferror(file.get()) != 0) {
return unexpected{
fmt::format("IncrementalReader: ReadFromFile: ferror {}",
std::ferror(file.get()))};
}
return std::string_view{buffer_.data(), read};
}
IncrementalReader::Iterator::Iterator(
gsl::not_null<IncrementalReader const*> const& owner,
std::size_t offset) noexcept
: owner_{owner}, offset_{offset} {}
auto IncrementalReader::Iterator::operator*() const noexcept
-> expected<std::string_view, std::string> {
return owner_->ReadChunk(offset_);
}
auto IncrementalReader::Iterator::operator++() noexcept
-> IncrementalReader::Iterator& {
offset_ += owner_->chunk_size_;
if (offset_ >= owner_->content_size_) {
offset_ = owner_->GetEndOffset();
}
return *this;
}
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