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https://github.com/revng/revng
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Giacomo Vercesi
e57442fafe
Split off the `GzipTarReader` into `Tar.h`, include a normal `TarWriter` class which leverages libarchive to generate the tar file.
68 lines
2.2 KiB
C++
68 lines
2.2 KiB
C++
#pragma once
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//
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// This file is distributed under the MIT License. See LICENSE.md for details.
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//
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#include "llvm/ADT/StringSet.h"
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#include "llvm/Support/raw_ostream.h"
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#include "revng/Support/Assert.h"
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namespace revng {
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struct OffsetDescriptor {
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size_t Start;
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size_t DataStart;
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size_t PaddingStart;
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size_t End;
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size_t headerSize() { return DataStart - Start; }
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size_t dataSize() { return PaddingStart - DataStart; }
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size_t paddingSize() { return End - PaddingStart; }
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};
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/// Class that allows writing a '.tar.gz' file conforming to the PAX archive
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/// format. The archive is created with these additional properties:
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/// * The header of each file is a stand-alone gzip stream
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/// * Each file is packaged in a stand-alone gzip stream
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/// * The trailing padding is also a stand-alone gzip stream
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///
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/// The most important property of this arrangement is that it allows each
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/// individual file to be read from the archive without decompressing the entire
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/// archive.
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///
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/// Given the offset and size of a single file, the following command line
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/// invocation will retrieve it:
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/// \code{.sh}
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/// dd if=archive bs=1 skip=$offset count=$size | gunzip
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/// \endcode
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/// Because of this, the ::append method, which is used to add a file to the
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/// archive, returns an OffsetDescriptor object describing the position in the
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/// compressed file of where each gzip stream starts and ends. This allows users
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/// of this class to make an index file that tracks the location of each file.
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///
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/// Additionally, since the gzip standard allows concatenating streams, the file
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/// produced is still a valid '.tar.gz' file that can be opened by any program
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/// that supports "ordinary" '.tar.gz' files.
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class GzipTarWriter {
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private:
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llvm::raw_ostream *OS = nullptr;
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llvm::StringSet<> Filenames;
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public:
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GzipTarWriter(llvm::raw_ostream &OS) : OS(&OS){};
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~GzipTarWriter() { revng_assert(OS == nullptr); }
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GzipTarWriter(const GzipTarWriter &Other) = delete;
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GzipTarWriter &operator=(const GzipTarWriter &Other) = delete;
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GzipTarWriter(GzipTarWriter &&Other) = default;
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GzipTarWriter &operator=(GzipTarWriter &&Other) = default;
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OffsetDescriptor append(llvm::StringRef Name, llvm::ArrayRef<char> Data);
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void close();
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};
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} // namespace revng
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