llvm/llvm/lib/Support/TarWriter.cpp

//===-- TarWriter.cpp - Tar archive file creator --------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// TarWriter class provides a feature to create a tar archive file.
//
// I put emphasis on simplicity over comprehensiveness when implementing this
// class because we don't need a full-fledged archive file generator in LLVM
// at the moment.
//
// The filename field in the Unix V7 tar header is 100 bytes. Longer filenames
// are stored using the PAX extension. The PAX header is standardized in
// POSIX.1-2001.
//
// The struct definition of UstarHeader is copied from
// https://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5
//
//===----------------------------------------------------------------------===//

#include "llvm/Support/TarWriter.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Path.h"

usingnamespacellvm;

// Each file in an archive must be aligned to this block size.
static const int BlockSize = …;

struct UstarHeader { … };
static_assert …;

static UstarHeader makeUstarHeader() { … }

// A PAX attribute is in the form of "<length> <key>=<value>\n"
// where <length> is the length of the entire string including
// the length field itself. An example string is this.
//
//   25 ctime=1084839148.1212\n
//
// This function create such string.
static std::string formatPax(StringRef Key, StringRef Val) { … }

// Headers in tar files must be aligned to 512 byte boundaries.
// This function forwards the current file position to the next boundary.
static void pad(raw_fd_ostream &OS) { … }

// Computes a checksum for a tar header.
static void computeChecksum(UstarHeader &Hdr) { … }

// Create a tar header and write it to a given output stream.
static void writePaxHeader(raw_fd_ostream &OS, StringRef Path) { … }

// Path fits in a Ustar header if
//
// - Path is less than 100 characters long, or
// - Path is in the form of "<prefix>/<name>" where <prefix> is less
//   than or equal to 155 characters long and <name> is less than 100
//   characters long. Both <prefix> and <name> can contain extra '/'.
//
// If Path fits in a Ustar header, updates Prefix and Name and returns true.
// Otherwise, returns false.
static bool splitUstar(StringRef Path, StringRef &Prefix, StringRef &Name) { … }

// The PAX header is an extended format, so a PAX header needs
// to be followed by a "real" header.
static void writeUstarHeader(raw_fd_ostream &OS, StringRef Prefix,
                             StringRef Name, size_t Size) { … }

// Creates a TarWriter instance and returns it.
Expected<std::unique_ptr<TarWriter>> TarWriter::create(StringRef OutputPath,
                                                       StringRef BaseDir) { … }

TarWriter::TarWriter(int FD, StringRef BaseDir)
    : … { … }

// Append a given file to an archive.
void TarWriter::append(StringRef Path, StringRef Data) { … }