text: //===- ArchiveWriter.cpp - ar File Format implementation --------*- C++ -*-===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the writeArchive function.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Object/ArchiveWriter.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/BinaryFormat/Magic.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/Object/Archive.h"
  #include "llvm/Object/ObjectFile.h"
  #include "llvm/Object/SymbolicFile.h"
  #include "llvm/Support/EndianStream.h"
  #include "llvm/Support/Errc.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/Format.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/ToolOutputFile.h"
  #include "llvm/Support/raw_ostream.h"
  
  #include <map>
  
  #if !defined(_MSC_VER) && !defined(__MINGW32__)
  #include <unistd.h>
  #else
  #include <io.h>
  #endif
  
  using namespace llvm;
  
  NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
      : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
        MemberName(BufRef.getBufferIdentifier()) {}
  
  Expected<NewArchiveMember>
  NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
                                 bool Deterministic) {
    Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef();
    if (!BufOrErr)
      return BufOrErr.takeError();
  
    NewArchiveMember M;
    assert(M.IsNew == false);
    M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
    M.MemberName = M.Buf->getBufferIdentifier();
    if (!Deterministic) {
      auto ModTimeOrErr = OldMember.getLastModified();
      if (!ModTimeOrErr)
        return ModTimeOrErr.takeError();
      M.ModTime = ModTimeOrErr.get();
      Expected<unsigned> UIDOrErr = OldMember.getUID();
      if (!UIDOrErr)
        return UIDOrErr.takeError();
      M.UID = UIDOrErr.get();
      Expected<unsigned> GIDOrErr = OldMember.getGID();
      if (!GIDOrErr)
        return GIDOrErr.takeError();
      M.GID = GIDOrErr.get();
      Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode();
      if (!AccessModeOrErr)
        return AccessModeOrErr.takeError();
      M.Perms = AccessModeOrErr.get();
    }
    return std::move(M);
  }
  
  Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
                                                       bool Deterministic) {
    sys::fs::file_status Status;
    int FD;
    if (auto EC = sys::fs::openFileForRead(FileName, FD))
      return errorCodeToError(EC);
    assert(FD != -1);
  
    if (auto EC = sys::fs::status(FD, Status))
      return errorCodeToError(EC);
  
    // Opening a directory doesn't make sense. Let it fail.
    // Linux cannot open directories with open(2), although
    // cygwin and *bsd can.
    if (Status.type() == sys::fs::file_type::directory_file)
      return errorCodeToError(make_error_code(errc::is_a_directory));
  
    ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr =
        MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false);
    if (!MemberBufferOrErr)
      return errorCodeToError(MemberBufferOrErr.getError());
  
    if (close(FD) != 0)
      return errorCodeToError(std::error_code(errno, std::generic_category()));
  
    NewArchiveMember M;
    M.IsNew = true;
    M.Buf = std::move(*MemberBufferOrErr);
    M.MemberName = M.Buf->getBufferIdentifier();
    if (!Deterministic) {
      M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
          Status.getLastModificationTime());
      M.UID = Status.getUser();
      M.GID = Status.getGroup();
      M.Perms = Status.permissions();
    }
    return std::move(M);
  }
  
  template <typename T>
  static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) {
    uint64_t OldPos = OS.tell();
    OS << Data;
    unsigned SizeSoFar = OS.tell() - OldPos;
    assert(SizeSoFar <= Size && "Data doesn't fit in Size");
    OS.indent(Size - SizeSoFar);
  }
  
  static bool isDarwin(object::Archive::Kind Kind) {
    return Kind == object::Archive::K_DARWIN ||
           Kind == object::Archive::K_DARWIN64;
  }
  
  static bool isBSDLike(object::Archive::Kind Kind) {
    switch (Kind) {
    case object::Archive::K_GNU:
    case object::Archive::K_GNU64:
      return false;
    case object::Archive::K_BSD:
    case object::Archive::K_DARWIN:
    case object::Archive::K_DARWIN64:
      return true;
    case object::Archive::K_COFF:
      break;
    }
    llvm_unreachable("not supported for writting");
  }
  
  template <class T>
  static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) {
    support::endian::write(Out, Val,
                           isBSDLike(Kind) ? support::little : support::big);
  }
  
  static void printRestOfMemberHeader(
      raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime,
      unsigned UID, unsigned GID, unsigned Perms, unsigned Size) {
    printWithSpacePadding(Out, sys::toTimeT(ModTime), 12);
  
    // The format has only 6 chars for uid and gid. Truncate if the provided
    // values don't fit.
    printWithSpacePadding(Out, UID % 1000000, 6);
    printWithSpacePadding(Out, GID % 1000000, 6);
  
    printWithSpacePadding(Out, format("%o", Perms), 8);
    printWithSpacePadding(Out, Size, 10);
    Out << "`\n";
  }
  
  static void
  printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name,
                            const sys::TimePoint<std::chrono::seconds> &ModTime,
                            unsigned UID, unsigned GID, unsigned Perms,
                            unsigned Size) {
    printWithSpacePadding(Out, Twine(Name) + "/", 16);
    printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size);
  }
  
  static void
  printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name,
                       const sys::TimePoint<std::chrono::seconds> &ModTime,
                       unsigned UID, unsigned GID, unsigned Perms,
                       unsigned Size) {
    uint64_t PosAfterHeader = Pos + 60 + Name.size();
    // Pad so that even 64 bit object files are aligned.
    unsigned Pad = OffsetToAlignment(PosAfterHeader, 8);
    unsigned NameWithPadding = Name.size() + Pad;
    printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16);
    printRestOfMemberHeader(Out, ModTime, UID, GID, Perms,
                            NameWithPadding + Size);
    Out << Name;
    while (Pad--)
      Out.write(uint8_t(0));
  }
  
  static bool useStringTable(bool Thin, StringRef Name) {
    return Thin || Name.size() >= 16 || Name.contains('/');
  }
  
  // Compute the relative path from From to To.
  static std::string computeRelativePath(StringRef From, StringRef To) {
    if (sys::path::is_absolute(From) || sys::path::is_absolute(To))
      return To;
  
    StringRef DirFrom = sys::path::parent_path(From);
    auto FromI = sys::path::begin(DirFrom);
    auto ToI = sys::path::begin(To);
    while (*FromI == *ToI) {
      ++FromI;
      ++ToI;
    }
  
    SmallString<128> Relative;
    for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI)
      sys::path::append(Relative, "..");
  
    for (auto ToE = sys::path::end(To); ToI != ToE; ++ToI)
      sys::path::append(Relative, *ToI);
  
  #ifdef _WIN32
    // Replace backslashes with slashes so that the path is portable between *nix
    // and Windows.
    std::replace(Relative.begin(), Relative.end(), '\\', '/');
  #endif
  
    return Relative.str();
  }
  
  static bool is64BitKind(object::Archive::Kind Kind) {
    switch (Kind) {
    case object::Archive::K_GNU:
    case object::Archive::K_BSD:
    case object::Archive::K_DARWIN:
    case object::Archive::K_COFF:
      return false;
    case object::Archive::K_DARWIN64:
    case object::Archive::K_GNU64:
      return true;
    }
    llvm_unreachable("not supported for writting");
  }
  
  static void addToStringTable(raw_ostream &Out, StringRef ArcName,
                               const NewArchiveMember &M, bool Thin) {
    StringRef ID = M.Buf->getBufferIdentifier();
    if (Thin) {
      if (M.IsNew)
        Out << computeRelativePath(ArcName, ID);
      else
        Out << ID;
    } else
      Out << M.MemberName;
    Out << "/\n";
  }
  
  static void printMemberHeader(raw_ostream &Out, uint64_t Pos,
                                raw_ostream &StringTable,
                                StringMap<uint64_t> &MemberNames,
                                object::Archive::Kind Kind, bool Thin,
                                StringRef ArcName, const NewArchiveMember &M,
                                sys::TimePoint<std::chrono::seconds> ModTime,
                                unsigned Size) {
  
    if (isBSDLike(Kind))
      return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
                                  M.Perms, Size);
    if (!useStringTable(Thin, M.MemberName))
      return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
                                       M.Perms, Size);
    Out << '/';
    uint64_t NamePos;
    if (Thin) {
      NamePos = StringTable.tell();
      addToStringTable(StringTable, ArcName, M, Thin);
    } else {
      auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
      if (Insertion.second) {
        Insertion.first->second = StringTable.tell();
        addToStringTable(StringTable, ArcName, M, Thin);
      }
      NamePos = Insertion.first->second;
    }
    printWithSpacePadding(Out, NamePos, 15);
    printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
  }
  
  namespace {
  struct MemberData {
    std::vector<unsigned> Symbols;
    std::string Header;
    StringRef Data;
    StringRef Padding;
  };
  } // namespace
  
  static MemberData computeStringTable(StringRef Names) {
    unsigned Size = Names.size();
    unsigned Pad = OffsetToAlignment(Size, 2);
    std::string Header;
    raw_string_ostream Out(Header);
    printWithSpacePadding(Out, "//", 48);
    printWithSpacePadding(Out, Size + Pad, 10);
    Out << "`\n";
    Out.flush();
    return {{}, std::move(Header), Names, Pad ? "\n" : ""};
  }
  
  static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) {
    using namespace std::chrono;
  
    if (!Deterministic)
      return time_point_cast<seconds>(system_clock::now());
    return sys::TimePoint<seconds>();
  }
  
  static bool isArchiveSymbol(const object::BasicSymbolRef &S) {
    uint32_t Symflags = S.getFlags();
    if (Symflags & object::SymbolRef::SF_FormatSpecific)
      return false;
    if (!(Symflags & object::SymbolRef::SF_Global))
      return false;
    if (Symflags & object::SymbolRef::SF_Undefined)
      return false;
    return true;
  }
  
  static void printNBits(raw_ostream &Out, object::Archive::Kind Kind,
                         uint64_t Val) {
    if (is64BitKind(Kind))
      print<uint64_t>(Out, Kind, Val);
    else
      print<uint32_t>(Out, Kind, Val);
  }
  
  static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
                               bool Deterministic, ArrayRef<MemberData> Members,
                               StringRef StringTable) {
    // We don't write a symbol table on an archive with no members -- except on
    // Darwin, where the linker will abort unless the archive has a symbol table.
    if (StringTable.empty() && !isDarwin(Kind))
      return;
  
    unsigned NumSyms = 0;
    for (const MemberData &M : Members)
      NumSyms += M.Symbols.size();
  
    unsigned Size = 0;
    unsigned OffsetSize = is64BitKind(Kind) ? sizeof(uint64_t) : sizeof(uint32_t);
  
    Size += OffsetSize; // Number of entries
    if (isBSDLike(Kind))
      Size += NumSyms * OffsetSize * 2; // Table
    else
      Size += NumSyms * OffsetSize; // Table
    if (isBSDLike(Kind))
      Size += OffsetSize; // byte count
    Size += StringTable.size();
    // ld64 expects the members to be 8-byte aligned for 64-bit content and at
    // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
    // uniformly.
    // We do this for all bsd formats because it simplifies aligning members.
    unsigned Alignment = isBSDLike(Kind) ? 8 : 2;
    unsigned Pad = OffsetToAlignment(Size, Alignment);
    Size += Pad;
  
    if (isBSDLike(Kind)) {
      const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF";
      printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0,
                           Size);
    } else {
      const char *Name = is64BitKind(Kind) ? "/SYM64" : "";
      printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size);
    }
  
    uint64_t Pos = Out.tell() + Size;
  
    if (isBSDLike(Kind))
      printNBits(Out, Kind, NumSyms * 2 * OffsetSize);
    else
      printNBits(Out, Kind, NumSyms);
  
    for (const MemberData &M : Members) {
      for (unsigned StringOffset : M.Symbols) {
        if (isBSDLike(Kind))
          printNBits(Out, Kind, StringOffset);
        printNBits(Out, Kind, Pos); // member offset
      }
      Pos += M.Header.size() + M.Data.size() + M.Padding.size();
    }
  
    if (isBSDLike(Kind))
      // byte count of the string table
      printNBits(Out, Kind, StringTable.size());
    Out << StringTable;
  
    while (Pad--)
      Out.write(uint8_t(0));
  }
  
  static Expected<std::vector<unsigned>>
  getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
    std::vector<unsigned> Ret;
  
    // In the scenario when LLVMContext is populated SymbolicFile will contain a
    // reference to it, thus SymbolicFile should be destroyed first.
    LLVMContext Context;
    std::unique_ptr<object::SymbolicFile> Obj;
    if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
      auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
          Buf, file_magic::bitcode, &Context);
      if (!ObjOrErr) {
        // FIXME: check only for "not an object file" errors.
        consumeError(ObjOrErr.takeError());
        return Ret;
      }
      Obj = std::move(*ObjOrErr);
    } else {
      auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
      if (!ObjOrErr) {
        // FIXME: check only for "not an object file" errors.
        consumeError(ObjOrErr.takeError());
        return Ret;
      }
      Obj = std::move(*ObjOrErr);
    }
  
    HasObject = true;
    for (const object::BasicSymbolRef &S : Obj->symbols()) {
      if (!isArchiveSymbol(S))
        continue;
      Ret.push_back(SymNames.tell());
      if (auto EC = S.printName(SymNames))
        return errorCodeToError(EC);
      SymNames << '\0';
    }
    return Ret;
  }
  
  static Expected<std::vector<MemberData>>
  computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
                    object::Archive::Kind Kind, bool Thin, StringRef ArcName,
                    bool Deterministic, ArrayRef<NewArchiveMember> NewMembers) {
    static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
  
    // This ignores the symbol table, but we only need the value mod 8 and the
    // symbol table is aligned to be a multiple of 8 bytes
    uint64_t Pos = 0;
  
    std::vector<MemberData> Ret;
    bool HasObject = false;
  
    // Deduplicate long member names in the string table and reuse earlier name
    // offsets. This especially saves space for COFF Import libraries where all
    // members have the same name.
    StringMap<uint64_t> MemberNames;
  
    // UniqueTimestamps is a special case to improve debugging on Darwin:
    //
    // The Darwin linker does not link debug info into the final
    // binary. Instead, it emits entries of type N_OSO in in the output
    // binary's symbol table, containing references to the linked-in
    // object files. Using that reference, the debugger can read the
    // debug data directly from the object files. Alternatively, an
    // invocation of 'dsymutil' will link the debug data from the object
    // files into a dSYM bundle, which can be loaded by the debugger,
    // instead of the object files.
    //
    // For an object file, the N_OSO entries contain the absolute path
    // path to the file, and the file's timestamp. For an object
    // included in an archive, the path is formatted like
    // "/absolute/path/to/archive.a(member.o)", and the timestamp is the
    // archive member's timestamp, rather than the archive's timestamp.
    //
    // However, this doesn't always uniquely identify an object within
    // an archive -- an archive file can have multiple entries with the
    // same filename. (This will happen commonly if the original object
    // files started in different directories.) The only way they get
    // distinguished, then, is via the timestamp. But this process is
    // unable to find the correct object file in the archive when there
    // are two files of the same name and timestamp.
    //
    // Additionally, timestamp==0 is treated specially, and causes the
    // timestamp to be ignored as a match criteria.
    //
    // That will "usually" work out okay when creating an archive not in
    // deterministic timestamp mode, because the objects will probably
    // have been created at different timestamps.
    //
    // To ameliorate this problem, in deterministic archive mode (which
    // is the default), on Darwin we will emit a unique non-zero
    // timestamp for each entry with a duplicated name. This is still
    // deterministic: the only thing affecting that timestamp is the
    // order of the files in the resultant archive.
    //
    // See also the functions that handle the lookup:
    // in lldb: ObjectContainerBSDArchive::Archive::FindObject()
    // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
    bool UniqueTimestamps = Deterministic && isDarwin(Kind);
    std::map<StringRef, unsigned> FilenameCount;
    if (UniqueTimestamps) {
      for (const NewArchiveMember &M : NewMembers)
        FilenameCount[M.MemberName]++;
      for (auto &Entry : FilenameCount)
        Entry.second = Entry.second > 1 ? 1 : 0;
    }
  
    for (const NewArchiveMember &M : NewMembers) {
      std::string Header;
      raw_string_ostream Out(Header);
  
      MemoryBufferRef Buf = M.Buf->getMemBufferRef();
      StringRef Data = Thin ? "" : Buf.getBuffer();
  
      // ld64 expects the members to be 8-byte aligned for 64-bit content and at
      // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
      // uniformly.  This matches the behaviour with cctools and ensures that ld64
      // is happy with archives that we generate.
      unsigned MemberPadding =
          isDarwin(Kind) ? OffsetToAlignment(Data.size(), 8) : 0;
      unsigned TailPadding = OffsetToAlignment(Data.size() + MemberPadding, 2);
      StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
  
      sys::TimePoint<std::chrono::seconds> ModTime;
      if (UniqueTimestamps)
        // Increment timestamp for each file of a given name.
        ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
      else
        ModTime = M.ModTime;
      printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, ArcName,
                        M, ModTime, Buf.getBufferSize() + MemberPadding);
      Out.flush();
  
      Expected<std::vector<unsigned>> Symbols =
          getSymbols(Buf, SymNames, HasObject);
      if (auto E = Symbols.takeError())
        return std::move(E);
  
      Pos += Header.size() + Data.size() + Padding.size();
      Ret.push_back({std::move(*Symbols), std::move(Header), Data, Padding});
    }
    // If there are no symbols, emit an empty symbol table, to satisfy Solaris
    // tools, older versions of which expect a symbol table in a non-empty
    // archive, regardless of whether there are any symbols in it.
    if (HasObject && SymNames.tell() == 0)
      SymNames << '\0' << '\0' << '\0';
    return Ret;
  }
  
  Error llvm::writeArchive(StringRef ArcName,
                           ArrayRef<NewArchiveMember> NewMembers,
                           bool WriteSymtab, object::Archive::Kind Kind,
                           bool Deterministic, bool Thin,
                           std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
    assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");
  
    SmallString<0> SymNamesBuf;
    raw_svector_ostream SymNames(SymNamesBuf);
    SmallString<0> StringTableBuf;
    raw_svector_ostream StringTable(StringTableBuf);
  
    Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
        StringTable, SymNames, Kind, Thin, ArcName, Deterministic, NewMembers);
    if (Error E = DataOrErr.takeError())
      return E;
    std::vector<MemberData> &Data = *DataOrErr;
  
    if (!StringTableBuf.empty())
      Data.insert(Data.begin(), computeStringTable(StringTableBuf));
  
    // We would like to detect if we need to switch to a 64-bit symbol table.
    if (WriteSymtab) {
      uint64_t MaxOffset = 0;
      uint64_t LastOffset = MaxOffset;
      for (const auto &M : Data) {
        // Record the start of the member's offset
        LastOffset = MaxOffset;
        // Account for the size of each part associated with the member.
        MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
        // We assume 32-bit symbols to see if 32-bit symbols are possible or not.
        MaxOffset += M.Symbols.size() * 4;
      }
  
      // The SYM64 format is used when an archive's member offsets are larger than
      // 32-bits can hold. The need for this shift in format is detected by
      // writeArchive. To test this we need to generate a file with a member that
      // has an offset larger than 32-bits but this demands a very slow test. To
      // speed the test up we use this environment variable to pretend like the
      // cutoff happens before 32-bits and instead happens at some much smaller
      // value.
      const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
      int Sym64Threshold = 32;
      if (Sym64Env)
        StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);
  
      // If LastOffset isn't going to fit in a 32-bit varible we need to switch
      // to 64-bit. Note that the file can be larger than 4GB as long as the last
      // member starts before the 4GB offset.
      if (LastOffset >= (1ULL << Sym64Threshold)) {
        if (Kind == object::Archive::K_DARWIN)
          Kind = object::Archive::K_DARWIN64;
        else
          Kind = object::Archive::K_GNU64;
      }
    }
  
    Expected<sys::fs::TempFile> Temp =
        sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
    if (!Temp)
      return Temp.takeError();
  
    raw_fd_ostream Out(Temp->FD, false);
    if (Thin)
      Out << "!<thin>\n";
    else
      Out << "!<arch>\n";
  
    if (WriteSymtab)
      writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);
  
    for (const MemberData &M : Data)
      Out << M.Header << M.Data << M.Padding;
  
    Out.flush();
  
    // At this point, we no longer need whatever backing memory
    // was used to generate the NewMembers. On Windows, this buffer
    // could be a mapped view of the file we want to replace (if
    // we're updating an existing archive, say). In that case, the
    // rename would still succeed, but it would leave behind a
    // temporary file (actually the original file renamed) because
    // a file cannot be deleted while there's a handle open on it,
    // only renamed. So by freeing this buffer, this ensures that
    // the last open handle on the destination file, if any, is
    // closed before we attempt to rename.
    OldArchiveBuf.reset();
  
    return Temp->keep(ArcName);
  }
  