gecko-dev/netwerk/base/nsFileStreams.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ipc/IPCMessageUtils.h"

#if defined(XP_UNIX) || defined(XP_BEOS)
#include <unistd.h>
#elif defined(XP_WIN)
#include <windows.h>
#include "nsILocalFileWin.h"
#else
// XXX add necessary include file for ftruncate (or equivalent)
#endif

#include "private/pprio.h"

#include "nsFileStreams.h"
#include "nsIFile.h"
#include "nsReadLine.h"
#include "nsIClassInfoImpl.h"
#include "mozilla/ipc/InputStreamUtils.h"
#include "mozilla/Unused.h"
#include "mozilla/FileUtils.h"
#include "nsNetCID.h"
#include "nsXULAppAPI.h"

typedef mozilla::ipc::FileDescriptor::PlatformHandleType FileHandleType;

using namespace mozilla::ipc;
using mozilla::DebugOnly;
using mozilla::Maybe;
using mozilla::Nothing;
using mozilla::Some;

////////////////////////////////////////////////////////////////////////////////
// nsFileStreamBase

nsFileStreamBase::nsFileStreamBase()
    : mFD(nullptr)
    , mBehaviorFlags(0)
    , mState(eUnitialized)
    , mErrorValue(NS_ERROR_FAILURE)
{
}

nsFileStreamBase::~nsFileStreamBase()
{
    // We don't want to try to rewrind the stream when shutting down.
    mBehaviorFlags &= ~nsIFileInputStream::REOPEN_ON_REWIND;

    Close();
}

NS_IMPL_ISUPPORTS(nsFileStreamBase,
                  nsISeekableStream,
                  nsIFileMetadata)

NS_IMETHODIMP
nsFileStreamBase::Seek(int32_t whence, int64_t offset)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    int64_t cnt = PR_Seek64(mFD, offset, (PRSeekWhence)whence);
    if (cnt == int64_t(-1)) {
        return NS_ErrorAccordingToNSPR();
    }
    return NS_OK;
}

NS_IMETHODIMP
nsFileStreamBase::Tell(int64_t *result)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    int64_t cnt = PR_Seek64(mFD, 0, PR_SEEK_CUR);
    if (cnt == int64_t(-1)) {
        return NS_ErrorAccordingToNSPR();
    }
    *result = cnt;
    return NS_OK;
}

NS_IMETHODIMP
nsFileStreamBase::SetEOF()
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

#if defined(XP_UNIX) || defined(XP_BEOS)
    // Some system calls require an EOF offset.
    int64_t offset;
    rv = Tell(&offset);
    if (NS_FAILED(rv)) return rv;
#endif

#if defined(XP_UNIX) || defined(XP_BEOS)
    if (ftruncate(PR_FileDesc2NativeHandle(mFD), offset) != 0) {
        NS_ERROR("ftruncate failed");
        return NS_ERROR_FAILURE;
    }
#elif defined(XP_WIN)
    if (!SetEndOfFile((HANDLE) PR_FileDesc2NativeHandle(mFD))) {
        NS_ERROR("SetEndOfFile failed");
        return NS_ERROR_FAILURE;
    }
#else
    // XXX not implemented
#endif

    return NS_OK;
}

NS_IMETHODIMP
nsFileStreamBase::GetSize(int64_t* _retval)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    PRFileInfo64 info;
    if (PR_GetOpenFileInfo64(mFD, &info) == PR_FAILURE) {
        return NS_BASE_STREAM_OSERROR;
    }

    *_retval = int64_t(info.size);

    return NS_OK;
}

NS_IMETHODIMP
nsFileStreamBase::GetLastModified(int64_t* _retval)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    PRFileInfo64 info;
    if (PR_GetOpenFileInfo64(mFD, &info) == PR_FAILURE) {
        return NS_BASE_STREAM_OSERROR;
    }

    int64_t modTime = int64_t(info.modifyTime);
    if (modTime == 0) {
        *_retval = 0;
    }
    else {
        *_retval = modTime / int64_t(PR_USEC_PER_MSEC);
    }

    return NS_OK;
}

NS_IMETHODIMP
nsFileStreamBase::GetFileDescriptor(PRFileDesc** _retval)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    *_retval = mFD;
    return NS_OK;
}

nsresult
nsFileStreamBase::Close()
{
    CleanUpOpen();

    nsresult rv = NS_OK;
    if (mFD) {
        if (PR_Close(mFD) == PR_FAILURE)
            rv = NS_BASE_STREAM_OSERROR;
        mFD = nullptr;
        mState = eClosed;
    }
    return rv;
}

nsresult
nsFileStreamBase::Available(uint64_t* aResult)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    // PR_Available with files over 4GB returns an error, so we have to
    // use the 64-bit version of PR_Available.
    int64_t avail = PR_Available64(mFD);
    if (avail == -1) {
        return NS_ErrorAccordingToNSPR();
    }

    // If available is greater than 4GB, return 4GB
    *aResult = (uint64_t)avail;
    return NS_OK;
}

nsresult
nsFileStreamBase::Read(char* aBuf, uint32_t aCount, uint32_t* aResult)
{
    nsresult rv = DoPendingOpen();
    if (rv == NS_BASE_STREAM_CLOSED) {
        *aResult = 0;
        return NS_OK;
    }

    if (NS_FAILED(rv)) {
        return rv;
    }

    int32_t bytesRead = PR_Read(mFD, aBuf, aCount);
    if (bytesRead == -1) {
        return NS_ErrorAccordingToNSPR();
    }

    *aResult = bytesRead;
    return NS_OK;
}

nsresult
nsFileStreamBase::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
                               uint32_t aCount, uint32_t* aResult)
{
    // ReadSegments is not implemented because it would be inefficient when
    // the writer does not consume all data.  If you want to call ReadSegments,
    // wrap a BufferedInputStream around the file stream.  That will call
    // Read().

    return NS_ERROR_NOT_IMPLEMENTED;
}

nsresult
nsFileStreamBase::IsNonBlocking(bool *aNonBlocking)
{
    *aNonBlocking = false;
    return NS_OK;
}

nsresult
nsFileStreamBase::Flush(void)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    int32_t cnt = PR_Sync(mFD);
    if (cnt == -1) {
        return NS_ErrorAccordingToNSPR();
    }
    return NS_OK;
}

nsresult
nsFileStreamBase::Write(const char *buf, uint32_t count, uint32_t *result)
{
    nsresult rv = DoPendingOpen();
    NS_ENSURE_SUCCESS(rv, rv);

    int32_t cnt = PR_Write(mFD, buf, count);
    if (cnt == -1) {
        return NS_ErrorAccordingToNSPR();
    }
    *result = cnt;
    return NS_OK;
}

nsresult
nsFileStreamBase::WriteFrom(nsIInputStream *inStr, uint32_t count, uint32_t *_retval)
{
    NS_NOTREACHED("WriteFrom (see source comment)");
    return NS_ERROR_NOT_IMPLEMENTED;
    // File streams intentionally do not support this method.
    // If you need something like this, then you should wrap
    // the file stream using nsIBufferedOutputStream
}

nsresult
nsFileStreamBase::WriteSegments(nsReadSegmentFun reader, void * closure, uint32_t count, uint32_t *_retval)
{
    return NS_ERROR_NOT_IMPLEMENTED;
    // File streams intentionally do not support this method.
    // If you need something like this, then you should wrap
    // the file stream using nsIBufferedOutputStream
}

nsresult
nsFileStreamBase::MaybeOpen(nsIFile* aFile, int32_t aIoFlags,
                            int32_t aPerm, bool aDeferred)
{
    NS_ENSURE_STATE(aFile);

    mOpenParams.ioFlags = aIoFlags;
    mOpenParams.perm = aPerm;

    if (aDeferred) {
        // Clone the file, as it may change between now and the deferred open
        nsCOMPtr<nsIFile> file;
        nsresult rv = aFile->Clone(getter_AddRefs(file));
        NS_ENSURE_SUCCESS(rv, rv);

        mOpenParams.localFile = do_QueryInterface(file);
        NS_ENSURE_TRUE(mOpenParams.localFile, NS_ERROR_UNEXPECTED);

        mState = eDeferredOpen;
        return NS_OK;
    }

    mOpenParams.localFile = aFile;

    // Following call open() at main thread.
    // Main thread might be blocked, while open a remote file.
    return DoOpen();
}

void
nsFileStreamBase::CleanUpOpen()
{
    mOpenParams.localFile = nullptr;
}

nsresult
nsFileStreamBase::DoOpen()
{
    MOZ_ASSERT(mState == eDeferredOpen || mState == eUnitialized ||
               mState == eClosed);
    NS_ASSERTION(!mFD, "Already have a file descriptor!");
    NS_ASSERTION(mOpenParams.localFile, "Must have a file to open");

    PRFileDesc* fd;
    nsresult rv;

    if (mOpenParams.ioFlags & PR_CREATE_FILE) {
        nsCOMPtr<nsIFile> parent;
        mOpenParams.localFile->GetParent(getter_AddRefs(parent));

        // Result doesn't need to be checked. If the file's parent path does not
        // exist, make it. If it does exist, do nothing.
        if (parent) {
            Unused << parent->Create(nsIFile::DIRECTORY_TYPE, 0755);
        }
    }

#ifdef XP_WIN
    if (mBehaviorFlags & nsIFileInputStream::SHARE_DELETE) {
      nsCOMPtr<nsILocalFileWin> file = do_QueryInterface(mOpenParams.localFile);
      MOZ_ASSERT(file);

      rv = file->OpenNSPRFileDescShareDelete(mOpenParams.ioFlags,
                                             mOpenParams.perm,
                                             &fd);
    } else
#endif // XP_WIN
    {
      rv = mOpenParams.localFile->OpenNSPRFileDesc(mOpenParams.ioFlags,
                                                   mOpenParams.perm,
                                                   &fd);
    }

    CleanUpOpen();
    if (NS_FAILED(rv)) {
        mState = eError;
        mErrorValue = rv;
        return rv;
    }

    mFD = fd;
    mState = eOpened;

    return NS_OK;
}

nsresult
nsFileStreamBase::DoPendingOpen()
{
    switch (mState) {
    case eUnitialized:
        MOZ_CRASH("This should not happen.");
        return NS_ERROR_FAILURE;

    case eDeferredOpen:
        return DoOpen();

    case eOpened:
        MOZ_ASSERT(mFD);
        if (NS_WARN_IF(!mFD)) {
          return NS_ERROR_FAILURE;
        }
        return NS_OK;

    case eClosed:
        MOZ_ASSERT(!mFD);
        return NS_BASE_STREAM_CLOSED;

    case eError:
        return mErrorValue;
    }

    MOZ_CRASH("Invalid mState value.");
    return NS_ERROR_FAILURE;
}


////////////////////////////////////////////////////////////////////////////////
// nsFileInputStream

NS_IMPL_ADDREF_INHERITED(nsFileInputStream, nsFileStreamBase)
NS_IMPL_RELEASE_INHERITED(nsFileInputStream, nsFileStreamBase)

NS_IMPL_CLASSINFO(nsFileInputStream, nullptr, nsIClassInfo::THREADSAFE,
                  NS_LOCALFILEINPUTSTREAM_CID)

NS_INTERFACE_MAP_BEGIN(nsFileInputStream)
    NS_INTERFACE_MAP_ENTRY(nsIInputStream)
    NS_INTERFACE_MAP_ENTRY(nsIFileInputStream)
    NS_INTERFACE_MAP_ENTRY(nsILineInputStream)
    NS_INTERFACE_MAP_ENTRY(nsIIPCSerializableInputStream)
    NS_IMPL_QUERY_CLASSINFO(nsFileInputStream)
    NS_INTERFACE_MAP_ENTRY_CONDITIONAL(nsICloneableInputStream, IsCloneable())
NS_INTERFACE_MAP_END_INHERITING(nsFileStreamBase)

NS_IMPL_CI_INTERFACE_GETTER(nsFileInputStream,
                            nsIInputStream,
                            nsIFileInputStream,
                            nsISeekableStream,
                            nsILineInputStream)

nsresult
nsFileInputStream::Create(nsISupports *aOuter, REFNSIID aIID, void **aResult)
{
    NS_ENSURE_NO_AGGREGATION(aOuter);

    nsFileInputStream* stream = new nsFileInputStream();
    if (stream == nullptr)
        return NS_ERROR_OUT_OF_MEMORY;
    NS_ADDREF(stream);
    nsresult rv = stream->QueryInterface(aIID, aResult);
    NS_RELEASE(stream);
    return rv;
}

nsresult
nsFileInputStream::Open(nsIFile* aFile, int32_t aIOFlags, int32_t aPerm)
{
    nsresult rv = NS_OK;

    // If the previous file is open, close it
    if (mFD) {
        rv = Close();
        if (NS_FAILED(rv)) return rv;
    }

    // Open the file
    if (aIOFlags == -1)
        aIOFlags = PR_RDONLY;
    if (aPerm == -1)
        aPerm = 0;

    return MaybeOpen(aFile, aIOFlags, aPerm,
                     mBehaviorFlags & nsIFileInputStream::DEFER_OPEN);
}

NS_IMETHODIMP
nsFileInputStream::Init(nsIFile* aFile, int32_t aIOFlags, int32_t aPerm,
                        int32_t aBehaviorFlags)
{
    NS_ENSURE_TRUE(!mFD, NS_ERROR_ALREADY_INITIALIZED);
    NS_ENSURE_TRUE(mState == eUnitialized || mState == eClosed,
                   NS_ERROR_ALREADY_INITIALIZED);

    mBehaviorFlags = aBehaviorFlags;
    mState = eUnitialized;

    mFile = aFile;
    mIOFlags = aIOFlags;
    mPerm = aPerm;

    return Open(aFile, aIOFlags, aPerm);
}

NS_IMETHODIMP
nsFileInputStream::Close()
{
    // Get the cache position at the time the file was close. This allows
    // NS_SEEK_CUR on a closed file that has been opened with
    // REOPEN_ON_REWIND.
    if (mBehaviorFlags & REOPEN_ON_REWIND) {
        // Get actual position. Not one modified by subclasses
        nsFileStreamBase::Tell(&mCachedPosition);
    }

    // null out mLineBuffer in case Close() is called again after failing
    mLineBuffer = nullptr;
    return nsFileStreamBase::Close();
}

NS_IMETHODIMP
nsFileInputStream::Read(char* aBuf, uint32_t aCount, uint32_t* _retval)
{
    nsresult rv = nsFileStreamBase::Read(aBuf, aCount, _retval);
    if (rv == NS_ERROR_FILE_NOT_FOUND) {
      // Don't warn if this is a deffered file not found.
      return rv;
    }

    NS_ENSURE_SUCCESS(rv, rv);

    // Check if we're at the end of file and need to close
    if (mBehaviorFlags & CLOSE_ON_EOF && *_retval == 0) {
        Close();
    }

    return NS_OK;
}

NS_IMETHODIMP
nsFileInputStream::ReadLine(nsACString& aLine, bool* aResult)
{
    if (!mLineBuffer) {
      mLineBuffer = new nsLineBuffer<char>;
    }
    return NS_ReadLine(this, mLineBuffer.get(), aLine, aResult);
}

NS_IMETHODIMP
nsFileInputStream::Seek(int32_t aWhence, int64_t aOffset)
{
  return SeekInternal(aWhence, aOffset);
}

nsresult
nsFileInputStream::SeekInternal(int32_t aWhence, int64_t aOffset, bool aClearBuf)
{
    nsresult rv = DoPendingOpen();
    if (rv != NS_OK && rv != NS_BASE_STREAM_CLOSED) {
        return rv;
    }

    if (aClearBuf) {
        mLineBuffer = nullptr;
    }

    if (rv == NS_BASE_STREAM_CLOSED) {
        if (mBehaviorFlags & REOPEN_ON_REWIND) {
            rv = Open(mFile, mIOFlags, mPerm);
            NS_ENSURE_SUCCESS(rv, rv);

            // If the file was closed, and we do a relative seek, use the
            // position we cached when we closed the file to seek to the right
            // location.
            if (aWhence == NS_SEEK_CUR) {
                aWhence = NS_SEEK_SET;
                aOffset += mCachedPosition;
            }
        } else {
            return NS_BASE_STREAM_CLOSED;
        }
    }

    return nsFileStreamBase::Seek(aWhence, aOffset);
}

NS_IMETHODIMP
nsFileInputStream::Tell(int64_t *aResult)
{
    return nsFileStreamBase::Tell(aResult);
}

NS_IMETHODIMP
nsFileInputStream::Available(uint64_t *aResult)
{
    return nsFileStreamBase::Available(aResult);
}

void
nsFileInputStream::Serialize(InputStreamParams& aParams,
                             FileDescriptorArray& aFileDescriptors)
{
    FileInputStreamParams params;

    if (NS_SUCCEEDED(DoPendingOpen())) {
        MOZ_ASSERT(mFD);
        FileHandleType fd = FileHandleType(PR_FileDesc2NativeHandle(mFD));
        NS_ASSERTION(fd, "This should never be null!");

        DebugOnly<FileDescriptor*> dbgFD = aFileDescriptors.AppendElement(fd);
        NS_ASSERTION(dbgFD->IsValid(), "Sending an invalid file descriptor!");

        params.fileDescriptorIndex() = aFileDescriptors.Length() - 1;

        Close();
    } else {
        NS_WARNING("This file has not been opened (or could not be opened). "
                   "Sending an invalid file descriptor to the other process!");

        params.fileDescriptorIndex() = UINT32_MAX;
    }

    int32_t behaviorFlags = mBehaviorFlags;

    // The receiving process (or thread) is going to have an open file
    // descriptor automatically so transferring this flag is meaningless.
    behaviorFlags &= ~nsIFileInputStream::DEFER_OPEN;

    params.behaviorFlags() = behaviorFlags;
    params.ioFlags() = mIOFlags;

    aParams = params;
}

bool
nsFileInputStream::Deserialize(const InputStreamParams& aParams,
                               const FileDescriptorArray& aFileDescriptors)
{
    NS_ASSERTION(!mFD, "Already have a file descriptor?!");
    NS_ASSERTION(mState == nsFileStreamBase::eUnitialized, "Deferring open?!");
    NS_ASSERTION(!mFile, "Should never have a file here!");
    NS_ASSERTION(!mPerm, "This should always be 0!");

    if (aParams.type() != InputStreamParams::TFileInputStreamParams) {
        NS_WARNING("Received unknown parameters from the other process!");
        return false;
    }

    const FileInputStreamParams& params = aParams.get_FileInputStreamParams();

    uint32_t fileDescriptorIndex = params.fileDescriptorIndex();

    FileDescriptor fd;
    if (fileDescriptorIndex < aFileDescriptors.Length()) {
        fd = aFileDescriptors[fileDescriptorIndex];
        NS_WARNING_ASSERTION(fd.IsValid(),
                             "Received an invalid file descriptor!");
    } else {
        NS_WARNING("Received a bad file descriptor index!");
    }

    if (fd.IsValid()) {
        auto rawFD = fd.ClonePlatformHandle();
        PRFileDesc* fileDesc = PR_ImportFile(PROsfd(rawFD.release()));
        if (!fileDesc) {
            NS_WARNING("Failed to import file handle!");
            return false;
        }
        mFD = fileDesc;
        mState = eOpened;
    } else {
      mState = eError;
      mErrorValue = NS_ERROR_FILE_NOT_FOUND;
    }

    mBehaviorFlags = params.behaviorFlags();

    if (!XRE_IsParentProcess()) {
        // A child process shouldn't close when it reads the end because it will
        // not be able to reopen the file later.
        mBehaviorFlags &= ~nsIFileInputStream::CLOSE_ON_EOF;

        // A child process will not be able to reopen the file so this flag is
        // meaningless.
        mBehaviorFlags &= ~nsIFileInputStream::REOPEN_ON_REWIND;
    }

    mIOFlags = params.ioFlags();

    return true;
}

Maybe<uint64_t>
nsFileInputStream::ExpectedSerializedLength()
{
    return Nothing();
}

bool
nsFileInputStream::IsCloneable() const
{
    // This inputStream is cloneable only if has been created using Init() and
    // it owns a nsIFile. This is not true when it is deserialized from IPC.
    return XRE_IsParentProcess() && mFile;
}

NS_IMETHODIMP
nsFileInputStream::GetCloneable(bool* aCloneable)
{
    *aCloneable = IsCloneable();
    return NS_OK;
}

NS_IMETHODIMP
nsFileInputStream::Clone(nsIInputStream** aResult)
{
    MOZ_ASSERT(IsCloneable());
    return NS_NewLocalFileInputStream(aResult, mFile, mIOFlags, mPerm,
                                      mBehaviorFlags);
}

////////////////////////////////////////////////////////////////////////////////
// nsFileOutputStream

NS_IMPL_ISUPPORTS_INHERITED(nsFileOutputStream,
                            nsFileStreamBase,
                            nsIOutputStream,
                            nsIFileOutputStream)

nsresult
nsFileOutputStream::Create(nsISupports *aOuter, REFNSIID aIID, void **aResult)
{
    NS_ENSURE_NO_AGGREGATION(aOuter);

    nsFileOutputStream* stream = new nsFileOutputStream();
    if (stream == nullptr)
        return NS_ERROR_OUT_OF_MEMORY;
    NS_ADDREF(stream);
    nsresult rv = stream->QueryInterface(aIID, aResult);
    NS_RELEASE(stream);
    return rv;
}

NS_IMETHODIMP
nsFileOutputStream::Init(nsIFile* file, int32_t ioFlags, int32_t perm,
                         int32_t behaviorFlags)
{
    NS_ENSURE_TRUE(mFD == nullptr, NS_ERROR_ALREADY_INITIALIZED);
    NS_ENSURE_TRUE(mState == eUnitialized || mState == eClosed,
                   NS_ERROR_ALREADY_INITIALIZED);

    mBehaviorFlags = behaviorFlags;
    mState = eUnitialized;

    if (ioFlags == -1)
        ioFlags = PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE;
    if (perm <= 0)
        perm = 0664;

    return MaybeOpen(file, ioFlags, perm,
                     mBehaviorFlags & nsIFileOutputStream::DEFER_OPEN);
}

NS_IMETHODIMP
nsFileOutputStream::Preallocate(int64_t aLength)
{
    if (!mFD) {
        return NS_ERROR_NOT_INITIALIZED;
    }

    if (!mozilla::fallocate(mFD, aLength)) {
        return NS_ERROR_FAILURE;
    }

    return NS_OK;
}

////////////////////////////////////////////////////////////////////////////////
// nsAtomicFileOutputStream

NS_IMPL_ISUPPORTS_INHERITED(nsAtomicFileOutputStream,
                            nsFileOutputStream,
                            nsISafeOutputStream,
                            nsIOutputStream,
                            nsIFileOutputStream)

NS_IMETHODIMP
nsAtomicFileOutputStream::Init(nsIFile* file, int32_t ioFlags, int32_t perm,
                             int32_t behaviorFlags)
{
    // While `PR_APPEND` is not supported, `-1` is used as `ioFlags` parameter
    // in some places, and `PR_APPEND | PR_TRUNCATE` does not require appending
    // to existing file. So, throw an exception only if `PR_APPEND` is
    // explicitly specified without `PR_TRUNCATE`.
    if ((ioFlags & PR_APPEND) && !(ioFlags & PR_TRUNCATE)) {
        return NS_ERROR_INVALID_ARG;
    }
    return nsFileOutputStream::Init(file, ioFlags, perm, behaviorFlags);
}

nsresult
nsAtomicFileOutputStream::DoOpen()
{
    // Make sure mOpenParams.localFile will be empty if we bail somewhere in
    // this function
    nsCOMPtr<nsIFile> file;
    file.swap(mOpenParams.localFile);

    if (!file) {
        return NS_ERROR_NOT_INITIALIZED;
    }
    nsresult rv = file->Exists(&mTargetFileExists);
    if (NS_FAILED(rv)) {
        NS_ERROR("Can't tell if target file exists");
        mTargetFileExists = true; // Safer to assume it exists - we just do more work.
    }

    // follow symlinks, for two reasons:
    // 1) if a user has deliberately set up a profile file as a symlink, we honor it
    // 2) to make the MoveToNative() in Finish() an atomic operation (which may not
    //    be the case if moving across directories on different filesystems).
    nsCOMPtr<nsIFile> tempResult;
    rv = file->Clone(getter_AddRefs(tempResult));
    if (NS_SUCCEEDED(rv)) {
        tempResult->SetFollowLinks(true);

        // XP_UNIX ignores SetFollowLinks(), so we have to normalize.
        if (mTargetFileExists) {
            tempResult->Normalize();
        }
    }

    if (NS_SUCCEEDED(rv) && mTargetFileExists) {
        // Abort if |file| is not writable; it won't work as an output stream.
        bool isWritable;
        if (NS_SUCCEEDED(file->IsWritable(&isWritable)) && !isWritable) {
            return NS_ERROR_FILE_ACCESS_DENIED;
        }

        uint32_t origPerm;
        if (NS_FAILED(file->GetPermissions(&origPerm))) {
            NS_ERROR("Can't get permissions of target file");
            origPerm = mOpenParams.perm;
        }

        // XXX What if |perm| is more restrictive then |origPerm|?
        // This leaves the user supplied permissions as they were.
        rv = tempResult->CreateUnique(nsIFile::NORMAL_FILE_TYPE, origPerm);
    }
    if (NS_SUCCEEDED(rv)) {
        // nsFileOutputStream::DoOpen will work on the temporary file, so we
        // prepare it and place it in mOpenParams.localFile.
        mOpenParams.localFile = tempResult;
        mTempFile = tempResult;
        mTargetFile = file;
        rv = nsFileOutputStream::DoOpen();
    }
    return rv;
}

NS_IMETHODIMP
nsAtomicFileOutputStream::Close()
{
    nsresult rv = nsFileOutputStream::Close();

    // the consumer doesn't want the original file overwritten -
    // so clean up by removing the temp file.
    if (mTempFile) {
        mTempFile->Remove(false);
        mTempFile = nullptr;
    }

    return rv;
}

NS_IMETHODIMP
nsAtomicFileOutputStream::Finish()
{
    nsresult rv = nsFileOutputStream::Close();

    // if there is no temp file, don't try to move it over the original target.
    // It would destroy the targetfile if close() is called twice.
    if (!mTempFile)
        return rv;

    // Only overwrite if everything was ok, and the temp file could be closed.
    if (NS_SUCCEEDED(mWriteResult) && NS_SUCCEEDED(rv)) {
        NS_ENSURE_STATE(mTargetFile);

        if (!mTargetFileExists) {
            // If the target file did not exist when we were initialized, then the
            // temp file we gave out was actually a reference to the target file.
            // since we succeeded in writing to the temp file (and hence succeeded
            // in writing to the target file), there is nothing more to do.
#ifdef DEBUG
            bool equal;
            if (NS_FAILED(mTargetFile->Equals(mTempFile, &equal)) || !equal)
                NS_WARNING("mTempFile not equal to mTargetFile");
#endif
        }
        else {
            nsAutoString targetFilename;
            rv = mTargetFile->GetLeafName(targetFilename);
            if (NS_SUCCEEDED(rv)) {
                // This will replace target.
                rv = mTempFile->MoveTo(nullptr, targetFilename);
                if (NS_FAILED(rv))
                    mTempFile->Remove(false);
            }
        }
    }
    else {
        mTempFile->Remove(false);

        // if writing failed, propagate the failure code to the caller.
        if (NS_FAILED(mWriteResult))
            rv = mWriteResult;
    }
    mTempFile = nullptr;
    return rv;
}

NS_IMETHODIMP
nsAtomicFileOutputStream::Write(const char *buf, uint32_t count, uint32_t *result)
{
    nsresult rv = nsFileOutputStream::Write(buf, count, result);
    if (NS_SUCCEEDED(mWriteResult)) {
        if (NS_FAILED(rv))
            mWriteResult = rv;
        else if (count != *result)
            mWriteResult = NS_ERROR_LOSS_OF_SIGNIFICANT_DATA;

        if (NS_FAILED(mWriteResult) && count > 0)
            NS_WARNING("writing to output stream failed! data may be lost");
    }
    return rv;
}

////////////////////////////////////////////////////////////////////////////////
// nsSafeFileOutputStream

NS_IMETHODIMP
nsSafeFileOutputStream::Finish()
{
    (void) Flush();
    return nsAtomicFileOutputStream::Finish();
}

////////////////////////////////////////////////////////////////////////////////
// nsFileStream

NS_IMPL_ISUPPORTS_INHERITED(nsFileStream,
                            nsFileStreamBase,
                            nsIInputStream,
                            nsIOutputStream,
                            nsIFileStream)

NS_IMETHODIMP
nsFileStream::Init(nsIFile* file, int32_t ioFlags, int32_t perm,
                   int32_t behaviorFlags)
{
    NS_ENSURE_TRUE(mFD == nullptr, NS_ERROR_ALREADY_INITIALIZED);
    NS_ENSURE_TRUE(mState == eUnitialized || mState == eClosed,
                   NS_ERROR_ALREADY_INITIALIZED);

    mBehaviorFlags = behaviorFlags;
    mState = eUnitialized;

    if (ioFlags == -1)
        ioFlags = PR_RDWR;
    if (perm <= 0)
        perm = 0;

    return MaybeOpen(file, ioFlags, perm,
                     mBehaviorFlags & nsIFileStream::DEFER_OPEN);
}

////////////////////////////////////////////////////////////////////////////////