gecko/netwerk/cache/nsDiskCacheStreams.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is nsDiskCacheStreams.cpp, released
 * June 13, 2001.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 2001
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Gordon Sheridan <gordon@netscape.com>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */


#include "nsDiskCache.h"
#include "nsDiskCacheDevice.h"
#include "nsDiskCacheStreams.h"
#include "nsCacheService.h"
#include "mozilla/FileUtils.h"



// Assumptions:
//      - cache descriptors live for life of streams
//      - streams will only be used by FileTransport,
//         they will not be directly accessible to clients
//      - overlapped I/O is NOT supported


/******************************************************************************
 *  nsDiskCacheInputStream
 *****************************************************************************/
#ifdef XP_MAC
#pragma mark nsDiskCacheInputStream
#endif
class nsDiskCacheInputStream : public nsIInputStream {

public:

    nsDiskCacheInputStream( nsDiskCacheStreamIO * parent,
                            PRFileDesc *          fileDesc,
                            const char *          buffer,
                            PRUint32              endOfStream);

    virtual ~nsDiskCacheInputStream();
    
    NS_DECL_ISUPPORTS
    NS_DECL_NSIINPUTSTREAM

private:
    nsDiskCacheStreamIO *           mStreamIO;  // backpointer to parent
    PRFileDesc *                    mFD;
    const char *                    mBuffer;
    PRUint32                        mStreamEnd;
    PRUint32                        mPos;       // stream position
    PRBool                          mClosed;
};


NS_IMPL_THREADSAFE_ISUPPORTS1(nsDiskCacheInputStream, nsIInputStream)


nsDiskCacheInputStream::nsDiskCacheInputStream( nsDiskCacheStreamIO * parent,
                                                PRFileDesc *          fileDesc,
                                                const char *          buffer,
                                                PRUint32              endOfStream)
    : mStreamIO(parent)
    , mFD(fileDesc)
    , mBuffer(buffer)
    , mStreamEnd(endOfStream)
    , mPos(0)
    , mClosed(PR_FALSE)
{
    NS_ADDREF(mStreamIO);
    mStreamIO->IncrementInputStreamCount();
}


nsDiskCacheInputStream::~nsDiskCacheInputStream()
{
    Close();
    mStreamIO->DecrementInputStreamCount();
    NS_RELEASE(mStreamIO);
}


NS_IMETHODIMP
nsDiskCacheInputStream::Close()
{
    if (!mClosed) {
        if (mFD) {
            (void) PR_Close(mFD);
            mFD = nsnull;
        }
        mClosed = PR_TRUE;
    }
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheInputStream::Available(PRUint32 * bytesAvailable)
{
    if (mClosed)  return NS_BASE_STREAM_CLOSED;
    if (mStreamEnd < mPos)  return NS_ERROR_UNEXPECTED;
    
    *bytesAvailable = mStreamEnd - mPos;
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheInputStream::Read(char * buffer, PRUint32 count, PRUint32 * bytesRead)
{
    *bytesRead = 0;

    if (mClosed)
        return NS_OK;
    
    if (mPos == mStreamEnd)  return NS_OK;
    if (mPos > mStreamEnd)   return NS_ERROR_UNEXPECTED;
    
    if (mFD) {
        // just read from file
        PRInt32  result = PR_Read(mFD, buffer, count);
        if (result < 0)  return  NS_ErrorAccordingToNSPR();
        
        mPos += (PRUint32)result;
        *bytesRead = (PRUint32)result;
        
    } else if (mBuffer) {
        // read data from mBuffer
        if (count > mStreamEnd - mPos)
            count = mStreamEnd - mPos;
    
        memcpy(buffer, mBuffer + mPos, count);
        mPos += count;
        *bytesRead = count;
    } else {
        // no data source for input stream
    }

    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheInputStream::ReadSegments(nsWriteSegmentFun writer,
                                     void *            closure,
                                     PRUint32          count,
                                     PRUint32 *        bytesRead)
{
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheInputStream::IsNonBlocking(PRBool * nonBlocking)
{
    *nonBlocking = PR_FALSE;
    return NS_OK;
}


/******************************************************************************
 *  nsDiskCacheOutputStream
 *****************************************************************************/
#ifdef XP_MAC
#pragma mark -
#pragma mark nsDiskCacheOutputStream
#endif
class nsDiskCacheOutputStream : public nsIOutputStream {
public:
    nsDiskCacheOutputStream( nsDiskCacheStreamIO * parent);
    virtual ~nsDiskCacheOutputStream();

    NS_DECL_ISUPPORTS
    NS_DECL_NSIOUTPUTSTREAM

    void ReleaseStreamIO() { NS_IF_RELEASE(mStreamIO); }

private:
    nsDiskCacheStreamIO *           mStreamIO;  // backpointer to parent
    PRBool                          mClosed;
};


NS_IMPL_THREADSAFE_ISUPPORTS1(nsDiskCacheOutputStream,
                              nsIOutputStream)

nsDiskCacheOutputStream::nsDiskCacheOutputStream( nsDiskCacheStreamIO * parent)
    : mStreamIO(parent)
    , mClosed(PR_FALSE)
{
    NS_ADDREF(mStreamIO);
}


nsDiskCacheOutputStream::~nsDiskCacheOutputStream()
{
    Close();
    ReleaseStreamIO();
}


NS_IMETHODIMP
nsDiskCacheOutputStream::Close()
{
    if (!mClosed) {
        mClosed = PR_TRUE;
        // tell parent streamIO we are closing
        mStreamIO->CloseOutputStream(this);
    }
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheOutputStream::Flush()
{
    if (mClosed)  return NS_BASE_STREAM_CLOSED;
    // yeah, yeah, well get to it...eventually...
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheOutputStream::Write(const char *buf, PRUint32 count, PRUint32 *bytesWritten)
{
    if (mClosed)  return NS_BASE_STREAM_CLOSED;
    return mStreamIO->Write(buf, count, bytesWritten);
}


NS_IMETHODIMP
nsDiskCacheOutputStream::WriteFrom(nsIInputStream *inStream, PRUint32 count, PRUint32 *bytesWritten)
{
    NS_NOTREACHED("WriteFrom");
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheOutputStream::WriteSegments( nsReadSegmentFun reader,
                                        void *           closure,
                                        PRUint32         count,
                                        PRUint32 *       bytesWritten)
{
    NS_NOTREACHED("WriteSegments");
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheOutputStream::IsNonBlocking(PRBool * nonBlocking)
{
    *nonBlocking = PR_FALSE;
    return NS_OK;
}



/******************************************************************************
 *  nsDiskCacheStreamIO
 *****************************************************************************/
#ifdef XP_MAC
#pragma mark -
#pragma mark nsDiskCacheStreamIO
#endif

NS_IMPL_THREADSAFE_ISUPPORTS0(nsDiskCacheStreamIO)

// we pick 16k as the max buffer size because that is the threshold above which
//      we are unable to store the data in the cache block files
//      see nsDiskCacheMap.[cpp,h]
#define kMaxBufferSize      (16 * 1024)

nsDiskCacheStreamIO::nsDiskCacheStreamIO(nsDiskCacheBinding *   binding)
    : mBinding(binding)
    , mOutStream(nsnull)
    , mInStreamCount(0)
    , mFD(nsnull)
    , mStreamPos(0)
    , mStreamEnd(0)
    , mBufPos(0)
    , mBufEnd(0)
    , mBufSize(0)
    , mBufDirty(PR_FALSE)
    , mBuffer(nsnull)
{
    mDevice = (nsDiskCacheDevice *)mBinding->mCacheEntry->CacheDevice();

    // acquire "death grip" on cache service
    nsCacheService *service = nsCacheService::GlobalInstance();
    NS_ADDREF(service);
}


nsDiskCacheStreamIO::~nsDiskCacheStreamIO()
{
    Close();

    // release "death grip" on cache service
    nsCacheService *service = nsCacheService::GlobalInstance();
    NS_RELEASE(service);
}


void
nsDiskCacheStreamIO::Close()
{
    // this should only be called from our destructor
    // no one is interested in us anymore, so we don't need to grab any locks
    
    // assert streams closed
    NS_ASSERTION(!mOutStream, "output stream still open");
    NS_ASSERTION(mInStreamCount == 0, "input stream still open");
    NS_ASSERTION(!mFD, "file descriptor not closed");

    DeleteBuffer();
}


// NOTE: called with service lock held
nsresult
nsDiskCacheStreamIO::GetInputStream(PRUint32 offset, nsIInputStream ** inputStream)
{
    NS_ENSURE_ARG_POINTER(inputStream);
    NS_ENSURE_TRUE(offset == 0, NS_ERROR_NOT_IMPLEMENTED);

    *inputStream = nsnull;
    
    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;

    if (mOutStream) {
        NS_WARNING("already have an output stream open");
        return NS_ERROR_NOT_AVAILABLE;
    }

    nsresult            rv;
    PRFileDesc *        fd = nsnull;

    mStreamEnd = mBinding->mCacheEntry->DataSize();
    if (mStreamEnd == 0) {
        // there's no data to read
        NS_ASSERTION(!mBinding->mRecord.DataLocationInitialized(), "storage allocated for zero data size");
    } else if (mBinding->mRecord.DataFile() == 0) {
        // open file desc for data
        rv = OpenCacheFile(PR_RDONLY, &fd);
        if (NS_FAILED(rv))  return rv;  // unable to open file        
        NS_ASSERTION(fd, "cache stream lacking open file.");
            
    } else if (!mBuffer) {
        // read block file for data
        rv = ReadCacheBlocks();
        if (NS_FAILED(rv))  return rv;
    }
    // else, mBuffer already contains all of the data (left over from a
    // previous block-file read or write).

    NS_ASSERTION(!(fd && mBuffer), "ambiguous data sources for input stream");

    // create a new input stream
    nsDiskCacheInputStream * inStream = new nsDiskCacheInputStream(this, fd, mBuffer, mStreamEnd);
    if (!inStream)  return NS_ERROR_OUT_OF_MEMORY;
    
    NS_ADDREF(*inputStream = inStream);
    return NS_OK;
}


// NOTE: called with service lock held
nsresult
nsDiskCacheStreamIO::GetOutputStream(PRUint32 offset, nsIOutputStream ** outputStream)
{
    NS_ENSURE_ARG_POINTER(outputStream);
    *outputStream = nsnull;

    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;
        
    NS_ASSERTION(!mOutStream, "already have an output stream open");
    NS_ASSERTION(mInStreamCount == 0, "we already have input streams open");
    if (mOutStream || mInStreamCount)  return NS_ERROR_NOT_AVAILABLE;
    
    // mBuffer lazily allocated, but might exist if a previous stream already
    // created one.
    mBufPos    = 0;
    mStreamPos = 0;
    mStreamEnd = mBinding->mCacheEntry->DataSize();

    nsresult rv;
    if (offset) {
        rv = Seek(PR_SEEK_SET, offset);
        if (NS_FAILED(rv)) return rv;
    }
    rv = SetEOF();
    if (NS_FAILED(rv)) return rv;

    // create a new output stream
    mOutStream = new nsDiskCacheOutputStream(this);
    if (!mOutStream)  return NS_ERROR_OUT_OF_MEMORY;
    
    NS_ADDREF(*outputStream = mOutStream);
    return NS_OK;
}

void
nsDiskCacheStreamIO::ClearBinding()
{
    if (mBinding && mOutStream)
        Flush();
    mBinding = nsnull;
}

nsresult
nsDiskCacheStreamIO::CloseOutputStream(nsDiskCacheOutputStream *  outputStream)
{
    nsCacheServiceAutoLock lock; // grab service lock
    nsresult   rv;

    if (outputStream != mOutStream) {
        NS_WARNING("mismatched output streams");
        return NS_ERROR_UNEXPECTED;
    }
    
    // output stream is closing
    if (!mBinding) {    // if we're severed, just clear member variables
        NS_ASSERTION(!mBufDirty, "oops");
        mOutStream = nsnull;
        outputStream->ReleaseStreamIO();
        return NS_ERROR_NOT_AVAILABLE;
    }

    rv = Flush();
    if (NS_FAILED(rv))
        NS_WARNING("Flush() failed");

    mOutStream = nsnull;
    return rv;
}

nsresult
nsDiskCacheStreamIO::Flush()
{
    NS_ASSERTION(mBinding, "oops");

    CACHE_LOG_DEBUG(("CACHE: Flush [%x doomed=%u]\n",
        mBinding->mRecord.HashNumber(), mBinding->mDoomed));

    if (!mBufDirty)
        return NS_OK;

    // write data to cache blocks, or flush mBuffer to file
    nsDiskCacheMap *cacheMap = mDevice->CacheMap();  // get map reference
    nsresult rv;
    
    if ((mStreamEnd > kMaxBufferSize) ||
        (mBinding->mCacheEntry->StoragePolicy() == nsICache::STORE_ON_DISK_AS_FILE)) {
        // make sure we save as separate file
        rv = FlushBufferToFile();       // will initialize DataFileLocation() if necessary

        if (mFD) {
          // Update the file size of the disk file in the cache
          UpdateFileSize();

          // close file descriptor
          (void) PR_Close(mFD);
          mFD = nsnull;
        }
        else
          NS_WARNING("no file descriptor");

        // close mFD first if possible before returning if FlushBufferToFile
        // failed
        NS_ENSURE_SUCCESS(rv, rv);

        // since the data location is on disk as a single file, the only value
        // in keeping mBuffer around is to avoid an extra malloc the next time
        // we need to write to this file.  reading will use a file descriptor.
        // therefore, it's probably not worth optimizing for the subsequent
        // write, so we unconditionally delete mBuffer here.
        DeleteBuffer();

    } else {
        // store data (if any) in cache block files

        mBufDirty = PR_FALSE;

        // delete existing storage
        nsDiskCacheRecord * record = &mBinding->mRecord;
        if (record->DataLocationInitialized()) {
            rv = cacheMap->DeleteStorage(record, nsDiskCache::kData);
            if (NS_FAILED(rv)) {
                NS_WARNING("cacheMap->DeleteStorage() failed.");
                cacheMap->DeleteRecord(record);
                return  rv;
            }
        }
    
        // flush buffer to block files
        if (mStreamEnd > 0) {
            rv = cacheMap->WriteDataCacheBlocks(mBinding, mBuffer, mBufEnd);
            if (NS_FAILED(rv)) {
                NS_WARNING("WriteDataCacheBlocks() failed.");
                nsCacheService::DoomEntry(mBinding->mCacheEntry);
                return rv;
            }
        }
    }
    
    // XXX do we need this here?  WriteDataCacheBlocks() calls UpdateRecord()
    // update cache map if entry isn't doomed
    if (!mBinding->mDoomed) {
        rv = cacheMap->UpdateRecord(&mBinding->mRecord);
        if (NS_FAILED(rv)) {
            NS_WARNING("cacheMap->UpdateRecord() failed.");
            return rv;   // XXX doom cache entry
        }
    }
    
    return NS_OK;
}


// assumptions:
//      only one thread writing at a time
//      never have both output and input streams open
//      OnDataSizeChanged() will have already been called to update entry->DataSize()

nsresult
nsDiskCacheStreamIO::Write( const char * buffer,
                            PRUint32     count,
                            PRUint32 *   bytesWritten)
{
    nsresult    rv = NS_OK;
    nsCacheServiceAutoLock lock; // grab service lock
    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;

    if (mInStreamCount) {
        // we have open input streams already
        // this is an error until we support overlapped I/O
        NS_WARNING("Attempting to write to cache entry with open input streams.\n");
        return NS_ERROR_NOT_AVAILABLE;
    }

    NS_ASSERTION(count, "Write called with count of zero");
    NS_ASSERTION(mBufPos <= mBufEnd, "streamIO buffer corrupted");

    PRUint32 bytesLeft = count;
    PRBool   flushed = PR_FALSE;
    
    while (bytesLeft) {
        if (mBufPos == mBufSize) {
            if (mBufSize < kMaxBufferSize) {
                mBufSize = kMaxBufferSize;
                char *buffer = mBuffer;

                mBuffer  = (char *) realloc(mBuffer, mBufSize);
                if (!mBuffer) {
                    free(buffer);
                    mBufSize = 0;
                    break;
                }
            } else {
                nsresult rv = FlushBufferToFile();
                if (NS_FAILED(rv))  break;
                flushed = PR_TRUE;
            }
        }
        
        PRUint32 chunkSize = bytesLeft;
        if (chunkSize > (mBufSize - mBufPos))
            chunkSize =  mBufSize - mBufPos;
        
        memcpy(mBuffer + mBufPos, buffer, chunkSize);
        mBufDirty = PR_TRUE;
        mBufPos += chunkSize;
        bytesLeft -= chunkSize;
        buffer += chunkSize;
        
        if (mBufEnd < mBufPos)
            mBufEnd = mBufPos;
    }
    if (bytesLeft) {
        *bytesWritten = 0;
        return NS_ERROR_FAILURE;
    }
    *bytesWritten = count;

    // update mStreamPos, mStreamEnd
    mStreamPos += count;
    if (mStreamEnd < mStreamPos) {
        mStreamEnd = mStreamPos;
        NS_ASSERTION(mBinding->mCacheEntry->DataSize() == mStreamEnd, "bad stream");

        // If we have flushed to a file, update the file size
        if (flushed && mFD) {
            UpdateFileSize();
        }
    }
    
    return rv;
}


void
nsDiskCacheStreamIO::UpdateFileSize()
{
    NS_ASSERTION(mFD, "nsDiskCacheStreamIO::UpdateFileSize should not have been called");
    
    nsDiskCacheRecord * record = &mBinding->mRecord;
    const PRUint32      oldSizeK  = record->DataFileSize();
    const PRUint32      newSizeK  = (mStreamEnd + 0x03FF) >> 10;
    
    if (newSizeK == oldSizeK)  return;
    
    record->SetDataFileSize(newSizeK);

    // update cache size totals
    nsDiskCacheMap * cacheMap = mDevice->CacheMap();
    cacheMap->DecrementTotalSize(oldSizeK);       // decrement old size
    cacheMap->IncrementTotalSize(newSizeK);       // increment new size
    
    if (!mBinding->mDoomed) {
        nsresult rv = cacheMap->UpdateRecord(record);
        if (NS_FAILED(rv)) {
            NS_WARNING("cacheMap->UpdateRecord() failed.");
            // XXX doom cache entry?
        }
    }
}


nsresult
nsDiskCacheStreamIO::OpenCacheFile(PRIntn flags, PRFileDesc ** fd)
{
    NS_ENSURE_ARG_POINTER(fd);
    
    nsresult         rv;
    nsDiskCacheMap * cacheMap = mDevice->CacheMap();
    
    rv = cacheMap->GetLocalFileForDiskCacheRecord(&mBinding->mRecord,
                                                  nsDiskCache::kData,
                                                  !!(flags & PR_CREATE_FILE),
                                                  getter_AddRefs(mLocalFile));
    if (NS_FAILED(rv))  return rv;
    
    // create PRFileDesc for input stream - the 00600 is just for consistency
    rv = mLocalFile->OpenNSPRFileDesc(flags, 00600, fd);
    if (NS_FAILED(rv))  return rv;  // unable to open file

    return NS_OK;
}


nsresult
nsDiskCacheStreamIO::ReadCacheBlocks()
{
    NS_ASSERTION(mStreamEnd == mBinding->mCacheEntry->DataSize(), "bad stream");
    NS_ASSERTION(mStreamEnd <= kMaxBufferSize, "data too large for buffer");

    nsDiskCacheRecord * record = &mBinding->mRecord;
    if (!record->DataLocationInitialized()) return NS_OK;

    NS_ASSERTION(record->DataFile() != kSeparateFile, "attempt to read cache blocks on separate file");

    if (!mBuffer) {
        // allocate buffer
        mBuffer = (char *) malloc(mStreamEnd);
        if (!mBuffer) {
            return NS_ERROR_OUT_OF_MEMORY;
        }
        mBufSize = mStreamEnd;
    }
    
    // read data stored in cache block files
    nsDiskCacheMap *map = mDevice->CacheMap();  // get map reference
    nsresult rv = map->ReadDataCacheBlocks(mBinding, mBuffer, mStreamEnd);
    if (NS_FAILED(rv)) return rv;

    // update streamIO variables
    mBufPos = 0;
    mBufEnd = mStreamEnd;
    
    return NS_OK;
}


nsresult
nsDiskCacheStreamIO::FlushBufferToFile()
{
    nsresult  rv;
    nsDiskCacheRecord * record = &mBinding->mRecord;
    
    if (!mFD) {
        if (record->DataLocationInitialized() && (record->DataFile() > 0)) {
            // remove cache block storage
            nsDiskCacheMap * cacheMap = mDevice->CacheMap();
            rv = cacheMap->DeleteStorage(record, nsDiskCache::kData);
            if (NS_FAILED(rv))  return rv;
        }
        record->SetDataFileGeneration(mBinding->mGeneration);
        
        // allocate file
        rv = OpenCacheFile(PR_RDWR | PR_CREATE_FILE, &mFD);
        if (NS_FAILED(rv))  return rv;

        PRInt64 dataSize = mBinding->mCacheEntry->PredictedDataSize();
// Appears to cause bug 617123?  Disabled for now.
#if 0
        if (dataSize != -1)
            mozilla::fallocate(mFD, PR_MIN(dataSize, kPreallocateLimit));
#endif
    }
    
    // write buffer
    PRInt32 bytesWritten = PR_Write(mFD, mBuffer, mBufEnd);
    if (PRUint32(bytesWritten) != mBufEnd) {
        NS_WARNING("failed to flush all data");
        return NS_ERROR_UNEXPECTED;     // NS_ErrorAccordingToNSPR()
    }
    mBufDirty = PR_FALSE;
    
    // reset buffer
    mBufPos = 0;
    mBufEnd = 0;
    
    return NS_OK;
}


void
nsDiskCacheStreamIO::DeleteBuffer()
{
    if (mBuffer) {
        NS_ASSERTION(!mBufDirty, "deleting dirty buffer");
        free(mBuffer);
        mBuffer = nsnull;
        mBufPos = 0;
        mBufEnd = 0;
        mBufSize = 0;
    }
}


// NOTE: called with service lock held
nsresult
nsDiskCacheStreamIO::Seek(PRInt32 whence, PRInt32 offset)
{
    PRInt32  newPos;
    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;

    if (PRUint32(offset) > mStreamEnd)  return NS_ERROR_FAILURE;
 
    if (mBinding->mRecord.DataLocationInitialized()) {
        if (mBinding->mRecord.DataFile() == 0) {
            if (!mFD) {
                // we need an mFD, we better open it now
                nsresult rv = OpenCacheFile(PR_RDWR | PR_CREATE_FILE, &mFD);
                if (NS_FAILED(rv))  return rv;
            }
        }
    }

    if (mFD) {
        // do we have data in the buffer that needs to be flushed?
        if (mBufDirty) {
            // XXX optimization: are we just moving within the current buffer?
            nsresult rv = FlushBufferToFile();
            if (NS_FAILED(rv))  return rv;
        }
    
        newPos = PR_Seek(mFD, offset, (PRSeekWhence)whence);
        if (newPos == -1)
            return NS_ErrorAccordingToNSPR();
        
        mStreamPos = (PRUint32) newPos;
        mBufPos = 0;
        mBufEnd = 0;
        return NS_OK;
    }
    
    // else, seek in mBuffer
    
    switch(whence) {
        case PR_SEEK_SET:
            newPos = offset;
            break;
        
        case PR_SEEK_CUR:   // relative from current posistion
            newPos = offset + (PRUint32)mStreamPos;
            break;
            
        case PR_SEEK_END:   // relative from end
            newPos = offset + (PRUint32)mBufEnd;
            break;
        
        default:
            return NS_ERROR_INVALID_ARG;
    }

    // read data into mBuffer if not read yet.
    if (mStreamEnd && !mBufEnd) {
        if (newPos > 0) {
            nsresult rv = ReadCacheBlocks();
            if (NS_FAILED(rv))  return rv;
        }
    }

    // stream buffer sanity checks
    NS_ASSERTION(mBufEnd <= kMaxBufferSize, "bad stream");
    NS_ASSERTION(mBufPos <= mBufEnd,     "bad stream");
    NS_ASSERTION(mStreamPos == mBufPos,  "bad stream");
    NS_ASSERTION(mStreamEnd == mBufEnd,  "bad stream");
    
    if ((newPos < 0) || (PRUint32(newPos) > mBufEnd)) {
        NS_WARNING("seek offset out of range");
        return NS_ERROR_INVALID_ARG;
    }

    mStreamPos = newPos;
    mBufPos    = newPos;
    return NS_OK;
}


// called only from nsDiskCacheOutputStream::Tell
nsresult
nsDiskCacheStreamIO::Tell(PRUint32 * result)
{
    NS_ENSURE_ARG_POINTER(result);
    *result = mStreamPos;
    return NS_OK;
}


// NOTE: called with service lock held
nsresult
nsDiskCacheStreamIO::SetEOF()
{
    nsresult    rv;
    PRBool      needToCloseFD = PR_FALSE;

    NS_ASSERTION(mStreamPos <= mStreamEnd, "bad stream");
    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;
    
    if (mBinding->mRecord.DataLocationInitialized()) {
        if (mBinding->mRecord.DataFile() == 0) {
            if (!mFD) {
                // we need an mFD, we better open it now
                rv = OpenCacheFile(PR_RDWR | PR_CREATE_FILE, &mFD);
                if (NS_FAILED(rv))  return rv;
                needToCloseFD = PR_TRUE;
            }
        } else {
            // data in cache block files
            if ((mStreamPos != 0) && (mStreamPos != mBufPos)) {
                // only read data if there will be some left after truncation
                rv = ReadCacheBlocks();
                if (NS_FAILED(rv))  return rv;
            }

            // We need to make sure we reflect this change in Flush().
            // In particular, if mStreamPos is 0 and we never write to
            // the buffer, we want the storage to be deleted.
            mBufDirty = PR_TRUE;
        }
    }
    
    if (mFD) {
        rv = nsDiskCache::Truncate(mFD, mStreamPos);
#ifdef DEBUG
        PRUint32 oldSizeK = (mStreamEnd + 0x03FF) >> 10;
        NS_ASSERTION(mBinding->mRecord.DataFileSize() == oldSizeK, "bad disk cache entry size");
    } else {
        // data stored in buffer.
        NS_ASSERTION(mStreamEnd <= kMaxBufferSize, "buffer truncation inadequate");
        NS_ASSERTION(mBufPos == mStreamPos, "bad stream");
        NS_ASSERTION(mBuffer ? mBufEnd == mStreamEnd : PR_TRUE, "bad stream");
#endif
    }

    NS_ASSERTION(mStreamEnd == mBinding->mCacheEntry->DataSize(), "cache entry not updated");
    // we expect nsCacheEntryDescriptor::TransportWrapper::OpenOutputStream()
    // to eventually update the cache entry    

    mStreamEnd  = mStreamPos;
    mBufEnd     = mBufPos;
    
    if (mFD) {
        UpdateFileSize();
        if (needToCloseFD) {
            (void) PR_Close(mFD);
            mFD = nsnull;
        } 
    }

    return  NS_OK;
}