summaryrefslogtreecommitdiff
path: root/netwerk/cache/nsDiskCacheStreams.cpp
blob: d58cca7fd8bec5c0ef345bb4f21425158c11e4ab (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
/* -*- 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 "nsCache.h"
#include "nsDiskCache.h"
#include "nsDiskCacheDevice.h"
#include "nsDiskCacheStreams.h"
#include "nsCacheService.h"
#include "mozilla/FileUtils.h"
#include "nsThreadUtils.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Telemetry.h"
#include "mozilla/TimeStamp.h"
#include <algorithm>

// 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)

// 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
 *****************************************************************************/
class nsDiskCacheInputStream : public nsIInputStream {

public:

    nsDiskCacheInputStream( nsDiskCacheStreamIO * parent,
                            PRFileDesc *          fileDesc,
                            const char *          buffer,
                            uint32_t              endOfStream);

    NS_DECL_THREADSAFE_ISUPPORTS
    NS_DECL_NSIINPUTSTREAM

private:
    virtual ~nsDiskCacheInputStream();

    nsDiskCacheStreamIO *           mStreamIO;  // backpointer to parent
    PRFileDesc *                    mFD;
    const char *                    mBuffer;
    uint32_t                        mStreamEnd;
    uint32_t                        mPos;       // stream position
    bool                            mClosed;
};


NS_IMPL_ISUPPORTS(nsDiskCacheInputStream, nsIInputStream)


nsDiskCacheInputStream::nsDiskCacheInputStream( nsDiskCacheStreamIO * parent,
                                                PRFileDesc *          fileDesc,
                                                const char *          buffer,
                                                uint32_t              endOfStream)
    : mStreamIO(parent)
    , mFD(fileDesc)
    , mBuffer(buffer)
    , mStreamEnd(endOfStream)
    , mPos(0)
    , mClosed(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 = nullptr;
        }
        mClosed = true;
    }
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheInputStream::Available(uint64_t * 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, uint32_t count, uint32_t * bytesRead)
{
    *bytesRead = 0;

    if (mClosed) {
        CACHE_LOG_DEBUG(("CACHE: nsDiskCacheInputStream::Read "
                         "[stream=%p] stream was closed",
                         this, buffer, count));
        return NS_OK;
    }
    
    if (mPos == mStreamEnd) {
        CACHE_LOG_DEBUG(("CACHE: nsDiskCacheInputStream::Read "
                         "[stream=%p] stream at end of file",
                         this, buffer, count));
        return NS_OK;
    }
    if (mPos > mStreamEnd) {
        CACHE_LOG_DEBUG(("CACHE: nsDiskCacheInputStream::Read "
                         "[stream=%p] stream past end of file (!)",
                         this, buffer, count));
        return NS_ERROR_UNEXPECTED;
    }
    
    if (count > mStreamEnd - mPos)
        count = mStreamEnd - mPos;

    if (mFD) {
        // just read from file
        int32_t  result = PR_Read(mFD, buffer, count);
        if (result < 0) {
            nsresult rv = NS_ErrorAccordingToNSPR();
            CACHE_LOG_DEBUG(("CACHE: nsDiskCacheInputStream::Read PR_Read failed"
                             "[stream=%p, rv=%d, NSPR error %s",
                             this, int(rv), PR_ErrorToName(PR_GetError())));
            return rv;
        }
        
        mPos += (uint32_t)result;
        *bytesRead = (uint32_t)result;
        
    } else if (mBuffer) {
        // read data from mBuffer
        memcpy(buffer, mBuffer + mPos, count);
        mPos += count;
        *bytesRead = count;
    } else {
        // no data source for input stream
    }

    CACHE_LOG_DEBUG(("CACHE: nsDiskCacheInputStream::Read "
                     "[stream=%p, count=%ud, byteRead=%ud] ",
                     this, unsigned(count), unsigned(*bytesRead)));
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheInputStream::ReadSegments(nsWriteSegmentFun writer,
                                     void *            closure,
                                     uint32_t          count,
                                     uint32_t *        bytesRead)
{
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheInputStream::IsNonBlocking(bool * nonBlocking)
{
    *nonBlocking = false;
    return NS_OK;
}




/******************************************************************************
 *  nsDiskCacheStreamIO
 *****************************************************************************/
NS_IMPL_ISUPPORTS(nsDiskCacheStreamIO, nsIOutputStream)

nsDiskCacheStreamIO::nsDiskCacheStreamIO(nsDiskCacheBinding *   binding)
    : mBinding(binding)
    , mInStreamCount(0)
    , mFD(nullptr)
    , mStreamEnd(0)
    , mBufSize(0)
    , mBuffer(nullptr)
    , mOutputStreamIsOpen(false)
{
    mDevice = (nsDiskCacheDevice *)mBinding->mCacheEntry->CacheDevice();

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


nsDiskCacheStreamIO::~nsDiskCacheStreamIO()
{
    nsCacheService::AssertOwnsLock();

    // Close the outputstream
    if (mBinding && mOutputStreamIsOpen) {
        (void)CloseOutputStream();
    }

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

    // assert streams closed
    NS_ASSERTION(!mOutputStreamIsOpen, "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(uint32_t offset, nsIInputStream ** inputStream)
{
    NS_ENSURE_ARG_POINTER(inputStream);
    NS_ENSURE_TRUE(offset == 0, NS_ERROR_NOT_IMPLEMENTED);

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

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

    nsresult            rv;
    PRFileDesc *        fd = nullptr;

    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(mStreamEnd);
        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(uint32_t offset, nsIOutputStream ** outputStream)
{
    NS_ENSURE_ARG_POINTER(outputStream);
    *outputStream = nullptr;

    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;
        
    NS_ASSERTION(!mOutputStreamIsOpen, "already have an output stream open");
    NS_ASSERTION(mInStreamCount == 0, "we already have input streams open");
    if (mOutputStreamIsOpen || mInStreamCount)  return NS_ERROR_NOT_AVAILABLE;
    
    mStreamEnd = mBinding->mCacheEntry->DataSize();

    // Inits file or buffer and truncate at the desired offset
    nsresult rv = SeekAndTruncate(offset);
    if (NS_FAILED(rv)) return rv;

    mOutputStreamIsOpen = true;
    NS_ADDREF(*outputStream = this);
    return NS_OK;
}

nsresult
nsDiskCacheStreamIO::ClearBinding()
{
    nsresult rv = NS_OK;
    if (mBinding && mOutputStreamIsOpen)
        rv = CloseOutputStream();
    mBinding = nullptr;
    return rv;
}

NS_IMETHODIMP
nsDiskCacheStreamIO::Close()
{
    if (!mOutputStreamIsOpen) return NS_OK;

    // grab service lock
    nsCacheServiceAutoLock lock;

    if (!mBinding) {    // if we're severed, just clear member variables
        mOutputStreamIsOpen = false;
        return NS_ERROR_NOT_AVAILABLE;
    }

    nsresult rv = CloseOutputStream();
    if (NS_FAILED(rv))
        NS_WARNING("CloseOutputStream() failed");

    return rv;
}

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

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

    // Mark outputstream as closed, even if saving the stream fails
    mOutputStreamIsOpen = false;

    // When writing to a file, just close the file
    if (mFD) {
        (void) PR_Close(mFD);
        mFD = nullptr;
        return NS_OK;
    }

    // write data to cache blocks, or flush mBuffer to file
    NS_ASSERTION(mStreamEnd <= kMaxBufferSize, "stream is bigger than buffer");

    nsDiskCacheMap *cacheMap = mDevice->CacheMap();  // get map reference
    nsDiskCacheRecord * record = &mBinding->mRecord;
    nsresult rv = NS_OK;

    // delete existing storage
    if (record->DataLocationInitialized()) {
        rv = cacheMap->DeleteStorage(record, nsDiskCache::kData);
        NS_ENSURE_SUCCESS(rv, rv);

        // Only call UpdateRecord when there is no data to write,
        // because WriteDataCacheBlocks / FlushBufferToFile calls it.
        if ((mStreamEnd == 0) && (!mBinding->mDoomed)) {
            rv = cacheMap->UpdateRecord(record);
            if (NS_FAILED(rv)) {
                NS_WARNING("cacheMap->UpdateRecord() failed.");
                return rv;   // XXX doom cache entry
            }
        }
    }
  
    if (mStreamEnd == 0) return NS_OK;     // nothing to write
 
    // try to write to the cache blocks
    rv = cacheMap->WriteDataCacheBlocks(mBinding, mBuffer, mStreamEnd);
    if (NS_FAILED(rv)) {
        NS_WARNING("WriteDataCacheBlocks() failed.");

        // failed to store in cacheblocks, save as separate file
        rv = FlushBufferToFile(); // initializes DataFileLocation() if necessary
        if (mFD) {
            UpdateFileSize();
            (void) PR_Close(mFD);
            mFD = nullptr;
        }
        else
            NS_WARNING("no file descriptor");
    }
   
    return rv;
}


// 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()

NS_IMETHODIMP
nsDiskCacheStreamIO::Write( const char * buffer,
                            uint32_t     count,
                            uint32_t *   bytesWritten)
{
    NS_ENSURE_ARG_POINTER(buffer);
    NS_ENSURE_ARG_POINTER(bytesWritten);
    if (!mOutputStreamIsOpen) return NS_BASE_STREAM_CLOSED;

    *bytesWritten = 0;  // always initialize to zero in case of errors

    NS_ASSERTION(count, "Write called with count of zero");
    if (count == 0) {
        return NS_OK;   // nothing to write
    }

    // grab service lock
    nsCacheServiceAutoLock 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;
    }

    // Not writing to file, and it will fit in the cachedatablocks?
    if (!mFD && (mStreamEnd + count <= kMaxBufferSize)) {

        // We have more data than the current buffer size?
        if ((mStreamEnd + count > mBufSize) && (mBufSize < kMaxBufferSize)) {
            // Increase buffer to the maximum size.
            mBuffer = (char *) moz_xrealloc(mBuffer, kMaxBufferSize);
            mBufSize = kMaxBufferSize;
        }

        // Store in the buffer but only if it fits
        if (mStreamEnd + count <= mBufSize) {
            memcpy(mBuffer + mStreamEnd, buffer, count);
            mStreamEnd += count;
            *bytesWritten = count;
            return NS_OK;
        }
    }

    // There are more bytes than fit in the buffer/cacheblocks, switch to file
    if (!mFD) {
        // Opens a cache file and write the buffer to it
        nsresult rv = FlushBufferToFile();
        if (NS_FAILED(rv)) {
            return rv;
        }
    }
    // Write directly to the file
    if (PR_Write(mFD, buffer, count) != (int32_t)count) {
        NS_WARNING("failed to write all data");
        return NS_ERROR_UNEXPECTED;     // NS_ErrorAccordingToNSPR()
    }
    mStreamEnd += count;
    *bytesWritten = count;

    UpdateFileSize();
    NS_ASSERTION(mBinding->mCacheEntry->DataSize() == mStreamEnd, "bad stream");

    return NS_OK;
}


void
nsDiskCacheStreamIO::UpdateFileSize()
{
    NS_ASSERTION(mFD, "nsDiskCacheStreamIO::UpdateFileSize should not have been called");
    
    nsDiskCacheRecord * record = &mBinding->mRecord;
    const uint32_t      oldSizeK  = record->DataFileSize();
    uint32_t            newSizeK  = (mStreamEnd + 0x03FF) >> 10;

    // make sure the size won't overflow (bug #651100)
    if (newSizeK > kMaxDataSizeK)
        newSizeK = kMaxDataSizeK;

    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(int flags, PRFileDesc ** fd)
{
    NS_ENSURE_ARG_POINTER(fd);
    
    CACHE_LOG_DEBUG(("nsDiskCacheStreamIO::OpenCacheFile"));

    nsresult         rv;
    nsDiskCacheMap * cacheMap = mDevice->CacheMap();
    nsCOMPtr<nsIFile>           localFile;
    
    rv = cacheMap->GetLocalFileForDiskCacheRecord(&mBinding->mRecord,
                                                  nsDiskCache::kData,
                                                  !!(flags & PR_CREATE_FILE),
                                                  getter_AddRefs(localFile));
    if (NS_FAILED(rv))  return rv;
    
    // create PRFileDesc for input stream - the 00600 is just for consistency
    return localFile->OpenNSPRFileDesc(flags, 00600, fd);
}


nsresult
nsDiskCacheStreamIO::ReadCacheBlocks(uint32_t bufferSize)
{
    NS_ASSERTION(mStreamEnd == mBinding->mCacheEntry->DataSize(), "bad stream");
    NS_ASSERTION(bufferSize <= kMaxBufferSize, "bufferSize too large for buffer");
    NS_ASSERTION(mStreamEnd <= bufferSize, "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) {
        mBuffer = (char *) moz_xmalloc(bufferSize);
        mBufSize = bufferSize;
    }
    
    // read data stored in cache block files
    nsDiskCacheMap *map = mDevice->CacheMap();  // get map reference
    return map->ReadDataCacheBlocks(mBinding, mBuffer, mStreamEnd);
}


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;

        int64_t dataSize = mBinding->mCacheEntry->PredictedDataSize();
        if (dataSize != -1)
            mozilla::fallocate(mFD, std::min<int64_t>(dataSize, kPreallocateLimit));
    }
    
    // write buffer to the file when there is data in it
    if (mStreamEnd > 0) {
        if (!mBuffer) {
            NS_RUNTIMEABORT("Fix me!");
        }
        if (PR_Write(mFD, mBuffer, mStreamEnd) != (int32_t)mStreamEnd) {
            NS_WARNING("failed to flush all data");
            return NS_ERROR_UNEXPECTED;     // NS_ErrorAccordingToNSPR()
        }
    }

    // buffer is no longer valid
    DeleteBuffer();
   
    return NS_OK;
}


void
nsDiskCacheStreamIO::DeleteBuffer()
{
    if (mBuffer) {
        free(mBuffer);
        mBuffer = nullptr;
        mBufSize = 0;
    }
}

size_t
nsDiskCacheStreamIO::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
{
    size_t usage = aMallocSizeOf(this);

    usage += aMallocSizeOf(mFD);
    usage += aMallocSizeOf(mBuffer);

    return usage;
}

nsresult
nsDiskCacheStreamIO::SeekAndTruncate(uint32_t offset)
{
    if (!mBinding)  return NS_ERROR_NOT_AVAILABLE;
    
    if (uint32_t(offset) > mStreamEnd)  return NS_ERROR_FAILURE;
    
    // Set the current end to the desired offset
    mStreamEnd = offset;

    // Currently stored in file?
    if (mBinding->mRecord.DataLocationInitialized() && 
        (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 (offset) {
            if (PR_Seek(mFD, offset, PR_SEEK_SET) == -1)
                return NS_ErrorAccordingToNSPR();
        }
        nsDiskCache::Truncate(mFD, offset);
        UpdateFileSize();

        // When we starting at zero again, close file and start with buffer.
        // If offset is non-zero (and within buffer) an option would be
        // to read the file into the buffer, but chance is high that it is 
        // rewritten to the file anyway.
        if (offset == 0) {
            // close file descriptor
            (void) PR_Close(mFD);
            mFD = nullptr;
        }
        return NS_OK;
    }
    
    // read data into mBuffer if not read yet.
    if (offset && !mBuffer) {
        nsresult rv = ReadCacheBlocks(kMaxBufferSize);
        if (NS_FAILED(rv))  return rv;
    }

    // stream buffer sanity check
    NS_ASSERTION(mStreamEnd <= kMaxBufferSize, "bad stream");
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheStreamIO::Flush()
{
    if (!mOutputStreamIsOpen)  return NS_BASE_STREAM_CLOSED;
    return NS_OK;
}


NS_IMETHODIMP
nsDiskCacheStreamIO::WriteFrom(nsIInputStream *inStream, uint32_t count, uint32_t *bytesWritten)
{
    NS_NOTREACHED("WriteFrom");
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheStreamIO::WriteSegments( nsReadSegmentFun reader,
                                        void *           closure,
                                        uint32_t         count,
                                        uint32_t *       bytesWritten)
{
    NS_NOTREACHED("WriteSegments");
    return NS_ERROR_NOT_IMPLEMENTED;
}


NS_IMETHODIMP
nsDiskCacheStreamIO::IsNonBlocking(bool * nonBlocking)
{
    *nonBlocking = false;
    return NS_OK;
}