Adding upstream version 7.0.14-dfsg.upstream/7.0.14-dfsg

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2581 insertions, 0 deletions

diff --git a/src/libs/xpcom18a4/xpcom/io/nsFastLoadFile.cpp b/src/libs/xpcom18a4/xpcom/io/nsFastLoadFile.cpp
new file mode 100644
index 00000000..56b09d22
--- /dev/null
+++ b/src/libs/xpcom18a4/xpcom/io/nsFastLoadFile.cpp
@@ -0,0 +1,2581 @@
+/* -*- 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 Mozilla FastLoad code.
+ *
+ * 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):
+ *   Brendan Eich <brendan@mozilla.org> (original author)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either of 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 <string.h>
+#include "prtypes.h"
+#include "nscore.h"
+#include "nsDebug.h"
+#include "nsEnumeratorUtils.h"
+#include "nsMemory.h"
+#include "nsXPIDLString.h"
+#include "nsString.h"
+#include "nsReadableUtils.h"
+
+#include "nsIComponentManager.h"
+#include "nsIFile.h"
+#include "nsILocalFile.h"
+#include "nsISeekableStream.h"
+#include "nsISerializable.h"
+#include "nsIStreamBufferAccess.h"
+
+#include "nsBinaryStream.h"
+#include "nsFastLoadFile.h"
+#include "nsInt64.h"
+
+#ifdef DEBUG_brendan
+# define METERING
+# define DEBUG_MUX
+#endif
+
+#ifdef METERING
+# define METER(x)       x
+#else
+# define METER(x)       /* nothing */
+#endif
+
+#ifdef DEBUG_MUX
+# include <stdio.h>
+# include <stdarg.h>
+
+static void trace_mux(char mode, const char *format, ...)
+{
+    va_list ap;
+    static FILE *tfp;
+    if (!tfp) {
+        char tfn[16];
+        sprintf(tfn, "/tmp/mux.%ctrace", mode);
+        tfp = fopen(tfn, "w");
+        if (!tfp)
+            return;
+        setvbuf(tfp, NULL, _IOLBF, 0);
+    }
+    va_start(ap, format);
+    vfprintf(tfp, format, ap);
+    va_end(ap);
+}
+
+# define TRACE_MUX(args) trace_mux args
+#else
+# define TRACE_MUX(args) /* nothing */
+#endif
+
+/*
+ * Fletcher's 16-bit checksum, using 32-bit two's-complement arithmetic.
+ */
+#define FOLD_ONES_COMPLEMENT_CARRY(X)   ((X) = ((X) & 0xffff) + ((X) >> 16))
+#define ONES_COMPLEMENT_ACCUMULATE(X,Y) (X) += (Y); if ((X) & 0x80000000)     \
+                                        FOLD_ONES_COMPLEMENT_CARRY(X)
+#define FLETCHER_ACCUMULATE(A,B,U)      ONES_COMPLEMENT_ACCUMULATE(A, U);     \
+                                        ONES_COMPLEMENT_ACCUMULATE(B, A)
+
+PR_IMPLEMENT(PRUint32)
+NS_AccumulateFastLoadChecksum(PRUint32 *aChecksum,
+                              const PRUint8* aBuffer,
+                              PRUint32 aLength,
+                              PRBool aLastBuffer)
+{
+    PRUint32 C = *aChecksum;
+    PRUint32 A = C & 0xffff;
+    PRUint32 B = C >> 16;
+
+    PRUint16 U = 0;
+    if (aLength >= 4) {
+        PRBool odd = PRWord(aBuffer) & 1;
+        switch (PRWord(aBuffer) & 3) {
+          case 3:
+            U = (aBuffer[0] << 8) | aBuffer[1];
+            FLETCHER_ACCUMULATE(A, B, U);
+            U = aBuffer[2];
+            aBuffer += 3;
+            aLength -= 3;
+            break;
+
+          case 2:
+            U = (aBuffer[0] << 8) | aBuffer[1];
+            FLETCHER_ACCUMULATE(A, B, U);
+            U = 0;
+            aBuffer += 2;
+            aLength -= 2;
+            break;
+
+          case 1:
+            U = *aBuffer++;
+            aLength--;
+            break;
+        }
+
+        PRUint32 W;
+        if (odd) {
+            while (aLength > 3) {
+                W = *NS_REINTERPRET_CAST(const PRUint32*, aBuffer);
+                U <<= 8;
+#ifdef IS_BIG_ENDIAN
+                U |= W >> 24;
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = PRUint16(W >> 8);
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = W & 0xff;
+#else
+                U |= W & 0xff;
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = PRUint16(W >> 8);
+                U = NS_SWAP16(U);
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = W >> 24;
+#endif
+                aBuffer += 4;
+                aLength -= 4;
+            }
+            aBuffer--;      // we're odd, we didn't checksum the last byte
+            aLength++;
+        } else {
+            while (aLength > 3) {
+                W = *NS_REINTERPRET_CAST(const PRUint32*, aBuffer);
+#ifdef IS_BIG_ENDIAN
+                U = W >> 16;
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = PRUint16(W);
+                FLETCHER_ACCUMULATE(A, B, U);
+#else
+                U = NS_SWAP16(W);
+                FLETCHER_ACCUMULATE(A, B, U);
+                U = W >> 16;
+                U = NS_SWAP16(W);
+                FLETCHER_ACCUMULATE(A, B, U);
+#endif
+                aBuffer += 4;
+                aLength -= 4;
+            }
+        }
+    }
+
+    if (aLastBuffer) {
+        NS_ASSERTION(aLength <= 4, "aLength botch");
+        switch (aLength) {
+          case 4:
+            U = (aBuffer[0] << 8) | aBuffer[1];
+            FLETCHER_ACCUMULATE(A, B, U);
+            U = (aBuffer[2] << 8) | aBuffer[3];
+            FLETCHER_ACCUMULATE(A, B, U);
+            break;
+
+          case 3:
+            U = (aBuffer[0] << 8) | aBuffer[1];
+            FLETCHER_ACCUMULATE(A, B, U);
+            U = aBuffer[2];
+            FLETCHER_ACCUMULATE(A, B, U);
+            break;
+
+          case 2:
+            U = (aBuffer[0] << 8) | aBuffer[1];
+            FLETCHER_ACCUMULATE(A, B, U);
+            break;
+
+          case 1:
+            U = aBuffer[0];
+            FLETCHER_ACCUMULATE(A, B, U);
+            break;
+        }
+
+        aLength = 0;
+    }
+
+    while (A >> 16)
+        FOLD_ONES_COMPLEMENT_CARRY(A);
+    while (B >> 16)
+        FOLD_ONES_COMPLEMENT_CARRY(B);
+
+    *aChecksum = (B << 16) | A;
+    return aLength;
+}
+
+PR_IMPLEMENT(PRUint32)
+NS_AddFastLoadChecksums(PRUint32 sum1, PRUint32 sum2, PRUint32 sum2ByteCount)
+{
+    PRUint32 A1 = sum1 & 0xffff;
+    PRUint32 B1 = sum1 >> 16;
+
+    PRUint32 A2 = sum2 & 0xffff;
+    PRUint32 B2 = sum2 >> 16;
+
+    PRUint32 A = A1 + A2;
+    while (A >> 16)
+        FOLD_ONES_COMPLEMENT_CARRY(A);
+
+    PRUint32 B = B2;
+    for (PRUint32 n = (sum2ByteCount + 1) / 2; n != 0; n--)
+        ONES_COMPLEMENT_ACCUMULATE(B, B1);
+    while (B >> 16)
+        FOLD_ONES_COMPLEMENT_CARRY(B);
+
+    return (B << 16) | A;
+}
+
+#undef FOLD_ONES_COMPLEMENT_CARRY
+#undef ONES_COMPLEMENT_ACCUMULATE
+#undef FLETCHER_ACCUMULATE
+
+static const char magic[] = MFL_FILE_MAGIC;
+
+// -------------------------- nsFastLoadFileReader --------------------------
+
+nsID nsFastLoadFileReader::nsFastLoadFooter::gDummyID;
+nsFastLoadFileReader::nsObjectMapEntry
+    nsFastLoadFileReader::nsFastLoadFooter::gDummySharpObjectEntry;
+
+NS_IMPL_ISUPPORTS_INHERITED5(nsFastLoadFileReader,
+                             nsBinaryInputStream,
+                             nsIObjectInputStream,
+                             nsIFastLoadFileControl,
+                             nsIFastLoadReadControl,
+                             nsISeekableStream,
+                             nsIFastLoadFileReader)
+
+MOZ_DECL_CTOR_COUNTER(nsFastLoadFileReader)
+
+nsresult
+nsFastLoadFileReader::ReadHeader(nsFastLoadHeader *aHeader)
+{
+    nsresult rv;
+    PRUint32 bytesRead;
+
+    rv = Read(NS_REINTERPRET_CAST(char*, aHeader), sizeof *aHeader, &bytesRead);
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (bytesRead != sizeof *aHeader ||
+        memcmp(aHeader->mMagic, magic, MFL_FILE_MAGIC_SIZE)) {
+        return NS_ERROR_UNEXPECTED;
+    }
+
+    aHeader->mChecksum     = NS_SWAP32(aHeader->mChecksum);
+    aHeader->mVersion      = NS_SWAP32(aHeader->mVersion);
+    aHeader->mFooterOffset = NS_SWAP32(aHeader->mFooterOffset);
+    aHeader->mFileSize     = NS_SWAP32(aHeader->mFileSize);
+
+    return NS_OK;
+}
+
+// nsIFastLoadFileControl methods:
+
+NS_IMETHODIMP
+nsFastLoadFileReader::GetChecksum(PRUint32 *aChecksum)
+{
+    *aChecksum = mHeader.mChecksum;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::SetChecksum(PRUint32 aChecksum)
+{
+    mHeader.mChecksum = aChecksum;
+    return NS_OK;
+}
+
+struct nsStringMapEntry : public PLDHashEntryHdr {
+    const char*     mString;            // key, must come first
+    nsISupports*    mURI;               // for SelectMuxedDocument return value
+};
+
+struct nsDocumentMapEntry : public nsStringMapEntry {
+    PRUint32    mInitialSegmentOffset;  // offset of URI's first segment in file
+};
+
+struct nsDocumentMapReadEntry : public nsDocumentMapEntry {
+    PRUint32    mNextSegmentOffset;     // offset of URI's next segment to read
+    PRUint32    mBytesLeft : 31,        // bytes remaining in current segment
+                mNeedToSeek : 1;        // flag to defer Seek from Select to
+                                        // Read, in case there is no Read before
+                                        // another entry is Selected (to improve
+                                        // input stream buffer utilization)
+    PRInt64     mSaveOffset;            // in case demux schedule differs from
+                                        // mux schedule
+};
+
+PR_STATIC_CALLBACK(void)
+strmap_ClearEntry(PLDHashTable *aTable, PLDHashEntryHdr *aHdr)
+{
+    nsStringMapEntry* entry = NS_STATIC_CAST(nsStringMapEntry*, aHdr);
+
+    if (entry->mString)
+        nsMemory::Free((void*) entry->mString);
+    NS_IF_RELEASE(entry->mURI);
+    PL_DHashClearEntryStub(aTable, aHdr);
+}
+
+static const PLDHashTableOps strmap_DHashTableOps = {
+    PL_DHashAllocTable,
+    PL_DHashFreeTable,
+    PL_DHashGetKeyStub,
+    PL_DHashStringKey,
+    PL_DHashMatchStringKey,
+    PL_DHashMoveEntryStub,
+    strmap_ClearEntry,
+    PL_DHashFinalizeStub,
+    NULL
+};
+
+// An nsObjectMapEntry holds a strong reference to an XPCOM object, unless the
+// mObject member, when cast to NSFastLoadOID, has its MFL_OBJECT_DEF_TAG bit
+// set.  NB: we rely on the fact that an nsISupports* is never an odd pointer.
+struct nsObjectMapEntry : public PLDHashEntryHdr {
+    nsISupports*            mObject;        // key, must come first
+};
+
+// Fast mapping from URI object pointer back to spec-indexed document info.
+struct nsURIMapReadEntry : public nsObjectMapEntry {
+    nsDocumentMapReadEntry* mDocMapEntry;
+};
+
+PR_STATIC_CALLBACK(void)
+objmap_ClearEntry(PLDHashTable *aTable, PLDHashEntryHdr *aHdr)
+{
+    nsObjectMapEntry* entry = NS_STATIC_CAST(nsObjectMapEntry*, aHdr);
+
+    // Ignore tagged object ids stored as object pointer keys (the updater
+    // code does this).
+    if ((NS_PTR_TO_INT32(entry->mObject) & MFL_OBJECT_DEF_TAG) == 0)
+        NS_IF_RELEASE(entry->mObject);
+    PL_DHashClearEntryStub(aTable, aHdr);
+}
+
+static const PLDHashTableOps objmap_DHashTableOps = {
+    PL_DHashAllocTable,
+    PL_DHashFreeTable,
+    PL_DHashGetKeyStub,
+    PL_DHashVoidPtrKeyStub,
+    PL_DHashMatchEntryStub,
+    PL_DHashMoveEntryStub,
+    objmap_ClearEntry,
+    PL_DHashFinalizeStub,
+    NULL
+};
+
+NS_IMETHODIMP
+nsFastLoadFileReader::HasMuxedDocument(const char* aURISpec, PRBool *aResult)
+{
+    nsDocumentMapReadEntry* docMapEntry =
+        NS_STATIC_CAST(nsDocumentMapReadEntry*,
+                       PL_DHashTableOperate(&mFooter.mDocumentMap, aURISpec,
+                                            PL_DHASH_LOOKUP));
+
+    *aResult = PL_DHASH_ENTRY_IS_BUSY(docMapEntry);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::StartMuxedDocument(nsISupports* aURI, const char* aURISpec)
+{
+    nsDocumentMapReadEntry* docMapEntry =
+        NS_STATIC_CAST(nsDocumentMapReadEntry*,
+                       PL_DHashTableOperate(&mFooter.mDocumentMap, aURISpec,
+                                            PL_DHASH_LOOKUP));
+
+    // If the spec isn't in the map, return NS_ERROR_NOT_AVAILABLE so the
+    // FastLoad service can try for a file update.
+    if (PL_DHASH_ENTRY_IS_FREE(docMapEntry))
+        return NS_ERROR_NOT_AVAILABLE;
+
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapReadEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapReadEntry*,
+                       PL_DHashTableOperate(&mFooter.mURIMap, key,
+                                            PL_DHASH_ADD));
+    if (!uriMapEntry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ASSERTION(uriMapEntry->mDocMapEntry == nsnull,
+                 "URI mapped to two different specs?");
+    if (uriMapEntry->mDocMapEntry)
+        return NS_ERROR_UNEXPECTED;
+
+    docMapEntry->mURI = aURI;
+    NS_ADDREF(docMapEntry->mURI);
+    uriMapEntry->mObject = key;
+    NS_ADDREF(uriMapEntry->mObject);
+    uriMapEntry->mDocMapEntry = docMapEntry;
+    TRACE_MUX(('r', "start %p (%p) %s\n", aURI, key.get(), aURISpec));
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::SelectMuxedDocument(nsISupports* aURI,
+                                          nsISupports** aResult)
+{
+    nsresult rv;
+
+    // Find the given URI's entry and select it for more reading.
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapReadEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapReadEntry*,
+                       PL_DHashTableOperate(&mFooter.mURIMap, key,
+                                            PL_DHASH_LOOKUP));
+
+    // If the URI isn't in the map, return NS_ERROR_NOT_AVAILABLE so the
+    // FastLoad service can try selecting the file updater.
+    if (PL_DHASH_ENTRY_IS_FREE(uriMapEntry))
+        return NS_ERROR_NOT_AVAILABLE;
+
+    // If we're interrupting another document's segment, save its offset so
+    // we can seek back when it's reselected.  If prevDocMapEntry->mNeedToSeek
+    // is set, that means the stream is not positioned for prevDocMapEntry, to
+    // avoid buffer thrashing.  See below in this function for more.
+    nsDocumentMapReadEntry* prevDocMapEntry = mCurrentDocumentMapEntry;
+    if (prevDocMapEntry &&
+        prevDocMapEntry->mBytesLeft &&
+        !prevDocMapEntry->mNeedToSeek) {
+        rv = Tell(&prevDocMapEntry->mSaveOffset);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // It turns out we get a fair amount of redundant select calls, thanks to
+    // non-blocking hunks of data from the parser that are devoid of scripts.
+    // As more data gets FastLoaded, the number of these useless selects will
+    // decline.
+    nsDocumentMapReadEntry* docMapEntry = uriMapEntry->mDocMapEntry;
+    if (docMapEntry == prevDocMapEntry) {
+        TRACE_MUX(('r', "select prev %s same as current!\n",
+                   docMapEntry->mString));
+    }
+
+    // Invariant: docMapEntry->mBytesLeft implies docMapEntry->mSaveOffset has
+    // been set non-zero by the Tell call above.
+    else if (docMapEntry->mBytesLeft) {
+        NS_ASSERTION(docMapEntry->mSaveOffset != 0,
+                     "reselecting from multiplex at unsaved offset?");
+
+        // Defer Seek till Read, in case of "ping-pong" Selects without any
+        // intervening Reads, to avoid dumping the underlying mInputStream's
+        // input buffer for cases where alternate "pongs" fall in the same
+        // buffer.
+        docMapEntry->mNeedToSeek = PR_TRUE;
+    }
+
+    *aResult = prevDocMapEntry ? prevDocMapEntry->mURI : nsnull;
+    NS_IF_ADDREF(*aResult);
+
+    mCurrentDocumentMapEntry = docMapEntry;
+#ifdef DEBUG_MUX
+    PRInt64 currentSegmentOffset;
+    Tell(&currentSegmentOffset);
+    trace_mux('r', "select %p (%p) offset %ld\n",
+              aURI, key.get(), (long) currentSegmentOffset);
+#endif
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::EndMuxedDocument(nsISupports* aURI)
+{
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapReadEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapReadEntry*,
+                       PL_DHashTableOperate(&mFooter.mURIMap, key,
+                                            PL_DHASH_LOOKUP));
+
+    // If the URI isn't in the map, return NS_ERROR_NOT_AVAILABLE so the
+    // FastLoad service can try to end a select on its file updater.
+    if (PL_DHASH_ENTRY_IS_FREE(uriMapEntry))
+        return NS_ERROR_NOT_AVAILABLE;
+
+    // Drop our ref to the URI object that was passed to StartMuxedDocument,
+    // we no longer need it, and we do not want to extend its lifetime.
+    if (uriMapEntry->mDocMapEntry)
+        NS_RELEASE(uriMapEntry->mDocMapEntry->mURI);
+
+    // Shrink the table if half the entries are removed sentinels.
+    PRUint32 size = PL_DHASH_TABLE_SIZE(&mFooter.mURIMap);
+    if (mFooter.mURIMap.removedCount >= (size >> 2))
+        PL_DHashTableOperate(&mFooter.mURIMap, key, PL_DHASH_REMOVE);
+    else
+        PL_DHashTableRawRemove(&mFooter.mURIMap, uriMapEntry);
+
+    TRACE_MUX(('r', "end %p (%p)\n", aURI, key.get()));
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::Read(char* aBuffer, PRUint32 aCount, PRUint32 *aBytesRead)
+{
+    nsresult rv;
+
+    nsDocumentMapReadEntry* entry = mCurrentDocumentMapEntry;
+    if (entry) {
+        // Don't call our Seek wrapper, as it clears mCurrentDocumentMapEntry.
+        nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+        if (entry->mNeedToSeek) {
+            rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                entry->mSaveOffset);
+            if (NS_FAILED(rv))
+                return rv;
+
+            entry->mNeedToSeek = PR_FALSE;
+        }
+
+        // Loop to handle empty segments, which may be generated by the
+        // writer, given Start A; Start B; Select A; Select B; write B data;
+        // multiplexing schedules, which do tend to occur given non-blocking
+        // i/o with LIFO scheduling.  XXXbe investigate LIFO issues
+        while (entry->mBytesLeft == 0) {
+            // Check for unexpected end of multiplexed stream.
+            NS_ASSERTION(entry->mNextSegmentOffset != 0,
+                         "document demuxed from FastLoad file more than once?");
+            if (entry->mNextSegmentOffset == 0)
+                return NS_ERROR_UNEXPECTED;
+
+            rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                entry->mNextSegmentOffset);
+            if (NS_FAILED(rv))
+                return rv;
+
+            // Clear mCurrentDocumentMapEntry temporarily to avoid recursion.
+            mCurrentDocumentMapEntry = nsnull;
+
+            rv = Read32(&entry->mNextSegmentOffset);
+            if (NS_SUCCEEDED(rv)) {
+                PRUint32 bytesLeft = 0;
+                rv = Read32(&bytesLeft);
+                entry->mBytesLeft = bytesLeft;
+            }
+
+            mCurrentDocumentMapEntry = entry;
+            if (NS_FAILED(rv))
+                return rv;
+
+            NS_ASSERTION(entry->mBytesLeft >= 8, "demux segment length botch!");
+            entry->mBytesLeft -= 8;
+        }
+    }
+
+    rv = mInputStream->Read(aBuffer, aCount, aBytesRead);
+
+    if (NS_SUCCEEDED(rv) && entry) {
+        NS_ASSERTION(entry->mBytesLeft >= *aBytesRead, "demux Read underflow!");
+        entry->mBytesLeft -= *aBytesRead;
+
+#ifdef NS_DEBUG
+        // Invariant: !entry->mBytesLeft implies entry->mSaveOffset == 0.
+        if (entry->mBytesLeft == 0)
+            entry->mSaveOffset = 0;
+#endif
+    }
+    return rv;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::ReadSegments(nsWriteSegmentFun aWriter, void* aClosure,
+                                   PRUint32 aCount, PRUint32 *aResult)
+{
+    nsDocumentMapReadEntry* entry = mCurrentDocumentMapEntry;
+
+    NS_ASSERTION(!entry || (!entry->mNeedToSeek && entry->mBytesLeft != 0),
+                 "ReadSegments called from above nsFastLoadFileReader layer?!");
+
+    nsresult rv = nsBinaryInputStream::ReadSegments(aWriter, aClosure, aCount,
+                                                    aResult);
+    if (NS_SUCCEEDED(rv) && entry) {
+        NS_ASSERTION(entry->mBytesLeft >= *aResult,
+                     "demux ReadSegments underflow!");
+        entry->mBytesLeft -= *aResult;
+
+#ifdef NS_DEBUG
+        // Invariant: !entry->mBytesLeft implies entry->mSaveOffset == 0.
+        if (entry->mBytesLeft == 0)
+            entry->mSaveOffset = 0;
+#endif
+    }
+    return rv;
+}
+
+/**
+ * XXX tuneme
+ */
+#define MFL_CHECKSUM_BUFSIZE    8192
+
+NS_IMETHODIMP
+nsFastLoadFileReader::ComputeChecksum(PRUint32 *aResult)
+{
+    nsCOMPtr<nsIInputStream> stream = mInputStream;
+
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(stream));
+    PRInt64 saveOffset;
+    nsresult rv = seekable->Tell(&saveOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    nsCOMPtr<nsIStreamBufferAccess> bufferAccess(do_QueryInterface(stream));
+    if (bufferAccess) {
+        rv = bufferAccess->GetUnbufferedStream(getter_AddRefs(stream));
+        if (NS_FAILED(rv))
+            return rv;
+
+        seekable = do_QueryInterface(stream);
+        if (!seekable)
+            return NS_ERROR_UNEXPECTED;
+    }
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, 0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    char buf[MFL_CHECKSUM_BUFSIZE];
+    PRUint32 len, rem;
+
+    rem = offsetof(nsFastLoadHeader, mChecksum);
+    rv = stream->Read(buf, rem, &len);
+    if (NS_FAILED(rv))
+        return rv;
+    if (len != rem)
+        return NS_ERROR_UNEXPECTED;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_CUR, 4);
+    if (NS_FAILED(rv))
+        return rv;
+    memset(buf + rem, 0, 4);
+    rem += 4;
+
+    PRUint32 checksum = 0;
+    while (NS_SUCCEEDED(rv = stream->Read(buf + rem, sizeof buf - rem, &len)) &&
+           len) {
+        len += rem;
+        rem = NS_AccumulateFastLoadChecksum(&checksum,
+                                            NS_REINTERPRET_CAST(PRUint8*, buf),
+                                            len,
+                                            PR_FALSE);
+        if (rem)
+            memcpy(buf, buf + len - rem, rem);
+    }
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (rem) {
+        NS_AccumulateFastLoadChecksum(&checksum,
+                                      NS_REINTERPRET_CAST(PRUint8*, buf),
+                                      rem,
+                                      PR_TRUE);
+    }
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, saveOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = checksum;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::GetDependencies(nsISimpleEnumerator* *aDependencies)
+{
+    return NS_NewArrayEnumerator(aDependencies, mFooter.mDependencies);
+}
+
+nsresult
+nsFastLoadFileReader::ReadFooter(nsFastLoadFooter *aFooter)
+{
+    nsresult rv;
+
+    rv = ReadFooterPrefix(aFooter);
+    if (NS_FAILED(rv))
+        return rv;
+
+    aFooter->mIDMap = new nsID[aFooter->mNumIDs];
+    if (!aFooter->mIDMap)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    PRUint32 i, n;
+    for (i = 0, n = aFooter->mNumIDs; i < n; i++) {
+        rv = ReadSlowID(&aFooter->mIDMap[i]);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    aFooter->mObjectMap = new nsObjectMapEntry[aFooter->mNumSharpObjects];
+    if (!aFooter->mObjectMap)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    for (i = 0, n = aFooter->mNumSharpObjects; i < n; i++) {
+        nsObjectMapEntry* entry = &aFooter->mObjectMap[i];
+
+        rv = ReadSharpObjectInfo(entry);
+        if (NS_FAILED(rv))
+            return rv;
+
+        entry->mReadObject = nsnull;
+        entry->mSkipOffset = 0;
+        entry->mSaveStrongRefCnt = entry->mStrongRefCnt;
+        entry->mSaveWeakRefCnt = entry->mWeakRefCnt;
+    }
+
+    if (!PL_DHashTableInit(&aFooter->mDocumentMap, &strmap_DHashTableOps,
+                           (void *)this, sizeof(nsDocumentMapReadEntry),
+                           aFooter->mNumMuxedDocuments)) {
+        aFooter->mDocumentMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    if (!PL_DHashTableInit(&aFooter->mURIMap, &objmap_DHashTableOps,
+                           (void *)this, sizeof(nsURIMapReadEntry),
+                           aFooter->mNumMuxedDocuments)) {
+        aFooter->mURIMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    for (i = 0, n = aFooter->mNumMuxedDocuments; i < n; i++) {
+        nsFastLoadMuxedDocumentInfo info;
+
+        rv = ReadMuxedDocumentInfo(&info);
+        if (NS_FAILED(rv))
+            return rv;
+
+        nsDocumentMapReadEntry* entry =
+            NS_STATIC_CAST(nsDocumentMapReadEntry*,
+                           PL_DHashTableOperate(&aFooter->mDocumentMap,
+                                                info.mURISpec,
+                                                PL_DHASH_ADD));
+        if (!entry) {
+            nsMemory::Free((void*) info.mURISpec);
+            return NS_ERROR_OUT_OF_MEMORY;
+        }
+
+        NS_ASSERTION(!entry->mString, "duplicate URISpec in MuxedDocumentMap");
+        entry->mString = info.mURISpec;
+        entry->mURI = nsnull;
+        entry->mInitialSegmentOffset = info.mInitialSegmentOffset;
+        entry->mNextSegmentOffset = info.mInitialSegmentOffset;
+        entry->mBytesLeft = 0;
+        entry->mNeedToSeek = PR_FALSE;
+        entry->mSaveOffset = 0;
+    }
+
+    nsCOMPtr<nsISupportsArray> readDeps;
+    rv = NS_NewISupportsArray(getter_AddRefs(readDeps));
+    if (NS_FAILED(rv))
+        return rv;
+
+    nsCAutoString filename;
+    for (i = 0, n = aFooter->mNumDependencies; i < n; i++) {
+        rv = ReadCString(filename);
+        if (NS_FAILED(rv))
+            return rv;
+
+        PRInt64 fastLoadMtime;
+        rv = Read64(NS_REINTERPRET_CAST(PRUint64*, &fastLoadMtime));
+        if (NS_FAILED(rv))
+            return rv;
+
+        nsCOMPtr<nsILocalFile> file;
+        rv = NS_NewNativeLocalFile(filename, PR_TRUE, getter_AddRefs(file));
+        if (NS_FAILED(rv))
+            return rv;
+
+        PRInt64 currentMtime;
+        rv = file->GetLastModifiedTime(&currentMtime);
+        if (NS_FAILED(rv))
+            return rv;
+
+        if (LL_NE(fastLoadMtime, currentMtime)) {
+#ifdef DEBUG
+            nsCAutoString path;
+            file->GetNativePath(path);
+            printf("%s mtime changed, invalidating FastLoad file\n",
+                   path.get());
+#endif
+            return NS_ERROR_FAILURE;
+        }
+
+        rv = readDeps->AppendElement(file);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    aFooter->mDependencies = readDeps;
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::ReadFooterPrefix(nsFastLoadFooterPrefix *aFooterPrefix)
+{
+    nsresult rv;
+
+    rv = Read32(&aFooterPrefix->mNumIDs);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read32(&aFooterPrefix->mNumSharpObjects);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read32(&aFooterPrefix->mNumMuxedDocuments);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read32(&aFooterPrefix->mNumDependencies);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::ReadSlowID(nsID *aID)
+{
+    nsresult rv;
+
+    rv = Read32(&aID->m0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read16(&aID->m1);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read16(&aID->m2);
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRUint32 bytesRead;
+    rv = Read(NS_REINTERPRET_CAST(char*, aID->m3), sizeof aID->m3, &bytesRead);
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (bytesRead != sizeof aID->m3)
+        return NS_ERROR_FAILURE;
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::ReadFastID(NSFastLoadID *aID)
+{
+    nsresult rv = Read32(aID);
+    if (NS_SUCCEEDED(rv))
+        *aID ^= MFL_ID_XOR_KEY;
+    return rv;
+}
+
+nsresult
+nsFastLoadFileReader::ReadSharpObjectInfo(nsFastLoadSharpObjectInfo *aInfo)
+{
+    nsresult rv;
+
+    rv = Read32(&aInfo->mCIDOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    NS_ASSERTION(aInfo->mCIDOffset != 0,
+                 "fastload reader: mCIDOffset cannot be zero!");
+
+    rv = Read16(&aInfo->mStrongRefCnt);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read16(&aInfo->mWeakRefCnt);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::ReadMuxedDocumentInfo(nsFastLoadMuxedDocumentInfo *aInfo)
+{
+    nsresult rv;
+
+    nsCAutoString spec;
+    rv = ReadCString(spec);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Read32(&aInfo->mInitialSegmentOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    aInfo->mURISpec = ToNewCString(spec);
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::Open()
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+    if (!seekable)
+        return NS_ERROR_UNEXPECTED;
+
+    nsresult rv;
+
+    // Don't bother buffering the header, as we immediately seek to EOF.
+    nsCOMPtr<nsIStreamBufferAccess>
+        bufferAccess(do_QueryInterface(mInputStream));
+    if (bufferAccess)
+        bufferAccess->DisableBuffering();
+
+    rv = ReadHeader(&mHeader);
+
+    if (bufferAccess)
+        bufferAccess->EnableBuffering();
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (mHeader.mVersion != MFL_FILE_VERSION)
+        return NS_ERROR_UNEXPECTED;
+    if (mHeader.mFooterOffset == 0)
+        return NS_ERROR_UNEXPECTED;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_END, 0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRInt64 fileSize;
+    rv = seekable->Tell(&fileSize);
+    if (NS_FAILED(rv))
+        return rv;
+
+    nsInt64 fileSize64 = fileSize;
+    const nsInt64 maxUint32 = PR_UINT32_MAX;
+    NS_ASSERTION(fileSize64 <= maxUint32, "fileSize must fit in 32 bits");
+    if ((PRUint32) fileSize64 != mHeader.mFileSize)
+        return NS_ERROR_UNEXPECTED;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                        PRInt32(mHeader.mFooterOffset));
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = ReadFooter(&mFooter);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                          sizeof(nsFastLoadHeader));
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::Close()
+{
+    // Give up our strong "keepalive" references, in case not all objects that
+    // were deserialized were fully re-connected.
+    //
+    // This happens for sure when an nsFastLoadFileUpdater is created and wraps
+    // an nsFastLoadFileReader whose data was already deserialized by an earlier
+    // FastLoad episode.  The reader is useful in the second such episode during
+    // a session not so much for reading objects as for its footer information,
+    // which primes the updater's tables so that after the update completes, the
+    // FastLoad file has a superset footer.
+
+    for (PRUint32 i = 0, n = mFooter.mNumSharpObjects; i < n; i++) {
+        nsObjectMapEntry* entry = &mFooter.mObjectMap[i];
+        entry->mReadObject = nsnull;
+    }
+
+    return mInputStream->Close();
+}
+
+nsresult
+nsFastLoadFileReader::DeserializeObject(nsISupports* *aObject)
+{
+    nsresult rv;
+    NSFastLoadID fastCID;
+
+    rv = ReadFastID(&fastCID);
+    if (NS_FAILED(rv))
+        return rv;
+
+    const nsID& slowCID = mFooter.GetID(fastCID);
+    nsCOMPtr<nsISupports> object(do_CreateInstance(slowCID, &rv));
+    if (NS_FAILED(rv))
+        return rv;
+
+    nsCOMPtr<nsISerializable> serializable(do_QueryInterface(object));
+    if (!serializable)
+        return NS_ERROR_FAILURE;
+
+    rv = serializable->Read(this);
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aObject = object;
+    NS_ADDREF(*aObject);
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileReader::ReadObject(PRBool aIsStrongRef, nsISupports* *aObject)
+{
+    nsresult rv;
+    NSFastLoadOID oid;
+
+    rv = Read32(&oid);
+    if (NS_FAILED(rv))
+        return rv;
+    oid ^= MFL_OID_XOR_KEY;
+
+    nsCOMPtr<nsISupports> object;
+
+    if (oid == MFL_DULL_OBJECT_OID) {
+        // A very dull object, defined at point of single (strong) reference.
+        NS_ASSERTION(aIsStrongRef, "dull object read via weak ref!");
+
+        rv = DeserializeObject(getter_AddRefs(object));
+        if (NS_FAILED(rv))
+            return rv;
+    } else {
+        NS_ASSERTION((oid & MFL_WEAK_REF_TAG) ==
+                     (aIsStrongRef ? 0 : MFL_WEAK_REF_TAG),
+                     "strong vs. weak ref deserialization mismatch!");
+
+        nsObjectMapEntry* entry = &mFooter.GetSharpObjectEntry(oid);
+
+        // Check whether we've already deserialized the object for this OID.
+        object = entry->mReadObject;
+        if (!object) {
+            nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+            PRInt64 saveOffset;
+            nsDocumentMapReadEntry* saveDocMapEntry = nsnull;
+
+            rv = seekable->Tell(&saveOffset);
+            if (NS_FAILED(rv))
+                return rv;
+
+            PRUint32 saveOffset32 = saveOffset;
+            if (entry->mCIDOffset != saveOffset32) {
+                // We skipped deserialization of this object from its position
+                // earlier in the input stream, presumably due to the reference
+                // there being an nsFastLoadPtr, or (more likely) because the
+                // object was muxed in another document, and deserialization
+                // order does not match serialization order.  So we must seek
+                // back and read it now.
+                NS_ASSERTION(entry->mCIDOffset < saveOffset32,
+                             "out of order object?!");
+
+                // Ape our Seek wrapper by clearing mCurrentDocumentMapEntry.
+                // This allows for a skipped object to be referenced from two
+                // or more multiplexed documents in the FastLoad file.
+                saveDocMapEntry = mCurrentDocumentMapEntry;
+                mCurrentDocumentMapEntry = nsnull;
+                rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                    entry->mCIDOffset);
+                if (NS_FAILED(rv))
+                    return rv;
+            }
+
+            rv = DeserializeObject(getter_AddRefs(object));
+            if (NS_FAILED(rv))
+                return rv;
+
+            if (entry->mCIDOffset != saveOffset32) {
+                // Save the "skip offset" in case we need to skip this object
+                // definition when reading forward, later on.
+                rv = seekable->Tell(&entry->mSkipOffset);
+                if (NS_FAILED(rv))
+                    return rv;
+
+                // Restore stream offset and mCurrentDocumentMapEntry in case
+                // we're still reading forward through a part of the multiplex
+                // to get object definitions eagerly.
+                rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, saveOffset);
+                if (NS_FAILED(rv))
+                    return rv;
+                mCurrentDocumentMapEntry = saveDocMapEntry;
+            }
+
+            // Save object until all refs have been deserialized.
+            entry->mReadObject = object;
+        } else {
+            // What if we are at a definition that's already been read?  This
+            // case arises when a sharp object's def is serialized before its
+            // refs, while a non-defining ref is deserialized before the def.
+            // We must skip over the object definition.
+            if (oid & MFL_OBJECT_DEF_TAG) {
+                NS_ASSERTION(entry->mSkipOffset != 0, "impossible! see above");
+                nsCOMPtr<nsISeekableStream>
+                    seekable(do_QueryInterface(mInputStream));
+                rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                    entry->mSkipOffset);
+                if (NS_FAILED(rv))
+                    return rv;
+            }
+        }
+
+        if (aIsStrongRef) {
+            NS_ASSERTION(entry->mStrongRefCnt != 0,
+                         "mStrongRefCnt underflow!");
+            --entry->mStrongRefCnt;
+        } else {
+            NS_ASSERTION(MFL_GET_WEAK_REFCNT(entry) != 0,
+                         "mWeakRefCnt underflow!");
+            MFL_DROP_WEAK_REFCNT(entry);
+        }
+
+        if (entry->mStrongRefCnt == 0 && MFL_GET_WEAK_REFCNT(entry) == 0)
+            entry->mReadObject = nsnull;
+    }
+
+    if (oid & MFL_QUERY_INTERFACE_TAG) {
+        NSFastLoadID iid;
+        rv = ReadFastID(&iid);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = object->QueryInterface(mFooter.GetID(iid),
+                                    NS_REINTERPRET_CAST(void**, aObject));
+        if (NS_FAILED(rv))
+            return rv;
+    } else {
+        *aObject = object;
+        NS_ADDREF(*aObject);
+    }
+
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::ReadID(nsID *aResult)
+{
+    nsresult rv;
+    NSFastLoadID fastID;
+
+    rv = ReadFastID(&fastID);
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = mFooter.GetID(fastID);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::Seek(PRInt32 aWhence, PRInt64 aOffset)
+{
+    mCurrentDocumentMapEntry = nsnull;
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+    return seekable->Seek(aWhence, aOffset);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::Tell(PRInt64 *aResult)
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+    return seekable->Tell(aResult);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileReader::SetEOF()
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mInputStream));
+    return seekable->SetEOF();
+}
+
+NS_COM nsresult
+NS_NewFastLoadFileReader(nsIObjectInputStream* *aResult,
+                         nsIInputStream* aSrcStream)
+{
+    nsFastLoadFileReader* reader = new nsFastLoadFileReader(aSrcStream);
+    if (!reader)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // Stabilize reader's refcnt.
+    nsCOMPtr<nsIObjectInputStream> stream(reader);
+
+    nsresult rv = reader->Open();
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = stream;
+    NS_ADDREF(*aResult);
+    return NS_OK;
+}
+
+// -------------------------- nsFastLoadFileWriter --------------------------
+
+NS_IMPL_ISUPPORTS_INHERITED4(nsFastLoadFileWriter,
+                             nsBinaryOutputStream,
+                             nsIObjectOutputStream,
+                             nsIFastLoadFileControl,
+                             nsIFastLoadWriteControl,
+                             nsISeekableStream)
+
+MOZ_DECL_CTOR_COUNTER(nsFastLoadFileWriter)
+
+struct nsIDMapEntry : public PLDHashEntryHdr {
+    NSFastLoadID    mFastID;            // 1 + nsFastLoadFooter::mIDMap index
+    nsID            mSlowID;            // key, used by PLDHashTableOps below
+};
+
+PR_STATIC_CALLBACK(const void *)
+idmap_GetKey(PLDHashTable *aTable, PLDHashEntryHdr *aHdr)
+{
+    nsIDMapEntry* entry = NS_STATIC_CAST(nsIDMapEntry*, aHdr);
+
+    return &entry->mSlowID;
+}
+
+PR_STATIC_CALLBACK(PLDHashNumber)
+idmap_HashKey(PLDHashTable *aTable, const void *aKey)
+{
+    const nsID *idp = NS_REINTERPRET_CAST(const nsID*, aKey);
+
+    return idp->m0;
+}
+
+PR_STATIC_CALLBACK(PRBool)
+idmap_MatchEntry(PLDHashTable *aTable,
+                const PLDHashEntryHdr *aHdr,
+                const void *aKey)
+{
+    const nsIDMapEntry* entry = NS_STATIC_CAST(const nsIDMapEntry*, aHdr);
+    const nsID *idp = NS_REINTERPRET_CAST(const nsID*, aKey);
+
+    return memcmp(&entry->mSlowID, idp, sizeof(nsID)) == 0;
+}
+
+static const PLDHashTableOps idmap_DHashTableOps = {
+    PL_DHashAllocTable,
+    PL_DHashFreeTable,
+    idmap_GetKey,
+    idmap_HashKey,
+    idmap_MatchEntry,
+    PL_DHashMoveEntryStub,
+    PL_DHashClearEntryStub,
+    PL_DHashFinalizeStub,
+    NULL
+};
+
+nsresult
+nsFastLoadFileWriter::MapID(const nsID& aSlowID, NSFastLoadID *aResult)
+{
+    nsIDMapEntry* entry =
+        NS_STATIC_CAST(nsIDMapEntry*,
+                       PL_DHashTableOperate(&mIDMap, &aSlowID, PL_DHASH_ADD));
+    if (!entry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    if (entry->mFastID == 0) {
+        entry->mFastID = mIDMap.entryCount;
+        entry->mSlowID = aSlowID;
+    }
+
+    *aResult = entry->mFastID;
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteHeader(nsFastLoadHeader *aHeader)
+{
+    nsresult rv;
+    PRUint32 bytesWritten;
+
+    rv = Write(aHeader->mMagic, MFL_FILE_MAGIC_SIZE, &bytesWritten);
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (bytesWritten != MFL_FILE_MAGIC_SIZE)
+        return NS_ERROR_FAILURE;
+
+    rv = Write32(aHeader->mChecksum);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aHeader->mVersion);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aHeader->mFooterOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aHeader->mFileSize);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+// nsIFastLoadFileControl methods:
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::GetChecksum(PRUint32 *aChecksum)
+{
+    if (mHeader.mChecksum == 0)
+        return NS_ERROR_NOT_AVAILABLE;
+    *aChecksum = mHeader.mChecksum;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::SetChecksum(PRUint32 aChecksum)
+{
+    mHeader.mChecksum = aChecksum;
+    return NS_OK;
+}
+
+struct nsDocumentMapWriteEntry : public nsDocumentMapEntry {
+    PRUint32    mCurrentSegmentOffset;      // last written segment's offset
+};
+
+// Fast mapping from URI object pointer back to spec-indexed document info.
+// We also may need the slow mapping from mURISpec to nsDocumentMapWriteEntry,
+// because the writer's mDocumentMap double hash table may grow "behind the
+// back of" each mURIMap entry's mDocMapEntry member.
+struct nsURIMapWriteEntry : public nsObjectMapEntry {
+    nsDocumentMapWriteEntry* mDocMapEntry;
+    PRUint32                 mGeneration;
+    const char*              mURISpec;
+};
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::HasMuxedDocument(const char* aURISpec, PRBool *aResult)
+{
+    nsDocumentMapWriteEntry* docMapEntry =
+        NS_STATIC_CAST(nsDocumentMapWriteEntry*,
+                       PL_DHashTableOperate(&mDocumentMap, aURISpec,
+                                            PL_DHASH_LOOKUP));
+
+    *aResult = PL_DHASH_ENTRY_IS_BUSY(docMapEntry);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::StartMuxedDocument(nsISupports* aURI,
+                                         const char* aURISpec)
+{
+    // Save mDocumentMap table generation and mCurrentDocumentMapEntry key in
+    // case the hash table grows during the PL_DHASH_ADD operation.
+    PRUint32 saveGeneration = mDocumentMap.generation;
+    const char* saveURISpec = mCurrentDocumentMapEntry
+                              ? mCurrentDocumentMapEntry->mString
+                              : nsnull;
+
+    nsDocumentMapWriteEntry* docMapEntry =
+        NS_STATIC_CAST(nsDocumentMapWriteEntry*,
+                       PL_DHashTableOperate(&mDocumentMap, aURISpec,
+                                            PL_DHASH_ADD));
+    if (!docMapEntry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // If the generation number changed, refresh mCurrentDocumentMapEntry.
+    if (mCurrentDocumentMapEntry && mDocumentMap.generation != saveGeneration) {
+        mCurrentDocumentMapEntry =
+            NS_STATIC_CAST(nsDocumentMapWriteEntry*,
+                           PL_DHashTableOperate(&mDocumentMap, saveURISpec,
+                                                PL_DHASH_LOOKUP));
+        NS_ASSERTION(PL_DHASH_ENTRY_IS_BUSY(mCurrentDocumentMapEntry),
+                     "mCurrentDocumentMapEntry lost during table growth?!");
+
+        // Refresh saveGeneration for use below when initializing uriMapEntry.
+        saveGeneration = mDocumentMap.generation;
+    }
+
+    NS_ASSERTION(docMapEntry->mString == nsnull,
+                 "redundant multiplexed document?");
+    if (docMapEntry->mString)
+        return NS_ERROR_UNEXPECTED;
+
+    void* spec = nsMemory::Clone(aURISpec, strlen(aURISpec) + 1);
+    if (!spec)
+        return NS_ERROR_OUT_OF_MEMORY;
+    docMapEntry->mString = NS_REINTERPRET_CAST(const char*, spec);
+    docMapEntry->mURI = aURI;
+    NS_ADDREF(docMapEntry->mURI);
+
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapWriteEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapWriteEntry*,
+                       PL_DHashTableOperate(&mURIMap, key, PL_DHASH_ADD));
+    if (!uriMapEntry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ASSERTION(uriMapEntry->mDocMapEntry == nsnull,
+                 "URI mapped to two different specs?");
+    if (uriMapEntry->mDocMapEntry)
+        return NS_ERROR_UNEXPECTED;
+
+    uriMapEntry->mObject = key;
+    NS_ADDREF(uriMapEntry->mObject);
+    uriMapEntry->mDocMapEntry = docMapEntry;
+    uriMapEntry->mGeneration = saveGeneration;
+    uriMapEntry->mURISpec = NS_REINTERPRET_CAST(const char*, spec);
+    TRACE_MUX(('w', "start %p (%p) %s\n", aURI, key.get(), aURISpec));
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::SelectMuxedDocument(nsISupports* aURI,
+                                          nsISupports** aResult)
+{
+    // Avoid repeatedly QI'ing to nsISeekableStream as we tell and seek.
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+
+    // Capture the current file offset (XXXbe maintain our own via Write?)
+    nsresult rv;
+    PRInt64 currentSegmentOffset;
+    rv = seekable->Tell(&currentSegmentOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRUint32 currentSegmentOffset32 = currentSegmentOffset;
+    // Look for an existing entry keyed by aURI, added by StartMuxedDocument.
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapWriteEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapWriteEntry*,
+                       PL_DHashTableOperate(&mURIMap, key, PL_DHASH_LOOKUP));
+    NS_ASSERTION(PL_DHASH_ENTRY_IS_BUSY(uriMapEntry),
+                 "SelectMuxedDocument without prior StartMuxedDocument?");
+    if (PL_DHASH_ENTRY_IS_FREE(uriMapEntry))
+        return NS_ERROR_UNEXPECTED;
+
+    // Beware that uriMapEntry->mDocMapEntry may be stale, if an mDocumentMap
+    // addition caused that table to grow.  We save the mDocumentMap generation
+    // in each uriMapEntry and compare it to the current generation, rehashing
+    // uriMapEntry->mURISpec if necessary.
+
+    nsDocumentMapWriteEntry* docMapEntry = uriMapEntry->mDocMapEntry;
+    if (uriMapEntry->mGeneration != mDocumentMap.generation) {
+        docMapEntry =
+            NS_STATIC_CAST(nsDocumentMapWriteEntry*,
+                           PL_DHashTableOperate(&mDocumentMap,
+                                                uriMapEntry->mURISpec,
+                                                PL_DHASH_LOOKUP));
+        NS_ASSERTION(PL_DHASH_ENTRY_IS_BUSY(docMapEntry), "lost mDocMapEntry!?");
+        uriMapEntry->mDocMapEntry = docMapEntry;
+        uriMapEntry->mGeneration = mDocumentMap.generation;
+    }
+    docMapEntry = uriMapEntry->mDocMapEntry;
+
+    // If there is a muxed document segment open, close it now by setting its
+    // length, stored in the second PRUint32 of the segment.
+    nsDocumentMapWriteEntry* prevDocMapEntry = mCurrentDocumentMapEntry;
+    if (prevDocMapEntry) {
+        if (prevDocMapEntry == docMapEntry) {
+            TRACE_MUX(('w', "select prev %s same as current!\n",
+                       prevDocMapEntry->mString));
+            *aResult = docMapEntry->mURI;
+            NS_ADDREF(*aResult);
+            return NS_OK;
+        }
+
+        PRUint32 prevSegmentOffset = prevDocMapEntry->mCurrentSegmentOffset;
+        TRACE_MUX(('w', "select prev %s offset %lu\n",
+                   prevDocMapEntry->mString, prevSegmentOffset));
+
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            prevSegmentOffset + 4);
+        if (NS_FAILED(rv))
+            return rv;
+
+        // The length counts all bytes in the segment, including the header
+        // that contains [nextSegmentOffset, length].
+        rv = Write32(currentSegmentOffset32 - prevSegmentOffset);
+        if (NS_FAILED(rv))
+            return rv;
+
+        // Seek back to the current offset only if we are not going to seek
+        // back to *this* entry's last "current" segment offset and write its
+        // next segment offset at the first PRUint32 of the segment.
+        if (!docMapEntry->mInitialSegmentOffset) {
+            rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                currentSegmentOffset);
+            if (NS_FAILED(rv))
+                return rv;
+        }
+    }
+
+    // If this entry was newly added, set its key and initial segment offset.
+    // Otherwise, seek back to write the next segment offset of the previous
+    // segment for this document in the multiplex.
+    if (!docMapEntry->mInitialSegmentOffset) {
+        docMapEntry->mInitialSegmentOffset = currentSegmentOffset32;
+    } else {
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            docMapEntry->mCurrentSegmentOffset);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = Write32(currentSegmentOffset32);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            currentSegmentOffset);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // Update this document's current segment offset so we can later fix its
+    // next segment offset (unless it is last, in which case we leave the zero
+    // placeholder as a terminator).
+    docMapEntry->mCurrentSegmentOffset = currentSegmentOffset32;
+
+    rv = Write32(0);    // nextSegmentOffset placeholder
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(0);    // length placeholder
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = prevDocMapEntry ? prevDocMapEntry->mURI : nsnull;
+    NS_IF_ADDREF(*aResult);
+
+    mCurrentDocumentMapEntry = docMapEntry;
+    TRACE_MUX(('w', "select %p (%p) offset %lu\n",
+               aURI, key.get(), currentSegmentOffset));
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::EndMuxedDocument(nsISupports* aURI)
+{
+    nsCOMPtr<nsISupports> key(do_QueryInterface(aURI));
+    nsURIMapWriteEntry* uriMapEntry =
+        NS_STATIC_CAST(nsURIMapWriteEntry*,
+                       PL_DHashTableOperate(&mURIMap, key, PL_DHASH_LOOKUP));
+
+    // If the URI isn't in the map, nsFastLoadFileWriter::StartMuxedDocument
+    // must have been called with a redundant URI, *and* its caller must have
+    // ignored the NS_ERROR_UNEXPECTED it returned in that case.
+    if (PL_DHASH_ENTRY_IS_FREE(uriMapEntry)) {
+        TRACE_MUX(('w', "bad end %p (%p)\n", aURI, key.get()));
+        return NS_ERROR_UNEXPECTED;
+    }
+
+    // Drop our ref to the URI object that was passed to StartMuxedDocument,
+    // we no longer need it, and we do not want to extend its lifetime.
+    if (uriMapEntry->mDocMapEntry)
+        NS_RELEASE(uriMapEntry->mDocMapEntry->mURI);
+
+    // Shrink the table if half the entries are removed sentinels.
+    PRUint32 size = PL_DHASH_TABLE_SIZE(&mURIMap);
+    if (mURIMap.removedCount >= (size >> 2))
+        PL_DHashTableOperate(&mURIMap, key, PL_DHASH_REMOVE);
+    else
+        PL_DHashTableRawRemove(&mURIMap, uriMapEntry);
+
+    TRACE_MUX(('w', "end %p (%p)\n", aURI, key.get()));
+    return NS_OK;
+}
+
+struct nsDependencyMapEntry : public nsStringMapEntry {
+    PRInt64 mLastModified;
+};
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::AddDependency(nsIFile* aFile)
+{
+    nsCAutoString path;
+    nsresult rv = aFile->GetNativePath(path);
+    if (NS_FAILED(rv))
+        return rv;
+
+    nsDependencyMapEntry* entry =
+        NS_STATIC_CAST(nsDependencyMapEntry*,
+                       PL_DHashTableOperate(&mDependencyMap, path.get(),
+                                            PL_DHASH_ADD));
+    if (!entry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    if (!entry->mString) {
+        const char *tmp = ToNewCString(path);
+        if (!tmp)
+            return NS_ERROR_OUT_OF_MEMORY;
+        entry->mString = tmp;
+
+        // If we can't get the last modified time from aFile, assume it does
+        // not exist, or is otherwise inaccessible to us (due to permissions),
+        // remove the dependency, and suppress the failure.
+        //
+        // Otherwise, we would end up aborting the fastload process due to a
+        // missing .js or .xul or other file on every startup.
+
+        rv = aFile->GetLastModifiedTime(&entry->mLastModified);
+        if (NS_FAILED(rv)) {
+            PL_DHashTableOperate(&mDependencyMap, path.get(), PL_DHASH_REMOVE);
+            rv = NS_OK;
+        }
+    }
+    return rv;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteFooterPrefix(const nsFastLoadFooterPrefix& aFooterPrefix)
+{
+    nsresult rv;
+
+    rv = Write32(aFooterPrefix.mNumIDs);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aFooterPrefix.mNumSharpObjects);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aFooterPrefix.mNumMuxedDocuments);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aFooterPrefix.mNumDependencies);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteSlowID(const nsID& aID)
+{
+    nsresult rv;
+
+    rv = Write32(aID.m0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write16(aID.m1);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write16(aID.m2);
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRUint32 bytesWritten;
+    rv = Write(NS_REINTERPRET_CAST(const char*, aID.m3), sizeof aID.m3,
+               &bytesWritten);
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (bytesWritten != sizeof aID.m3)
+        return NS_ERROR_FAILURE;
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteFastID(NSFastLoadID aID)
+{
+    return Write32(aID ^ MFL_ID_XOR_KEY);
+}
+
+nsresult
+nsFastLoadFileWriter::WriteSharpObjectInfo(const nsFastLoadSharpObjectInfo& aInfo)
+{
+    nsresult rv;
+
+    NS_ASSERTION(aInfo.mCIDOffset != 0,
+                 "fastload writer: mCIDOffset cannot be zero!");
+
+    rv = Write32(aInfo.mCIDOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write16(aInfo.mStrongRefCnt);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write16(aInfo.mWeakRefCnt);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteMuxedDocumentInfo(const nsFastLoadMuxedDocumentInfo& aInfo)
+{
+    nsresult rv;
+
+    rv = WriteStringZ(aInfo.mURISpec);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(aInfo.mInitialSegmentOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+PLDHashOperator PR_CALLBACK
+nsFastLoadFileWriter::IDMapEnumerate(PLDHashTable *aTable,
+                                     PLDHashEntryHdr *aHdr,
+                                     PRUint32 aNumber,
+                                     void *aData)
+{
+    nsIDMapEntry* entry = NS_STATIC_CAST(nsIDMapEntry*, aHdr);
+    PRUint32 index = entry->mFastID - 1;
+    nsID* vector = NS_REINTERPRET_CAST(nsID*, aData);
+
+    NS_ASSERTION(index < aTable->entryCount, "bad nsIDMap index!");
+    vector[index] = entry->mSlowID;
+    return PL_DHASH_NEXT;
+}
+
+struct nsSharpObjectMapEntry : public nsObjectMapEntry {
+    NSFastLoadOID               mOID;
+    nsFastLoadSharpObjectInfo   mInfo;
+};
+
+PLDHashOperator PR_CALLBACK
+nsFastLoadFileWriter::ObjectMapEnumerate(PLDHashTable *aTable,
+                                         PLDHashEntryHdr *aHdr,
+                                         PRUint32 aNumber,
+                                         void *aData)
+{
+    nsSharpObjectMapEntry* entry = NS_STATIC_CAST(nsSharpObjectMapEntry*, aHdr);
+    PRUint32 index = MFL_OID_TO_SHARP_INDEX(entry->mOID);
+    nsFastLoadSharpObjectInfo* vector =
+        NS_REINTERPRET_CAST(nsFastLoadSharpObjectInfo*, aData);
+
+    NS_ASSERTION(index < aTable->entryCount, "bad nsObjectMap index!");
+    vector[index] = entry->mInfo;
+
+    NS_ASSERTION(entry->mInfo.mStrongRefCnt, "no strong ref in serialization!");
+
+    // Ignore tagged object ids stored as object pointer keys (the updater
+    // code does this).
+    if ((NS_PTR_TO_INT32(entry->mObject) & MFL_OBJECT_DEF_TAG) == 0)
+        NS_RELEASE(entry->mObject);
+
+    return PL_DHASH_NEXT;
+}
+
+PLDHashOperator PR_CALLBACK
+nsFastLoadFileWriter::DocumentMapEnumerate(PLDHashTable *aTable,
+                                           PLDHashEntryHdr *aHdr,
+                                           PRUint32 aNumber,
+                                           void *aData)
+{
+    nsFastLoadFileWriter* writer =
+        NS_REINTERPRET_CAST(nsFastLoadFileWriter*, aTable->data);
+    nsDocumentMapWriteEntry* entry =
+        NS_STATIC_CAST(nsDocumentMapWriteEntry*, aHdr);
+    nsresult* rvp = NS_REINTERPRET_CAST(nsresult*, aData);
+
+    nsFastLoadMuxedDocumentInfo info;
+    info.mURISpec = entry->mString;
+    info.mInitialSegmentOffset = entry->mInitialSegmentOffset;
+    *rvp = writer->WriteMuxedDocumentInfo(info);
+
+    return NS_FAILED(*rvp) ? PL_DHASH_STOP : PL_DHASH_NEXT;
+}
+
+PLDHashOperator PR_CALLBACK
+nsFastLoadFileWriter::DependencyMapEnumerate(PLDHashTable *aTable,
+                                             PLDHashEntryHdr *aHdr,
+                                             PRUint32 aNumber,
+                                             void *aData)
+{
+    nsFastLoadFileWriter* writer =
+        NS_REINTERPRET_CAST(nsFastLoadFileWriter*, aTable->data);
+    nsDependencyMapEntry* entry = NS_STATIC_CAST(nsDependencyMapEntry*, aHdr);
+    nsresult* rvp = NS_REINTERPRET_CAST(nsresult*, aData);
+
+    *rvp = writer->WriteStringZ(entry->mString);
+    if (NS_SUCCEEDED(*rvp))
+        *rvp = writer->Write64(entry->mLastModified);
+
+    return NS_FAILED(*rvp) ? PL_DHASH_STOP :PL_DHASH_NEXT;
+}
+
+nsresult
+nsFastLoadFileWriter::WriteFooter()
+{
+    nsresult rv;
+    PRUint32 i, count;
+
+    nsFastLoadFooterPrefix footerPrefix;
+    footerPrefix.mNumIDs = mIDMap.entryCount;
+    footerPrefix.mNumSharpObjects = mObjectMap.entryCount;
+    footerPrefix.mNumMuxedDocuments = mDocumentMap.entryCount;
+    footerPrefix.mNumDependencies = mDependencyMap.entryCount;
+
+    rv = WriteFooterPrefix(footerPrefix);
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Enumerate mIDMap into a vector indexed by mFastID and write it.
+    nsID* idvec = new nsID[footerPrefix.mNumIDs];
+    if (!idvec)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    count = PL_DHashTableEnumerate(&mIDMap, IDMapEnumerate, idvec);
+    NS_ASSERTION(count == footerPrefix.mNumIDs, "bad mIDMap enumeration!");
+    for (i = 0; i < count; i++) {
+        rv = WriteSlowID(idvec[i]);
+        if (NS_FAILED(rv)) break;
+    }
+
+    delete[] idvec;
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Enumerate mObjectMap into a vector indexed by mOID and write it.
+    nsFastLoadSharpObjectInfo* objvec =
+        new nsFastLoadSharpObjectInfo[footerPrefix.mNumSharpObjects];
+    if (!objvec)
+        return NS_ERROR_OUT_OF_MEMORY;
+#ifdef NS_DEBUG
+    memset(objvec, 0, footerPrefix.mNumSharpObjects *
+                      sizeof(nsFastLoadSharpObjectInfo));
+#endif
+
+    count = PL_DHashTableEnumerate(&mObjectMap, ObjectMapEnumerate, objvec);
+    NS_ASSERTION(count == footerPrefix.mNumSharpObjects,
+                 "bad mObjectMap enumeration!");
+    for (i = 0; i < count; i++) {
+        rv = WriteSharpObjectInfo(objvec[i]);
+        if (NS_FAILED(rv)) break;
+    }
+
+    delete[] objvec;
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Enumerate mDocumentMap, writing nsFastLoadMuxedDocumentInfo records
+    count = PL_DHashTableEnumerate(&mDocumentMap, DocumentMapEnumerate, &rv);
+    if (NS_FAILED(rv))
+        return rv;
+
+    NS_ASSERTION(count == footerPrefix.mNumMuxedDocuments,
+                 "bad mDocumentMap enumeration!");
+
+    // Write out make-like file dependencies.
+    count = PL_DHashTableEnumerate(&mDependencyMap, DependencyMapEnumerate, &rv);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::Init()
+{
+    if (!PL_DHashTableInit(&mIDMap, &idmap_DHashTableOps, (void *)this,
+                           sizeof(nsIDMapEntry), PL_DHASH_MIN_SIZE)) {
+        mIDMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    if (!PL_DHashTableInit(&mObjectMap, &objmap_DHashTableOps, (void *)this,
+                           sizeof(nsSharpObjectMapEntry), PL_DHASH_MIN_SIZE)) {
+        mObjectMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    if (!PL_DHashTableInit(&mDocumentMap, &strmap_DHashTableOps, (void *)this,
+                           sizeof(nsDocumentMapWriteEntry),
+                           PL_DHASH_MIN_SIZE)) {
+        mDocumentMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    if (!PL_DHashTableInit(&mURIMap, &objmap_DHashTableOps, (void *)this,
+                           sizeof(nsURIMapWriteEntry), PL_DHASH_MIN_SIZE)) {
+        mURIMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    if (!PL_DHashTableInit(&mDependencyMap, &strmap_DHashTableOps, (void *)this,
+                           sizeof(nsDependencyMapEntry), PL_DHASH_MIN_SIZE)) {
+        mDependencyMap.ops = nsnull;
+        return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    return NS_OK;
+}
+
+nsresult
+nsFastLoadFileWriter::Open()
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+    if (!seekable)
+        return NS_ERROR_UNEXPECTED;
+
+    nsresult rv;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                        sizeof(nsFastLoadHeader));
+    if (NS_FAILED(rv))
+        return rv;
+
+    return Init();
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::Close()
+{
+    nsresult rv;
+
+    memcpy(mHeader.mMagic, magic, MFL_FILE_MAGIC_SIZE);
+    mHeader.mChecksum = 0;
+    mHeader.mVersion = MFL_FILE_VERSION;
+
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+
+    PRInt64 footerOffset;
+    rv = seekable->Tell(&footerOffset);
+
+    LL_L2UI(mHeader.mFooterOffset, footerOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    // If there is a muxed document segment open, close it now by setting its
+    // length, stored in the second PRUint32 of the segment.
+    if (mCurrentDocumentMapEntry) {
+        PRUint32 currentSegmentOffset =
+            mCurrentDocumentMapEntry->mCurrentSegmentOffset;
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            currentSegmentOffset + 4);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = Write32(mHeader.mFooterOffset - currentSegmentOffset);
+        if (NS_FAILED(rv))
+            return rv;
+
+        // Seek back to the current offset to write the footer.
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            mHeader.mFooterOffset);
+        if (NS_FAILED(rv))
+            return rv;
+
+        mCurrentDocumentMapEntry = nsnull;
+    }
+
+    rv = WriteFooter();
+    if (NS_FAILED(rv))
+        return rv;
+    PRInt64 fileSize;
+    rv = seekable->Tell(&fileSize);
+    LL_L2UI(mHeader.mFileSize, fileSize);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, 0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = WriteHeader(&mHeader);
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Now compute the checksum, using mFileIO to get an input stream on the
+    // underlying FastLoad file.
+    if (mFileIO) {
+        // Get the unbuffered output stream, which flushes the buffered header
+        // so we can read and checksum it along with the rest of the file, and
+        // which allows us to write the checksum directly.
+        nsCOMPtr<nsIStreamBufferAccess>
+            bufferAccess(do_QueryInterface(mOutputStream));
+        nsCOMPtr<nsIOutputStream> output;
+        rv = bufferAccess->GetUnbufferedStream(getter_AddRefs(output));
+        if (NS_FAILED(rv) || !output)
+            return NS_ERROR_UNEXPECTED;
+
+        nsCOMPtr<nsIInputStream> input;
+        rv = mFileIO->GetInputStream(getter_AddRefs(input));
+        if (NS_FAILED(rv))
+            return rv;
+
+        // Get the unbuffered input stream, to avoid copying overhead and to
+        // keep our view of the file coherent with the writer -- we don't want
+        // to hit a stale buffer in the reader's underlying stream.
+        bufferAccess = do_QueryInterface(input);
+        rv = bufferAccess->GetUnbufferedStream(getter_AddRefs(input));
+        if (NS_FAILED(rv) || !input)
+            return NS_ERROR_UNEXPECTED;
+
+        // Seek the input stream to offset 0, in case it's a reader who has
+        // already been used to consume some of the FastLoad file.
+        seekable = do_QueryInterface(input);
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET, 0);
+        if (NS_FAILED(rv))
+            return rv;
+
+        char buf[MFL_CHECKSUM_BUFSIZE];
+        PRUint32 len, rem = 0;
+        PRUint32 checksum = 0;
+
+        // Ok, we're finally ready to checksum the FastLoad file we just wrote!
+        while (NS_SUCCEEDED(rv =
+                            input->Read(buf + rem, sizeof buf - rem, &len)) &&
+               len) {
+            len += rem;
+            rem = NS_AccumulateFastLoadChecksum(&checksum,
+                                                NS_REINTERPRET_CAST(PRUint8*,
+                                                                    buf),
+                                                len,
+                                                PR_FALSE);
+            if (rem)
+                memcpy(buf, buf + len - rem, rem);
+        }
+        if (NS_FAILED(rv))
+            return rv;
+
+        if (rem) {
+            NS_AccumulateFastLoadChecksum(&checksum,
+                                          NS_REINTERPRET_CAST(PRUint8*, buf),
+                                          rem,
+                                          PR_TRUE);
+        }
+
+        // Store the checksum in the FastLoad file header and remember it via
+        // mHeader.mChecksum, for GetChecksum.
+        seekable = do_QueryInterface(output);
+        rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                            offsetof(nsFastLoadHeader, mChecksum));
+        if (NS_FAILED(rv))
+            return rv;
+
+        mHeader.mChecksum = checksum;
+        checksum = NS_SWAP32(checksum);
+        PRUint32 bytesWritten;
+        rv = output->Write(NS_REINTERPRET_CAST(char*, &checksum),
+                           sizeof checksum,
+                           &bytesWritten);
+        if (NS_FAILED(rv))
+            return rv;
+        if (bytesWritten != sizeof checksum)
+            return NS_ERROR_FAILURE;
+    }
+
+    return mOutputStream->Close();
+}
+
+// Psuedo-tag used as flag between WriteSingleRefObject and WriteObjectCommon.
+#define MFL_SINGLE_REF_PSEUDO_TAG       PR_BIT(MFL_OBJECT_TAG_BITS)
+
+nsresult
+nsFastLoadFileWriter::WriteObjectCommon(nsISupports* aObject,
+                                        PRBool aIsStrongRef,
+                                        PRUint32 aTags)
+{
+    nsrefcnt rc;
+    nsresult rv;
+
+    NS_ASSERTION((NS_PTR_TO_INT32(aObject) & MFL_OBJECT_DEF_TAG) == 0,
+                 "odd nsISupports*, oh no!");
+
+    // Here be manual refcounting dragons!
+    rc = aObject->AddRef();
+    NS_ASSERTION(rc != 0, "bad refcnt when writing aObject!");
+
+    NSFastLoadOID oid;
+    nsCOMPtr<nsIClassInfo> classInfo;
+
+    if (rc == 2 && (aTags & MFL_SINGLE_REF_PSEUDO_TAG)) {
+        // Dull object: only one strong ref and no weak refs in serialization.
+        // Conservative: we don't trust the caller if there are more than two
+        // refs (one from the AddRef above, one from the data structure that's
+        // being serialized).
+        oid = MFL_DULL_OBJECT_OID;
+        aObject->Release();
+    } else {
+        // Object is presumed to be multiply connected through some combo of
+        // strong and weak refs.  Hold onto it via mObjectMap.
+        nsSharpObjectMapEntry* entry =
+            NS_STATIC_CAST(nsSharpObjectMapEntry*,
+                           PL_DHashTableOperate(&mObjectMap, aObject,
+                                                PL_DHASH_ADD));
+        if (!entry) {
+            aObject->Release();
+            return NS_ERROR_OUT_OF_MEMORY;
+        }
+
+        if (!entry->mObject) {
+            // First time we've seen this object address: add it to mObjectMap
+            // and serialize the object at the current stream offset.
+            PRInt64 thisOffset;
+            rv = Tell(&thisOffset);
+            if (NS_FAILED(rv)) {
+                aObject->Release();
+                return rv;
+            }
+
+            // NB: aObject was already held, and mObject is a raw nsISupports*.
+            entry->mObject = aObject;
+
+            oid = (mObjectMap.entryCount << MFL_OBJECT_TAG_BITS);
+            entry->mOID = oid;
+
+            // NB: the (32-bit, fast) CID and object data follow the OID.
+            entry->mInfo.mCIDOffset = thisOffset + sizeof(oid);
+            entry->mInfo.mStrongRefCnt = aIsStrongRef ? 1 : 0;
+            entry->mInfo.mWeakRefCnt   = aIsStrongRef ? 0 : 1;
+
+            // Record in oid the fact that we're defining this object in the
+            // stream, and get the object's class info here, so we can take
+            // note of singletons in order to avoid reserializing them when
+            // updating after reading.
+            oid |= MFL_OBJECT_DEF_TAG;
+            classInfo = do_QueryInterface(aObject);
+            if (!classInfo)
+                return NS_ERROR_FAILURE;
+
+            PRUint32 flags;
+            if (NS_SUCCEEDED(classInfo->GetFlags(&flags)) &&
+                (flags & nsIClassInfo::SINGLETON)) {
+                MFL_SET_SINGLETON_FLAG(&entry->mInfo);
+            }
+        } else {
+            // Already serialized, recover oid and update the desired refcnt.
+            oid = entry->mOID;
+            if (aIsStrongRef) {
+                ++entry->mInfo.mStrongRefCnt;
+                NS_ASSERTION(entry->mInfo.mStrongRefCnt != 0,
+                             "mStrongRefCnt overflow");
+            } else {
+                MFL_BUMP_WEAK_REFCNT(&entry->mInfo);
+                NS_ASSERTION(MFL_GET_WEAK_REFCNT(&entry->mInfo) != 0,
+                             "mWeakRefCnt overflow");
+            }
+
+            aObject->Release();
+        }
+    }
+
+    if (!aIsStrongRef)
+        oid |= MFL_WEAK_REF_TAG;
+    oid |= (aTags & MFL_QUERY_INTERFACE_TAG);
+
+    rv = Write32(oid ^ MFL_OID_XOR_KEY);
+    if (NS_FAILED(rv))
+        return rv;
+
+    if (oid & MFL_OBJECT_DEF_TAG) {
+        nsCOMPtr<nsISerializable> serializable(do_QueryInterface(aObject));
+        if (!serializable)
+            return NS_ERROR_FAILURE;
+
+        nsCID slowCID;
+        rv = classInfo->GetClassIDNoAlloc(&slowCID);
+        if (NS_FAILED(rv))
+            return rv;
+
+        NSFastLoadID fastCID;
+        rv = MapID(slowCID, &fastCID);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = WriteFastID(fastCID);
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = serializable->Write(this);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::WriteObject(nsISupports* aObject, PRBool aIsStrongRef)
+{
+#ifdef NS_DEBUG
+    nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+    NS_ASSERTION(rootObject.get() == aObject,
+                 "bad call to WriteObject -- call WriteCompoundObject!");
+#endif
+
+    return WriteObjectCommon(aObject, aIsStrongRef, 0);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::WriteSingleRefObject(nsISupports* aObject)
+{
+#ifdef NS_DEBUG
+    nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+    NS_ASSERTION(rootObject.get() == aObject,
+                 "bad call to WriteSingleRefObject -- call WriteCompoundObject!");
+#endif
+
+    return WriteObjectCommon(aObject, PR_TRUE, MFL_SINGLE_REF_PSEUDO_TAG);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::WriteCompoundObject(nsISupports* aObject,
+                                          const nsIID& aIID,
+                                          PRBool aIsStrongRef)
+{
+    nsresult rv;
+    nsCOMPtr<nsISupports> rootObject(do_QueryInterface(aObject));
+
+#ifdef NS_DEBUG
+    nsCOMPtr<nsISupports> roundtrip;
+    rootObject->QueryInterface(aIID, getter_AddRefs(roundtrip));
+
+    NS_ASSERTION(rootObject.get() != aObject,
+                 "wasteful call to WriteCompoundObject -- call WriteObject!");
+    NS_ASSERTION(roundtrip.get() == aObject,
+                 "bad aggregation or multiple inheritance detected by call to "
+                 "WriteCompoundObject!");
+#endif
+
+    rv = WriteObjectCommon(rootObject, aIsStrongRef, MFL_QUERY_INTERFACE_TAG);
+    if (NS_FAILED(rv))
+        return rv;
+
+    NSFastLoadID iid;
+    rv = MapID(aIID, &iid);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return WriteFastID(iid);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::WriteID(const nsID& aID)
+{
+    nsresult rv;
+    NSFastLoadID fastID;
+
+    rv = MapID(aID, &fastID);
+    if (NS_FAILED(rv))
+        return rv;
+
+    return WriteFastID(fastID);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::Seek(PRInt32 aWhence, PRInt64 aOffset)
+{
+    mCurrentDocumentMapEntry = nsnull;
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+    return seekable->Seek(aWhence, aOffset);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::Tell(PRInt64 *aResult)
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+    return seekable->Tell(aResult);
+}
+
+NS_IMETHODIMP
+nsFastLoadFileWriter::SetEOF()
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+    return seekable->SetEOF();
+}
+
+NS_COM nsresult
+NS_NewFastLoadFileWriter(nsIObjectOutputStream* *aResult,
+                         nsIOutputStream* aDestStream,
+                         nsIFastLoadFileIO* aFileIO)
+{
+    nsFastLoadFileWriter* writer =
+        new nsFastLoadFileWriter(aDestStream, aFileIO);
+    if (!writer)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // Stabilize writer's refcnt.
+    nsCOMPtr<nsIObjectOutputStream> stream(writer);
+
+    nsresult rv = writer->Open();
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = stream;
+    NS_ADDREF(*aResult);
+    return NS_OK;
+}
+
+// -------------------------- nsFastLoadFileUpdater --------------------------
+
+NS_IMPL_ISUPPORTS_INHERITED1(nsFastLoadFileUpdater,
+                             nsFastLoadFileWriter,
+                             nsIFastLoadFileIO)
+
+NS_IMETHODIMP
+nsFastLoadFileUpdater::GetInputStream(nsIInputStream** aResult)
+{
+    *aResult = mInputStream;
+    NS_IF_ADDREF(*aResult);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileUpdater::GetOutputStream(nsIOutputStream** aResult)
+{
+    *aResult = nsnull;
+    return NS_OK;
+}
+
+PLDHashOperator PR_CALLBACK
+nsFastLoadFileUpdater::CopyReadDocumentMapEntryToUpdater(PLDHashTable *aTable,
+                                                         PLDHashEntryHdr *aHdr,
+                                                         PRUint32 aNumber,
+                                                         void *aData)
+{
+    nsDocumentMapReadEntry* readEntry =
+        NS_STATIC_CAST(nsDocumentMapReadEntry*, aHdr);
+    nsFastLoadFileUpdater* updater =
+        NS_REINTERPRET_CAST(nsFastLoadFileUpdater*, aData);
+
+    void* spec = nsMemory::Clone(readEntry->mString,
+                                 strlen(readEntry->mString) + 1);
+    if (!spec)
+        return PL_DHASH_STOP;
+
+    nsDocumentMapWriteEntry* writeEntry =
+        NS_STATIC_CAST(nsDocumentMapWriteEntry*,
+                       PL_DHashTableOperate(&updater->mDocumentMap, spec,
+                                            PL_DHASH_ADD));
+    if (!writeEntry) {
+        nsMemory::Free(spec);
+        return PL_DHASH_STOP;
+    }
+
+    writeEntry->mString = NS_REINTERPRET_CAST(const char*, spec);
+    writeEntry->mURI = nsnull;
+    writeEntry->mInitialSegmentOffset = readEntry->mInitialSegmentOffset;
+    writeEntry->mCurrentSegmentOffset = 0;
+    return PL_DHASH_NEXT;
+}
+
+nsresult
+nsFastLoadFileUpdater::Open(nsFastLoadFileReader* aReader)
+{
+    nsCOMPtr<nsISeekableStream> seekable(do_QueryInterface(mOutputStream));
+    if (!seekable)
+        return NS_ERROR_UNEXPECTED;
+
+    nsresult rv;
+    rv = nsFastLoadFileWriter::Init();
+    if (NS_FAILED(rv))
+        return rv;
+
+    PRUint32 i, n;
+
+    // Map from dense, zero-based, uint32 NSFastLoadID in reader to 16-byte
+    // nsID in updater.
+    nsID* readIDMap = aReader->mFooter.mIDMap;
+    for (i = 0, n = aReader->mFooter.mNumIDs; i < n; i++) {
+        NSFastLoadID fastID;
+        rv = MapID(readIDMap[i], &fastID);
+        NS_ASSERTION(fastID == i + 1, "huh?");
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // Map from reader dense, zero-based MFL_OID_TO_SHARP_INDEX(oid) to sharp
+    // object offset and refcnt information in updater.
+    nsFastLoadFileReader::nsObjectMapEntry* readObjectMap =
+        aReader->mFooter.mObjectMap;
+
+    // Prepare to save aReader state in case we need to seek back and read a
+    // singleton object that might otherwise get written by this updater.
+    nsDocumentMapReadEntry* saveDocMapEntry = nsnull;
+    nsCOMPtr<nsISeekableStream> inputSeekable;
+    PRInt64 saveOffset = 0;
+
+    for (i = 0, n = aReader->mFooter.mNumSharpObjects; i < n; i++) {
+        nsFastLoadFileReader::nsObjectMapEntry* readEntry = &readObjectMap[i];
+
+        NS_ASSERTION(readEntry->mCIDOffset != 0,
+                     "fastload updater: mCIDOffset cannot be zero!");
+
+        // If the reader didn't read this object but it's a singleton, we must
+        // "deserialize" it now, to discover its one and only root nsISupports
+        // address.  The object already exists in memory if it was created at
+        // startup without resort to the FastLoad file.  The canonical example
+        // is the system principal object held by all XUL JS scripts.
+
+        nsISupports* obj = readEntry->mReadObject;
+        if (!obj && MFL_GET_SINGLETON_FLAG(readEntry)) {
+            if (!saveDocMapEntry) {
+                inputSeekable = do_QueryInterface(aReader->mInputStream);
+                rv = inputSeekable->Tell(&saveOffset);
+                if (NS_FAILED(rv))
+                    return rv;
+
+                saveDocMapEntry = aReader->mCurrentDocumentMapEntry;
+                aReader->mCurrentDocumentMapEntry = nsnull;
+            }
+
+            rv = inputSeekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                                     readEntry->mCIDOffset);
+            if (NS_FAILED(rv))
+                return rv;
+
+            rv = aReader
+                 ->DeserializeObject(getter_AddRefs(readEntry->mReadObject));
+            if (NS_FAILED(rv))
+                return rv;
+            obj = readEntry->mReadObject;
+
+            // Don't forget to set mSkipOffset in case someone calls the reader
+            // to "deserialize" (yet again) the object we just read.
+            //
+            // Say the singleton is the system principal, and the FastLoad file
+            // contains data for navigator.xul including scripts and functions.
+            // If we update the FastLoad file to contain data for messenger.xul
+            // in a separate session started via mozilla -mail, *and during the
+            // same FastLoad episode in this session* race to open a navigator
+            // window, we will attempt to read all objects serialized in the
+            // navigator.xul portion of the FastLoad file.
+            //
+            // mSkipOffset must be set in such a case so the reader can skip
+            // the system principal's serialized data, because the updater for
+            // messenger.xul being opened here has already read it.
+
+            rv = inputSeekable->Tell(&readEntry->mSkipOffset);
+            if (NS_FAILED(rv))
+                return rv;
+        }
+
+        NSFastLoadOID oid = MFL_SHARP_INDEX_TO_OID(i);
+        void* key = obj
+                    ? NS_REINTERPRET_CAST(void*, obj)
+                    : NS_REINTERPRET_CAST(void*, (oid | MFL_OBJECT_DEF_TAG));
+
+        nsSharpObjectMapEntry* writeEntry =
+            NS_STATIC_CAST(nsSharpObjectMapEntry*,
+                           PL_DHashTableOperate(&mObjectMap, key,
+                                                PL_DHASH_ADD));
+        if (!writeEntry)
+            return NS_ERROR_OUT_OF_MEMORY;
+
+        // Hold the object if there is one, so that objmap_ClearEntry can
+        // release the reference.
+        NS_IF_ADDREF(obj);
+        writeEntry->mObject = NS_REINTERPRET_CAST(nsISupports*, key);
+        writeEntry->mOID = oid;
+        writeEntry->mInfo.mCIDOffset = readEntry->mCIDOffset;
+        writeEntry->mInfo.mStrongRefCnt = readEntry->mSaveStrongRefCnt;
+        writeEntry->mInfo.mWeakRefCnt = readEntry->mSaveWeakRefCnt;
+    }
+
+    // If we had to read any singletons, restore aReader's saved state.
+    if (saveDocMapEntry) {
+        rv = inputSeekable->Seek(nsISeekableStream::NS_SEEK_SET, saveOffset);
+        if (NS_FAILED(rv))
+            return rv;
+
+        aReader->mCurrentDocumentMapEntry = saveDocMapEntry;
+    }
+
+    // Copy URI spec string and initial segment offset in FastLoad file from
+    // nsDocumentMapReadEntry in reader to nsDocumentMapWriteEntry in updater.
+    // If we didn't enumerate all entries, we ran out of memory.
+    n = PL_DHashTableEnumerate(&aReader->mFooter.mDocumentMap,
+                               CopyReadDocumentMapEntryToUpdater,
+                               this);
+    if (n != aReader->mFooter.mDocumentMap.entryCount)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // Copy source filename dependencies from reader to updater.
+    nsISupportsArray* readDeps = aReader->mFooter.mDependencies;
+    rv = readDeps->Count(&n);
+    if (NS_FAILED(rv))
+        return rv;
+
+    for (i = 0; i < n; i++) {
+        nsCOMPtr<nsIFile> file;
+        rv = readDeps->GetElementAt(i, getter_AddRefs(file));
+        if (NS_FAILED(rv))
+            return rv;
+
+        rv = AddDependency(file);
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // Seek to the reader's footer offset so we overwrite the footer.  First,
+    // update the header to have a zero mFooterOffset, which will invalidate
+    // the FastLoad file on next startup read attempt, should we crash before
+    // completing this update.
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                        offsetof(nsFastLoadHeader, mFooterOffset));
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = Write32(0);
+    if (NS_FAILED(rv))
+        return rv;
+
+    rv = seekable->Seek(nsISeekableStream::NS_SEEK_SET,
+                        aReader->mHeader.mFooterOffset);
+    if (NS_FAILED(rv))
+        return rv;
+
+    // Avoid creating yet another object by implementing nsIFastLoadFileIO on
+    // this updater, and save aReader's input stream so it can be returned by
+    // GetInputStream called from nsFastLoadFileWriter::Close.  This requires
+    // that we override Close to break the resulting zero-length cycle.
+    mFileIO = this;
+    mInputStream = aReader->mInputStream;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFastLoadFileUpdater::Close()
+{
+    // Call base-class Close implementation, which uses mFileIO.
+    nsresult rv = nsFastLoadFileWriter::Close();
+
+    // Break degenerate cycle from this->mFileIO to this.
+    mFileIO = nsnull;
+    return rv;
+}
+
+NS_COM nsresult
+NS_NewFastLoadFileUpdater(nsIObjectOutputStream* *aResult,
+                          nsIOutputStream* aOutputStream,
+                          nsIObjectInputStream* aReaderAsStream)
+{
+    // Make sure that aReaderAsStream is an nsFastLoadFileReader.
+    nsCOMPtr<nsIFastLoadFileReader> reader(do_QueryInterface(aReaderAsStream));
+    if (!reader)
+        return NS_ERROR_UNEXPECTED;
+
+    nsFastLoadFileUpdater* updater = new nsFastLoadFileUpdater(aOutputStream);
+    if (!updater)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // Stabilize updater's refcnt.
+    nsCOMPtr<nsIObjectOutputStream> stream(updater);
+
+    nsresult rv = updater->Open(NS_STATIC_CAST(nsFastLoadFileReader*,
+                                               aReaderAsStream));
+    if (NS_FAILED(rv))
+        return rv;
+
+    *aResult = stream;
+    NS_ADDREF(*aResult);
+    return NS_OK;
+}