Add m-esr52 at 52.6.0

1 files changed, 1358 insertions, 0 deletions

diff --git a/rdf/base/nsCompositeDataSource.cpp b/rdf/base/nsCompositeDataSource.cpp
new file mode 100644
index 000000000..37167d356
--- /dev/null
+++ b/rdf/base/nsCompositeDataSource.cpp
@@ -0,0 +1,1358 @@
+/* -*- 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/. */
+
+/*
+
+  A simple composite data source implementation. A composit data
+  source is just a strategy for combining individual data sources into
+  a collective graph.
+
+
+  1) A composite data source holds a sequence of data sources. The set
+     of data sources can be specified during creation of the
+     database. Data sources can also be added/deleted from a database
+     later.
+
+  2) The aggregation mechanism is based on simple super-positioning of
+     the graphs from the datasources. If there is a conflict (i.e., 
+     data source A has a true arc from foo to bar while data source B
+     has a false arc from foo to bar), the data source that it earlier
+     in the sequence wins.
+
+     The implementation below doesn't really do this and needs to be
+     fixed.
+
+*/
+
+#include "xpcom-config.h"
+#include "nsCOMPtr.h"
+#include "nsIComponentManager.h"
+#include "nsIRDFCompositeDataSource.h"
+#include "nsIRDFNode.h"
+#include "nsIRDFObserver.h"
+#include "nsIRDFRemoteDataSource.h"
+#include "nsTArray.h"
+#include "nsCOMArray.h"
+#include "nsArrayEnumerator.h"
+#include "nsXPIDLString.h"
+#include "rdf.h"
+#include "nsCycleCollectionParticipant.h"
+
+#include "nsEnumeratorUtils.h"
+
+#include "mozilla/Logging.h"
+#include "prprf.h"
+#include <stdio.h>
+mozilla::LazyLogModule nsRDFLog("RDF");
+
+//----------------------------------------------------------------------
+//
+// CompositeDataSourceImpl
+//
+
+class CompositeEnumeratorImpl;
+class CompositeArcsInOutEnumeratorImpl;
+class CompositeAssertionEnumeratorImpl;
+
+class CompositeDataSourceImpl : public nsIRDFCompositeDataSource,
+                                public nsIRDFObserver
+{
+public:
+    CompositeDataSourceImpl(void);
+    explicit CompositeDataSourceImpl(char** dataSources);
+
+    // nsISupports interface
+    NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+    NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(CompositeDataSourceImpl,
+                                             nsIRDFCompositeDataSource)
+
+    // nsIRDFDataSource interface
+    NS_DECL_NSIRDFDATASOURCE
+
+    // nsIRDFCompositeDataSource interface
+    NS_DECL_NSIRDFCOMPOSITEDATASOURCE
+
+    // nsIRDFObserver interface
+    NS_DECL_NSIRDFOBSERVER
+
+    bool HasAssertionN(int n, nsIRDFResource* source,
+                            nsIRDFResource* property,
+                            nsIRDFNode* target,
+                            bool tv);
+
+protected:
+    nsCOMArray<nsIRDFObserver> mObservers;
+    nsCOMArray<nsIRDFDataSource> mDataSources;
+
+    bool        mAllowNegativeAssertions;
+    bool        mCoalesceDuplicateArcs;
+    int32_t     mUpdateBatchNest;
+
+    virtual ~CompositeDataSourceImpl() {}
+
+    friend class CompositeEnumeratorImpl;
+    friend class CompositeArcsInOutEnumeratorImpl;
+    friend class CompositeAssertionEnumeratorImpl;
+};
+
+//----------------------------------------------------------------------
+//
+// CompositeEnumeratorImpl
+//
+
+class CompositeEnumeratorImpl : public nsISimpleEnumerator
+{
+    // nsISupports
+    NS_DECL_ISUPPORTS
+
+    // nsISimpleEnumerator interface
+    NS_DECL_NSISIMPLEENUMERATOR
+
+    // pure abstract methods to be overridden
+    virtual nsresult
+    GetEnumerator(nsIRDFDataSource* aDataSource, nsISimpleEnumerator** aResult) = 0;
+
+    virtual nsresult
+    HasNegation(nsIRDFDataSource* aDataSource, nsIRDFNode* aNode, bool* aResult) = 0;
+
+protected:
+    CompositeEnumeratorImpl(CompositeDataSourceImpl* aCompositeDataSource,
+                            bool aAllowNegativeAssertions,
+                            bool aCoalesceDuplicateArcs);
+
+    virtual ~CompositeEnumeratorImpl();
+
+    CompositeDataSourceImpl* mCompositeDataSource;
+
+    nsISimpleEnumerator* mCurrent;
+    nsIRDFNode*  mResult;
+    int32_t      mNext;
+    AutoTArray<nsCOMPtr<nsIRDFNode>, 8>  mAlreadyReturned;
+    bool mAllowNegativeAssertions;
+    bool mCoalesceDuplicateArcs;
+};
+
+
+CompositeEnumeratorImpl::CompositeEnumeratorImpl(CompositeDataSourceImpl* aCompositeDataSource,
+                                                 bool aAllowNegativeAssertions,
+                                                 bool aCoalesceDuplicateArcs)
+    : mCompositeDataSource(aCompositeDataSource),
+      mCurrent(nullptr),
+      mResult(nullptr),
+	  mNext(0),
+      mAllowNegativeAssertions(aAllowNegativeAssertions),
+      mCoalesceDuplicateArcs(aCoalesceDuplicateArcs)
+{
+    NS_ADDREF(mCompositeDataSource);
+}
+
+
+CompositeEnumeratorImpl::~CompositeEnumeratorImpl(void)
+{
+    NS_IF_RELEASE(mCurrent);
+    NS_IF_RELEASE(mResult);
+    NS_RELEASE(mCompositeDataSource);
+}
+
+NS_IMPL_ADDREF(CompositeEnumeratorImpl)
+NS_IMPL_RELEASE(CompositeEnumeratorImpl)
+NS_IMPL_QUERY_INTERFACE(CompositeEnumeratorImpl, nsISimpleEnumerator)
+
+NS_IMETHODIMP
+CompositeEnumeratorImpl::HasMoreElements(bool* aResult)
+{
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    nsresult rv;
+
+    // If we've already queued up a next target, then yep, there are
+    // more elements.
+    if (mResult) {
+        *aResult = true;
+        return NS_OK;
+    }
+
+    // Otherwise, we'll need to find a next target, switching cursors
+    // if necessary.
+    for ( ; mNext < mCompositeDataSource->mDataSources.Count(); ++mNext) {
+        if (! mCurrent) {
+            // We don't have a current enumerator, so create a new one on
+            // the next data source.
+            nsIRDFDataSource* datasource =
+                mCompositeDataSource->mDataSources[mNext];
+
+            rv = GetEnumerator(datasource, &mCurrent);
+            if (NS_FAILED(rv)) return rv;
+            if (rv == NS_RDF_NO_VALUE)
+                continue;
+
+            NS_ASSERTION(mCurrent != nullptr, "you're always supposed to return an enumerator from GetEnumerator, punk.");
+            if (! mCurrent)
+                continue;
+        }
+
+        do {
+            int32_t i;
+
+            bool hasMore;
+            rv = mCurrent->HasMoreElements(&hasMore);
+            if (NS_FAILED(rv)) return rv;
+
+            // Is the current enumerator depleted?
+            if (! hasMore) {
+                NS_RELEASE(mCurrent);
+                break;
+            }
+
+            // Even if the current enumerator has more elements, we still
+            // need to check that the current element isn't masked by
+            // a negation in an earlier data source.
+
+            // "Peek" ahead and pull out the next target.
+            nsCOMPtr<nsISupports> result;
+            rv = mCurrent->GetNext(getter_AddRefs(result));
+            if (NS_FAILED(rv)) return rv;
+
+            rv = result->QueryInterface(NS_GET_IID(nsIRDFNode), (void**) &mResult);
+            if (NS_FAILED(rv)) return rv;
+
+            if (mAllowNegativeAssertions)
+            {
+                // See if any previous data source negates this
+                bool hasNegation = false;
+                for (i = mNext - 1; i >= 0; --i)
+                {
+                    nsIRDFDataSource* datasource =
+                        mCompositeDataSource->mDataSources[i];
+
+                    rv = HasNegation(datasource, mResult, &hasNegation);
+                    if (NS_FAILED(rv)) return rv;
+
+                    if (hasNegation)
+                        break;
+                }
+
+                // if so, we've gotta keep looking
+                if (hasNegation)
+                {
+                    NS_RELEASE(mResult);
+                    continue;
+                }
+            }
+
+            if (mCoalesceDuplicateArcs)
+            {
+                // Now see if we've returned it once already.
+                // XXX N.B. performance here...may want to hash if things get large?
+                bool alreadyReturned = false;
+                for (i = mAlreadyReturned.Length() - 1; i >= 0; --i)
+                {
+                    if (mAlreadyReturned[i] == mResult)
+                    {
+                        alreadyReturned = true;
+                        break;
+                    }
+                }
+                if (alreadyReturned)
+                {
+                    NS_RELEASE(mResult);
+                    continue;
+                }
+            }
+
+            // If we get here, then we've really found one. It'll
+            // remain cached in mResult until GetNext() sucks it out.
+            *aResult = true;
+
+            // Remember that we returned it, so we don't return duplicates.
+
+            // XXX I wonder if we should make unique-checking be
+            // optional. This could get to be pretty expensive (this
+            // implementation turns iteration into O(n^2)).
+
+            if (mCoalesceDuplicateArcs)
+            {
+                mAlreadyReturned.AppendElement(mResult);
+            }
+
+            return NS_OK;
+        } while (1);
+    }
+
+    // if we get here, there aren't any elements left.
+    *aResult = false;
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeEnumeratorImpl::GetNext(nsISupports** aResult)
+{
+    nsresult rv;
+
+    bool hasMore;
+    rv = HasMoreElements(&hasMore);
+    if (NS_FAILED(rv)) return rv;
+
+    if (! hasMore)
+        return NS_ERROR_UNEXPECTED;
+
+    // Don't AddRef: we "transfer" ownership to the caller
+    *aResult = mResult;
+    mResult = nullptr;
+
+    return NS_OK;
+}
+
+//----------------------------------------------------------------------
+//
+// CompositeArcsInOutEnumeratorImpl
+//
+//
+
+class CompositeArcsInOutEnumeratorImpl : public CompositeEnumeratorImpl
+{
+public:
+    enum Type { eArcsIn, eArcsOut };
+
+    virtual ~CompositeArcsInOutEnumeratorImpl();
+
+    virtual nsresult
+    GetEnumerator(nsIRDFDataSource* aDataSource, nsISimpleEnumerator** aResult);
+
+    virtual nsresult
+    HasNegation(nsIRDFDataSource* aDataSource, nsIRDFNode* aNode, bool* aResult);
+
+    CompositeArcsInOutEnumeratorImpl(CompositeDataSourceImpl* aCompositeDataSource,
+                                     nsIRDFNode* aNode,
+                                     Type aType,
+                                     bool aAllowNegativeAssertions,
+                                     bool aCoalesceDuplicateArcs);
+
+private:
+    nsIRDFNode* mNode;
+    Type        mType;
+};
+
+
+CompositeArcsInOutEnumeratorImpl::CompositeArcsInOutEnumeratorImpl(
+                CompositeDataSourceImpl* aCompositeDataSource,
+                nsIRDFNode* aNode,
+                Type aType,
+                bool aAllowNegativeAssertions,
+                bool aCoalesceDuplicateArcs)
+    : CompositeEnumeratorImpl(aCompositeDataSource, aAllowNegativeAssertions, aCoalesceDuplicateArcs),
+      mNode(aNode),
+      mType(aType)
+{
+    NS_ADDREF(mNode);
+}
+
+CompositeArcsInOutEnumeratorImpl::~CompositeArcsInOutEnumeratorImpl()
+{
+    NS_RELEASE(mNode);
+}
+
+
+nsresult
+CompositeArcsInOutEnumeratorImpl::GetEnumerator(
+                 nsIRDFDataSource* aDataSource,
+                 nsISimpleEnumerator** aResult)
+{
+    if (mType == eArcsIn) {
+        return aDataSource->ArcLabelsIn(mNode, aResult);
+    }
+    else {
+        nsCOMPtr<nsIRDFResource> resource( do_QueryInterface(mNode) );
+        return aDataSource->ArcLabelsOut(resource, aResult);
+    }
+}
+
+nsresult
+CompositeArcsInOutEnumeratorImpl::HasNegation(
+                 nsIRDFDataSource* aDataSource,
+                 nsIRDFNode* aNode,
+                 bool* aResult)
+{
+    *aResult = false;
+    return NS_OK;
+}
+
+
+//----------------------------------------------------------------------
+//
+// CompositeAssertionEnumeratorImpl
+//
+
+class CompositeAssertionEnumeratorImpl : public CompositeEnumeratorImpl
+{
+public:
+    virtual nsresult
+    GetEnumerator(nsIRDFDataSource* aDataSource, nsISimpleEnumerator** aResult);
+
+    virtual nsresult
+    HasNegation(nsIRDFDataSource* aDataSource, nsIRDFNode* aNode, bool* aResult);
+
+    CompositeAssertionEnumeratorImpl(CompositeDataSourceImpl* aCompositeDataSource,
+                                     nsIRDFResource* aSource,
+                                     nsIRDFResource* aProperty,
+                                     nsIRDFNode* aTarget,
+                                     bool aTruthValue,
+                                     bool aAllowNegativeAssertions,
+                                     bool aCoalesceDuplicateArcs);
+
+    virtual ~CompositeAssertionEnumeratorImpl();
+
+private:
+    nsIRDFResource* mSource;
+    nsIRDFResource* mProperty;
+    nsIRDFNode*     mTarget;
+    bool            mTruthValue;
+};
+
+
+CompositeAssertionEnumeratorImpl::CompositeAssertionEnumeratorImpl(
+                  CompositeDataSourceImpl* aCompositeDataSource,
+                  nsIRDFResource* aSource,
+                  nsIRDFResource* aProperty,
+                  nsIRDFNode* aTarget,
+                  bool aTruthValue,
+                  bool aAllowNegativeAssertions,
+                  bool aCoalesceDuplicateArcs)
+    : CompositeEnumeratorImpl(aCompositeDataSource, aAllowNegativeAssertions, aCoalesceDuplicateArcs),
+      mSource(aSource),
+      mProperty(aProperty),
+      mTarget(aTarget),
+      mTruthValue(aTruthValue)
+{
+    NS_IF_ADDREF(mSource);
+    NS_ADDREF(mProperty); // always must be specified
+    NS_IF_ADDREF(mTarget);
+}
+
+CompositeAssertionEnumeratorImpl::~CompositeAssertionEnumeratorImpl()
+{
+    NS_IF_RELEASE(mSource);
+    NS_RELEASE(mProperty);
+    NS_IF_RELEASE(mTarget);
+}
+
+
+nsresult
+CompositeAssertionEnumeratorImpl::GetEnumerator(
+                 nsIRDFDataSource* aDataSource,
+                 nsISimpleEnumerator** aResult)
+{
+    if (mSource) {
+        return aDataSource->GetTargets(mSource, mProperty, mTruthValue, aResult);
+    }
+    else {
+        return aDataSource->GetSources(mProperty, mTarget, mTruthValue, aResult);
+    }
+}
+
+nsresult
+CompositeAssertionEnumeratorImpl::HasNegation(
+                 nsIRDFDataSource* aDataSource,
+                 nsIRDFNode* aNode,
+                 bool* aResult)
+{
+    if (mSource) {
+        return aDataSource->HasAssertion(mSource, mProperty, aNode, !mTruthValue, aResult);
+    }
+    else {
+        nsCOMPtr<nsIRDFResource> source( do_QueryInterface(aNode) );
+        return aDataSource->HasAssertion(source, mProperty, mTarget, !mTruthValue, aResult);
+    }
+}
+
+////////////////////////////////////////////////////////////////////////
+
+nsresult
+NS_NewRDFCompositeDataSource(nsIRDFCompositeDataSource** result)
+{
+    CompositeDataSourceImpl* db = new CompositeDataSourceImpl();
+    if (! db)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    *result = db;
+    NS_ADDREF(*result);
+    return NS_OK;
+}
+
+
+CompositeDataSourceImpl::CompositeDataSourceImpl(void)
+	: mAllowNegativeAssertions(true),
+	  mCoalesceDuplicateArcs(true),
+      mUpdateBatchNest(0)
+{
+}
+
+//----------------------------------------------------------------------
+//
+// nsISupports interface
+//
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(CompositeDataSourceImpl)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(CompositeDataSourceImpl)
+    uint32_t i, count = tmp->mDataSources.Count();
+    for (i = count; i > 0; --i) {
+        tmp->mDataSources[i - 1]->RemoveObserver(tmp);
+        tmp->mDataSources.RemoveObjectAt(i - 1);
+    }
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mObservers);
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(CompositeDataSourceImpl)
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mObservers)
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDataSources)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(CompositeDataSourceImpl)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(CompositeDataSourceImpl)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(CompositeDataSourceImpl)
+    NS_INTERFACE_MAP_ENTRY(nsIRDFCompositeDataSource)
+    NS_INTERFACE_MAP_ENTRY(nsIRDFDataSource)
+    NS_INTERFACE_MAP_ENTRY(nsIRDFObserver)
+    NS_INTERFACE_MAP_ENTRY(nsIRDFCompositeDataSource)
+    NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIRDFCompositeDataSource)
+NS_INTERFACE_MAP_END
+
+
+//----------------------------------------------------------------------
+//
+// nsIRDFDataSource interface
+//
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetURI(char* *uri)
+{
+    *uri = nullptr;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetSource(nsIRDFResource* property,
+                                   nsIRDFNode* target,
+                                   bool tv,
+                                   nsIRDFResource** source)
+{
+	if (!mAllowNegativeAssertions && !tv)
+		return(NS_RDF_NO_VALUE);
+
+    int32_t count = mDataSources.Count();
+    for (int32_t i = 0; i < count; ++i) {
+        nsresult rv;
+        rv = mDataSources[i]->GetSource(property, target, tv, source);
+        if (NS_FAILED(rv)) return rv;
+
+        if (rv == NS_RDF_NO_VALUE)
+            continue;
+
+        if (!mAllowNegativeAssertions) return(NS_OK);
+
+        // okay, found it. make sure we don't have the opposite
+        // asserted in a more local data source
+        if (!HasAssertionN(count-1, *source, property, target, !tv)) 
+            return NS_OK;
+
+        NS_RELEASE(*source);
+        return NS_RDF_NO_VALUE;
+    }
+    return NS_RDF_NO_VALUE;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetSources(nsIRDFResource* aProperty,
+                                    nsIRDFNode* aTarget,
+                                    bool aTruthValue,
+                                    nsISimpleEnumerator** aResult)
+{
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aTarget != nullptr, "null ptr");
+    if (! aTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (! mAllowNegativeAssertions && ! aTruthValue)
+        return(NS_RDF_NO_VALUE);
+
+    *aResult = new CompositeAssertionEnumeratorImpl(this, nullptr, aProperty,
+                                                    aTarget, aTruthValue,
+                                                    mAllowNegativeAssertions,
+                                                    mCoalesceDuplicateArcs);
+
+    if (! *aResult)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(*aResult);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetTarget(nsIRDFResource* aSource,
+                                   nsIRDFResource* aProperty,
+                                   bool aTruthValue,
+                                   nsIRDFNode** aResult)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (! mAllowNegativeAssertions && ! aTruthValue)
+        return(NS_RDF_NO_VALUE);
+
+    int32_t count = mDataSources.Count();
+    for (int32_t i = 0; i < count; ++i) {
+        nsresult rv;
+        rv = mDataSources[i]->GetTarget(aSource, aProperty, aTruthValue,
+                                        aResult);
+        if (NS_FAILED(rv))
+            return rv;
+
+        if (rv == NS_OK) {
+            // okay, found it. make sure we don't have the opposite
+            // asserted in an earlier data source
+
+            if (mAllowNegativeAssertions) {
+                if (HasAssertionN(count-1, aSource, aProperty, *aResult, !aTruthValue)) {
+                    // whoops, it's been negated.
+                    NS_RELEASE(*aResult);
+                    return NS_RDF_NO_VALUE;
+                }
+            }
+            return NS_OK;
+        }
+    }
+
+    // Otherwise, we couldn't find it at all.
+    return NS_RDF_NO_VALUE;
+}
+
+bool
+CompositeDataSourceImpl::HasAssertionN(int n,
+                                       nsIRDFResource* aSource,
+                                       nsIRDFResource* aProperty,
+                                       nsIRDFNode* aTarget,
+                                       bool aTruthValue)
+{
+    nsresult rv;
+    for (int32_t m = 0; m < n; ++m) {
+        bool result;
+        rv = mDataSources[m]->HasAssertion(aSource, aProperty, aTarget,
+                                           aTruthValue, &result);
+        if (NS_FAILED(rv))
+            return false;
+
+        // found it!
+        if (result)
+            return true;
+    }
+    return false;
+}
+    
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetTargets(nsIRDFResource* aSource,
+                                    nsIRDFResource* aProperty,
+                                    bool aTruthValue,
+                                    nsISimpleEnumerator** aResult)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (! mAllowNegativeAssertions && ! aTruthValue)
+        return(NS_RDF_NO_VALUE);
+
+    *aResult =
+        new CompositeAssertionEnumeratorImpl(this,
+                                             aSource, aProperty, nullptr,
+                                             aTruthValue,
+                                             mAllowNegativeAssertions,
+                                             mCoalesceDuplicateArcs);
+
+    if (! *aResult)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(*aResult);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::Assert(nsIRDFResource* aSource, 
+                                nsIRDFResource* aProperty, 
+                                nsIRDFNode* aTarget,
+                                bool aTruthValue)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aTarget != nullptr, "null ptr");
+    if (! aTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    if (! mAllowNegativeAssertions && ! aTruthValue)
+        return(NS_RDF_ASSERTION_REJECTED);
+
+    nsresult rv;
+
+    // XXX Need to add back the stuff for unblocking ...
+
+    // We iterate backwards from the last data source which was added
+    // ("the most remote") to the first ("the most local"), trying to
+    // apply the assertion in each.
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        rv = mDataSources[i]->Assert(aSource, aProperty, aTarget, aTruthValue);
+        if (NS_RDF_ASSERTION_ACCEPTED == rv)
+            return rv;
+
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // nobody wanted to accept it
+    return NS_RDF_ASSERTION_REJECTED;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::Unassert(nsIRDFResource* aSource,
+                                  nsIRDFResource* aProperty,
+                                  nsIRDFNode* aTarget)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aTarget != nullptr, "null ptr");
+    if (! aTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    nsresult rv;
+
+    // Iterate through each of the datasources, starting with "the
+    // most local" and moving to "the most remote". If _any_ of the
+    // datasources have the assertion, attempt to unassert it.
+    bool unasserted = true;
+    int32_t i;
+    int32_t count = mDataSources.Count();
+    for (i = 0; i < count; ++i) {
+        nsIRDFDataSource* ds = mDataSources[i];
+
+        bool hasAssertion;
+        rv = ds->HasAssertion(aSource, aProperty, aTarget, true, &hasAssertion);
+        if (NS_FAILED(rv)) return rv;
+
+        if (hasAssertion) {
+            rv = ds->Unassert(aSource, aProperty, aTarget);
+            if (NS_FAILED(rv)) return rv;
+
+            if (rv != NS_RDF_ASSERTION_ACCEPTED) {
+                unasserted = false;
+                break;
+            }
+        }
+    }
+
+    // Either none of the datasources had it, or they were all willing
+    // to let it be unasserted.
+    if (unasserted)
+        return NS_RDF_ASSERTION_ACCEPTED;
+
+    // If we get here, one of the datasources already had the
+    // assertion, and was adamant about not letting us remove
+    // it. Iterate from the "most local" to the "most remote"
+    // attempting to assert the negation...
+    for (i = 0; i < count; ++i) {
+        rv = mDataSources[i]->Assert(aSource, aProperty, aTarget, false);
+        if (NS_FAILED(rv)) return rv;
+
+        // Did it take?
+        if (rv == NS_RDF_ASSERTION_ACCEPTED)
+            return rv;
+    }
+
+    // Couln't get anyone to accept the negation, either.
+    return NS_RDF_ASSERTION_REJECTED;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::Change(nsIRDFResource* aSource,
+                                nsIRDFResource* aProperty,
+                                nsIRDFNode* aOldTarget,
+                                nsIRDFNode* aNewTarget)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aOldTarget != nullptr, "null ptr");
+    if (! aOldTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aNewTarget != nullptr, "null ptr");
+    if (! aNewTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    nsresult rv;
+
+    // XXX So we're assuming that a datasource _must_ accept the
+    // atomic change; i.e., we can't split it up across two
+    // datasources. That sucks.
+
+    // We iterate backwards from the last data source which was added
+    // ("the most remote") to the first ("the most local"), trying to
+    // apply the change in each.
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        rv = mDataSources[i]->Change(aSource, aProperty, aOldTarget, aNewTarget);
+        if (NS_RDF_ASSERTION_ACCEPTED == rv)
+            return rv;
+
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // nobody wanted to accept it
+    return NS_RDF_ASSERTION_REJECTED;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::Move(nsIRDFResource* aOldSource,
+                              nsIRDFResource* aNewSource,
+                              nsIRDFResource* aProperty,
+                              nsIRDFNode* aTarget)
+{
+    NS_PRECONDITION(aOldSource != nullptr, "null ptr");
+    if (! aOldSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aNewSource != nullptr, "null ptr");
+    if (! aNewSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aTarget != nullptr, "null ptr");
+    if (! aTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    nsresult rv;
+
+    // XXX So we're assuming that a datasource _must_ accept the
+    // atomic move; i.e., we can't split it up across two
+    // datasources. That sucks.
+
+    // We iterate backwards from the last data source which was added
+    // ("the most remote") to the first ("the most local"), trying to
+    // apply the assertion in each.
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        rv = mDataSources[i]->Move(aOldSource, aNewSource, aProperty, aTarget);
+        if (NS_RDF_ASSERTION_ACCEPTED == rv)
+            return rv;
+
+        if (NS_FAILED(rv))
+            return rv;
+    }
+
+    // nobody wanted to accept it
+    return NS_RDF_ASSERTION_REJECTED;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::HasAssertion(nsIRDFResource* aSource,
+                                      nsIRDFResource* aProperty,
+                                      nsIRDFNode* aTarget,
+                                      bool aTruthValue,
+                                      bool* aResult)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aProperty != nullptr, "null ptr");
+    if (! aProperty)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    if (! mAllowNegativeAssertions && ! aTruthValue)
+    {
+        *aResult = false;
+        return(NS_OK);
+    }
+
+    nsresult rv;
+
+    // Otherwise, look through all the data sources to see if anyone
+    // has the positive...
+    int32_t count = mDataSources.Count();
+    for (int32_t i = 0; i < count; ++i) {
+        nsIRDFDataSource* datasource = mDataSources[i];
+        rv = datasource->HasAssertion(aSource, aProperty, aTarget, aTruthValue, aResult);
+        if (NS_FAILED(rv)) return rv;
+
+        if (*aResult)
+            return NS_OK;
+
+        if (mAllowNegativeAssertions)
+        {
+            bool hasNegation;
+            rv = datasource->HasAssertion(aSource, aProperty, aTarget, !aTruthValue, &hasNegation);
+            if (NS_FAILED(rv)) return rv;
+
+            if (hasNegation)
+            {
+                *aResult = false;
+                return NS_OK;
+            }
+        }
+    }
+
+    // If we get here, nobody had the assertion at all
+    *aResult = false;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::AddObserver(nsIRDFObserver* aObserver)
+{
+    NS_PRECONDITION(aObserver != nullptr, "null ptr");
+    if (! aObserver)
+        return NS_ERROR_NULL_POINTER;
+
+    // XXX ensure uniqueness?
+    mObservers.AppendObject(aObserver);
+
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::RemoveObserver(nsIRDFObserver* aObserver)
+{
+    NS_PRECONDITION(aObserver != nullptr, "null ptr");
+    if (! aObserver)
+        return NS_ERROR_NULL_POINTER;
+
+    mObservers.RemoveObject(aObserver);
+
+    return NS_OK;
+}
+
+NS_IMETHODIMP 
+CompositeDataSourceImpl::HasArcIn(nsIRDFNode *aNode, nsIRDFResource *aArc, bool *result)
+{
+    nsresult rv;
+    *result = false;
+    int32_t count = mDataSources.Count();
+    for (int32_t i = 0; i < count; ++i) {
+        rv = mDataSources[i]->HasArcIn(aNode, aArc, result);
+        if (NS_FAILED(rv)) return rv;
+        if (*result)
+            return NS_OK;
+    }
+    return NS_OK;
+}
+
+NS_IMETHODIMP 
+CompositeDataSourceImpl::HasArcOut(nsIRDFResource *aSource, nsIRDFResource *aArc, bool *result)
+{
+    nsresult rv;
+    *result = false;
+    int32_t count = mDataSources.Count();
+    for (int32_t i = 0; i < count; ++i) {
+        rv = mDataSources[i]->HasArcOut(aSource, aArc, result);
+        if (NS_FAILED(rv)) return rv;
+        if (*result)
+            return NS_OK;
+    }
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::ArcLabelsIn(nsIRDFNode* aTarget, nsISimpleEnumerator** aResult)
+{
+    NS_PRECONDITION(aTarget != nullptr, "null ptr");
+    if (! aTarget)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    nsISimpleEnumerator* result =
+        new CompositeArcsInOutEnumeratorImpl(this, aTarget,
+                                             CompositeArcsInOutEnumeratorImpl::eArcsIn,
+                                             mAllowNegativeAssertions,
+                                             mCoalesceDuplicateArcs);
+
+    if (! result)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(result);
+    *aResult = result;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::ArcLabelsOut(nsIRDFResource* aSource,
+                                      nsISimpleEnumerator** aResult)
+{
+    NS_PRECONDITION(aSource != nullptr, "null ptr");
+    if (! aSource)
+        return NS_ERROR_NULL_POINTER;
+
+    NS_PRECONDITION(aResult != nullptr, "null ptr");
+    if (! aResult)
+        return NS_ERROR_NULL_POINTER;
+
+    nsISimpleEnumerator* result =
+        new CompositeArcsInOutEnumeratorImpl(this, aSource,
+                                             CompositeArcsInOutEnumeratorImpl::eArcsOut,
+                                             mAllowNegativeAssertions,
+                                             mCoalesceDuplicateArcs);
+
+    if (! result)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(result);
+    *aResult = result;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetAllResources(nsISimpleEnumerator** aResult)
+{
+    NS_NOTYETIMPLEMENTED("CompositeDataSourceImpl::GetAllResources");
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetAllCmds(nsIRDFResource* source,
+                                    nsISimpleEnumerator/*<nsIRDFResource>*/** result)
+{
+    nsresult rv;
+    nsCOMPtr<nsISimpleEnumerator> set;
+
+    for (int32_t i = 0; i < mDataSources.Count(); i++)
+    {
+        nsCOMPtr<nsISimpleEnumerator> dsCmds;
+
+        rv = mDataSources[i]->GetAllCmds(source, getter_AddRefs(dsCmds));
+        if (NS_SUCCEEDED(rv))
+        {
+            nsCOMPtr<nsISimpleEnumerator> tmp;
+            rv = NS_NewUnionEnumerator(getter_AddRefs(tmp), set, dsCmds);
+            set.swap(tmp);
+            if (NS_FAILED(rv)) return(rv);
+        }
+    }
+
+    set.forget(result);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::IsCommandEnabled(nsISupports/* nsIRDFResource container */* aSources,
+                                          nsIRDFResource*   aCommand,
+                                          nsISupports/* nsIRDFResource container */* aArguments,
+                                          bool* aResult)
+{
+    nsresult rv;
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        bool enabled = true;
+        rv = mDataSources[i]->IsCommandEnabled(aSources, aCommand, aArguments, &enabled);
+        if (NS_FAILED(rv) && (rv != NS_ERROR_NOT_IMPLEMENTED))
+        {
+            return(rv);
+        }
+
+        if (! enabled) {
+            *aResult = false;
+            return(NS_OK);
+        }
+    }
+    *aResult = true;
+    return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::DoCommand(nsISupports/* nsIRDFResource container */* aSources,
+                                   nsIRDFResource*   aCommand,
+                                   nsISupports/* nsIRDFResource container */* aArguments)
+{
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        nsresult rv = mDataSources[i]->DoCommand(aSources, aCommand, aArguments);
+        if (NS_FAILED(rv) && (rv != NS_ERROR_NOT_IMPLEMENTED))
+        {
+            return(rv);   // all datasources must succeed
+        }
+    }
+    return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::BeginUpdateBatch()
+{
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        mDataSources[i]->BeginUpdateBatch();
+    }
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::EndUpdateBatch()
+{
+    for (int32_t i = mDataSources.Count() - 1; i >= 0; --i) {
+        mDataSources[i]->EndUpdateBatch();
+    }
+    return NS_OK;
+}
+
+////////////////////////////////////////////////////////////////////////
+// nsIRDFCompositeDataSource methods
+// XXX rvg We should make this take an additional argument specifying where
+// in the sequence of data sources (of the db), the new data source should
+// fit in. Right now, the new datasource gets stuck at the end.
+// need to add the observers of the CompositeDataSourceImpl to the new data source.
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetAllowNegativeAssertions(bool *aAllowNegativeAssertions)
+{
+	*aAllowNegativeAssertions = mAllowNegativeAssertions;
+	return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::SetAllowNegativeAssertions(bool aAllowNegativeAssertions)
+{
+	mAllowNegativeAssertions = aAllowNegativeAssertions;
+	return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetCoalesceDuplicateArcs(bool *aCoalesceDuplicateArcs)
+{
+	*aCoalesceDuplicateArcs = mCoalesceDuplicateArcs;
+	return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::SetCoalesceDuplicateArcs(bool aCoalesceDuplicateArcs)
+{
+	mCoalesceDuplicateArcs = aCoalesceDuplicateArcs;
+	return(NS_OK);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::AddDataSource(nsIRDFDataSource* aDataSource)
+{
+    NS_ASSERTION(aDataSource != nullptr, "null ptr");
+    if (! aDataSource)
+        return NS_ERROR_NULL_POINTER;
+
+    mDataSources.AppendObject(aDataSource);
+    aDataSource->AddObserver(this);
+    return NS_OK;
+}
+
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::RemoveDataSource(nsIRDFDataSource* aDataSource)
+{
+    NS_ASSERTION(aDataSource != nullptr, "null ptr");
+    if (! aDataSource)
+        return NS_ERROR_NULL_POINTER;
+
+
+    if (mDataSources.IndexOf(aDataSource) >= 0) {
+        aDataSource->RemoveObserver(this);
+        mDataSources.RemoveObject(aDataSource);
+    }
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::GetDataSources(nsISimpleEnumerator** _result)
+{
+    // NS_NewArrayEnumerator for an nsCOMArray takes a snapshot of the
+    // current state.
+    return NS_NewArrayEnumerator(_result, mDataSources);
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnAssert(nsIRDFDataSource* aDataSource,
+                                  nsIRDFResource* aSource,
+                                  nsIRDFResource* aProperty,
+                                  nsIRDFNode* aTarget)
+{
+    // Make sure that the assertion isn't masked by another
+    // datasource.
+    //
+    // XXX We could make this more efficient if we knew _which_
+    // datasource actually served up the OnAssert(): we could use
+    // HasAssertionN() to only search datasources _before_ the
+    // datasource that coughed up the assertion.
+	nsresult	rv = NS_OK;
+
+	if (mAllowNegativeAssertions)
+	{   
+		bool hasAssertion;
+		rv = HasAssertion(aSource, aProperty, aTarget, true, &hasAssertion);
+		if (NS_FAILED(rv)) return rv;
+
+		if (! hasAssertion)
+			return(NS_OK);
+	}
+
+    for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+        mObservers[i]->OnAssert(this, aSource, aProperty, aTarget);
+    }
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnUnassert(nsIRDFDataSource* aDataSource,
+                                    nsIRDFResource* aSource,
+                                    nsIRDFResource* aProperty,
+                                    nsIRDFNode* aTarget)
+{
+    // Make sure that the un-assertion doesn't just unmask the
+    // same assertion in a different datasource.
+    //
+    // XXX We could make this more efficient if we knew _which_
+    // datasource actually served up the OnAssert(): we could use
+    // HasAssertionN() to only search datasources _before_ the
+    // datasource that coughed up the assertion.
+    nsresult rv;
+
+	if (mAllowNegativeAssertions)
+	{   
+		bool hasAssertion;
+		rv = HasAssertion(aSource, aProperty, aTarget, true, &hasAssertion);
+		if (NS_FAILED(rv)) return rv;
+
+		if (hasAssertion)
+			return NS_OK;
+	}
+
+    for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+        mObservers[i]->OnUnassert(this, aSource, aProperty, aTarget);
+    }
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnChange(nsIRDFDataSource* aDataSource,
+                                  nsIRDFResource* aSource,
+                                  nsIRDFResource* aProperty,
+                                  nsIRDFNode* aOldTarget,
+                                  nsIRDFNode* aNewTarget)
+{
+    // Make sure that the change is actually visible, and not hidden
+    // by an assertion in a different datasource.
+    //
+    // XXX Because of aggregation, this could actually mutate into a
+    // variety of OnAssert or OnChange notifications, which we'll
+    // ignore for now :-/.
+    for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+        mObservers[i]->OnChange(this, aSource, aProperty,
+                                aOldTarget, aNewTarget);
+    }
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnMove(nsIRDFDataSource* aDataSource,
+                                nsIRDFResource* aOldSource,
+                                nsIRDFResource* aNewSource,
+                                nsIRDFResource* aProperty,
+                                nsIRDFNode* aTarget)
+{
+    // Make sure that the move is actually visible, and not hidden
+    // by an assertion in a different datasource.
+    //
+    // XXX Because of aggregation, this could actually mutate into a
+    // variety of OnAssert or OnMove notifications, which we'll
+    // ignore for now :-/.
+    for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+        mObservers[i]->OnMove(this, aOldSource, aNewSource,
+                              aProperty, aTarget);
+    }
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnBeginUpdateBatch(nsIRDFDataSource* aDataSource)
+{
+    if (mUpdateBatchNest++ == 0) {
+        for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+            mObservers[i]->OnBeginUpdateBatch(this);
+        }
+    }
+    return NS_OK;
+}
+
+
+NS_IMETHODIMP
+CompositeDataSourceImpl::OnEndUpdateBatch(nsIRDFDataSource* aDataSource)
+{
+    NS_ASSERTION(mUpdateBatchNest > 0, "badly nested update batch");
+    if (--mUpdateBatchNest == 0) {
+        for (int32_t i = mObservers.Count() - 1; i >= 0; --i) {
+            mObservers[i]->OnEndUpdateBatch(this);
+        }
+    }
+    return NS_OK;
+}