// Initializes the BFS state table.
static PLDHashOperator
InitBFSTable(const nsACString &aKey, nsCOMArray<nsIAtom> *aData, void* aClosure) {
MOZ_ASSERT(aData, "no data in the table enumeration");
BFSHashTable *bfsTable = static_cast<BFSHashTable*>(aClosure);
if (!bfsTable) return PL_DHASH_STOP;
BFSTableData *data = new BFSTableData(aKey);
bfsTable->Put(aKey, data);
return PL_DHASH_NEXT;
}
// walks the graph using a breadth-first-search algorithm which generates a discovered
// verticies tree. This tree is then walked up (from destination vertex, to origin vertex)
// and each link in the chain is added to an nsStringArray. A direct lookup for the given
// CONTRACTID should be made prior to calling this method in an attempt to find a direct
// converter rather than walking the graph.
nsresult
nsStreamConverterService::FindConverter(const char *aContractID, nsTArray<nsCString> **aEdgeList) {
nsresult rv;
if (!aEdgeList) return NS_ERROR_NULL_POINTER;
*aEdgeList = nullptr;
// walk the graph in search of the appropriate converter.
uint32_t vertexCount = mAdjacencyList.Count();
if (0 >= vertexCount) return NS_ERROR_FAILURE;
// Create a corresponding color table for each vertex in the graph.
BFSHashTable lBFSTable;
mAdjacencyList.EnumerateRead(InitBFSTable, &lBFSTable);
NS_ASSERTION(lBFSTable.Count() == vertexCount, "strmconv BFS table init problem");
// This is our source vertex; our starting point.
nsAutoCString fromC, toC;
rv = ParseFromTo(aContractID, fromC, toC);
if (NS_FAILED(rv)) return rv;
BFSTableData *data = lBFSTable.Get(fromC);
if (!data) {
return NS_ERROR_FAILURE;
}
data->color = gray;
data->distance = 0;
CStreamConvDeallocator *dtorFunc = new CStreamConvDeallocator();
nsDeque grayQ(dtorFunc);
// Now generate the shortest path tree.
grayQ.Push(new nsCString(fromC));
while (0 < grayQ.GetSize()) {
nsCString *currentHead = (nsCString*)grayQ.PeekFront();
nsCOMArray<nsIAtom> *data2 = mAdjacencyList.Get(*currentHead);
if (!data2) return NS_ERROR_FAILURE;
// Get the state of the current head to calculate the distance of each
// reachable vertex in the loop.
BFSTableData *headVertexState = lBFSTable.Get(*currentHead);
if (!headVertexState) return NS_ERROR_FAILURE;
int32_t edgeCount = data2->Count();
for (int32_t i = 0; i < edgeCount; i++) {
nsIAtom* curVertexAtom = data2->ObjectAt(i);
nsCString *curVertex = new nsCString();
curVertexAtom->ToUTF8String(*curVertex);
BFSTableData *curVertexState = lBFSTable.Get(*curVertex);
if (!curVertexState) {
delete curVertex;
return NS_ERROR_FAILURE;
}
if (white == curVertexState->color) {
curVertexState->color = gray;
curVertexState->distance = headVertexState->distance + 1;
curVertexState->predecessor = new nsCString(*currentHead);
grayQ.Push(curVertex);
} else {
delete curVertex; // if this vertex has already been discovered, we don't want
// to leak it. (non-discovered vertex's get cleaned up when
// they're popped).
}
}
headVertexState->color = black;
nsCString *cur = (nsCString*)grayQ.PopFront();
delete cur;
cur = nullptr;
}
// The shortest path (if any) has been generated and is represented by the chain of
// BFSTableData->predecessor keys. Start at the bottom and work our way up.
// first parse out the FROM and TO MIME-types being registered.
nsAutoCString fromStr, toMIMEType;
rv = ParseFromTo(aContractID, fromStr, toMIMEType);
if (NS_FAILED(rv)) return rv;
// get the root CONTRACTID
nsAutoCString ContractIDPrefix(NS_ISTREAMCONVERTER_KEY);
nsTArray<nsCString> *shortestPath = new nsTArray<nsCString>();
data = lBFSTable.Get(toMIMEType);
if (!data) {
// If this vertex isn't in the BFSTable, then no-one has registered for it,
// therefore we can't do the conversion.
delete shortestPath;
return NS_ERROR_FAILURE;
}
while (data) {
if (fromStr.Equals(data->key)) {
// found it. We're done here.
*aEdgeList = shortestPath;
return NS_OK;
}
// reconstruct the CONTRACTID.
// Get the predecessor.
if (!data->predecessor) break; // no predecessor
BFSTableData *predecessorData = lBFSTable.Get(*data->predecessor);
if (!predecessorData) break; // no predecessor, chain doesn't exist.
// build out the CONTRACTID.
nsAutoCString newContractID(ContractIDPrefix);
newContractID.AppendLiteral("?from=");
newContractID.Append(predecessorData->key);
newContractID.AppendLiteral("&to=");
newContractID.Append(data->key);
// Add this CONTRACTID to the chain.
rv = shortestPath->AppendElement(newContractID) ? NS_OK : NS_ERROR_FAILURE; // XXX this method incorrectly returns a bool
NS_ASSERTION(NS_SUCCEEDED(rv), "AppendElement failed");
// move up the tree.
data = predecessorData;
}
delete shortestPath;
return NS_ERROR_FAILURE; // couldn't find a stream converter or chain.
}
