Fix bug 111049 "add attribute to nsICacheSession to detect device availability". sr=darin.

netwerk/cache/public/nsICacheSession.idl

@@ -71,4 +71,10 @@ interface nsICacheSession : nsISupports
      * Evict all entries for this session's clientID according to its storagePolicy.
      */
     void evictEntries();
+    
+    /**
+     * Return whether any of the cache devices implied by the session storage policy
+     * are currently enabled for instantiation if they don't already exist.
+     */
+    PRBool isStorageEnabled();
 };

netwerk/cache/src/nsCacheService.cpp

@@ -555,6 +555,31 @@ nsCacheService::EvictEntriesForClient(const char *          clientID,
 }
 
 
+nsresult        
+nsCacheService::IsStorageEnabledForPolicy(nsCacheStoragePolicy  storagePolicy,
+                                          PRBool *              result)
+{
+    if (gService == nsnull) return NS_ERROR_NOT_AVAILABLE;
+    nsAutoLock lock(gService->mCacheServiceLock);
+        
+    if (gService->mEnableMemoryDevice &&
+        (storagePolicy == nsICache::STORE_ANYWHERE ||
+         storagePolicy == nsICache::STORE_IN_MEMORY)) {
+        *result = PR_TRUE;   
+    }
+    else if (gService->mEnableDiskDevice &&
+             (storagePolicy == nsICache::STORE_ANYWHERE ||
+              storagePolicy == nsICache::STORE_ON_DISK  ||
+              storagePolicy == nsICache::STORE_ON_DISK_AS_FILE)) {
+        *result = PR_TRUE;         
+    } else {
+        *result = PR_FALSE;
+    }
+    
+    return NS_OK;
+}
+
+
 NS_IMETHODIMP nsCacheService::VisitEntries(nsICacheVisitor *visitor)
 {
     nsAutoLock lock(mCacheServiceLock);

netwerk/cache/src/nsCacheService.h

@@ -77,6 +77,9 @@ public:
     nsresult         EvictEntriesForClient(const char *          clientID,
                                            nsCacheStoragePolicy  storagePolicy);
 
+    static nsresult  IsStorageEnabledForPolicy(nsCacheStoragePolicy  storagePolicy,
+                                               PRBool *              result);
+
     /**
      * Methods called by nsCacheEntryDescriptor
      */

netwerk/cache/src/nsCacheSession.cpp

@@ -104,3 +104,11 @@ NS_IMETHODIMP nsCacheSession::EvictEntries()
 {
     return nsCacheService::GlobalInstance()->EvictEntriesForSession(this);
 }
+
+
+NS_IMETHODIMP nsCacheSession::IsStorageEnabled(PRBool *result)
+{
+
+    return nsCacheService::IsStorageEnabledForPolicy(StoragePolicy(), result);
+}
+