fix bug 650750, perf slowdown with NFS local mailboxes, r=bienvenu

mailnews/base/util/nsMsgFileStream.cpp

@@ -30,6 +30,7 @@ ErrorAccordingToNSPR()
 nsMsgFileStream::nsMsgFileStream() 
 {
   mFileDesc = nsnull;
+  mSeekedToEnd = PR_FALSE;
 }
 
 nsMsgFileStream::~nsMsgFileStream()
@@ -50,11 +51,17 @@ nsMsgFileStream::Seek(PRInt32 whence, PRInt64 offset)
 {
   if (mFileDesc == nsnull)
     return NS_BASE_STREAM_CLOSED;
-  
+
+  PRBool seekingToEnd = whence == PR_SEEK_END && offset == 0;
+  if (seekingToEnd && mSeekedToEnd)
+    return NS_OK;
+
   PRInt64 cnt = PR_Seek64(mFileDesc, offset, (PRSeekWhence)whence);
   if (cnt == PRInt64(-1)) {
     return ErrorAccordingToNSPR();
   }
+
+  mSeekedToEnd = seekingToEnd;
   return NS_OK;
 }
 

mailnews/base/util/nsMsgFileStream.h

@@ -11,15 +11,15 @@ public:
   ~nsMsgFileStream();
 
   NS_DECL_ISUPPORTS
-    
+
   NS_IMETHOD Available(PRUint32 *_retval); 
   NS_IMETHOD Read(char * aBuf, PRUint32 aCount, PRUint32 *_retval); 
   NS_IMETHOD ReadSegments(nsWriteSegmentFun aWriter, void * aClosure, PRUint32 aCount, PRUint32 *_retval);
   NS_DECL_NSIOUTPUTSTREAM
   NS_DECL_NSISEEKABLESTREAM
-    
+
   nsresult InitWithFile(nsILocalFile *localFile);
 protected:
   PRFileDesc *mFileDesc;
+  PRBool mSeekedToEnd;
 };
-