Bug 599300: Make FileReader work correctly for empty files. r=smaug a=blocker

content/base/src/nsDOMFileReader.cpp

@@ -143,7 +143,7 @@ nsDOMFileReader::SetOnloadend(nsIDOMEventListener* aOnloadend)
 NS_IMETHODIMP
 nsDOMFileReader::Notify(const char *aCharset, nsDetectionConfident aConf)
 {
-  CopyASCIItoUTF16(aCharset, mCharset);
+  mCharset = aCharset;
   return NS_OK;
 }
 
@@ -463,6 +463,8 @@ nsDOMFileReader::OnStopRequest(nsIRequest *aRequest,
       rv = GetAsDataURL(mFile, mFileData, mDataLen, mResult);
       break;
   }
+  
+  mResult.SetIsVoid(PR_FALSE);
 
   FreeFileData();
 
@@ -499,7 +501,7 @@ nsDOMFileReader::ReadFileContent(nsIDOMFile* aFile,
 
   mFile = aFile;
   mDataFormat = aDataFormat;
-  mCharset = aCharset;
+  CopyUTF16toUTF8(aCharset, mCharset);
 
   //Establish a channel with our file
   {
@@ -580,7 +582,7 @@ nsDOMFileReader::DispatchProgressEvent(const nsAString& aType)
 }
 
 nsresult
-nsDOMFileReader::GetAsText(const nsAString &aCharset,
+nsDOMFileReader::GetAsText(const nsACString &aCharset,
                            const char *aFileData,
                            PRUint32 aDataLen,
                            nsAString& aResult)
@@ -588,7 +590,7 @@ nsDOMFileReader::GetAsText(const nsAString &aCharset,
   nsresult rv;
   nsCAutoString charsetGuess;
   if (!aCharset.IsEmpty()) {
-    CopyUTF16toUTF8(aCharset, charsetGuess);
+    charsetGuess = aCharset;
   } else {
     rv = GuessCharset(aFileData, aDataLen, charsetGuess);
     NS_ENSURE_SUCCESS(rv, rv);
@@ -625,7 +627,7 @@ nsDOMFileReader::GetAsDataURL(nsIDOMFile *aFile,
   aResult.AppendLiteral(";base64,");
 
   PRUint32 totalRead = 0;
-  do {
+  while (aDataLen > totalRead) {
     PRUint32 numEncode = 4096;
     PRUint32 amtRemaining = aDataLen - totalRead;
     if (numEncode > amtRemaining)
@@ -643,8 +645,7 @@ nsDOMFileReader::GetAsDataURL(nsIDOMFile *aFile,
     PR_Free(base64);
 
     totalRead += numEncode;
-
-  } while (aDataLen > totalRead);
+  }
 
   return NS_OK;
 }
@@ -700,7 +701,9 @@ nsDOMFileReader::GuessCharset(const char *aFileData,
   }
 
   nsresult rv;
-  if (detector) {
+  // The charset detector doesn't work for empty (null) aFileData. Testing
+  // aDataLen instead of aFileData so that we catch potential errors.
+  if (detector && aDataLen != 0) {
     mCharset.Truncate();
     detector->Init(this);
 
@@ -712,7 +715,7 @@ nsDOMFileReader::GuessCharset(const char *aFileData,
     rv = detector->Done();
     NS_ENSURE_SUCCESS(rv, rv);
 
-    CopyUTF16toUTF8(mCharset, aCharset);
+    aCharset = mCharset;
   } else {
     // no charset detector available, check the BOM
     unsigned char sniffBuf[4];

content/base/src/nsDOMFileReader.h

@@ -118,7 +118,7 @@ protected:
   };
 
   nsresult ReadFileContent(nsIDOMFile *aFile, const nsAString &aCharset, eDataFormat aDataFormat); 
-  nsresult GetAsText(const nsAString &aCharset,
+  nsresult GetAsText(const nsACString &aCharset,
                      const char *aFileData, PRUint32 aDataLen, nsAString &aResult);
   nsresult GetAsDataURL(nsIDOMFile *aFile, const char *aFileData, PRUint32 aDataLen, nsAString &aResult); 
   nsresult GuessCharset(const char *aFileData, PRUint32 aDataLen, nsACString &aCharset); 
@@ -134,7 +134,7 @@ protected:
 
   char *mFileData;
   nsCOMPtr<nsIDOMFile> mFile;
-  nsString mCharset;
+  nsCString mCharset;
   PRUint32 mDataLen;
 
   eDataFormat mDataFormat;

content/base/test/test_fileapi.html

@@ -62,6 +62,7 @@ var nonExistingFile = fileList.files[0];
 
 // Test that plain reading works and fires events as expected, both
 // for text and binary reading
+
 var onloadHasRunText = false;
 var onloadStartHasRunText = false;
 r = new FileReader();
@@ -122,6 +123,35 @@ r.readAsText(createFileWithData(convertToUTF32(testTextData)), "UTF-32");
 expectedTestCount++;
 
 
+// Test loading an empty file works (and doesn't crash!)
+var emptyFile = createFileWithData("");
+dump("hello nurse");
+r = new FileReader();
+r.onload = getLoadHandler("", 0, "empty no encoding reading");
+r.readAsText(emptyFile, "");
+expectedTestCount++;
+
+r = new FileReader();
+r.onload = getLoadHandler("", 0, "empty utf8 reading");
+r.readAsText(emptyFile, "utf8");
+expectedTestCount++;
+
+r = new FileReader();
+r.onload = getLoadHandler("", 0, "empty utf16 reading");
+r.readAsText(emptyFile, "utf-16");
+expectedTestCount++;
+
+r = new FileReader();
+r.onload = getLoadHandler("", 0, "empty binary string reading");
+r.readAsBinaryString(emptyFile);
+expectedTestCount++;
+
+r = new FileReader();
+r.onload = getLoadHandler(convertToDataURL(""), 0, "empt binary string reading");
+r.readAsDataURL(emptyFile);
+expectedTestCount++;
+
+
 // Test reusing a FileReader to read multiple times
 r = new FileReader();
 r.onload = getLoadHandler(testASCIIData,