diff -r 000000000000 -r 6474c204b198 xpcom/io/nsScriptableInputStream.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/io/nsScriptableInputStream.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,116 @@
+/* -*- 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/. */
+
+#include "nsScriptableInputStream.h"
+#include "nsMemory.h"
+#include "nsString.h"
+
+NS_IMPL_ISUPPORTS(nsScriptableInputStream, nsIScriptableInputStream)
+
+// nsIScriptableInputStream methods
+NS_IMETHODIMP
+nsScriptableInputStream::Close(void) {
+    if (!mInputStream) return NS_ERROR_NOT_INITIALIZED;
+    return mInputStream->Close();
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Init(nsIInputStream *aInputStream) {
+    if (!aInputStream) return NS_ERROR_NULL_POINTER;
+    mInputStream = aInputStream;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Available(uint64_t *_retval) {
+    if (!mInputStream) return NS_ERROR_NOT_INITIALIZED;
+    return mInputStream->Available(_retval);
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::Read(uint32_t aCount, char **_retval) {
+    nsresult rv = NS_OK;
+    uint64_t count64 = 0;
+    char *buffer = nullptr;
+
+    if (!mInputStream) return NS_ERROR_NOT_INITIALIZED;
+
+    rv = mInputStream->Available(&count64);
+    if (NS_FAILED(rv)) return rv;
+
+    // bug716556 - Ensure count+1 doesn't overflow
+    uint32_t count = XPCOM_MIN((uint32_t)XPCOM_MIN<uint64_t>(count64, aCount), UINT32_MAX - 1);
+    buffer = (char*)moz_malloc(count+1); // make room for '\0'
+    if (!buffer) return NS_ERROR_OUT_OF_MEMORY;
+
+    rv = ReadHelper(buffer, count);
+    if (NS_FAILED(rv)) {
+        nsMemory::Free(buffer);
+        return rv;
+    }
+
+    buffer[count] = '\0';
+    *_retval = buffer;
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptableInputStream::ReadBytes(uint32_t aCount, nsACString &_retval) {
+    if (!mInputStream) {
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    _retval.SetLength(aCount);
+    if (_retval.Length() != aCount) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    char *ptr = _retval.BeginWriting();
+    nsresult rv = ReadHelper(ptr, aCount);
+    if (NS_FAILED(rv)) {
+      _retval.Truncate();
+    }
+    return rv;
+}
+
+nsresult
+nsScriptableInputStream::ReadHelper(char* aBuffer, uint32_t aCount)
+{
+    uint32_t totalBytesRead = 0;
+    while (1) {
+      uint32_t bytesRead;
+      nsresult rv = mInputStream->Read(aBuffer + totalBytesRead,
+                                       aCount - totalBytesRead,
+                                       &bytesRead);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      totalBytesRead += bytesRead;
+      if (totalBytesRead == aCount) {
+        break;
+      }
+
+      // If we have read zero bytes, we have hit EOF.
+      if (bytesRead == 0) {
+        return NS_ERROR_FAILURE;
+      }
+
+    }
+    return NS_OK;
+}
+
+nsresult
+nsScriptableInputStream::Create(nsISupports *aOuter, REFNSIID aIID, void **aResult) {
+    if (aOuter) return NS_ERROR_NO_AGGREGATION;
+
+    nsScriptableInputStream *sis = new nsScriptableInputStream();
+    if (!sis) return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_ADDREF(sis);
+    nsresult rv = sis->QueryInterface(aIID, aResult);
+    NS_RELEASE(sis);
+    return rv;
+}