[Binding] Load 4 bytes to detect BOM

third_party/WebKit/Source/bindings/core/v8/ScriptStreamer.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "bindings/core/v8/ScriptStreamer.h"
 
 #include "bindings/core/v8/ScriptStreamerThread.h"
 #include "bindings/core/v8/V8ScriptRunner.h"
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
@@ skipping 480 matching lines @@
         m_haveEnoughDataForStreaming = true;
 
         // Encoding should be detected only when we have some data. It's
         // possible that resource->encoding() returns a different encoding
         // before the loading has started and after we got some data.  In
         // addition, check for byte order marks. Note that checking the byte
         // order mark might change the encoding. We cannot decode the full text
         // here, because it might contain incomplete UTF-8 characters. Also note
         // that have at least s_smallScriptThreshold worth of data, which is more
         // than enough for detecting a BOM.
-        const char* data = 0;
-        size_t length = resource->resourceBuffer()->getSomeData(data, static_cast<size_t>(0));
+        constexpr size_t maximumLengthOfBOM = 4;
+        char maybeBOM[maximumLengthOfBOM] = {};
+        if (!resource->resourceBuffer()->getPartAsBytes(maybeBOM, static_cast<size_t>(0), maximumLengthOfBOM)) {
+            NOTREACHED();
+            return;
+        }
 
         std::unique_ptr<TextResourceDecoder> decoder(TextResourceDecoder::create("application/javascript", resource->encoding()));
-        lengthOfBOM = decoder->checkForBOM(data, length);
+        lengthOfBOM = decoder->checkForBOM(maybeBOM, maximumLengthOfBOM);
 
         // Maybe the encoding changed because we saw the BOM; get the encoding
         // from the decoder.
         if (!convertEncoding(decoder->encoding().name(), &m_encoding)) {
             suppressStreaming();
             recordNotStreamingReasonHistogram(m_scriptType, EncodingNotSupported);
             recordStartedStreamingHistogram(m_scriptType, 0);
             return;
         }
         if (ScriptStreamerThread::shared()->isRunningTask()) {
@@ skipping 157 matching lines @@
 
     // The Resource might go out of scope if the script is no longer
     // needed. This makes PendingScript notify the ScriptStreamer when it is
     // destroyed.
     script->setStreamer(ScriptStreamer::create(script, scriptType, scriptState, compileOption, loadingTaskRunner));
 
     return true;
 }
 
 } // namespace blink