Avoid overflow on left shift in HpackVarintDecoder::Resume().

net/http2/hpack/decoder/hpack_varint_decoder.h

 // Copyright 2016 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.
 
 // HpackVarintDecoder decodes HPACK variable length unsigned integers. These
 // integers are used to identify static or dynamic table index entries, to
 // specify string lengths, and to update the size limit of the dynamic table.
 //
 // The caller will need to validate that the decoded value is in an acceptable
 // range.
@@ skipping 77 matching lines @@
 
   // Resume decoding a variable length integer after an earlier
   // call to Start or StartExtended returned kDecodeInProgress.
   DecodeStatus Resume(DecodeBuffer* db) {
     CheckNotDone();
     do {
       if (db->Empty()) {
         return DecodeStatus::kDecodeInProgress;
       }
       uint8_t byte = db->DecodeUInt8();
+      if (offset_ == MaxOffset() && byte != 0)

[xunjieli, 2017/04/17 20:51:34]

Can we change this to a while-loop to be more readable? It's hard to know what's
going on in this if-conditional.


    while (offset_ <= std::min(MaxOffset(), sizeof(value_) - sizeof(uint8))) {
      if (db->Empty()) {
        return DecodeStatus::kDecodeInProgress;
      }
      uint8_t byte = db->DecodeUInt8();
      value_ += (byte & 0x7f) << offset_;
      if ((byte & 0x80) == 0) {
          MarkDone();
          return DecodeStatus::kDecodeDone;
      }
      offset_ += 7;
    }

+        break;
       value_ += (byte & 0x7f) << offset_;
       if ((byte & 0x80) == 0) {
-        if (offset_ < MaxOffset() || byte == 0) {
-          MarkDone();
-          return DecodeStatus::kDecodeDone;
-        }
-        break;
+        MarkDone();
+        return DecodeStatus::kDecodeDone;
       }
       offset_ += 7;
     } while (offset_ <= MaxOffset());
     DLOG(WARNING) << "Variable length int encoding is too large or too long. "
                   << DebugString();
     MarkDone();
     return DecodeStatus::kDecodeError;
   }
 
   uint32_t value() const {
@@ skipping 57 matching lines @@
   // them from DebugString().
   uint32_t value_ = 0;
   uint32_t offset_ = 0;
 };
 
 std::ostream& operator<<(std::ostream& out, const HpackVarintDecoder& v);
 
 }  // namespace net
 
 #endif  // NET_HTTP2_HPACK_DECODER_HPACK_VARINT_DECODER_H_