Implement better HPACK Huffman code decoder.

net/spdy/hpack/hpack_input_stream.cc

 // 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 "net/spdy/hpack/hpack_input_stream.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
+#include "net/spdy/hpack/hpack_huffman_decoder.h"
 
 namespace net {
 
 using base::StringPiece;
 using std::string;
 
 HpackInputStream::HpackInputStream(uint32_t max_string_literal_size,
                                    StringPiece buffer)
     : max_string_literal_size_(max_string_literal_size),
       buffer_(buffer),
@@ skipping 18 matching lines @@
 
   if ((peeked >> (32 - prefix.bit_size)) == prefix.bits) {
     ConsumeBits(prefix.bit_size);
     return true;
   }
   return false;
 }
 
 bool HpackInputStream::PeekNextOctet(uint8_t* next_octet) {
   if ((bit_offset_ > 0) || buffer_.empty()) {
+    DVLOG(1) << "HpackInputStream::PeekNextOctet bit_offset_=" << bit_offset_;
     return false;
   }
 
   *next_octet = buffer_[0];
   return true;
 }
 
 bool HpackInputStream::DecodeNextOctet(uint8_t* next_octet) {
   if (!PeekNextOctet(next_octet)) {
     return false;
   }
 
   buffer_.remove_prefix(1);
   return true;
 }
 
 bool HpackInputStream::DecodeNextUint32(uint32_t* I) {
   size_t N = 8 - bit_offset_;
   DCHECK_GT(N, 0u);
   DCHECK_LE(N, 8u);
 
   bit_offset_ = 0;
 
   *I = 0;
 
   uint8_t next_marker = (1 << N) - 1;
   uint8_t next_octet = 0;
   if (!DecodeNextOctet(&next_octet)) {
+    DVLOG(1) << "HpackInputStream::DecodeNextUint32 initial octet error";
     return false;
   }
   *I = next_octet & next_marker;
 
   bool has_more = (*I == next_marker);
   size_t shift = 0;
   while (has_more && (shift < 32)) {
     uint8_t next_octet = 0;
     if (!DecodeNextOctet(&next_octet)) {
+      DVLOG(1) << "HpackInputStream::DecodeNextUint32 shift=" << shift;
       return false;
     }
     has_more = (next_octet & 0x80) != 0;
     next_octet &= 0x7f;
     uint32_t addend = next_octet << shift;
     // Check for overflow.
     if ((addend >> shift) != next_octet) {
+      DVLOG(1) << "HpackInputStream::DecodeNextUint32 overflow";
       return false;
     }
     *I += addend;
     shift += 7;
   }
 
   return !has_more;
 }
 
 bool HpackInputStream::DecodeNextIdentityString(StringPiece* str) {
   uint32_t size = 0;
   if (!DecodeNextUint32(&size)) {
     return false;
   }
 
   if (size > max_string_literal_size_) {
     return false;
   }
 
   if (size > buffer_.size()) {
     return false;
   }
 
   *str = StringPiece(buffer_.data(), size);
   buffer_.remove_prefix(size);
   return true;
 }
 
-bool HpackInputStream::DecodeNextHuffmanString(const HpackHuffmanTable& table,
-                                               string* str) {
+bool HpackInputStream::DecodeNextHuffmanString(string* str) {
   uint32_t encoded_size = 0;
   if (!DecodeNextUint32(&encoded_size)) {
+    DVLOG(1) << "HpackInputStream::DecodeNextHuffmanString "
+             << "unable to decode size";
     return false;
   }
 
   if (encoded_size > buffer_.size()) {
+    DVLOG(1) << "HpackInputStream::DecodeNextHuffmanString " << encoded_size
+             << " > " << buffer_.size();
     return false;
   }
 
   HpackInputStream bounded_reader(max_string_literal_size_,
                                   StringPiece(buffer_.data(), encoded_size));
   buffer_.remove_prefix(encoded_size);
 
-  // HpackHuffmanTable will not decode beyond |max_string_literal_size_|.
-  return table.DecodeString(&bounded_reader, max_string_literal_size_, str);
+  // DecodeString will not append more than |max_string_literal_size_| chars
+  // to |str|.
+  return HpackHuffmanDecoder::DecodeString(&bounded_reader,
+                                           max_string_literal_size_, str);
 }
 
 bool HpackInputStream::PeekBits(size_t* peeked_count, uint32_t* out) const {
   size_t byte_offset = (bit_offset_ + *peeked_count) / 8;
   size_t bit_offset = (bit_offset_ + *peeked_count) % 8;
 
   if (*peeked_count >= 32 || byte_offset >= buffer_.size()) {
     return false;
   }
   // We'll read the minimum of the current byte remainder,
   // and the remaining unfilled bits of |out|.
   size_t bits_to_read = std::min(32 - *peeked_count, 8 - bit_offset);
 
   uint32_t new_bits = static_cast<uint32_t>(buffer_[byte_offset]);
   // Shift byte remainder to most-signifcant bits of |new_bits|.
   // This drops the leading |bit_offset| bits of the byte.
   new_bits = new_bits << (24 + bit_offset);
   // Shift bits to the most-significant open bits of |out|.
   new_bits = new_bits >> *peeked_count;
 
   CHECK_EQ(*out & new_bits, 0u);
   *out |= new_bits;
 
   *peeked_count += bits_to_read;
   return true;
 }
 
+std::pair<size_t, uint32_t> HpackInputStream::InitializePeekBits() {
+  size_t peeked_count = 0;
+  uint32_t bits = 0;
+  if (bit_offset_ == 0) {
+    switch (buffer_.size()) {
+      default:
+        DCHECK_LE(4u, buffer_.size());
+        bits = static_cast<uint32_t>(static_cast<unsigned char>(buffer_[3]));
+        peeked_count += 8;
+      /* FALLTHROUGH */
+      case 3:
+        bits |= (static_cast<uint32_t>(static_cast<unsigned char>(buffer_[2]))
+                 << 8);
+        peeked_count += 8;
+      /* FALLTHROUGH */
+      case 2:
+        bits |= (static_cast<uint32_t>(static_cast<unsigned char>(buffer_[1]))
+                 << 16);
+        peeked_count += 8;
+      /* FALLTHROUGH */
+      case 1:
+        bits |= (static_cast<uint32_t>(static_cast<unsigned char>(buffer_[0]))
+                 << 24);
+        peeked_count += 8;
+        break;
+      case 0:
+        break;
+    }
+  } else {
+    LOG(DFATAL) << "InitializePeekBits called with non-zero bit_offset_: "
+                << bit_offset_;
+  }
+  return std::make_pair(peeked_count, bits);
+}
+
 void HpackInputStream::ConsumeBits(size_t bit_count) {
   size_t byte_count = (bit_offset_ + bit_count) / 8;
   bit_offset_ = (bit_offset_ + bit_count) % 8;
   CHECK_GE(buffer_.size(), byte_count);
   if (bit_offset_ != 0) {
     CHECK_GT(buffer_.size(), 0u);
   }
   buffer_.remove_prefix(byte_count);
 }
 
 void HpackInputStream::ConsumeByteRemainder() {
   if (bit_offset_ != 0) {
     ConsumeBits(8 - bit_offset_);
   }
 }
 
 }  // namespace net