Module: Quicsilver::Protocol::Qpack::Decoder

Included in:
HeaderBlockDecoder
Defined in:
lib/quicsilver/protocol/qpack/decoder.rb

Constant Summary collapse

DQS_CACHE =

Cache for decode_qpack_string

{}
DQS_OID_CACHE =

array-content → [str, consumed]

{}
DQS_CACHE_MAX =

object_id|offset → [str, consumed]

128
DQS_LAST_A =

2-slot last-result cache for decode_qpack_string

[nil, nil, nil]
DQS_LAST_B = 
[nil, nil, nil]

Instance Method Summary collapse

Instance Method Details

#decode_prefix_integer(bytes, offset, prefix_bits, pattern_mask) ⇒ Object

RFC 7541 prefix integer decoding Returns [value, bytes_consumed]



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# File 'lib/quicsilver/protocol/qpack/decoder.rb', line 138

def decode_prefix_integer(bytes, offset, prefix_bits, pattern_mask)
  max_prefix = (1 << prefix_bits) - 1

  first_byte = bytes[offset]
  value = first_byte & max_prefix
  bytes_consumed = 1

  if value == max_prefix
    multiplier = 1
    loop do
      return [value, bytes_consumed] if offset + bytes_consumed >= bytes.size

      next_byte = bytes[offset + bytes_consumed]
      bytes_consumed += 1

      value += (next_byte & 0x7F) * multiplier
      break if (next_byte & 0x80) == 0

      multiplier *= 128
    end
  end

  [value, bytes_consumed]
end

#decode_prefix_integer_str(data, offset, prefix_bits, pattern_mask) ⇒ Object

String-based prefix integer decoding



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# File 'lib/quicsilver/protocol/qpack/decoder.rb', line 115

def decode_prefix_integer_str(data, offset, prefix_bits, pattern_mask)
  max_prefix = (1 << prefix_bits) - 1
  first_byte = data.getbyte(offset)
  value = first_byte & max_prefix
  bytes_consumed = 1

  if value == max_prefix
    multiplier = 1
    loop do
      return [value, bytes_consumed] if offset + bytes_consumed >= data.bytesize
      next_byte = data.getbyte(offset + bytes_consumed)
      bytes_consumed += 1
      value += (next_byte & 0x7F) * multiplier
      break if (next_byte & 0x80) == 0
      multiplier *= 128
    end
  end

  [value, bytes_consumed]
end

#decode_qpack_string(bytes, offset) ⇒ Object 



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# File 'lib/quicsilver/protocol/qpack/decoder.rb', line 50

def decode_qpack_string(bytes, offset)
  # 2-slot equal? fast path (covers alternating-object patterns)
  return DQS_LAST_A[2] if bytes.equal?(DQS_LAST_A[0]) && offset == DQS_LAST_A[1]
  return DQS_LAST_B[2] if bytes.equal?(DQS_LAST_B[0]) && offset == DQS_LAST_B[1]

  # Object-id cache
  oid_key = (bytes.object_id << 16) | offset
  cached = DQS_OID_CACHE[oid_key]
  if cached
    # Rotate 2-slot cache
    DQS_LAST_B[0], DQS_LAST_B[1], DQS_LAST_B[2] = DQS_LAST_A[0], DQS_LAST_A[1], DQS_LAST_A[2]
    DQS_LAST_A[0], DQS_LAST_A[1], DQS_LAST_A[2] = bytes, offset, cached
    return cached
  end

  # Dispatch to string variant if given a String
  return decode_qpack_string_from_str(bytes, offset) if bytes.is_a?(String)

  # Content-based cache for offset=0
  if offset == 0
    cached = DQS_CACHE[bytes]
    if cached
      DQS_OID_CACHE[oid_key] = cached
      return cached
    end
  end

  first = bytes[offset]
  huffman = (first & 0x80) != 0

  # Inline 7-bit prefix integer decode to avoid method call
  length = first & 0x7F
  len_bytes = 1
  if length == 0x7F
    multiplier = 1
    while offset + len_bytes < bytes.size
      next_byte = bytes[offset + len_bytes]
      len_bytes += 1
      length += (next_byte & 0x7F) * multiplier
      break if (next_byte & 0x80) == 0
      multiplier *= 128
    end
  end

  data_offset = offset + len_bytes
  raw = bytes[data_offset, length].pack("C*")

  str = if huffman
    Huffman.decode(raw) || raw
  else
    raw
  end

  result = [str, len_bytes + length].freeze

  # Cache for offset=0 (common case: standalone decode)
  if offset == 0 && DQS_CACHE.size < DQS_CACHE_MAX
    DQS_CACHE[bytes.frozen? ? bytes : bytes.dup.freeze] = result
  end
  DQS_OID_CACHE[oid_key] = result if DQS_OID_CACHE.size < DQS_CACHE_MAX

  result
end

#decode_qpack_string_from_str(data, offset) ⇒ Object

Decode a QPACK string literal (RFC 9204 Section 4.1.2) Returns [string, bytes_consumed] String-based variant: accepts a binary String instead of byte array



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# File 'lib/quicsilver/protocol/qpack/decoder.rb', line 12

def decode_qpack_string_from_str(data, offset)
  first = data.getbyte(offset)
  huffman = (first & 0x80) != 0

  length = first & 0x7F
  len_bytes = 1
  if length == 0x7F
    multiplier = 1
    while offset + len_bytes < data.bytesize
      next_byte = data.getbyte(offset + len_bytes)
      len_bytes += 1
      length += (next_byte & 0x7F) * multiplier
      break if (next_byte & 0x80) == 0
      multiplier *= 128
    end
  end

  data_offset = offset + len_bytes
  raw = data.byteslice(data_offset, length)

  str = if huffman
    Huffman.decode(raw) || raw
  else
    raw
  end

  [str, len_bytes + length]
end