Class: BufferCursor

Inherits:
Object
  • Object
show all
Defined in:
lib/innodb/util/buffer_cursor.rb

Overview

A cursor to walk through data structures to read fields. The cursor can move forwards, backwards, is seekable, and supports peeking without moving the cursor. The BinData module is used for interpreting bytes as desired.

Defined Under Namespace

Classes: StackEntry

Constant Summary collapse

VERSION = 
"0.9.0"

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(buffer, position) ⇒ BufferCursor

Initialize a cursor within a buffer at the given position.



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# File 'lib/innodb/util/buffer_cursor.rb', line 52

def initialize(buffer, position)
  @buffer = buffer
  @stack = [StackEntry.new(self, position)]

  trace false
  trace_with :print_trace
  trace_to $stdout
end

Class Method Details

.global_tracing? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/innodb/util/buffer_cursor.rb', line 47

def self.global_tracing?
  @global_tracing
end

.trace!(arg = true) ⇒ Object

Enable tracing for all BufferCursor objects globally.



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# File 'lib/innodb/util/buffer_cursor.rb', line 43

def self.trace!(arg = true) # rubocop:disable Style/OptionalBooleanParameter
  @global_tracing = arg
end

Instance Method Details

#adjust(relative_position) ⇒ Object

Adjust the current cursor to a new relative position.



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# File 'lib/innodb/util/buffer_cursor.rb', line 176

def adjust(relative_position)
  current.position += relative_position

  self
end

#backward ⇒ Object

Set the direction of the cursor to “backward”.



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# File 'lib/innodb/util/buffer_cursor.rb', line 159

def backward
  direction(:backward)
end

#current ⇒ Object

The current cursor object; the top of the stack.



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# File 'lib/innodb/util/buffer_cursor.rb', line 120

def current
  @stack.last
end

#direction(direction_arg = nil) ⇒ Object

Return the direction of the current cursor.



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# File 'lib/innodb/util/buffer_cursor.rb', line 145

def direction(direction_arg = nil)
  return current.direction if direction_arg.nil?

  current.direction = direction_arg

  self
end

#each_byte_as_uint8(length, &block) ⇒ Object

Iterate through length bytes returning each as an unsigned 8-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 240

def each_byte_as_uint8(length, &block)
  return enum_for(:each_byte_as_uint8, length) unless block_given?

  read_and_advance(length).bytes.each(&block)

  nil
end

#forward ⇒ Object

Set the direction of the cursor to “forward”.



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# File 'lib/innodb/util/buffer_cursor.rb', line 154

def forward
  direction(:forward)
end

#inspect ⇒ Object 



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# File 'lib/innodb/util/buffer_cursor.rb', line 61

def inspect
  "<%s size=%i current=%s>" % [
    self.class.name,
    @buffer.size,
    current.inspect,
  ]
end

#name(name_arg = nil) ⇒ Object

Set the field name.



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# File 'lib/innodb/util/buffer_cursor.rb', line 133

def name(name_arg = nil)
  return current.name if name_arg.nil?

  raise "No block given" unless block_given?

  current.name.push name_arg
  ret = yield(self)
  current.name.pop
  ret
end

#peek(position = nil) ⇒ Object

Execute a block and restore the cursor to the previous position after the block returns. Return the block’s return value after restoring the cursor. Optionally seek to provided position before executing block.



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# File 'lib/innodb/util/buffer_cursor.rb', line 202

def peek(position = nil)
  raise "No block given" unless block_given?

  push(position)
  result = yield(self)
  pop
  result
end

#pop ⇒ Object

Restore the last cursor position.



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# File 'lib/innodb/util/buffer_cursor.rb', line 191

def pop
  raise "No cursors to pop" unless @stack.size > 1

  @stack.pop

  self
end

#pop_name ⇒ Object 



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# File 'lib/innodb/util/buffer_cursor.rb', line 128

def pop_name
  current.name.pop
end

#position ⇒ Object

Return the position of the current cursor.



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# File 'lib/innodb/util/buffer_cursor.rb', line 164

def position
  current.position
end

#print_trace(_cursor, position, bytes, name) ⇒ Object

Print a trace output for this cursor. The method is passed a cursor object, position, raw byte buffer, and array of names.



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# File 'lib/innodb/util/buffer_cursor.rb', line 77

def print_trace(_cursor, position, bytes, name)
  slice_size = 16
  bytes.each_slice(slice_size).each_with_index do |slice_bytes, slice_count|
    @trace_io.puts "%06i %s %-32s  %s" % [
      position + (slice_count * slice_size),
      direction == :backward ? "←" : "→",
      slice_bytes.map { |n| "%02x" % n }.join,
      slice_count.zero? ? name.join(".") : "↵",
    ]
  end
end

#push(position = nil) ⇒ Object

Save the current cursor position and start a new (nested, stacked) cursor.



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# File 'lib/innodb/util/buffer_cursor.rb', line 183

def push(position = nil)
  @stack.push current.dup
  seek(position)

  self
end

#push_name(name_arg) ⇒ Object 



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# File 'lib/innodb/util/buffer_cursor.rb', line 124

def push_name(name_arg)
  current.name.push name_arg
end

#read_and_advance(length) ⇒ Object

Read a number of bytes forwards or backwards from the current cursor position and adjust the cursor position by that amount.



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# File 'lib/innodb/util/buffer_cursor.rb', line 213

def read_and_advance(length)
  data = nil
  cursor_start = current.position
  case current.direction
  when :forward
    data = @buffer.slice(current.position, length)
    adjust(length)
  when :backward
    adjust(-length)
    data = @buffer.slice(current.position, length)
  end

  record_trace(cursor_start, data.bytes, current.name)
  data
end

#read_bit_array(num_bits) ⇒ Object

Read an array of 1-bit integers.



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# File 'lib/innodb/util/buffer_cursor.rb', line 402

def read_bit_array(num_bits)
  size = (num_bits + 7) / 8
  data = read_and_advance(size)
  bit_array = BinData::Array.new(type: :bit1, initial_length: size * 8)
  bit_array.read(data).to_ary
end

#read_bytes(length) ⇒ Object

Return raw bytes.



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# File 'lib/innodb/util/buffer_cursor.rb', line 230

def read_bytes(length)
  read_and_advance(length)
end

#read_hex(length) ⇒ Object

Return raw bytes as hex.



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# File 'lib/innodb/util/buffer_cursor.rb', line 249

def read_hex(length)
  read_and_advance(length).bytes.map { |c| "%02x" % c }.join
end

#read_ic_uint32(flag = nil) ⇒ Object

Read an InnoDB-compressed unsigned 32-bit integer (1-5 bytes).

The first byte makes up part of the value stored as well as indicating the number of bytes stored, maximally an additional 4 bytes after the flag for integers >= 0xf0000000.

Optionally accept a flag (first byte) if it has already been read (as is the case in read_imc_uint64).



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# File 'lib/innodb/util/buffer_cursor.rb', line 335

def read_ic_uint32(flag = nil)
  name("ic_uint32") do
    flag ||= peek { name("uint8_or_flag") { read_uint8 } }

    case
    when flag < 0x80
      adjust(+1)
      flag
    when flag < 0xc0
      name("uint16") { read_uint16 } & 0x7fff
    when flag < 0xe0
      name("uint24") { read_uint24 } & 0x3fffff
    when flag < 0xf0
      name("uint32") { read_uint32 } & 0x1fffffff
    when flag == 0xf0
      adjust(+1) # Skip the flag byte.
      name("uint32+1") { read_uint32 }
    else
      raise "Invalid flag #{flag} seen"
    end
  end
end

#read_ic_uint64 ⇒ Object

Read an InnoDB-compressed unsigned 64-bit integer (5-9 bytes).

The high 32 bits are stored as an InnoDB-compressed unsigned 32-bit integer (1-5 bytes) while the low 32 bits are stored as a standard big-endian 32-bit integer (4 bytes). This makes a combined size of between 5 and 9 bytes.



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# File 'lib/innodb/util/buffer_cursor.rb', line 364

def read_ic_uint64
  name("ic_uint64") do
    high = name("high") { read_ic_uint32 }
    low = name("low") { name("uint32") { read_uint32 } }

    (high << 32) | low
  end
end

#read_imc_uint64 ⇒ Object

Read an InnoDB-“much compressed” unsigned 64-bit integer (1-11 bytes).

If the first byte is 0xff, this indicates that the high 32 bits are stored immediately afterwards as an InnoDB-compressed 32-bit unsigned integer. If it is any other value it represents the first byte (which is also a flag) of the low 32 bits of the value, also as an InnoDB- compressed 32-bit unsigned integer. This makes for a combined size of between 1 and 11 bytes.



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# File 'lib/innodb/util/buffer_cursor.rb', line 381

def read_imc_uint64
  name("imc_uint64") do
    high = 0
    flag = peek { name("uint8_or_flag") { read_uint8 } }

    if flag == 0xff
      # The high 32-bits are stored first as an ic_uint32.
      adjust(+1) # Skip the flag byte.
      high = name("high") { read_ic_uint32 }
      flag = nil
    end

    # The low 32-bits are stored as an ic_uint32; pass the flag we already
    # read, so we don't have to read it again.
    low = name("low") { read_ic_uint32(flag) }

    (high << 32) | low
  end
end

#read_sint16(position = nil) ⇒ Object

Read a big-endian signed 16-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 268

def read_sint16(position = nil)
  seek(position)
  data = read_and_advance(2)
  BinData::Int16be.read(data).to_i
end

#read_string(length) ⇒ Object

Return a null-terminated string.



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# File 'lib/innodb/util/buffer_cursor.rb', line 235

def read_string(length)
  BinData::Stringz.read(read_and_advance(length))
end

#read_uint16(position = nil) ⇒ Object

Read a big-endian unsigned 16-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 261

def read_uint16(position = nil)
  seek(position)
  data = read_and_advance(2)
  BinData::Uint16be.read(data).to_i
end

#read_uint24(position = nil) ⇒ Object

Read a big-endian unsigned 24-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 275

def read_uint24(position = nil)
  seek(position)
  data = read_and_advance(3)
  BinData::Uint24be.read(data).to_i
end

#read_uint32(position = nil) ⇒ Object

Read a big-endian unsigned 32-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 282

def read_uint32(position = nil)
  seek(position)
  data = read_and_advance(4)
  BinData::Uint32be.read(data).to_i
end

#read_uint48(position = nil) ⇒ Object

Read a big-endian unsigned 48-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 289

def read_uint48(position = nil)
  seek(position)
  data = read_and_advance(6)
  BinData::Uint48be.read(data).to_i
end

#read_uint64(position = nil) ⇒ Object

Read a big-endian unsigned 64-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 296

def read_uint64(position = nil)
  seek(position)
  data = read_and_advance(8)
  BinData::Uint64be.read(data).to_i
end

#read_uint8(position = nil) ⇒ Object

Read an unsigned 8-bit integer.



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# File 'lib/innodb/util/buffer_cursor.rb', line 254

def read_uint8(position = nil)
  seek(position)
  data = read_and_advance(1)
  BinData::Uint8.read(data).to_i
end

#read_uint_array_by_size(size, count) ⇒ Object

Read an array of count unsigned integers given their size in bytes.



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# File 'lib/innodb/util/buffer_cursor.rb', line 323

def read_uint_array_by_size(size, count)
  count.times.map { read_uint_by_size(size) }
end

#read_uint_by_size(size) ⇒ Object

Read a big-endian unsigned integer given its size in bytes.



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# File 'lib/innodb/util/buffer_cursor.rb', line 303

def read_uint_by_size(size)
  case size
  when 1
    read_uint8
  when 2
    read_uint16
  when 3
    read_uint24
  when 4
    read_uint32
  when 6
    read_uint48
  when 8
    read_uint64
  else
    raise "Integer size #{size} not implemented"
  end
end

#record_trace(position, bytes, name) ⇒ Object

Generate a trace record from the current cursor.



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# File 'lib/innodb/util/buffer_cursor.rb', line 115

def record_trace(position, bytes, name)
  @trace_proc.call(self, position, bytes, name) if tracing_enabled?
end

#seek(position) ⇒ Object

Move the current cursor to a new absolute position.



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# File 'lib/innodb/util/buffer_cursor.rb', line 169

def seek(position)
  current.position = position if position

  self
end

#trace(arg = true) ⇒ Object

rubocop:disable Style/OptionalBooleanParameter



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# File 'lib/innodb/util/buffer_cursor.rb', line 69

def trace(arg = true) # rubocop:disable Style/OptionalBooleanParameter
  @instance_tracing = arg

  self
end

#trace_to(file) ⇒ Object 



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# File 'lib/innodb/util/buffer_cursor.rb', line 89

def trace_to(file)
  @trace_io = file

  self
end

#trace_with(arg = nil) ⇒ Object

Set a Proc or method on self to trace with.



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# File 'lib/innodb/util/buffer_cursor.rb', line 96

def trace_with(arg = nil)
  if arg.nil?
    @trace_proc = nil
  elsif arg.instance_of?(Proc)
    @trace_proc = arg
  elsif arg.instance_of?(Symbol)
    @trace_proc = ->(cursor, position, bytes, name) { send(arg, cursor, position, bytes, name) }
  else
    raise "Don't know how to trace with #{arg}"
  end

  self
end

#tracing_enabled? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/innodb/util/buffer_cursor.rb', line 110

def tracing_enabled?
  (self.class.global_tracing? || @instance_tracing) && @trace_proc
end