Class: Kafka::Protocol::Decoder

Inherits:
Object
  • Object
show all
Defined in:
lib/kafka/protocol/decoder.rb

Overview

A decoder wraps an IO object, making it easy to read specific data types from it. The Kafka protocol is not self-describing, so a client must call these methods in just the right order for things to work.

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(io) ⇒ Decoder

Initializes a new decoder.


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# File 'lib/kafka/protocol/decoder.rb', line 16

def initialize(io)
  @io = io
end

Class Method Details

.from_string(str) ⇒ Object


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# File 'lib/kafka/protocol/decoder.rb', line 9

def self.from_string(str)
  new(StringIO.new(str))
end

Instance Method Details

#array(&block) ⇒ Array

Decodes an array from the IO object.

The provided block will be called once for each item in the array. It is the responsibility of the block to decode the proper type in the block, since there's no information that allows the type to be inferred automatically.


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# File 'lib/kafka/protocol/decoder.rb', line 77

def array(&block)
  size = int32
  size.times.map(&block)
end

#booleanBoolean

Decodes an 8-bit boolean from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 37

def boolean
  read(1) == 0x1
end

#bytesString

Decodes a list of bytes from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 135

def bytes
  size = int32

  if size == -1
    nil
  else
    read(size)
  end
end

#eof?Boolean


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# File 'lib/kafka/protocol/decoder.rb', line 20

def eof?
  @io.eof?
end

#int16Integer

Decodes a 16-bit integer from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 51

def int16
  read(2).unpack("s>").first
end

#int32Integer

Decodes a 32-bit integer from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 58

def int32
  read(4).unpack("l>").first
end

#int64Integer

Decodes a 64-bit integer from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 65

def int64
  read(8).unpack("q>").first
end

#int8Integer

Decodes an 8-bit integer from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 44

def int8
  read(1).unpack("C").first
end

#peek(offset, length) ⇒ Integer

Get some next bytes without touching the current io offset


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# File 'lib/kafka/protocol/decoder.rb', line 27

def peek(offset, length)
  data = @io.read(offset + length)
  return [] if data.nil?
  @io.ungetc(data)
  data.bytes[offset, offset + length] || []
end

#read(number_of_bytes) ⇒ String

Reads the specified number of bytes from the IO object, returning them as a String.

Raises:

  • (EOFError)

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# File 'lib/kafka/protocol/decoder.rb', line 162

def read(number_of_bytes)
  return "" if number_of_bytes == 0

  data = @io.read(number_of_bytes) or raise EOFError

  # If the `read` call returned less data than expected we should not
  # proceed.
  raise EOFError if data.size != number_of_bytes

  data
end

#stringString

Decodes a string from the IO object.


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# File 'lib/kafka/protocol/decoder.rb', line 94

def string
  size = int16

  if size == -1
    nil
  else
    read(size)
  end
end

#varintInteger

Read an integer under varints serializing from the IO object. https://developers.google.com/protocol-buffers/docs/encoding#varints


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# File 'lib/kafka/protocol/decoder.rb', line 121

def varint
  group = 0
  data = 0
  while (chunk = int8) & 0x80 != 0
    data |= (chunk & 0x7f) << group
    group += 7
  end
  data |= chunk << group
  data & 0b1 != 0 ? ~(data >> 1) : (data >> 1)
end

#varint_array(&block) ⇒ Array

Decodes an array from the IO object. Just like #array except the size is in varint format


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# File 'lib/kafka/protocol/decoder.rb', line 86

def varint_array(&block)
  size = varint
  size.times.map(&block)
end

#varint_bytesString

Decodes a list of bytes from the IO object. The size is in varint format


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# File 'lib/kafka/protocol/decoder.rb', line 148

def varint_bytes
  size =  varint

  if size == -1
    nil
  else
    read(size)
  end
end

#varint_stringString

Decodes a string from the IO object, the size is in varint format


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# File 'lib/kafka/protocol/decoder.rb', line 107

def varint_string
  size = varint

  if size == -1
    nil
  else
    read(size)
  end
end