Class: ZMQ::Message

Inherits:
Object
  • Object
show all
Includes:
Util
Defined in:
lib/ffi-rzmq/message.rb

Overview

The factory constructor optionally takes a string as an argument. It will copy this string to native memory in preparation for transmission. So, don’t pass a string unless you intend to send it. Internally it calls #copy_in_string.

Call #close to release buffers when you are done with the data.

(This class is not really zero-copy. Ruby makes this near impossible since Ruby objects can be relocated in memory by the GC at any time. There is no way to peg them to native memory or have them use non-movable native memory as backing store.)

Message represents ruby equivalent of the zmq_msg_t C struct. Access the underlying memory buffer and the buffer size using the #data and #size methods respectively.

It is recommended that this class be composed inside another class for access to the underlying buffer. The outer wrapper class can provide nice accessors for the information in the data buffer; a clever implementation can probably lazily encode/decode the data buffer on demand. Lots of protocols send more information than is strictly necessary, so only decode (copy from the 0mq buffer to Ruby) that which is necessary.

When you are done using a received message object, call #close to release the associated buffers.

received_message = Message.create
if received_message
  rc = socket.recv(received_message)
  if ZMQ::Util.resultcode_ok?(rc)
    puts "Message contained: #{received_message.copy_out_string}"
  else
    STDERR.puts "Error when receiving message: #{ZMQ::Util.error_string}"
  end

Define a custom layout for the data sent between 0mq peers.

class MyMessage
  class Layout < FFI::Struct
    layout :value1, :uint8,
           :value2, :uint64,
           :value3, :uint32,
           :value4, [:char, 30]
  end

  def initialize msg_struct = nil
    if msg_struct
      @msg_t = msg_struct
      @data = Layout.new(@msg_t.data)
    else
      @pointer = FFI::MemoryPointer.new :byte, Layout.size, true
      @data = Layout.new @pointer
    end
  end

  def size() @size = @msg_t.size; end

  def value1
    @data[:value1]
  end

  def value4
    @data[:value4].to_ptr.read_string
  end

  def value1=(val)
    @data[:value1] = val
  end

  def create_sendable_message
    msg = Message.new
    msg.copy_in_bytes @pointer, Layout.size
  end

message = Message.new
successful_read = socket.recv message
message = MyMessage.new message if successful_read
puts "value1 is #{message.value1}"

Direct Known Subclasses

ManagedMessage

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Util

errno, error_string, nonblocking_flag, resultcode_ok?, version

Constructor Details

#initialize(message = nil) ⇒ Message

Returns a new instance of Message.



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# File 'lib/ffi-rzmq/message.rb', line 96

def initialize message = nil
  @state = :uninitialized

  # allocate our own pointer so that we can tell it to *not* zero out
  # the memory; it's pointless work since the library is going to
  # overwrite it anyway.
  @pointer = FFI::MemoryPointer.new LibZMQ::Msg.size, 1, false

  if message
    copy_in_string message
  else
    # initialize an empty message structure to receive a message
    result_code = LibZMQ.zmq_msg_init @pointer
    raise unless Util.resultcode_ok?(result_code)
  end
end

Class Method Details

.create(message = nil) ⇒ Object

Recommended way to create a standard message. A Message object is returned upon success, nil when allocation fails.



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# File 'lib/ffi-rzmq/message.rb', line 92

def self.create message = nil
  new(message) rescue nil
end

Instance Method Details

#address ⇒ Object Also known as: pointer

Provides the memory address of the zmq_msg_t struct. Used mostly for passing to other methods accessing the underlying library that require a real data address.



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# File 'lib/ffi-rzmq/message.rb', line 144

def address
  @pointer
end

#close ⇒ Object

Manually release the message struct and its associated data buffer.

Only releases the buffer a single time. Subsequent calls are no ops.



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# File 'lib/ffi-rzmq/message.rb', line 186

def close
  rc = 0
  
  if @pointer
    rc = LibZMQ.zmq_msg_close @pointer
    @pointer = nil
  end
  
  rc
end

#copy(source) ⇒ Object 



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# File 'lib/ffi-rzmq/message.rb', line 149

def copy source
  LibZMQ.zmq_msg_copy @pointer, source.address
end

#copy_in_bytes(bytes, len) ⇒ Object

Makes a copy of len bytes from the ruby string bytes. Library handles deallocation of the native memory buffer.

Can only be initialized via #copy_in_string or #copy_in_bytes once.



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# File 'lib/ffi-rzmq/message.rb', line 129

def copy_in_bytes bytes, len
  data_buffer = LibC.malloc len
  # writes the exact number of bytes, no null byte to terminate string
  data_buffer.write_string bytes, len

  # use libC to call free on the data buffer; earlier versions used an
  # FFI::Function here that called back into Ruby, but Rubinius won't 
  # support that and there are issues with the other runtimes too
  LibZMQ.zmq_msg_init_data @pointer, data_buffer, len, LibC::Free, nil
end

#copy_in_string(string) ⇒ Object

Makes a copy of the ruby string into a native memory buffer so that libzmq can send it. The underlying library will handle deallocation of the native memory buffer.

Can only be initialized via #copy_in_string or #copy_in_bytes once.



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# File 'lib/ffi-rzmq/message.rb', line 119

def copy_in_string string
  string_size = string.respond_to?(:bytesize) ? string.bytesize : string.size
  copy_in_bytes string, string_size if string
end

#copy_out_string ⇒ Object

Returns the data buffer as a string.

Note: If this is binary data, it won’t print very prettily.



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# File 'lib/ffi-rzmq/message.rb', line 176

def copy_out_string
  data.read_string(size)
end

#data ⇒ Object

Returns a pointer to the data buffer. This pointer should never be freed. It will automatically be freed when the message object goes out of scope and gets garbage collected.



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# File 'lib/ffi-rzmq/message.rb', line 168

def data
  LibZMQ.zmq_msg_data @pointer
end

#move(source) ⇒ Object 



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# File 'lib/ffi-rzmq/message.rb', line 153

def move source
  LibZMQ.zmq_msg_move @pointer, source.address
end

#size ⇒ Object

Provides the size of the data buffer for this zmq_msg_t C struct.



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# File 'lib/ffi-rzmq/message.rb', line 159

def size
  LibZMQ.zmq_msg_size @pointer
end