class ZMQ::Message

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.recvmsg(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}"

Public Class Methods

create(message = nil) click to toggle source

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

# File lib/ffi-rzmq/message.rb, line 91
def self.create message = nil
  new(message) rescue nil
end
msg_size() click to toggle source
# File lib/ffi-rzmq/message.rb, line 198
def self.msg_size() @msg_size; end
new(message = nil) click to toggle source
# File lib/ffi-rzmq/message.rb, line 95
def initialize message = nil
  # 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 Message.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

Public Instance Methods

address() click to toggle source

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.

# File lib/ffi-rzmq/message.rb, line 141
def address
  @pointer
end
Also aliased as: pointer
close() click to toggle source

Manually release the message struct and its associated data buffer.

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

# File lib/ffi-rzmq/message.rb, line 183
def close
  rc = 0

  if @pointer
    rc = LibZMQ.zmq_msg_close @pointer
    @pointer = nil
  end

  rc
end
copy(source) click to toggle source
# File lib/ffi-rzmq/message.rb, line 146
def copy source
  LibZMQ.zmq_msg_copy @pointer, source
end
copy_in_bytes(bytes, len) click to toggle source

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.

# File lib/ffi-rzmq/message.rb, line 126
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) click to toggle source

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.

# File lib/ffi-rzmq/message.rb, line 116
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() click to toggle source

Returns the data buffer as a string.

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

# File lib/ffi-rzmq/message.rb, line 173
def copy_out_string
  data.read_string(size)
end
data() click to toggle source

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.

# File lib/ffi-rzmq/message.rb, line 165
def data
  LibZMQ.zmq_msg_data @pointer
end
get(property) click to toggle source
# File lib/ffi-rzmq/message.rb, line 203
def get(property)
  LibZMQ.zmq_msg_get(@pointer, property)
end
more?() click to toggle source

Returns true if this message has additional parts coming.

# File lib/ffi-rzmq/message.rb, line 209
def more?
  Util.resultcode_ok?(get(MORE))
end
move(source) click to toggle source
# File lib/ffi-rzmq/message.rb, line 150
def move source
  LibZMQ.zmq_msg_move @pointer, source
end
pointer()
Alias for: address
set(property, value) click to toggle source
# File lib/ffi-rzmq/message.rb, line 213
def set(property, value)
  LibZMQ.zmq_msg_set(@pointer, property, value)
end
size() click to toggle source

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

# File lib/ffi-rzmq/message.rb, line 156
def size
  LibZMQ.zmq_msg_size @pointer
end