Class: DICOM::Link

Inherits:
Object
  • Object
show all
Includes:
Logging
Defined in:
lib/dicom/link.rb

Overview

This class handles the construction and interpretation of network packages as well as network communication.

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Logging

included, #logger

Constructor Details

#initialize(options = {}) ⇒ Link

Creates a Link instance, which is used by both DClient and DServer to handle network communication.

Parameters

  • options – A hash of parameters.

Options

  • :ae – String. The name of the client (application entity).

  • :file_handler – A customized FileHandler class to use instead of the default FileHandler.

  • :host_ae – String. The name of the server (application entity).

  • :max_package_size – Fixnum. The maximum allowed size of network packages (in bytes).

  • :timeout – Fixnum. The maximum period to wait for an answer before aborting the communication.



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# File 'lib/dicom/link.rb', line 32

def initialize(options={})
  require 'socket'
  # Optional parameters (and default values):

  @file_handler = options[:file_handler] || FileHandler
  @ae =  options[:ae]  || "RUBY_DICOM"
  @host_ae =  options[:host_ae]  || "DEFAULT"
  @max_package_size = options[:max_package_size] || 32768 # 16384

  @max_receive_size = @max_package_size
  @timeout = options[:timeout] || 10 # seconds

  @min_length = 10 # minimum number of bytes to expect in an incoming transmission

  # Variables used for monitoring state of transmission:

  @session = nil # TCP connection

  @association = nil # DICOM Association status

  @request_approved = nil # Status of our DICOM request

  @release = nil # Status of received, valid release response

  @command_request = Hash.new
  @presentation_contexts = Hash.new # Keeps track of the relationship between pc id and it's transfer syntax

  set_default_values
  set_user_information_array
  @outgoing = Stream.new(string=nil, endian=true)
end

Instance Attribute Details

#file_handler ⇒ Object

A customized FileHandler class to use instead of the default FileHandler included with Ruby DICOM.



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# File 'lib/dicom/link.rb', line 10

def file_handler
  @file_handler
end

#max_package_size ⇒ Object

The maximum allowed size of network packages (in bytes).



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# File 'lib/dicom/link.rb', line 12

def max_package_size
  @max_package_size
end

#presentation_contexts ⇒ Object

A hash which keeps track of the relationship between context ID and chosen transfer syntax.



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# File 'lib/dicom/link.rb', line 14

def presentation_contexts
  @presentation_contexts
end

#session ⇒ Object (readonly)

A TCP network session where the DICOM communication is done with a remote host or client.



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# File 'lib/dicom/link.rb', line 16

def session
  @session
end

Instance Method Details

#await_release ⇒ Object

Waits for an SCU to issue a release request, and answers it by launching the handle_release method. If invalid or no message is received, the connection is closed.



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# File 'lib/dicom/link.rb', line 57

def await_release
  segments = receive_single_transmission
  info = segments.first
  if info[:pdu] != PDU_RELEASE_REQUEST
    # For some reason we didn't get our expected release request. Determine why:

    if info[:valid]
      logger.error("Unexpected message type received (PDU: #{info[:pdu]}). Expected a release request. Closing the connection.")
      handle_abort(false)
    else
      logger.error("Timed out while waiting for a release request. Closing the connection.")
    end
    stop_session
  else
    # Properly release the association:

    handle_release
  end
end

#build_association_abort ⇒ Object

Builds the abort message which is transmitted when the server wishes to (abruptly) abort the connection.

Restrictions

For now, no reasons for the abortion are provided (and source of problems will always be set as client side).



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# File 'lib/dicom/link.rb', line 81

def build_association_abort
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Reserved (2 bytes)

  @outgoing.encode_last("00"*2, "HEX")
  # Source (1 byte)

  source = "00" # (client side error)

  @outgoing.encode_last(source, "HEX")
  # Reason/Diag. (1 byte)

  reason = "00" # (Reason not specified)

  @outgoing.encode_last(reason, "HEX")
  append_header(PDU_ABORT)
end

#build_association_accept(info) ⇒ Object

Builds the binary string which is sent as the association accept (in response to an association request).

Parameters

  • info – The association information hash.



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# File 'lib/dicom/link.rb', line 103

def build_association_accept(info)
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # No abstract syntax in association response. To make this work with the method that

  # encodes the presentation context, we pass on a one-element array containing nil).

  abstract_syntaxes = Array.new(1, nil)
  # Note: The order of which these components are built is not arbitrary.

  append_application_context
  # Reset the presentation context instance variable:

  @presentation_contexts = Hash.new
  # Create the presentation context hash object that will be passed to the builder method:

  p_contexts = Hash.new
  # Build the presentation context strings, one by one:

  info[:pc].each do |pc|
    @presentation_contexts[pc[:presentation_context_id]] = pc[:selected_transfer_syntax]
    # Add the information from this pc item to the p_contexts hash:

    p_contexts[pc[:abstract_syntax]] = Hash.new unless p_contexts[pc[:abstract_syntax]]
    p_contexts[pc[:abstract_syntax]][pc[:presentation_context_id]] = {:transfer_syntaxes => [pc[:selected_transfer_syntax]], :result => pc[:result]}
  end
  append_presentation_contexts(p_contexts, ITEM_PRESENTATION_CONTEXT_RESPONSE)
  append_user_information(@user_information)
  # Header must be built last, because we need to know the length of the other components.

  append_association_header(PDU_ASSOCIATION_ACCEPT, info[:called_ae])
end

#build_association_reject(info) ⇒ Object

Builds the binary string which is sent as the association reject (in response to an association request).

Parameters

  • info – The association information hash.

Restrictions

  • For now, this method will only customize the “reason” value.

  • For a list of error codes, see the DICOM standard, PS3.8 Chapter 9.3.4, Table 9-21.



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# File 'lib/dicom/link.rb', line 141

def build_association_reject(info)
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Reserved (1 byte)

  @outgoing.encode_last("00", "HEX")
  # Result (1 byte)

  @outgoing.encode_last("01", "HEX") # 1 for permament, 2 for transient

  # Source (1 byte)

  # (1: Service user, 2: Service provider (ACSE related function), 3: Service provider (Presentation related function)

  @outgoing.encode_last("01", "HEX")
  # Reason (1 byte)

  reason = info[:reason]
  @outgoing.encode_last(reason, "HEX")
  append_header(PDU_ASSOCIATION_REJECT)
end

#build_association_request(presentation_contexts, user_info) ⇒ Object

Builds the binary string which is sent as the association request.

Parameters

  • presentation_contexts – A hash containing abstract_syntaxes, presentation context ids and transfer syntaxes.

  • user_info – A user information items array.



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# File 'lib/dicom/link.rb', line 166

def build_association_request(presentation_contexts, )
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Note: The order of which these components are built is not arbitrary.

  # (The first three are built 'in order of appearance', the header is built last, but is put first in the message)

  append_application_context
  append_presentation_contexts(presentation_contexts, ITEM_PRESENTATION_CONTEXT_REQUEST, request=true)
  append_user_information()
  # Header must be built last, because we need to know the length of the other components.

  append_association_header(PDU_ASSOCIATION_REQUEST, @host_ae)
end

#build_command_fragment(pdu, context, flags, command_elements) ⇒ Object

Builds the binary string which is sent as a command fragment.

Parameters

  • pdu – The command fragment’s PDU string.

  • context – Presentation context ID byte (references a presentation context from the association).

  • flags – The flag string, which identifies if this is the last command fragment or not.

  • command_elements – An array of command elements.



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# File 'lib/dicom/link.rb', line 189

def build_command_fragment(pdu, context, flags, command_elements)
  # Little endian encoding:

  @outgoing.endian = @data_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Build the last part first, the Command items:

  command_elements.each do |element|
    # Tag (4 bytes)

    @outgoing.add_last(@outgoing.encode_tag(element[0]))
    # Encode the value first, so we know its length:

    value = @outgoing.encode_value(element[2], element[1])
    # Length (2 bytes)

    @outgoing.encode_last(value.length, "US")
    # Reserved (2 bytes)

    @outgoing.encode_last("0000", "HEX")
    # Value (variable length)

    @outgoing.add_last(value)
  end
  # The rest of the command fragment will be buildt in reverse, all the time

  # putting the elements first in the outgoing binary string.

  # Group length item:

  # Value (4 bytes)

  @outgoing.encode_first(@outgoing.string.length, "UL")
  # Reserved (2 bytes)

  @outgoing.encode_first("0000", "HEX")
  # Length (2 bytes)

  @outgoing.encode_first(4, "US")
  # Tag (4 bytes)

  @outgoing.add_first(@outgoing.encode_tag("0000,0000"))
  # Big endian encoding from now on:

  @outgoing.endian = @net_endian
  # Flags (1 byte)

  @outgoing.encode_first(flags, "HEX")
  # Presentation context ID (1 byte)

  @outgoing.encode_first(context, "BY")
  # Length (of remaining data) (4 bytes)

  @outgoing.encode_first(@outgoing.string.length, "UL")
  # PRESENTATION DATA VALUE (the above)

  append_header(pdu)
end

#build_data_fragment(data_elements, presentation_context_id) ⇒ Object

Builds the binary string which is sent as a data fragment.

Notes

  • The style of encoding will depend on whether we have an implicit or explicit transfer syntax.

Parameters

  • data_elements – An array of data elements.

  • presentation_context_id – Presentation context ID byte (references a presentation context from the association).



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# File 'lib/dicom/link.rb', line 241

def build_data_fragment(data_elements, presentation_context_id)
  # Set the transfer syntax to be used for encoding the data fragment:

  set_transfer_syntax(@presentation_contexts[presentation_context_id])
  # Endianness of data fragment:

  @outgoing.endian = @data_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Build the last part first, the Data items:

  data_elements.each do |element|
    # Encode all tags (even tags which are empty):

    # Tag (4 bytes)

    @outgoing.add_last(@outgoing.encode_tag(element[0]))
    # Encode the value in advance of putting it into the message, so we know its length:

    vr = LIBRARY.element(element[0]).vr
    value = @outgoing.encode_value(element[1], vr)
    if @explicit
      # Type (VR) (2 bytes)

      @outgoing.encode_last(vr, "STR")
      # Length (2 bytes)

      @outgoing.encode_last(value.length, "US")
    else
      # Implicit:

      # Length (4 bytes)

      @outgoing.encode_last(value.length, "UL")
    end
    # Value (variable length)

    @outgoing.add_last(value)
  end
  # The rest of the data fragment will be built in reverse, all the time

  # putting the elements first in the outgoing binary string.

  # Big endian encoding from now on:

  @outgoing.endian = @net_endian
  # Flags (1 byte)

  @outgoing.encode_first("02", "HEX") # Data, last fragment (identifier)

  # Presentation context ID (1 byte)

  @outgoing.encode_first(presentation_context_id, "BY")
  # Length (of remaining data) (4 bytes)

  @outgoing.encode_first(@outgoing.string.length, "UL")
  # PRESENTATION DATA VALUE (the above)

  append_header(PDU_DATA)
end

#build_release_request ⇒ Object

Builds the binary string which is sent as the release request.



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# File 'lib/dicom/link.rb', line 285

def build_release_request
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Reserved (4 bytes)

  @outgoing.encode_last("00"*4, "HEX")
  append_header(PDU_RELEASE_REQUEST)
end

#build_release_response ⇒ Object

Builds the binary string which is sent as the release response (which follows a release request).



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# File 'lib/dicom/link.rb', line 297

def build_release_response
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Reserved (4 bytes)

  @outgoing.encode_last("00000000", "HEX")
  append_header(PDU_RELEASE_RESPONSE)
end

#build_storage_fragment(pdu, context, flags, body) ⇒ Object

Builds the binary string which makes up a C-STORE data fragment.

Parameters

  • pdu – The data fragment’s PDU string.

  • context – Presentation context ID byte (references a presentation context from the association).

  • flags – The flag string, which identifies if this is the last data fragment or not.

  • body – A pre-encoded binary string (typicall a segment of a DICOM file to be transmitted).



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# File 'lib/dicom/link.rb', line 316

def build_storage_fragment(pdu, context, flags, body)
  # Big endian encoding:

  @outgoing.endian = @net_endian
  # Clear the outgoing binary string:

  @outgoing.reset
  # Build in reverse, putting elements in front of the binary string:

  # Insert the data (body):

  @outgoing.add_last(body)
  # Flags (1 byte)

  @outgoing.encode_first(flags, "HEX")
  # Context ID (1 byte)

  @outgoing.encode_first(context, "BY")
  # PDV Length (of remaining data) (4 bytes)

  @outgoing.encode_first(@outgoing.string.length, "UL")
  # PRESENTATION DATA VALUE (the above)

  append_header(pdu)
end

#forward_to_interpret(message, pdu, file = nil) ⇒ Object

Delegates an incoming message to its appropriate interpreter method, based on its pdu type. Returns the interpreted information hash.

Parameters

  • message – The binary message string.

  • pdu – The PDU string of the message.

  • file – A boolean used to inform whether an incoming data fragment is part of a DICOM file reception or not.



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# File 'lib/dicom/link.rb', line 343

def forward_to_interpret(message, pdu, file=nil)
  case pdu
    when PDU_ASSOCIATION_REQUEST
      info = interpret_association_request(message)
    when PDU_ASSOCIATION_ACCEPT
      info = interpret_association_accept(message)
    when PDU_ASSOCIATION_REJECT
      info = interpret_association_reject(message)
    when PDU_DATA
      info = interpret_command_and_data(message, file)
    when PDU_RELEASE_REQUEST
      info = interpret_release_request(message)
    when PDU_RELEASE_RESPONSE
      info = interpret_release_response(message)
    when PDU_ABORT
      info = interpret_abort(message)
    else
      info = {:valid => false}
      logger.error("An unknown PDU type was received in the incoming transmission. Can not decode this message. (PDU: #{pdu})")
  end
  return info
end

#handle_abort(default_message = true) ⇒ Object

Handles the abortion of a session, when a non-valid or unexpected message has been received.

Parameters

  • default_message – A boolean which unless set as nil/false will make the method print the default status message.



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# File 'lib/dicom/link.rb', line 372

def handle_abort(default_message=true)
  logger.warn("An unregonizable (non-DICOM) message was received.") if default_message
  build_association_abort
  transmit
end

#handle_association_accept(info) ⇒ Object

Handles the outgoing association accept message.

Parameters

  • info – The association information hash.



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# File 'lib/dicom/link.rb', line 384

def handle_association_accept(info)
  # Update the variable for calling ae (information gathered in the association request):

  @ae = info[:calling_ae]
  # Build message string and send it:

  set_user_information_array(info)
  build_association_accept(info)
  transmit
end

#handle_incoming_data(path) ⇒ Object

Processes incoming command & data fragments for the DServer. Returns a success boolean and an array of status messages.

Notes

The incoming traffic will in most cases be: A C-STORE-RQ (command fragment) followed by a bunch of data fragments. However, it may also be a C-ECHO-RQ command fragment, which is used to test connections.

Parameters

  • path – The path used to save incoming DICOM files.

– FIXME: The code which handles incoming data isnt quite satisfactory. It would probably be wise to rewrite it at some stage to clean up the code somewhat. Probably a better handling of command requests (and their corresponding data fragments) would be a good idea.



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# File 'lib/dicom/link.rb', line 409

def handle_incoming_data(path)
  # Wait for incoming data:

  segments = receive_multiple_transmissions(file=true)
  # Reset command results arrays:

  @command_results = Array.new
  @data_results = Array.new
  file_transfer_syntaxes = Array.new
  files = Array.new
  single_file_data = Array.new
  # Proceed to extract data from the captured segments:

  segments.each do |info|
    if info[:valid]
      # Determine if it is command or data:

      if info[:presentation_context_flag] == DATA_MORE_FRAGMENTS
        @data_results << info[:results]
        single_file_data  << info[:bin]
      elsif info[:presentation_context_flag] == DATA_LAST_FRAGMENT
        @data_results << info[:results]
        single_file_data  << info[:bin]
        # Join the recorded data binary strings together to make a DICOM file binary string and put it in our files Array:

        files << single_file_data.join
        single_file_data = Array.new
      elsif info[:presentation_context_flag] == COMMAND_LAST_FRAGMENT
        @command_results << info[:results]
        @presentation_context_id = info[:presentation_context_id] # Does this actually do anything useful?

        file_transfer_syntaxes << @presentation_contexts[info[:presentation_context_id]]
      end
    end
  end
  # Process the received files using the customizable FileHandler class:

  success, messages = @file_handler.receive_files(path, files, file_transfer_syntaxes)
  return success, messages
end

#handle_rejection ⇒ Object

Handles the rejection message (The response used to an association request when its formalities are not correct).



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# File 'lib/dicom/link.rb', line 445

def handle_rejection
  logger.warn("An incoming association request was rejected. Error code: #{association_error}")
  # Insert the error code in the info hash:

  info[:reason] = association_error
  # Send an association rejection:

  build_association_reject(info)
  transmit
end

#handle_release ⇒ Object

Handles the release message (which is the response to a release request).



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# File 'lib/dicom/link.rb', line 456

def handle_release
  stop_receiving
  logger.info("Received a release request. Releasing association.")
  build_release_response
  transmit
  stop_session
end

#handle_response ⇒ Object

Handles the command fragment response.

Notes

This is usually a C-STORE-RSP which follows the (successful) reception of a DICOM file, but may also be a C-ECHO-RSP in response to an echo request.



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# File 'lib/dicom/link.rb', line 471

def handle_response
  # Need to construct the command elements array:

  command_elements = Array.new
  # SOP Class UID:

  command_elements << ["0000,0002", "UI", @command_request["0000,0002"]]
  # Command Field:

  command_elements << ["0000,0100", "US", command_field_response(@command_request["0000,0100"])]
  # Message ID Being Responded To:

  command_elements << ["0000,0120", "US", @command_request["0000,0110"]]
  # Data Set Type:

  command_elements << ["0000,0800", "US", NO_DATA_SET_PRESENT]
  # Status:

  command_elements << ["0000,0900", "US", SUCCESS]
  # Affected SOP Instance UID:

  command_elements << ["0000,1000", "UI", @command_request["0000,1000"]] if @command_request["0000,1000"]
  build_command_fragment(PDU_DATA, @presentation_context_id, COMMAND_LAST_FRAGMENT, command_elements)
  transmit
end

#interpret(message, file = nil) ⇒ Object

Decodes the header of an incoming message, analyzes its real length versus expected length, and handles any deviations to make sure that message strings are split up appropriately before they are being forwarded to interpretation. Returns an array of information hashes.

Parameters

  • message – The binary message string.

  • file – A boolean used to inform whether an incoming data fragment is part of a DICOM file reception or not.

– FIXME: This method is rather complex and doesnt feature the best readability. A rewrite that is able to simplify it would be lovely.



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# File 'lib/dicom/link.rb', line 502

def interpret(message, file=nil)
  if @first_part
    message = @first_part + message
    @first_part = nil
  end
  segments = Array.new
  # If the message is at least 8 bytes we can start decoding it:

  if message.length > 8
    # Create a new Stream instance to handle this response.

    msg = Stream.new(message, @net_endian)
    # PDU type ( 1 byte)

    pdu = msg.decode(1, "HEX")
    # Reserved (1 byte)

    msg.skip(1)
    # Length of remaining data (4 bytes)

    specified_length = msg.decode(4, "UL")
    # Analyze the remaining length of the message versurs the specified_length value:

    if msg.rest_length > specified_length
      # If the remaining length of the string itself is bigger than this specified_length value,

      # then it seems that we have another message appended in our incoming transmission.

      fragment = msg.extract(specified_length)
      info = forward_to_interpret(fragment, pdu, file)
      info[:pdu] = pdu
      segments << info
      # It is possible that a fragment contains both a command and a data fragment. If so, we need to make sure we collect all the information:

      if info[:rest_string]
        additional_info = forward_to_interpret(info[:rest_string], pdu, file)
        segments << additional_info
      end
      # The information gathered from the interpretation is appended to a segments array,

      # and in the case of a recursive call some special logic is needed to build this array in the expected fashion.

      remaining_segments = interpret(msg.rest_string, file)
      remaining_segments.each do |remaining|
        segments << remaining
      end
    elsif msg.rest_length == specified_length
      # Proceed to analyze the rest of the message:

      fragment = msg.extract(specified_length)
      info = forward_to_interpret(fragment, pdu, file)
      info[:pdu] = pdu
      segments << info
      # It is possible that a fragment contains both a command and a data fragment. If so, we need to make sure we collect all the information:

      if info[:rest_string]
        additional_info = forward_to_interpret(info[:rest_string], pdu, file)
        segments << additional_info
      end
    else
      # Length of the message is less than what is specified in the message. Need to listen for more. This is hopefully handled properly now.

      #logger.error("Error. The length of the received message (#{msg.rest_length}) is smaller than what it claims (#{specified_length}). Aborting.")

      @first_part = msg.string
    end
  else
    # Assume that this is only the start of the message, and add it to the next incoming string:

    @first_part = message
  end
  return segments
end

#interpret_abort(message) ⇒ Object

Decodes the message received when the remote node wishes to abort the session. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 567

def interpret_abort(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Reserved (2 bytes)

  reserved_bytes = msg.skip(2)
  # Source (1 byte)

  info[:source] = msg.decode(1, "HEX")
  # Reason/Diag. (1 byte)

  info[:reason] = msg.decode(1, "HEX")
  # Analyse the results:

  process_source(info[:source])
  process_reason(info[:reason])
  stop_receiving
  @abort = true
  info[:valid] = true
  return info
end

#interpret_association_accept(message) ⇒ Object

Decodes the message received in the association response, and interprets its content. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 592

def interpret_association_accept(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Protocol version (2 bytes)

  info[:protocol_version] = msg.decode(2, "HEX")
  # Reserved (2 bytes)

  msg.skip(2)
  # Called AE (shall be identical to the one sent in the request, but not tested against) (16 bytes)

  info[:called_ae] = msg.decode(16, "STR")
  # Calling AE (shall be identical to the one sent in the request, but not tested against) (16 bytes)

  info[:calling_ae] = msg.decode(16, "STR")
  # Reserved (32 bytes)

  msg.skip(32)
  # APPLICATION CONTEXT:

  # Item type (1 byte)

  info[:application_item_type] = msg.decode(1, "HEX")
  # Reserved (1 byte)

  msg.skip(1)
  # Application item length (2 bytes)

  info[:application_item_length] = msg.decode(2, "US")
  # Application context (variable length)

  info[:application_context] = msg.decode(info[:application_item_length], "STR")
  # PRESENTATION CONTEXT:

  # As multiple presentation contexts may occur, we need a loop to catch them all:

  # Each presentation context hash will be put in an array, which will be put in the info hash.

  presentation_contexts = Array.new
  pc_loop = true
  while pc_loop do
    # Item type (1 byte)

    item_type = msg.decode(1, "HEX")
    if item_type == ITEM_PRESENTATION_CONTEXT_RESPONSE
      pc = Hash.new
      pc[:presentation_item_type] = item_type
      # Reserved (1 byte)

      msg.skip(1)
      # Presentation item length (2 bytes)

      pc[:presentation_item_length] = msg.decode(2, "US")
      # Presentation context ID (1 byte)

      pc[:presentation_context_id] = msg.decode(1, "BY")
      # Reserved (1 byte)

      msg.skip(1)
      # Result (& Reason) (1 byte)

      pc[:result] = msg.decode(1, "BY")
      process_result(pc[:result])
      # Reserved (1 byte)

      msg.skip(1)
      # Transfer syntax sub-item:

      # Item type (1 byte)

      pc[:transfer_syntax_item_type] = msg.decode(1, "HEX")
      # Reserved (1 byte)

      msg.skip(1)
      # Transfer syntax item length (2 bytes)

      pc[:transfer_syntax_item_length] = msg.decode(2, "US")
      # Transfer syntax name (variable length)

      pc[:transfer_syntax] = msg.decode(pc[:transfer_syntax_item_length], "STR")
      presentation_contexts << pc
    else
      # Break the presentation context loop, as we have probably reached the next stage, which is user info. Rewind:

      msg.skip(-1)
      pc_loop = false
    end
  end
  info[:pc] = presentation_contexts
  # USER INFORMATION:

  # Item type (1 byte)

  info[:user_info_item_type] = msg.decode(1, "HEX")
  # Reserved (1 byte)

  msg.skip(1)
  # User information item length (2 bytes)

  info[:user_info_item_length] = msg.decode(2, "US")
  while msg.index < msg.length do
    # Item type (1 byte)

    item_type = msg.decode(1, "HEX")
    # Reserved (1 byte)

    msg.skip(1)
    # Item length (2 bytes)

    item_length = msg.decode(2, "US")
    case item_type
      when ITEM_MAX_LENGTH
        info[:max_pdu_length] = msg.decode(item_length, "UL")
        @max_receive_size = info[:max_pdu_length]
      when ITEM_IMPLEMENTATION_UID
        info[:implementation_class_uid] = msg.decode(item_length, "STR")
      when ITEM_MAX_OPERATIONS_INVOKED
        # Asynchronous operations window negotiation (PS 3.7: D.3.3.3) (2*2 bytes)

        info[:maxnum_operations_invoked] = msg.decode(2, "US")
        info[:maxnum_operations_performed] = msg.decode(2, "US")
      when ITEM_ROLE_NEGOTIATION
        # SCP/SCU Role Selection Negotiation (PS 3.7 D.3.3.4)

        # Note: An association response may contain several instances of this item type (each with a different abstract syntax).

        uid_length = msg.decode(2, "US")
        role = Hash.new
        # SOP Class UID (Abstract syntax):

        role[:sop_uid] = msg.decode(uid_length, "STR")
        # SCU Role (1 byte):

        role[:scu] = msg.decode(1, "BY")
        # SCP Role (1 byte):

        role[:scp] = msg.decode(1, "BY")
        if info[:role_negotiation]
          info[:role_negotiation] << role
        else
          info[:role_negotiation] = [role]
        end
      when ITEM_IMPLEMENTATION_VERSION
        info[:implementation_version] = msg.decode(item_length, "STR")
      else
        # Value (variable length)

        value = msg.decode(item_length, "STR")
        logger.warn("Unknown user info item type received. Please update source code or contact author. (item type: #{item_type})")
    end
  end
  stop_receiving
  info[:valid] = true
  return info
end

#interpret_association_reject(message) ⇒ Object

Decodes the association reject message and extracts the error reasons given. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 715

def interpret_association_reject(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Reserved (1 byte)

  msg.skip(1)
  # Result (1 byte)

  info[:result] = msg.decode(1, "BY") # 1 for permanent and 2 for transient rejection

  # Source (1 byte)

  info[:source] = msg.decode(1, "BY")
  # Reason (1 byte)

  info[:reason] = msg.decode(1, "BY")
  logger.warn("ASSOCIATE Request was rejected by the host. Error codes: Result: #{info[:result]}, Source: #{info[:source]}, Reason: #{info[:reason]} (See DICOM PS3.8: Table 9-21 for details.)")
  stop_receiving
  info[:valid] = true
  return info
end

#interpret_association_request(message) ⇒ Object

Decodes the binary string received in the association request, and interprets its content. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 739

def interpret_association_request(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Protocol version (2 bytes)

  info[:protocol_version] = msg.decode(2, "HEX")
  # Reserved (2 bytes)

  msg.skip(2)
  # Called AE (shall be returned in the association response) (16 bytes)

  info[:called_ae] = msg.decode(16, "STR")
  # Calling AE (shall be returned in the association response) (16 bytes)

  info[:calling_ae] = msg.decode(16, "STR")
  # Reserved (32 bytes)

  msg.skip(32)
  # APPLICATION CONTEXT:

  # Item type (1 byte)

  info[:application_item_type] = msg.decode(1, "HEX") # 10H

  # Reserved (1 byte)

  msg.skip(1)
  # Application item length (2 bytes)

  info[:application_item_length] = msg.decode(2, "US")
  # Application context (variable length)

  info[:application_context] = msg.decode(info[:application_item_length], "STR")
  # PRESENTATION CONTEXT:

  # As multiple presentation contexts may occur, we need a loop to catch them all:

  # Each presentation context hash will be put in an array, which will be put in the info hash.

  presentation_contexts = Array.new
  pc_loop = true
  while pc_loop do
    # Item type (1 byte)

    item_type = msg.decode(1, "HEX")
    if item_type == ITEM_PRESENTATION_CONTEXT_REQUEST
      pc = Hash.new
      pc[:presentation_item_type] = item_type
      # Reserved (1 byte)

      msg.skip(1)
      # Presentation context item length (2 bytes)

      pc[:presentation_item_length] = msg.decode(2, "US")
      # Presentation context id (1 byte)

      pc[:presentation_context_id] = msg.decode(1, "BY")
      # Reserved (3 bytes)

      msg.skip(3)
      presentation_contexts << pc
      # A presentation context contains an abstract syntax and one or more transfer syntaxes.

      # ABSTRACT SYNTAX SUB-ITEM:

      # Abstract syntax item type (1 byte)

      pc[:abstract_syntax_item_type] = msg.decode(1, "HEX")
      # Reserved (1 byte)

      msg.skip(1)
      # Abstract syntax item length (2 bytes)

      pc[:abstract_syntax_item_length] = msg.decode(2, "US")
      # Abstract syntax (variable length)

      pc[:abstract_syntax] = msg.decode(pc[:abstract_syntax_item_length], "STR")
      ## TRANSFER SYNTAX SUB-ITEM(S):

      # As multiple transfer syntaxes may occur, we need a loop to catch them all:

      # Each transfer syntax hash will be put in an array, which will be put in the presentation context hash.

      transfer_syntaxes = Array.new
      ts_loop = true
      while ts_loop do
        # Item type (1 byte)

        item_type = msg.decode(1, "HEX")
        if item_type == ITEM_TRANSFER_SYNTAX
          ts = Hash.new
          ts[:transfer_syntax_item_type] = item_type
          # Reserved (1 byte)

          msg.skip(1)
          # Transfer syntax item length (2 bytes)

          ts[:transfer_syntax_item_length] = msg.decode(2, "US")
          # Transfer syntax name (variable length)

          ts[:transfer_syntax] = msg.decode(ts[:transfer_syntax_item_length], "STR")
          transfer_syntaxes << ts
        else
          # Break the transfer syntax loop, as we have probably reached the next stage,

          # which is either user info or a new presentation context entry. Rewind:

          msg.skip(-1)
          ts_loop = false
        end
      end
      pc[:ts] = transfer_syntaxes
    else
      # Break the presentation context loop, as we have probably reached the next stage, which is user info. Rewind:

      msg.skip(-1)
      pc_loop = false
    end
  end
  info[:pc] = presentation_contexts
  # USER INFORMATION:

  # Item type (1 byte)

  info[:user_info_item_type] = msg.decode(1, "HEX")
  # Reserved (1 byte)

  msg.skip(1)
  # User information item length (2 bytes)

  info[:user_info_item_length] = msg.decode(2, "US")
  # User data (variable length):

  while msg.index < msg.length do
    # Item type (1 byte)

    item_type = msg.decode(1, "HEX")
    # Reserved (1 byte)

    msg.skip(1)
    # Item length (2 bytes)

    item_length = msg.decode(2, "US")
    case item_type
      when ITEM_MAX_LENGTH
        info[:max_pdu_length] = msg.decode(item_length, "UL")
      when ITEM_IMPLEMENTATION_UID
        info[:implementation_class_uid] = msg.decode(item_length, "STR")
      when ITEM_MAX_OPERATIONS_INVOKED
        # Asynchronous operations window negotiation (PS 3.7: D.3.3.3) (2*2 bytes)

        info[:maxnum_operations_invoked] = msg.decode(2, "US")
        info[:maxnum_operations_performed] = msg.decode(2, "US")
      when ITEM_ROLE_NEGOTIATION
        # SCP/SCU Role Selection Negotiation (PS 3.7 D.3.3.4)

        # Note: An association request may contain several instances of this item type (each with a different abstract syntax).

        uid_length = msg.decode(2, "US")
        role = Hash.new
        # SOP Class UID (Abstract syntax):

        role[:sop_uid] = msg.decode(uid_length, "STR")
        # SCU Role (1 byte):

        role[:scu] = msg.decode(1, "BY")
        # SCP Role (1 byte):

        role[:scp] = msg.decode(1, "BY")
        if info[:role_negotiation]
          info[:role_negotiation] << role
        else
          info[:role_negotiation] = [role]
        end
      when ITEM_IMPLEMENTATION_VERSION
        info[:implementation_version] = msg.decode(item_length, "STR")
      else
        # Unknown item type:

        # Value (variable length)

        value = msg.decode(item_length, "STR")
        logger.warn("Unknown user info item type received. Please update source code or contact author. (item type: " + item_type + ")")
    end
  end
  stop_receiving
  info[:valid] = true
  return info
end

#interpret_command_and_data(message, file = nil) ⇒ Object

Decodes the received command/data fragment message, and interprets its content. Returns the processed information hash.

Notes

  • Decoding of a data fragment depends on the explicitness of the transmission.

Parameters

  • message – The binary message string.

  • file – A boolean used to inform whether an incoming data fragment is part of a DICOM file reception or not.



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# File 'lib/dicom/link.rb', line 890

def interpret_command_and_data(message, file=nil)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Length (of remaining PDV data) (4 bytes)

  info[:presentation_data_value_length] = msg.decode(4, "UL")
  # Calculate the last index position of this message element:

  last_index = info[:presentation_data_value_length] + msg.index
  # Presentation context ID (1 byte)

  info[:presentation_context_id] = msg.decode(1, "BY")
  @presentation_context_id = info[:presentation_context_id]
  # Flags (1 byte)

  info[:presentation_context_flag] = msg.decode(1, "HEX") # "03" for command (last fragment), "02" for data

  # Apply the proper transfer syntax for this presentation context:

  set_transfer_syntax(@presentation_contexts[info[:presentation_context_id]])
  # "Data endian" encoding from now on:

  msg.endian = @data_endian
  # We will put the results in a hash:

  results = Hash.new
  if info[:presentation_context_flag] == COMMAND_LAST_FRAGMENT
    # COMMAND, LAST FRAGMENT:

    while msg.index < last_index do
      # Tag (4 bytes)

      tag = msg.decode_tag
      # Length (2 bytes)

      length = msg.decode(2, "US")
      if length > msg.rest_length
        logger.error("Specified length of command element value exceeds remaining length of the received message! Something is wrong.")
      end
      # Reserved (2 bytes)

      msg.skip(2)
      # VR (from library - not the stream):

      vr = LIBRARY.element(tag).vr
      # Value (variable length)

      value = msg.decode(length, vr)
      # Put tag and value in a hash:

      results[tag] = value
    end
    # The results hash is put in an array along with (possibly) other results:

    info[:results] = results
    # Store the results in an instance variable (to be used later when sending a receipt for received data):

    @command_request = results
    # Check if the command fragment indicates that this was the last of the response fragments for this query:

    status = results["0000,0900"]
    if status
      # Note: This method will also stop the packet receiver if indicated by the status mesasge.

      process_status(status)
    end
    # Special case: Handle a possible C-ECHO-RQ:

    if info[:results]["0000,0100"] == C_ECHO_RQ
      logger.info("Received an Echo request. Returning an Echo response.")
      handle_response
    end
  elsif info[:presentation_context_flag] == DATA_MORE_FRAGMENTS or info[:presentation_context_flag] == DATA_LAST_FRAGMENT
    # DATA FRAGMENT:

    # If this is a file transmission, we will delay the decoding for later:

    if file
      # Just store the binary string:

      info[:bin] = msg.rest_string
      # If this was the last data fragment of a C-STORE, we need to send a receipt:

      # (However, for, say a C-FIND-RSP, which indicates the end of the query results, this method shall not be called) (Command Field (0000,0100) holds information on this)

      handle_response if info[:presentation_context_flag] == DATA_LAST_FRAGMENT
    else
      # Decode data elements:

      while msg.index < last_index do
        # Tag (4 bytes)

        tag = msg.decode_tag
        if @explicit
          # Type (VR) (2 bytes):

          type = msg.decode(2, "STR")
          # Length (2 bytes)

          length = msg.decode(2, "US")
        else
          # Implicit:

          type = nil # (needs to be defined as nil here or it will take the value from the previous step in the loop)

          # Length (4 bytes)

          length = msg.decode(4, "UL")
        end
        if length > msg.rest_length
          logger.error("The specified length of the data element value exceeds the remaining length of the received message!")
        end
        # Fetch type (if not defined already) for this data element:

        type = LIBRARY.element(tag).vr unless type
        # Value (variable length)

        value = msg.decode(length, type)
        # Put tag and value in a hash:

        results[tag] = value
      end
      # The results hash is put in an array along with (possibly) other results:

      info[:results] = results
    end
  else
    # Unknown.

    logger.error("Unknown presentation context flag received in the query/command response. (#{info[:presentation_context_flag]})")
    stop_receiving
  end
  # If only parts of the string was read, return the rest:

  info[:rest_string] = msg.rest_string if last_index < msg.length
  info[:valid] = true
  return info
end

#interpret_release_request(message) ⇒ Object

Decodes the message received in the release request and calls the handle_release method. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 998

def interpret_release_request(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Reserved (4 bytes)

  reserved_bytes = msg.decode(4, "HEX")
  handle_release
  info[:valid] = true
  return info
end

#interpret_release_response(message) ⇒ Object

Decodes the message received in the release response and closes the connection. Returns the processed information hash.

Parameters

  • message – The binary message string.



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# File 'lib/dicom/link.rb', line 1015

def interpret_release_response(message)
  info = Hash.new
  msg = Stream.new(message, @net_endian)
  # Reserved (4 bytes)

  reserved_bytes = msg.decode(4, "HEX")
  stop_receiving
  info[:valid] = true
  return info
end

#receive_multiple_transmissions(file = nil) ⇒ Object

Handles the reception of multiple incoming transmissions. Returns an array of interpreted message information hashes.

Parameters

  • file – A boolean used to inform whether an incoming data fragment is part of a DICOM file reception or not.



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# File 'lib/dicom/link.rb', line 1032

def receive_multiple_transmissions(file=nil)
  # FIXME: The code which waits for incoming network packets seems to be very CPU intensive.

  # Perhaps there is a more elegant way to wait for incoming messages?

  #

  @listen = true
  segments = Array.new
  while @listen
    # Receive data and append the current data to our segments array, which will be returned.

    data = receive_transmission(@min_length)
    current_segments = interpret(data, file)
    if current_segments
      current_segments.each do |cs|
        segments << cs
      end
    end
  end
  segments << {:valid => false} unless segments
  return segments
end

#receive_single_transmission ⇒ Object

Handles the reception of a single, expected incoming transmission and returns the interpreted, received data.



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# File 'lib/dicom/link.rb', line 1054

def receive_single_transmission
  min_length = 8
  data = receive_transmission(min_length)
  segments = interpret(data)
  segments << {:valid => false} unless segments.length > 0
  return segments
end

#set_session(session) ⇒ Object

Sets the session of this Link instance (used when this session is already established externally).

Parameters

  • session – A TCP network connection that has been established with a remote node.



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# File 'lib/dicom/link.rb', line 1068

def set_session(session)
  @session = session
end

#start_session(adress, port) ⇒ Object

Establishes a new session with a remote network node.

Parameters

  • adress – String. The adress (IP) of the remote node.

  • port – Fixnum. The network port to be used in the network communication.



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# File 'lib/dicom/link.rb', line 1079

def start_session(adress, port)
  @session = TCPSocket.new(adress, port)
end

#stop_session ⇒ Object

Ends the current session by closing the connection.



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# File 'lib/dicom/link.rb', line 1085

def stop_session
  @session.close unless @session.closed?
end

#transmit ⇒ Object

Sends the outgoing message (encoded binary string) to the remote node.



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# File 'lib/dicom/link.rb', line 1091

def transmit
  @session.send(@outgoing.string, 0)
end