/// <summary>
/// Receive an HL7 message over the connected network stream.
/// </summary>
/// <param name="messageDelimiters">Initial HL7 message delimiters - updated to actual delimters during method.</param>
/// <returns>Correctly instantiated HL7 message.</returns>
public Hl7Message ReceiveMessage(out Hl7MessageDelimiters messageDelimiters)
{
// initialize the message delimiters to the default values
messageDelimiters = new Hl7MessageDelimiters();
Hl7Message hl7Message = new Hl7Message();
if (_networkStream == null)
{
return(null);
}
// set the read / write timeouts for this stream - zero means no timeout.
if (_readTimeout != 0)
{
_networkStream.ReadTimeout = _readTimeout;
}
if (_writeTimeout != 0)
{
_networkStream.WriteTimeout = _writeTimeout;
}
// initialise the segment content
System.String rxSegment = System.String.Empty;
// initialise the MLLP state
MllpStateEnum mllpState = MllpStateEnum.WaitingForStartOfMessageChar;
// loop waiting for the end of message character
while (mllpState != MllpStateEnum.DoneWaiting)
{
// check if data is available on network
try
{
// get the next character from the stream
int rxCode = _networkStream.ReadByte();
if (rxCode < 0)
{
return(null);
}
char rxChar = (char)rxCode;
// switch on MLLP state
switch (mllpState)
{
case MllpStateEnum.WaitingForStartOfMessageChar:
// check if we have got the SOM
if (rxChar == _StartOfMessageChar)
{
// reset the segment
rxSegment = System.String.Empty;
// change state to waiting for end of segment
mllpState = MllpStateEnum.WaitingForEndOfSegmentChar;
}
else
{
Console.WriteLine("HL7 - MLLP: Waiting for SOM - got {0}...", rxChar);
}
break;
case MllpStateEnum.WaitingForEndOfSegmentChar:
// check if we have got the end of segment
if (rxChar == _EndOfSegmentChar)
{
// check if we have the MSH segment
// - we need to get the message delimiters
if (rxSegment.StartsWith("MSH") == true)
{
// set the message delimiters to the values received
// - we assume that the MSH segment is formatted properly at least in the first few bytes
messageDelimiters = new Hl7MessageDelimiters(rxSegment.Substring(3, 5));
}
// segment is complete
Hl7Segment segment = new Hl7Segment();
segment.Decode(rxSegment, messageDelimiters);
// add the segment to the HL7 message
hl7Message.AddSegment(segment);
// reset the segment
rxSegment = System.String.Empty;
}
else if (rxChar == _EndOfMessageChar1)
{
// we have the first end of message - that's OK
// check if any characters have been received since the last end of segment
if (rxSegment == System.String.Empty)
{
// change state to waiting for second end of message
mllpState = MllpStateEnum.WaitingForEndOfMessageChar;
}
else
{
Console.WriteLine("HL7 - MLLP: First EOM does not immediately follow an EOS");
return(null);
}
}
else
{
// save the received character in the current segment
rxSegment += rxChar;
}
break;
case MllpStateEnum.WaitingForEndOfMessageChar:
// check if we have got the second end of message
if (rxChar == _EndOfMessageChar2)
{
// message is complete
mllpState = MllpStateEnum.DoneWaiting;
}
else
{
Console.WriteLine("HL7 - MLLP: Second EOM does not immediately follow first EOM");
return(null);
}
break;
default:
break;
}
}
catch (System.Exception e)
{
Console.WriteLine("HL7 - MLLP: ReceiveMessage() Exception: {0}", e.Message);
return(null);
}
}
// return the correct instantiation of the received HL7 message
return(Hl7MessageFactory.CreateHl7Message(hl7Message, messageDelimiters));
}