Receive

Starts an MLLP server that collects incoming HL7 messages for the configured duration.

Task version: 2.1.0

Required Frends version: 5.7+

Required .NET version: 8.0

Compatible Agents: Crossplatform

Source code: https://github.com/FrendsPlatform/Frends.Mllp/tree/main/Frends.Mllp.Receive

Task Parameters

Input

Name	Description
ListenAddress : String	IP address or hostname to bind to. Leave empty to listen on all interfaces. Default: - Example: 127.0.0.1
Port : Int32	TCP port the server listens on. Default: 2575 Example: 2575

Connection

Name	Description
TlsMode : TlsMode	The TLS encryption mode to use for the connection. Possible values: None: No encryption. Data is sent in plain text (standard TCP). Mtls: Mutual TLS. Both client and server must provide valid certificates to establish a secure, encrypted connection. Default: None Example: TlsMode.None
ServerCertPath : String	Path to the server certificate file (PFX or P12 format). Required only for MTLS mode. Default: - Example: C:\certs\client.pfx
🗝ServerCertPassword : String	Password for the server certificate. Default: - Example: MyStrongPassword123
ListenDurationSeconds : Int32	How long the listener waits for incoming messages before shutting down. Value in seconds. Default: 30 Example: 30
BufferSize : Int32	Size of the buffer used when reading data from clients. Default: 8192 Example: 8192
SendAcknowledgement : Boolean	Whether to send a simple acknowledgement for each message. Default: True Example: true
AcknowledgementType : AcknowledgementType	ACK type to use. AA = Application Accept, AE = Application Error, AR = Application Reject. Possible values: AA: Application Accept AE: Application Error AR: Application Reject Default: AA Example: AA
AckSenderApplication : String	Sender application name (MSH-3) used in the generated ACK message. If empty, uses the receiving application (MSH-5) from the incoming message. Default: - Example: ACK_APP
AckReceiverApplication : String	Receiver application name (MSH-5) used in the generated ACK message. If empty, uses the sending application (MSH-3) from the incoming message. Default: - Example: SENDING_APP
AckHl7Version : String	HL7 version used in the generated ACK message (MSH-12). If empty, uses the version from the incoming message. Default: - Example: 2.5
IgnoreClientCertificateErrors : Boolean	If enabled, the server will accept client certificates even if they are self-signed or have validation errors (Mutual TLS only). Default: False Example: false
ClientCertificateThumbprints : String[]	Expected client certificate thumbprint(s) for validation. Only used when IgnoreClientCertificateErrors is false. Used in MTLS mode for certificate pinning. Default: - Example: E5FA62B8B5F3B0B2B3B4B5B6B7B8B9B0B1B2B3B
Encoding : FileEncoding	Encoding used to read incoming HL7 messages. Possible values: UTF8: UTF-8 encoding. Default: The system default encoding. ASCII: ASCII encoding. Unicode: Unicode (UTF-16) encoding. Windows1252: Windows-1252 encoding. Other: A custom encoding specified as a string. Default: UTF8 Example: FileEncoding.UTF8
EncodingInString : String	Custom encoding name, used when Encoding is set to Other. Default: - Example: iso-8859-1

Options

Name	Description
StartBlockByte : Byte	The MLLP start-block framing byte (decimal). Default is 11 (0x0B, vertical tab). Default: 11 Example: 11
EndBlockByte : Byte	The MLLP end-block framing byte (decimal). Default is 28 (0x1C, file separator). Default: 28 Example: 28
CarriageReturnByte : Byte	The MLLP end-of-block trailer byte (decimal). Default is 13 (0x0D, carriage return). Default: 13 Example: 13
CarriageReturnRequired : Boolean	Whether the CarriageReturn character is required. If false, EndBlock marks end of message. Default: True Example: true
MaxConcurrentConnections : Int32	Maximum number of concurrent connections allowed. 0 means unlimited. Default: 0 Example: 10
MaxMessageSize : Int32	Maximum message size in bytes. Messages exceeding this limit will be rejected. 0 means unlimited. Default: 0 Example: 1048576
AcknowledgementFormat : AcknowledgementFormat	Format used for outbound acknowledgement responses. Possible values: Hl7: Sends a standard HL7 ACK message wrapped in configured framing bytes. ControlByte: Sends a framed single-byte control acknowledgement. Default: Hl7 Example: AcknowledgementFormat.Hl7
AcknowledgementByte : Byte	Positive acknowledgement control byte used when AcknowledgementFormat is set to ControlByte. Default: 6 Example: 6
EnableLogging : Boolean	Enable message processing logging to file. Default: False Example: true
LogFilePath : String	File path for logging message processing events. If not specified, logs to a default location. Default: - Example: C:\Logs\mllp-messages.log
LogMessageContent : Boolean	Include full message content in logs. If false, only logs message metadata and status. Default: False Example: false
WriteMessagesToFile : Boolean	When enabled, messages are written directly to temp files during receive, reducing memory usage. Note: uses synchronous file I/O which may impact throughput under high load. Output contains file paths instead of message content. Users are responsible for managing and deleting files. Default: False Example: false
MessageOutputDirectory : String	Directory for temp files when WriteMessagesToFile is enabled. If empty, uses system temp directory. Default: - Example: C:\Temp\mllp
ThrowErrorOnFailure : Boolean	Whether to throw an error on failure. Default: True Example: false
ErrorMessageOnFailure : String	Overrides the error message on failure. Default: - Example: Custom error message

Task Result

Name	Description
Success : Boolean	Indicates if the task completed successfully. Example: true
Output : String[]	Messages received while the listener was running. Example: ACK
Error : Error	Error that occurred during task execution. Example: object { string Message, Exception AdditionalInfo }
Error.Message : String	Summary of the error. Example: Unable to receive HL7 message.
Error.AdditionalInfo : Exception	Additional information about the error. Example: object { Exception AdditionalInfo }

Task Changelog

Changelog for Task Frends.Mllp.Receive.

[2.1.0] - 2026-08-06

Changed

• Updated package copyright to comply with Frends task standards.

[2.0.0] - 2026-06-05

Added

• WriteMessagesToFile and MessageOutputDirectory options to handle streaming messages to temp files instead of memory - Output returns file paths. Users are responsible for managing temp files.
• MaxConcurrentConnections option to limit simultaneous connections - excess connections are rejected and logged.
• MaxMessageSize option to reject oversized messages with a NACK.
• EnableLogging, LogFilePath and LogMessageContent options to log message events to a file.
• StartBlockByte, EndBlockByte, CarriageReturnByte and CarriageReturnRequired options to configure MLLP framing.
• AcknowledgementFormat, AckSenderApplication, AckReceiverApplication, AckHl7Version and AcknowledgementType options to configure ACK/NACK behavior.

Changed

• ACK generation now uses only the MSH line instead of full payload - fixes crash on large messages.
• [Breaking change] AcknowledgementMessage renamed to AcknowledgementType in Connection and changed from string to AcknowledgementType enum. Valid values: AA, AE, AR.

[1.4.0] - 2026-05-18

Added

• Options.AcknowledgementFormat with Hl7 (default) and ControlByte to configure outbound acknowledgement format.
• Options.AcknowledgementByte (default 0x06) for the positive control-byte acknowledgement value.

[1.3.0] - 2026-05-06

Added

• Options.StartBlockByte, Options.EndBlockByte, and Options.CarriageReturnByte to allow configuring MLLP framing bytes (defaults: 11, 28, 13)

[1.2.0] - 2026-04-17

Added

• Connection.ClientCertificateThumbprints property to specify client certificate thumbprints for authentication in MTLS mode

[1.1.0] - 2026-04-13

Added

• Connection.Encoding is now selectable and can be set custom by user

[1.0.0] - 2026-02-06

Added

• Initial implementation