Warning and error codes

Every code on this page is part of the public API. Renaming or removing one is a breaking change, so log pipelines and dashboards can key on them. No warning, error or event carries a run of message content; where a code reports a field, it reports its byte length. The types behind each family are in the API reference.

Framing warnings

The decoder's and the encoder's codes, of type WarningCode. Each reaches you as an MllpWarning with a byteOffset, or, where it is fatal, as an MllpFramingError with the same code. The one exception is leading whitespace: when it is refused, the error's code is MLLP_MISSING_LEADING_VT, so MLLP_LEADING_WHITESPACE only ever arrives as a warning.

Code	Raised when	Warning or error
MLLP_MISSING_LEADING_VT	a frame begins without VT	warning with allowMissingLeadingVt, otherwise an error
MLLP_FS_WITHOUT_CR	a frame ends FS with no CR	warning with allowFsOnly, otherwise an error
MLLP_LF_AFTER_FS	a line feed follows FS	warning with allowLfAfterFs, otherwise an error
MLLP_LEADING_WHITESPACE	padding precedes VT	warning with allowLeadingWhitespace; never thrown, see below
MLLP_TRAILING_BYTES	a VT arrives inside a payload: the bytes before it are discarded and a new frame starts	always a warning; the auto-ACK path never answers it AA
MLLP_EMPTY_PAYLOAD	nothing lies between VT and FS	always a warning
MLLP_FRAME_TOO_LARGE	a frame grows past maxFrameSizeBytes (16 MiB by default)	always an error
MLLP_PAYLOAD_CONTAINS_VT	the encoder is given a payload holding 0x0B	an error; a warning with allowDelimiterBytesInPayload
MLLP_PAYLOAD_CONTAINS_FS	the encoder is given a payload holding 0x1C	an error; a warning with allowDelimiterBytesInPayload

Without allowLeadingWhitespace, padding before VT is refused with an MllpFramingError whose code is MLLP_MISSING_LEADING_VT, not MLLP_LEADING_WHITESPACE. strict: true makes the first four errors whatever their flags say, and strict leading whitespace is refused with MLLP_MISSING_LEADING_VT too. A framing error on a server or a client closes that one connection, with connectionCause: "framing-fatal", and a client does not reconnect into it. Framing and tolerance explains why.

Correlation warnings

Raised on the client's warning event, of type AckCorrelationCode. Both are also members of WarningCode. The payload is an AckCorrelationWarning carrying controlIdBytes (the control ID's byte length) and elapsedSinceSendMs; its message is the fixed text ackDiagnosticMessage(code) returns.

Code	Raised when
MLLP_ACK_UNMATCHED_CONTROL_ID	an acknowledgment's MSA-2 matches no pending send
MLLP_ACK_AFTER_TIMEOUT	an acknowledgment arrives for a send that already timed out; it is dropped

Acknowledgment-mode warnings

Codes about the enhanced acknowledgment protocol, of type AckModeCode. The client reports them on its warning event as an AckModeWarning; the server reports MLLP_ACK_ACCEPT_TYPE_UNRECOGNISED on its ackModeWarning event. Their text is ackModeDiagnosticMessage(code). None of them refuses or changes a message.

Code	Raised when
MLLP_ACK_ACCEPT_TYPE_UNRECOGNISED	MSH-15 holds a value outside HL7 Table 0155; it is read as its default
MLLP_ACK_APPLICATION_TYPE_UNRECOGNISED	MSH-16 holds a value outside HL7 Table 0155; it is read as its default
MLLP_ACK_TWO_PHASE_UNAVAILABLE	an enhanced-mode send is made on a FIFO client, so the first acknowledgment matched settles it
MLLP_ACK_COMMIT_ALREADY_REPORTED	a further CA arrives for a send whose commit was already reported; the send stays pending
MLLP_ACK_MSA1_ABSENT	an acknowledgment for an enhanced-mode send has no MSA-1; the send stays pending
MLLP_ACK_MSA1_UNCLASSIFIABLE	an acknowledgment for an enhanced-mode send has an MSA-1 outside HL7 Table 0008; the send stays pending
MLLP_ACK_SEND_ALREADY_DISPOSED	an acknowledgment arrives for a send already settled or failed; it is dropped

ack-from-hl7 warnings

Carried in the warnings of an MllpAck built by the @cosyte/mllp/ack-from-hl7 subpath.

Code	Raised when
MLLP_ACK_INBOUND_UNPARSEABLE	the inbound could not be parsed, or is an FHS/BHS batch; the acknowledgment is a non-positive AE with no correlation ID
MLLP_ACK_CONTROL_ID_NOT_VERBATIM	on a Buffer inbound, the MSA-2 written differs from the inbound MSH-10 bytes
MLLP_ACK_CONTROL_ID_UNVERIFIABLE	on a string or parsed inbound, the control ID holds a character outside ASCII, so the echo cannot be checked byte for byte
ACK_NO_CORRELATION_ID	from @cosyte/hl7: the inbound has no MSH-10, so a requested positive code was downgraded

TLS and bind codes

Security warnings are emitted on the client's or the server's securityWarning event as a SecurityWarning, and through process.emitWarning:

Code	Raised when
MLLP_TLS_VERIFY_DISABLED	a client configured with tls.allowUnverified completes a handshake, on every connect
MLLP_BIND_ALL_INTERFACES	a server created with allowWildcardBind: true binds a wildcard host

TLS configuration errors reject connect() or listen() with an MllpTlsConfigurationError before any socket exists:

Code	Raised when
MLLP_TLS_CIPHER_LIST_REJECTED	the TLS library accepts no suite in the ciphers list; there is no fallback to its default list
MLLP_TLS_CIPHER_OPTION_CONFLICT	both atnaTransportSecurity and ciphers are set
MLLP_TLS_DH_PARAMETERS_REJECTED	the server's dhParameters cannot be used

Server connection codes

Emitted on the server's connectionRejected event as a ConnectionRejectedEvent, only when maxConnections is set:

Code	Raised when
MLLP_CONNECTION_LIMIT_REACHED	a connection arrives while the server holds maxConnections; it is closed at accept

Connection causes

The connectionCause of an MllpConnectionError, of type ConnectionErrorCause. An error without one is a plain socket failure, such as ECONNREFUSED.

Cause	Meaning	Reconnect
in-flight-orphan	a FIFO client lost the link with this send already written; it may have been committed	the link, not the send
fifo-unsafe	a FIFO client lost the link with this send still queued; it was never written	the link, not the send
tls-verify	certificate verification failed on the initial connect()	no: permanent
tls-handshake	the TLS handshake failed for a protocol reason on the initial connect()	no: permanent
framing-fatal	the peer sent bytes the decoder could not accept, or a frame past the size cap	no: permanent

isTransientConnectionError(err) gives the same classification the client's reconnect uses, and Connection, reconnect and backpressure has the full table.

Negative acknowledgment reasons

The reason of the server's nack event, a NackEvent, of type NackReason:

Reason	The server answered negatively because
handler-rejected	your commit-gated onMessage handler threw or rejected
uncorrelatable-inbound	the inbound had no readable MSH, an empty MSH-10, or more than one message (a batch, or two MSH)
discarded-bytes	the decoder discarded part of the frame (MLLP_TRAILING_BYTES)

Error types

Narrow with instanceof, never on the text of a message.

Error	Reaches you when	Stable field
MllpFramingError	a FrameReader meets a fatal framing violation, or encodeFrame a payload it cannot frame	code, byteOffset
MllpConnectionError	a socket-level failure, a send before the client is connected, or a refused bind	phase, connectionCause
MllpTimeoutError	no acknowledgment arrives within ackTimeoutMs of the write	messageControlIdBytes
MllpBackpressureError	a send would pass highWaterMark with onBackpressure: "reject"	queueDepth, queueBytes
MllpCommitRejectedError	the peer answers an enhanced-mode send with CE or CR	commitCode
MllpApplicationAckError	the peer committed an enhanced-mode send and its application acknowledgment never came	commitCode, reason
MllpNeverDeliveredError	close() ends with this send never written; resending it is safe	byteCount
MllpUnknownFateError	close() ends with this send written and unacknowledged; it may be committed	flushedAt, byteCount
MllpTlsConfigurationError	a TLS configuration is refused before any socket exists	code
MllpDifferentialConfigurationError	runDifferential is given a peer address that is not host:port (code MLLP_DIFF_PEER_UNPARSEABLE)	code
MllpPeerMissingError	ack-from-hl7 is called without @cosyte/hl7 installed (code MLLP_PEER_MISSING)	code
MllpAckError	not thrown by the package: you throw it from a handler to choose AR over AE	ackCode

buildMllpAck and its siblings also throw a TypeError for an encoding that is not a text codec, and for a code outside HL7 Table 0008.