TCP Receive (tcp-in)

Listens on a TCP port (server) or dials a remote (client) and emits one message per received frame on its single output. Every accepted server-mode connection is registered with the engine's session registry as a msg.session handle so a paired tcp-out reply can write back on the same socket.

Inputs	Outputs
0	1

Modes

Mode	Behaviour
server	Bind host:port, accept many concurrent peers, emit messages from each.
client	Dial the remote host:port, read frames, reconnect on drop with exponential backoff.

Configuration

Common

Field	Default	Description
mode	server	server or client.
host	0.0.0.0	Bind address (server) or target host (client).
port	7000	TCP port.
framing	stream	See framing: stream / delimiter / length-prefix / fixed-length.
delimiter	\n	Only with framing=delimiter. JS-style escapes supported.
lengthPrefix	—	Only with framing=length-prefix. {bytes, endianness, includesHeader}.
fixedLength	—	Only with framing=fixed-length. Frame size in bytes.
payloadEncoding	buffer	buffer (number array), string, or base64.
maxFrameBytes	1048576	Hard cap per frame. Oversize → catchable error + close.
keepAlive	true	Enable TCP keep-alive on the socket.
keepAliveInterval	30s	Keep-alive idle interval.
nodelay	false	Disable Nagle's algorithm (TCP_NODELAY).
emitCloseEvent	false	When true, emit a marker message with payload=null and _event="close" on disconnect.

Server-only

Field	Default	Description
maxConnections	0	Concurrency cap; 0 = unbounded. Excess connections are closed on accept.
allowedRemotes	[]	CIDR allowlist. Empty list = allow all.

Client-only

Field	Default	Description
reconnect	true	Auto-reconnect with exponential backoff.
reconnectInitialDelay	1000	First retry delay in milliseconds.
reconnectMaxDelay	30000	Backoff cap in milliseconds.
dialTimeout	10	Connect timeout in seconds.
tls	—	See TLS configuration. Server-mode TLS is deferred to a future release.

Outgoing message

{
  "_msgid": "...",
  "payload": "<bytes — encoded per payloadEncoding>",
  "session": "<opaque tcp-session handle>",
  "remoteAddr": "192.0.2.10:53412",
  "localAddr":  "0.0.0.0:7000",
  "ip":   "192.0.2.10",
  "port": 53412,
  "frameSize": 137
}

Server mode emits a unique session per accepted connection (reused across frames from that peer). Client mode emits the same session for the lifetime of the dialed connection — a new one is registered after each reconnect.

When emitCloseEvent=true, on peer disconnect a marker message is emitted with payload=null, _event="close", and the same session, remoteAddr, ip, port. Off by default to keep the data stream clean.

Status

• Server: green listening · :7000 · 3 conn — live count comes from the session registry.
• Client: green connected · host:port; yellow retry: … during backoff; red on configuration errors.

Examples

Echo server with line framing.

[tcp-in  server :7000  delim=\n] → [Function: transform] → [tcp-out reply]

Pull from a remote sensor with reconnect.

[tcp-in client device:9100  delim=\n] → [Function: parse NMEA] → [Debug]

See also

• TCP Send — paired writes via msg.session.
• TCP Request — short-lived synchronous round-trips.
• Framing — explainer for the four framing strategies.