logwisp/doc/networking.md

Networking

Everything LogWisp does over a socket, and the knobs that shape it. For certificates and trust see Security; for multi-node topologies see Chaining.

Address Family

All listeners bind tcp4 and all dialers dial tcp4. IPv6 is not supported, deliberately. An IPv6 client cannot connect and will simply see a connection failure.

When testing locally use 127.0.0.1, not localhost — the latter may resolve to ::1 and appear as an unexplained connection refusal.

Network Plugins

Plugin	Role	Protocol	Purpose
tcp sink	Listener	Raw stream	Broadcast formatted payloads to clients
http sink	Listener	HTTP SSE	Browser-friendly live stream plus status JSON
tcp_chain source	Listener	Chain v1	Ingest a persistent NDJSON stream
http_chain source	Listener	Chain v1	Ingest NDJSON batches over POST
tcp_chain sink	Dialer	Chain v1	Forward entries over a persistent connection
http_chain sink	Dialer	Chain v1	Forward entries as batched POSTs

There is no port registry and no default port: port is required on every network plugin. There is also no cross-pipeline conflict detection — two sinks on the same port fail at bind time when the pipeline starts:

ERROR msg="Failed to start sink" error="tcp sink bind 0.0.0.0:9090: listen tcp4 0.0.0.0:9090: bind: address already in use"

Timeouts

Every network plugin exposes the deadlines relevant to its role. Zero means "no deadline" wherever the table says so.

Plugin	Option	Default	Bounds
tcp sink	write_timeout_ms	5000	One write to one client; a miss disconnects that client
http sink	write_timeout_ms	0 (none)	One SSE event write
tcp_chain source	hello_timeout_ms	10000	Reading the protocol preamble
tcp_chain source	read_timeout_ms	0 (none)	Idle time between entries
http_chain source	read_timeout_ms	30000	Reading a whole request body
tcp_chain sink	dial_timeout_ms	5000	TCP connect
tcp_chain sink	write_timeout_ms	5000	One line write
http_chain sink	request_timeout_ms	10000	Dial plus write plus response

Fixed, non-configurable bounds:

Bound	Value	Applies to
TLS handshake	10 s	All TLS listeners and dialers
HTTP read-header timeout	10 s	http sink, http_chain source
HTTP server shutdown grace	2 s	http sink, http_chain source
Max single entry line	1 MiB	Chain listeners

The http sink deliberately leaves the server's WriteTimeout unset, since it would terminate long-lived SSE streams; per-event deadlines come from write_timeout_ms instead.

Connection Limits

max_connections caps concurrent connections on the tcp sink, the http sink, and the tcp_chain source. 0 means unlimited.

• Admission is a load-then-check, so a burst can over-admit by roughly one connection. This is accepted, not a bug to work around.
• On the tcp sink and tcp_chain source the count is taken at accept, so it bounds concurrent TLS handshakes as well as established sessions.
• Over-limit connections are closed immediately and counted in rejected_conns (TCP) or rejected_clients (HTTP, which first answers 503).

The http_chain source has no connection cap; it bounds work with max_body_bytes and read_timeout_ms instead.

There is no per-IP limiting and no IP allow/deny list. flow.rate_limit is a pipeline-wide entry rate limit, not a network-level one — it cannot distinguish or throttle an individual peer.

Keep-Alive

TCP keep-alive is available on the tcp sink (for accepted connections) and the tcp_chain sink (for its outbound connection):

keep_alive           = true
keep_alive_period_ms = 30000

This is kernel-level keep-alive; it detects a dead peer but does not keep an application-level stream flowing. For that, use a heartbeat.

Heartbeats

Heartbeats are a flow-level feature, not a per-sink one. Enabling one injects a synthetic entry into the pipeline at a fixed interval; it reaches every sink and traverses chain links as an ordinary structured entry.

[pipelines.flow.heartbeat]
enabled           = true
interval_ms       = 30000
include_timestamp = true
include_stats     = false
format            = "txt"      # txt | json | raw

Use it to keep idle SSE clients, TCP clients, and chain links from being reaped by intermediate NAT or proxy timeouts, and to make an idle pipeline visibly alive.

format = "comment" (SSE : comment framing) is rejected by validation despite appearing in older documentation and in a still-present code branch. A pipeline configured with it fails to start.

Reconnection

Chain sinks reconnect on their own. Both use exponential backoff between backoff_min_ms and backoff_max_ms with ±20 % jitter, and both are interruptible by shutdown.

backoff_min_ms = 500
backoff_max_ms = 30000

The connection is established lazily, so an edge node starts cleanly even when its relay is down and connects as soon as the relay appears. Reconnect counts are reported in the sink's reconnects statistic.

Server-side sinks (tcp, http) do not reconnect; clients are expected to retry. Browsers reconnect SSE streams automatically.

Protocol Details

HTTP sink (SSE) — HTTP/1.1 in plaintext; HTTP/2 is negotiated via ALPN when TLS is enabled. Only GET is routed to the stream and status paths. Each event is framed as one data: line per newline in the payload, so multi-line entries stream intact. Response headers set Cache-Control: no-cache, X-Accel-Buffering: no, and Access-Control-Allow-Origin: *.

TCP sink — raw payload bytes, no framing added by the sink. Whether entries are newline-delimited depends on the formatter.

Chain transports — see Chaining for the hello preamble, headers, and entry encoding.

Troubleshooting

Connection refused

• Confirm the pipeline started; a bind failure is logged at ERROR.
• Confirm you are dialing IPv4. localhost may resolve to ::1.
• Check the port is not already bound by another pipeline in the same process.

TLS handshake failure

• client didn't provide a certificate — the listener has client_auth = true and the dialer has no cert_file/key_file.
• certificate signed by unknown authority — the dialer's ca_file does not contain the issuer of the server certificate, or the listener's client_ca_file does not contain the issuer of the client certificate.
• certificate is not valid for any names / SAN mismatch — the dialed host is not covered by the server certificate's SANs; set server_name.
• protocol version not supported — one side is pinned to min_version = "1.3" and the other cannot negotiate it.
• Handshake failures appear as WARN with the remote address, and increment tls_handshake_errors.

Entries not arriving over a chain link

• Check the sink's connected statistic and its reconnects count.
• Check the source's parse_errors — a version skew shows up here.
• On http_chain, remember entries wait up to flush_interval_ms before a batch is sent.

Clients connect but see nothing

• The pipeline may be filtering everything out; check flow.filters stats.
• The rate limiter may be dropping everything; check rate_limiter stats.
• Nothing may be arriving from the sources; check source total_entries.

Entries missing under load

• Compare dropped_writes (per-client queue full — raise client_buffer_size) against total_dropped_by_sink (sink input queue full — raise buffer_size or reduce sink latency).