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Slack sink

Posts to a Slack incoming-webhook URL. One sink instance per destination channel; the webhook URL fixes which Slack channel the message lands in.

import (
    "github.com/frankbardon/parsec"
    "github.com/frankbardon/parsec/sinks/slack"
)

s, _ := slack.New(slack.Config{
    WebhookURL: os.Getenv("PARSEC_SLACK_WEBHOOK"),
})

p, _ := parsec.New(parsec.Options{})
p.Sinks().Register(s)

Then:

_, _ = p.PublishOrSink(ctx,
    "private:agent.analysis.42.failures",
    []byte(`{"job":42,"err":"timeout"}`),
    "slack",
    nil, // recipient is ignored
    parsec.Message{
        Subject: "Job 42 failed",
        Body:    "timeout while fetching artifacts",
    })

Configuration

slack.Config:

FieldRequiredNotes
WebhookURLyesThe full Slack incoming-webhook URL.
HTTPClientnoDefaults to http.DefaultClient. Override to inject timeouts / tracing.

Recipient

slack.Recipient is an empty struct — the channel is determined by the webhook URL itself. Callers may pass nil to Send; the sink ignores the value.

If you need to post to multiple Slack channels, register multiple sink instances under different names (e.g. "slack-alerts", "slack-deploys") and pick the right one per call.

Payload shape

The sink posts a JSON body like:

{
  "text": "*Job 42 failed*\ntimeout while fetching artifacts",
  "metadata": {"trace_id": "..."}
}

Subject becomes a bold prefix on text; an empty Subject posts the body alone. Metadata is attached verbatim so it appears in Slack webhook metadata where supported.

Failure semantics

ConditionReturned code
Missing WebhookURL at constructionPARSEC_SINK_CONFIG_INVALID
http.Client.Do returns an errorPARSEC_SINK_UNAVAILABLE
Slack returns a >= 300 statusPARSEC_SINK_UNAVAILABLE (carries the status line)

The sink does not retry. Slack rate-limits webhooks; downstream clients that hit 429 should back off — the sink does not.

Common gotchas

  • Slack webhooks are long-lived but per-channel. If you change the destination Slack channel, mint a new webhook and re-register.
  • Slack does not signal whether the human at the keyboard saw the message — Send returning nil means “Slack accepted the post”, not “the user saw it”. Real delivery confirmation needs the Slack Web API and a different sink.

See also