Go SDK - Logging - Westyx Nexus

Changed in v0.11.0: Config.Logger is a *slog.Logger. The nexus.Logger interface and NoopLogger are gone.

client, err := nexus.NewClient(ctx, nexus.Config{
    BaseURL: "https://<slug>.westyx.dev",
    APIKey:  os.Getenv("NEXUS_API_KEY"),
    Logger:  slog.Default(),
})

A nil Logger discards everything.

Why `*slog.Logger`

log/slog is the standard library’s structured logger and the ecosystem has settled on its Handler interface, so accepting a *slog.Logger reaches every backend without the SDK depending on any of them. zap, zerolog and logrus all provide a handler, and so does anything else worth using. It also makes the output aggregatable. Values arrive as attributes rather than baked into the message text, so every occurrence of an event shares one message template: “how often did the stream drop” becomes a countable query rather than a substring search over lines that are each slightly different.

What the output looks like

level=INFO  msg="client ready" component=client key_type=sk kind=backend ttl=1m0s wif=off stream_idle_timeout=1m30s
level=DEBUG msg="sync complete" component=client configs=12 secrets=3 flags=7 key_type=sk kind=backend
level=DEBUG msg="sync not modified - cache retained" component=client
level=INFO  msg="stream connected" component=stream
level=DEBUG msg="received event - triggering sync" component=stream event=config.updated
level=ERROR msg="stream transport error" component=stream attempt=1 max_attempts=3 error="..."
level=INFO  msg="stream reconnect scheduled" component=stream delay=5m0s
level=INFO  msg="session refreshed" component=wif provider=kubernetes kind=backend expires_in_seconds=3600

Every record carries a component attribute naming the subsystem:

`component`	Covers
`client`	construction, sync, cache, billing, file-secret materialisation
`stream`	the SSE connection, reconnects, fallbacks, observer faults
`wif`	token exchange and session refresh

So the three can be routed or filtered independently without parsing message text.

Levels

Level	Used for
`Debug`	every sync (success or 304), every SSE event
`Info`	client ready, stream connected, reconnect scheduled, session refreshed
`Error`	transport failures, background sync failures, a panicking observer callback, the billing halt

Nothing above Error is ever emitted: the SDK does not decide that an application should stop.

Scoping the SDK’s output

Pass a logger that already carries attributes of your own and everything the SDK emits inherits them:

Logger: slog.Default().With("subsystem", "nexus", "service", serviceName)

To send SDK output somewhere separate from the rest of the application, hand it a different handler:

f, err := os.OpenFile("nexus.log", os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o600)
if err != nil {
    return err
}
Logger: slog.New(slog.NewJSONHandler(f, &slog.HandlerOptions{Level: slog.LevelInfo}))

To suppress the SDK’s debug records while keeping your own, set the level on the handler you pass in - the SDK has no level setting of its own.

Secrets never appear

Secret values are never logged, as a message or as an attribute, and neither are secret key names. The same holds for the API key, the workload OIDC token and the session JWT. A test drives a sync carrying both a text and a file-type secret through a capturing handler at debug level and fails if any of them shows up in the output, so this is a checked property rather than a convention.

Observer faults

A StreamObserver callback that panics is recovered, and the fault is reported here at Error with the hook name and a stack trace:

level=ERROR msg="observer callback panicked and was skipped" component=stream hook=OnEvent panic="..." stack="..."

The stream stays up.

Overview

Backend SDKs

Browser SDKs

OpenFeature Providers

Go SDK - Logging

Why `*slog.Logger`

What the output looks like

Levels

Scoping the SDK’s output

Secrets never appear

Observer faults

Next

​Why *slog.Logger

​What the output looks like

​Levels

​Scoping the SDK’s output

​Secrets never appear

​Observer faults

​Next

Why `*slog.Logger`

What the output looks like

Levels

Scoping the SDK’s output

Secrets never appear

Observer faults

Next