webhooker/internal/handlers/settings.go

package handlers

import (
	"net/http"
	"net/netip"
	"strconv"
	"strings"

	"sneak.berlin/go/webhooker/internal/config"
)

// notSet is what the Settings page shows for a value that is empty.
const notSet = "not set"

// settingRow is one line of the Settings page: an environment
// variable, what it controls, and the value the server loaded for it.
type settingRow struct {
	Name        string
	Description string
	Value       string
}

// HandleSettings returns a handler for the read-only Settings page,
// which lists the configuration the server started with.
func (h *Handlers) HandleSettings() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		h.renderTemplate(w, r, "settings.html", map[string]any{
			"Settings": settingRows(h.params.Config),
		})
	}
}

// settingRows lists every field of cfg under the environment variable
// it is read from, with the description the README's configuration
// table gives it (less its pointers to other README sections), in the
// table's order. METRICS_PASSWORD and SENTRY_DSN are credentials, so
// their values never reach the page: only whether they are set.
func settingRows(cfg *config.Config) []settingRow {
	metricsUsername := cfg.MetricsUsername
	if metricsUsername == "" {
		metricsUsername = notSet
	}

	return []settingRow{
		{"WEBHOOKER_ENVIRONMENT", "dev or prod", cfg.Environment},
		{"PORT", "HTTP listen port", strconv.Itoa(cfg.Port)},
		{
			"BIND_ADDRESS",
			"IP address the HTTP listener binds. Loopback by default, " +
				"so the cleartext listener is not published on every " +
				"interface. The Docker image ships 0.0.0.0 instead",
			cfg.BindAddress,
		},
		{"DATA_DIR", "Directory for all SQLite databases", cfg.DataDir},
		{"DEBUG", "Enable debug logging", strconv.FormatBool(cfg.Debug)},
		{
			"METRICS_USERNAME",
			"Basic auth username for /metrics. Must be set together " +
				"with METRICS_PASSWORD; one without the other fails " +
				"startup",
			metricsUsername,
		},
		{
			"METRICS_PASSWORD",
			"Basic auth password for /metrics. Must be set together " +
				"with METRICS_USERNAME; one without the other fails " +
				"startup",
			setOrNotSet(cfg.MetricsPassword),
		},
		{
			"SENTRY_DSN",
			"Sentry error reporting DSN. Unset leaves error reporting " +
				"off; a value the Sentry SDK cannot parse fails startup " +
				"rather than serving with reporting silently off",
			setOrNotSet(cfg.SentryDSN),
		},
		{
			"RETENTION_SWEEP_INTERVAL",
			"How often the retention reaper and archive sweeper run " +
				"(Go duration, must be positive)",
			cfg.RetentionSweepInterval.String(),
		},
		{
			"SESSION_IDLE_TIMEOUT",
			"Idle session timeout (Go duration)",
			cfg.SessionIdleTimeout.String(),
		},
		{
			"RECEIVER_RATE_LIMIT",
			"Receiver requests/minute per IP per entrypoint " +
				"(10x that per IP across the route)",
			strconv.Itoa(cfg.ReceiverRateLimit),
		},
		{
			"TRUSTED_PROXIES",
			"CIDRs whose forwarded headers are trusted. A set value " +
				"replaces the default. If any client can reach webhooker, " +
				"or the proxy in front of it, from an RFC 1918 source " +
				"address, set it to the proxy's address alone",
			cidrList(cfg.TrustedProxies),
		},
		{
			"ALLOWED_EGRESS_CIDRS",
			"CIDRs that delivery targets may reach despite the " +
				"SSRF blocklist",
			cidrList(cfg.AllowedEgressCIDRs),
		},
	}
}

// setOrNotSet is how the Settings page shows a credential: whether it
// has a value, never the value itself.
func setOrNotSet(value string) string {
	if value == "" {
		return notSet
	}

	return "set"
}

// cidrList renders a CIDR list setting for the Settings page.
func cidrList(prefixes []netip.Prefix) string {
	if len(prefixes) == 0 {
		return "none"
	}

	return strings.Join(config.PrefixStrings(prefixes), ", ")
}