Stop startup when a setting does not parse (closes #219)

config.New read the number and true/false settings with viper's
GetInt, GetFloat64 and GetBool. These return zero or false for a value
that does not parse, so a typo silently changed how the server ran.

config.New now parses these settings with strconv. It also checks that
MESSAGE_MAX_AGE, QUEUE_MAX_AGE and SESSION_IDLE_TIMEOUT are valid Go
durations. A value that does not parse makes config.New return an
error naming the setting and its value, and startup stops. Unset
settings keep their defaults.

Model: opus-5-5

internal/config/config.go

@@ -3,8 +3,11 @@ package config
 
 import (
 	"errors"
+	"fmt"
 	"log/slog"
 	"os"
+	"strconv"
+	"time"
 
 	"github.com/spf13/viper"
 	"go.uber.org/fx"
@@ -63,6 +66,8 @@ type Config struct {
 }
 
 // New creates a new Config by reading from files and environment variables.
+// It returns an error when a number, true/false or duration setting does
+// not parse.
 func New(
 	_ fx.Lifecycle, params Params,
 ) (*Config, error) {
@@ -107,29 +112,27 @@ func New(
 
 	cfg := &Config{
 		DBURL:              viper.GetString("DBURL"),
-		Debug:              viper.GetBool("DEBUG"),
-		Port:               viper.GetInt("PORT"),
 		SentryDSN:          viper.GetString("SENTRY_DSN"),
-		MaintenanceMode:    viper.GetBool("MAINTENANCE_MODE"),
 		MetricsUsername:    viper.GetString("METRICS_USERNAME"),
 		MetricsPassword:    viper.GetString("METRICS_PASSWORD"),
 		MessageMaxAge:      viper.GetString("MESSAGE_MAX_AGE"),
-		MaxMessageSize:     viper.GetInt("MAX_MESSAGE_SIZE"),
 		QueueMaxAge:        viper.GetString("QUEUE_MAX_AGE"),
 		MOTD:               viper.GetString("MOTD"),
 		ServerName:         viper.GetString("SERVER_NAME"),
 		FederationKey:      viper.GetString("FEDERATION_KEY"),
 		SessionIdleTimeout: viper.GetString("SESSION_IDLE_TIMEOUT"),
-		HashcashBits:       viper.GetInt("NEOIRC_HASHCASH_BITS"),
 		OperName:           viper.GetString("NEOIRC_OPER_NAME"),
 		OperPassword:       viper.GetString("NEOIRC_OPER_PASSWORD"),
-		LoginRateLimit:     viper.GetFloat64("LOGIN_RATE_LIMIT"),
-		LoginRateBurst:     viper.GetInt("LOGIN_RATE_BURST"),
 		IRCListenAddr:      viper.GetString("IRC_LISTEN_ADDR"),
 		log:                log,
 		params:             &params,
 	}
 
+	err = parseSettings(cfg)
+	if err != nil {
+		return nil, err
+	}
+
 	// Viper counts an empty environment variable as unset, but an
 	// empty IRC_LISTEN_ADDR must turn the IRC listener off.
 	ircListenAddr, set := os.LookupEnv("IRC_LISTEN_ADDR")
@@ -144,3 +147,68 @@ func New(
 
 	return cfg, nil
 }
+
+// parseSettings reads the number and true/false settings into cfg and
+// checks that each duration setting is a valid Go duration. Its error
+// names each setting whose value does not parse.
+func parseSettings(cfg *Config) error {
+	return errors.Join(
+		parseInt("PORT", &cfg.Port),
+		parseInt("MAX_MESSAGE_SIZE", &cfg.MaxMessageSize),
+		parseInt("NEOIRC_HASHCASH_BITS", &cfg.HashcashBits),
+		parseInt("LOGIN_RATE_BURST", &cfg.LoginRateBurst),
+		parseFloat("LOGIN_RATE_LIMIT", &cfg.LoginRateLimit),
+		parseBool("DEBUG", &cfg.Debug),
+		parseBool("MAINTENANCE_MODE", &cfg.MaintenanceMode),
+		checkDuration("MESSAGE_MAX_AGE", cfg.MessageMaxAge),
+		checkDuration("QUEUE_MAX_AGE", cfg.QueueMaxAge),
+		checkDuration("SESSION_IDLE_TIMEOUT", cfg.SessionIdleTimeout),
+	)
+}
+
+// parseInt sets *value to the setting key read as a whole number.
+func parseInt(key string, value *int) error {
+	parsed, err := strconv.Atoi(viper.GetString(key))
+	if err != nil {
+		return fmt.Errorf("cannot parse %s: %w", key, err)
+	}
+
+	*value = parsed
+
+	return nil
+}
+
+// parseFloat sets *value to the setting key read as a decimal number.
+func parseFloat(key string, value *float64) error {
+	parsed, err := strconv.ParseFloat(viper.GetString(key), 64)
+	if err != nil {
+		return fmt.Errorf("cannot parse %s: %w", key, err)
+	}
+
+	*value = parsed
+
+	return nil
+}
+
+// parseBool sets *value to the setting key read as true or false.
+func parseBool(key string, value *bool) error {
+	parsed, err := strconv.ParseBool(viper.GetString(key))
+	if err != nil {
+		return fmt.Errorf("cannot parse %s: %w", key, err)
+	}
+
+	*value = parsed
+
+	return nil
+}
+
+// checkDuration returns an error naming the setting key when value is
+// not a valid Go duration.
+func checkDuration(key, value string) error {
+	_, err := time.ParseDuration(value)
+	if err != nil {
+		return fmt.Errorf("cannot parse %s: %w", key, err)
+	}
+
+	return nil
+}