Fail loudly on set-but-unparseable env config values (closes #80)

The config env helpers silently substituted the documented default
whenever a variable was set but could not be parsed, so a typo in an
operator-supplied value produced a running daemon with configuration
nobody asked for instead of a startup failure. `PORT=eighty` quietly
listened on 8080 and `DEBUG=ture` quietly disabled debug logging.

Defaults now apply only to variables that are unset or empty. Any
variable that is set but unparseable is a hard error that names the
key and the offending value and aborts startup through fx.

- add `envPositiveInt` with `ErrNonPositiveValue`, copied verbatim
  from the definition on the unmerged #87 so that rebasing after it
  lands is a delete-one-copy operation rather than a semantic merge
- remove `envInt` entirely; `PORT` is parsed by a new `envPort`,
  which adds the TCP upper bound (`ErrInvalidPort`, 1..65535)
- change `envBool` to return an error and parse with
  `strconv.ParseBool`, so `yes`, `on`, and typos are rejected rather
  than silently treated as false; callers are `DEBUG` and
  `MAINTENANCE_MODE`
- move env loading into `loadFromEnv`, with the environment check
  extracted to `resolveEnvironment` (also as #87 defines it), keeping
  `New` within the funlen budget

`envString` parses nothing and `envDuration` was already fail-loud,
so both are unchanged. A repo-wide audit of `os.Getenv`/`os.LookupEnv`
found no parse sites outside `internal/config`.

Tests cover each helper with a table (unset, valid, set-but-invalid)
plus `config.New`-level cases proving a bad `PORT`, `DEBUG`, or
`MAINTENANCE_MODE` aborts startup while unset variables still get
their defaults. README documents the fail-loud rule and the accepted
boolean spellings.

README.md

@@ -89,10 +89,27 @@ TTY detection, and security headers are always applied.
 | `PORT`                  | HTTP listen port                    | `8080`   |
 | `DATA_DIR`              | Directory for all SQLite databases  | `/var/lib/webhooker` |
 | `DEBUG`                 | Enable debug logging                | `false`  |
+| `MAINTENANCE_MODE`      | Serve the maintenance page          | `false`  |
 | `METRICS_USERNAME`      | Basic auth username for `/metrics`  | `""`     |
 | `METRICS_PASSWORD`      | Basic auth password for `/metrics`  | `""`     |
 | `SENTRY_DSN`            | Sentry error reporting DSN          | `""`     |
 
+#### Invalid values abort startup
+
+The defaults above apply **only** to variables that are unset (or set
+to an empty string). A variable that is set but cannot be parsed is a
+fatal configuration error: webhooker logs the offending variable and
+its value and refuses to start, rather than silently running with a
+substituted default. `PORT=eighty`, `DEBUG=ture`, and
+`RETENTION_SWEEP_INTERVAL=1 hour` all abort startup. `PORT` must
+additionally be a number in the range 1–65535.
+
+Boolean variables (`DEBUG`, `MAINTENANCE_MODE`) accept exactly the
+spellings Go's `strconv.ParseBool` accepts — `1`, `t`, `T`, `TRUE`,
+`true`, `True`, `0`, `f`, `F`, `FALSE`, `false`, `False` — and nothing
+else. `yes`, `on`, and `off` are rejected rather than quietly treated
+as false.
+
 On first startup, webhooker automatically generates a cryptographically
 secure session encryption key and stores it in the database. This key
 persists across restarts — no manual key management is needed.

TODO.md

@@ -10,24 +10,28 @@
 
 # Status
 
-pre-1.0. No git tags exist. main (afe88c6) is a working webhook proxy
+pre-1.0. No git tags exist. main (4f5ecb1) is a working webhook proxy
 with auth, CSRF/SSRF protections, login rate limiting, Slack target,
-policy compliance (#6), and pinned lint tooling (#55). Note: TODO.md was
+policy compliance (#6), pinned lint tooling (#55), a per-webhook event
-deliberately deleted from this repo in f9a9569 (2026-03-01, #6); its
+retention reaper (#63), and fail-loud configuration parsing (#80). Note:
-content was folded into the README TODO section, which this draft
+TODO.md was deliberately deleted from this repo in f9a9569 (2026-03-01,
-reconstructs as of 2026-07-06.
+#6); its content was folded into the README TODO section, which this
+draft reconstructs as of 2026-07-06.
 
 # Next Step
 
-Implement automatic event retention cleanup based on retention_days: a
+Manual event redelivery from the web UI (replay is a core promised
-periodic maintenance job that deletes Events, Deliveries, and
+capability in the README rationale).
-DeliveryResults older than the parent webhook's retention_days from each
-per-webhook event database. The field exists on the Webhook model and
-the README promises the behavior, but nothing enforces it, so event
-databases currently grow without bound.
 
 # Completed Steps
 
+- 2026-08-09 Configuration parsing fails loudly on set-but-unparseable
+  environment values: `envInt` removed in favour of `envPositiveInt`
+  plus a `PORT` range check, `envBool` now parses with
+  `strconv.ParseBool`, and defaults apply only to unset variables (#80)
+- 2026-08-07 Automatic event retention cleanup based on
+  `retention_days`, deleting expired events, deliveries, and delivery
+  results from each per-webhook event database (#63)
 - 2026-08-07 Update golangci-lint to v2.12.2 (Docker image digest in
   `Dockerfile`, release-archive sha256 pins in `script/bootstrap`),
   adopt the canonical `.golangci.yml` (v2 `linters.settings` layout so
@@ -56,8 +60,6 @@ databases currently grow without bound.
 
 # Future Steps
 
-- Manual event redelivery from the web UI (replay is a core promised
-  capability in the README rationale)
 - Delivery status and retry management UI
 - Per-webhook rate limiting in the receiver handler (per-webhook config
   plus handler enforcement; global limits must not apply to receiver

internal/config/config.go

@@ -7,7 +7,6 @@ import (
 	"log/slog"
 	"os"
 	"strconv"
-	"strings"
 	"time"
 
 	"go.uber.org/fx"
@@ -31,12 +30,24 @@ const (
 	// defaultRetentionSweepInterval is how often the retention
 	// reaper deletes events older than each webhook's RetentionDays.
 	defaultRetentionSweepInterval = time.Hour
+
+	// maxPort is the highest valid TCP port number. The lower
+	// bound (at least 1) is enforced by envPositiveInt.
+	maxPort = 65535
 )
 
 // ErrInvalidEnvironment is returned when WEBHOOKER_ENVIRONMENT
 // contains an unrecognised value.
 var ErrInvalidEnvironment = errors.New("invalid environment")
 
+// ErrNonPositiveValue is returned when an environment variable that
+// requires a positive integer is set to zero or a negative number.
+var ErrNonPositiveValue = errors.New("value must be positive")
+
+// ErrInvalidPort is returned when an environment variable holding a
+// TCP port number is set above the valid port range.
+var ErrInvalidPort = errors.New("invalid port")
+
 //nolint:revive // ConfigParams is a standard fx naming convention.
 type ConfigParams struct {
 	fx.In
@@ -81,27 +92,81 @@ func envString(key string) string {
 }
 
 // envBool returns the value of the named environment variable
-// parsed as a boolean. Returns defaultValue if not set.
+// parsed as a boolean. Returns defaultValue if not set. If the
-func envBool(key string, defaultValue bool) bool {
+// variable is set but cannot be parsed, it returns a wrapped error
-	if v := os.Getenv(key); v != "" {
+// naming the key and the bad value, so startup fails loudly rather
-		return strings.EqualFold(v, "true") || v == "1"
+// than silently falling back to the default.
+//
+// Parsing is strconv.ParseBool, which accepts 1, t, T, TRUE, true,
+// True, 0, f, F, FALSE, false and False. Anything else — "yes",
+// "on", or a typo like "ture" — is an error rather than a silent
+// false.
+func envBool(key string, defaultValue bool) (bool, error) {
+	v := os.Getenv(key)
+	if v == "" {
+		return defaultValue, nil
 	}
 
-	return defaultValue
+	b, err := strconv.ParseBool(v)
+	if err != nil {
+		return false, fmt.Errorf(
+			"invalid boolean for %s: %q: %w", key, v, err,
+		)
+	}
+
+	return b, nil
+}
+
+// envPositiveInt returns the value of the named environment variable
+// parsed as a positive integer. Returns defaultValue if not set. If
+// the variable is set but cannot be parsed, or parses to less than
+// one, it returns a wrapped error naming the key and the bad value,
+// so startup fails loudly rather than silently falling back to the
+// default.
+func envPositiveInt(
+	key string,
+	defaultValue int,
+) (int, error) {
+	v := os.Getenv(key)
+	if v == "" {
+		return defaultValue, nil
 	}
 
-// envInt returns the value of the named environment variable
-// parsed as an integer. Returns defaultValue if not set or
-// unparseable.
-func envInt(key string, defaultValue int) int {
-	if v := os.Getenv(key); v != "" {
 	i, err := strconv.Atoi(v)
-		if err == nil {
+	if err != nil {
-			return i
+		return 0, fmt.Errorf(
-		}
+			"invalid integer for %s: %q: %w", key, v, err,
+		)
 	}
 
-	return defaultValue
+	if i < 1 {
+		return 0, fmt.Errorf(
+			"%w: %s must be at least 1, got %q",
+			ErrNonPositiveValue, key, v,
+		)
+	}
+
+	return i, nil
+}
+
+// envPort returns the value of the named environment variable parsed
+// as a TCP port number. Returns defaultValue if not set. A set value
+// that is unparseable, below 1, or above maxPort is a hard error
+// naming the key and the bad value.
+func envPort(key string, defaultValue int) (int, error) {
+	port, err := envPositiveInt(key, defaultValue)
+	if err != nil {
+		return 0, err
+	}
+
+	if port > maxPort {
+		return 0, fmt.Errorf(
+			"%w: %s must be at most %d, got %d",
+			ErrInvalidPort, key, maxPort, port,
+		)
+	}
+
+	return port, nil
 }
 
 // envDuration returns the value of the named environment variable
@@ -128,32 +193,52 @@ func envDuration(
 	return d, nil
 }
 
-// New creates a Config by reading environment variables.
+// resolveEnvironment reads WEBHOOKER_ENVIRONMENT, defaulting to
-//
+// dev, and rejects unrecognised values.
-//nolint:revive // lc parameter is required by fx even if unused.
+func resolveEnvironment() (string, error) {
-func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
-	log := params.Logger.Get()
-
-	// Determine environment from WEBHOOKER_ENVIRONMENT env var,
-	// default to dev
 	environment := os.Getenv("WEBHOOKER_ENVIRONMENT")
 	if environment == "" {
 		environment = EnvironmentDev
 	}
 
-	// Validate environment
 	if environment != EnvironmentDev &&
 		environment != EnvironmentProd {
-		return nil, fmt.Errorf(
+		return "", fmt.Errorf(
 			"%w: WEBHOOKER_ENVIRONMENT must be '%s' or '%s', got '%s'",
 			ErrInvalidEnvironment,
 			EnvironmentDev, EnvironmentProd, environment,
 		)
 	}
 
-	// Parse the retention sweep interval; a set-but-unparseable value
+	return environment, nil
-	// is a hard error so fx aborts startup rather than silently using
+}
-	// the default.
+
+// loadFromEnv builds a Config from the environment. Every value that
+// needs parsing fails loudly when it is set but unparseable: the
+// documented defaults apply only to variables that are unset (or
+// empty), never as a substitute for a value the operator actually
+// provided.
+func loadFromEnv() (*Config, error) {
+	environment, err := resolveEnvironment()
+	if err != nil {
+		return nil, err
+	}
+
+	port, err := envPort("PORT", defaultPort)
+	if err != nil {
+		return nil, err
+	}
+
+	debug, err := envBool("DEBUG", false)
+	if err != nil {
+		return nil, err
+	}
+
+	maintenanceMode, err := envBool("MAINTENANCE_MODE", false)
+	if err != nil {
+		return nil, err
+	}
+
 	retentionSweepInterval, err := envDuration(
 		"RETENTION_SWEEP_INTERVAL",
 		defaultRetentionSweepInterval,
@@ -162,21 +247,36 @@ func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 		return nil, err
 	}
 
-	// Load configuration values from environment variables
+	return &Config{
-	s := &Config{
 		DataDir:                envString("DATA_DIR"),
-		Debug:                  envBool("DEBUG", false),
+		Debug:                  debug,
-		MaintenanceMode:        envBool("MAINTENANCE_MODE", false),
+		MaintenanceMode:        maintenanceMode,
 		Environment:            environment,
 		MetricsUsername:        envString("METRICS_USERNAME"),
 		MetricsPassword:        envString("METRICS_PASSWORD"),
-		Port:                   envInt("PORT", defaultPort),
+		Port:                   port,
 		SentryDSN:              envString("SENTRY_DSN"),
 		RetentionSweepInterval: retentionSweepInterval,
-		log:                    log,
+	}, nil
-		params:                 &params,
 }
 
+// New creates a Config by reading environment variables.
+//
+//nolint:revive // lc parameter is required by fx even if unused.
+func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
+	log := params.Logger.Get()
+
+	// A set-but-unparseable value anywhere in the environment is a
+	// hard error, so fx aborts startup rather than running with a
+	// silently substituted default.
+	s, err := loadFromEnv()
+	if err != nil {
+		return nil, err
+	}
+
+	s.log = log
+	s.params = &params
+
 	// Set default DataDir. All SQLite databases (main application
 	// DB and per-webhook event DBs) live here. The same default is
 	// used regardless of environment; override with DATA_DIR if

internal/config/env_test.go

@@ -0,0 +1,409 @@
+package config_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/fx"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/globals"
+	"sneak.berlin/go/webhooker/internal/logger"
+)
+
+// testEnvKey is a throwaway variable name used only by the helper
+// tables below, so they cannot disturb real configuration.
+const testEnvKey = "WEBHOOKER_TEST_VALUE"
+
+// Real configuration variables exercised by the config.New tests.
+const (
+	envKeyPort            = "PORT"
+	envKeyDebug           = "DEBUG"
+	envKeyMaintenanceMode = "MAINTENANCE_MODE"
+)
+
+// envBoolCase is one row of the envBool table.
+type envBoolCase struct {
+	name         string
+	set          bool
+	value        string
+	defaultValue bool
+	expectError  bool
+	expected     bool
+}
+
+// envBoolCases is the envBool table, kept out of the test body so
+// the test itself stays readable.
+func envBoolCases() []envBoolCase {
+	return []envBoolCase{
+		{
+			name:         "unset uses default false",
+			defaultValue: false,
+			expected:     false,
+		},
+		{
+			name:         "unset uses default true",
+			defaultValue: true,
+			expected:     true,
+		},
+		{
+			name:         "empty uses default true",
+			set:          true,
+			value:        "",
+			defaultValue: true,
+			expected:     true,
+		},
+		{
+			name:     "true is parsed",
+			set:      true,
+			value:    "true",
+			expected: true,
+		},
+		{
+			name:     "one is parsed",
+			set:      true,
+			value:    "1",
+			expected: true,
+		},
+		{
+			name:         "False is parsed",
+			set:          true,
+			value:        "False",
+			defaultValue: true,
+			expected:     false,
+		},
+		{
+			name:         "zero is parsed",
+			set:          true,
+			value:        "0",
+			defaultValue: true,
+			expected:     false,
+		},
+		{
+			name:        "yes is rejected",
+			set:         true,
+			value:       "yes",
+			expectError: true,
+		},
+		{
+			name:        "on is rejected",
+			set:         true,
+			value:       "on",
+			expectError: true,
+		},
+		{
+			name:        "typo is rejected",
+			set:         true,
+			value:       "ture",
+			expectError: true,
+		},
+	}
+}
+
+func TestEnvBool(t *testing.T) {
+	for _, tt := range envBoolCases() {
+		t.Run(tt.name, func(t *testing.T) {
+			// Cannot use t.Parallel() here because t.Setenv
+			// is incompatible with parallel subtests.
+			if tt.set {
+				t.Setenv(testEnvKey, tt.value)
+			} else {
+				require.NoError(t, os.Unsetenv(testEnvKey))
+			}
+
+			got, err := config.EnvBoolForTest(
+				testEnvKey, tt.defaultValue,
+			)
+
+			if tt.expectError {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), testEnvKey)
+				assert.Contains(t, err.Error(), tt.value)
+
+				return
+			}
+
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
+func TestEnvPositiveInt(t *testing.T) {
+	const defaultValue = 7
+
+	tests := []struct {
+		name        string
+		set         bool
+		value       string
+		expectError bool
+		errIs       error
+		expected    int
+	}{
+		{
+			name:     "unset returns the default integer",
+			expected: defaultValue,
+		},
+		{
+			name:     "empty returns the default integer",
+			set:      true,
+			value:    "",
+			expected: defaultValue,
+		},
+		{
+			name:     "positive value is parsed",
+			set:      true,
+			value:    "42",
+			expected: 42,
+		},
+		{
+			name:        "unparseable value is rejected",
+			set:         true,
+			value:       "not-a-number",
+			expectError: true,
+		},
+		{
+			name:        "zero is rejected",
+			set:         true,
+			value:       "0",
+			expectError: true,
+			errIs:       config.ErrNonPositiveValue,
+		},
+		{
+			name:        "negative is rejected",
+			set:         true,
+			value:       "-5",
+			expectError: true,
+			errIs:       config.ErrNonPositiveValue,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Cannot use t.Parallel() here because t.Setenv
+			// is incompatible with parallel subtests.
+			if tt.set {
+				t.Setenv(testEnvKey, tt.value)
+			} else {
+				require.NoError(t, os.Unsetenv(testEnvKey))
+			}
+
+			got, err := config.EnvPositiveIntForTest(
+				testEnvKey, defaultValue,
+			)
+
+			if tt.expectError {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), testEnvKey)
+				assert.Contains(t, err.Error(), tt.value)
+
+				if tt.errIs != nil {
+					require.ErrorIs(t, err, tt.errIs)
+				}
+
+				return
+			}
+
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
+func TestEnvPort(t *testing.T) {
+	const defaultValue = 8080
+
+	tests := []struct {
+		name        string
+		set         bool
+		value       string
+		expectError bool
+		errIs       error
+		expected    int
+	}{
+		{
+			name:     "unset returns the default port",
+			expected: defaultValue,
+		},
+		{
+			name:     "valid port is parsed",
+			set:      true,
+			value:    "9000",
+			expected: 9000,
+		},
+		{
+			name:     "highest port is accepted",
+			set:      true,
+			value:    "65535",
+			expected: 65535,
+		},
+		{
+			name:        "unparseable value is rejected",
+			set:         true,
+			value:       "not-a-port",
+			expectError: true,
+		},
+		{
+			name:        "zero is rejected",
+			set:         true,
+			value:       "0",
+			expectError: true,
+			errIs:       config.ErrNonPositiveValue,
+		},
+		{
+			name:        "above the port range is rejected",
+			set:         true,
+			value:       "65536",
+			expectError: true,
+			errIs:       config.ErrInvalidPort,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Cannot use t.Parallel() here because t.Setenv
+			// is incompatible with parallel subtests.
+			if tt.set {
+				t.Setenv(testEnvKey, tt.value)
+			} else {
+				require.NoError(t, os.Unsetenv(testEnvKey))
+			}
+
+			got, err := config.EnvPortForTest(
+				testEnvKey, defaultValue,
+			)
+
+			if tt.expectError {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), testEnvKey)
+
+				if tt.errIs != nil {
+					require.ErrorIs(t, err, tt.errIs)
+				}
+
+				return
+			}
+
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
+// buildConfig constructs a Config through fx exactly as the
+// application does, returning the config and any construction error.
+func buildConfig(t *testing.T) (*config.Config, error) {
+	t.Helper()
+
+	var cfg *config.Config
+
+	app := fx.New(
+		fx.NopLogger,
+		fx.Provide(
+			globals.New,
+			logger.New,
+			config.New,
+		),
+		fx.Populate(&cfg),
+	)
+
+	return cfg, app.Err()
+}
+
+func TestNewRejectsBadEnvValues(t *testing.T) {
+	tests := []struct {
+		name        string
+		key         string
+		value       string
+		expectError bool
+		check       func(t *testing.T, cfg *config.Config)
+	}{
+		{
+			name:  "valid PORT is used",
+			key:   envKeyPort,
+			value: "9001",
+			check: func(t *testing.T, cfg *config.Config) {
+				t.Helper()
+				assert.Equal(t, 9001, cfg.Port)
+			},
+		},
+		{
+			name:        "unparseable PORT aborts startup",
+			key:         envKeyPort,
+			value:       "eighty-eighty",
+			expectError: true,
+		},
+		{
+			name:        "out-of-range PORT aborts startup",
+			key:         envKeyPort,
+			value:       "70000",
+			expectError: true,
+		},
+		{
+			name:  "valid DEBUG is used",
+			key:   envKeyDebug,
+			value: "true",
+			check: func(t *testing.T, cfg *config.Config) {
+				t.Helper()
+				assert.True(t, cfg.Debug)
+			},
+		},
+		{
+			name:        "unparseable DEBUG aborts startup",
+			key:         envKeyDebug,
+			value:       "ture",
+			expectError: true,
+		},
+		{
+			name:        "unparseable MAINTENANCE_MODE aborts startup",
+			key:         envKeyMaintenanceMode,
+			value:       "sometimes",
+			expectError: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Cannot use t.Parallel() here because t.Setenv
+			// is incompatible with parallel subtests.
+			t.Setenv("WEBHOOKER_ENVIRONMENT", "dev")
+			t.Setenv(tt.key, tt.value)
+
+			cfg, err := buildConfig(t)
+
+			if tt.expectError {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), tt.key)
+				assert.Contains(t, err.Error(), tt.value)
+
+				return
+			}
+
+			require.NoError(t, err)
+			require.NotNil(t, cfg)
+			tt.check(t, cfg)
+		})
+	}
+}
+
+// TestNewUsesDefaultsWhenUnset proves the fail-loud behaviour did not
+// break the legitimate unset case: absent variables still get their
+// documented defaults.
+func TestNewUsesDefaultsWhenUnset(t *testing.T) {
+	t.Setenv("WEBHOOKER_ENVIRONMENT", "dev")
+
+	for _, key := range []string{
+		envKeyPort, envKeyDebug, envKeyMaintenanceMode,
+	} {
+		require.NoError(t, os.Unsetenv(key))
+	}
+
+	cfg, err := buildConfig(t)
+	require.NoError(t, err)
+	require.NotNil(t, cfg)
+
+	assert.Equal(t, 8080, cfg.Port)
+	assert.False(t, cfg.Debug)
+	assert.False(t, cfg.MaintenanceMode)
+}

internal/config/export_test.go

@@ -0,0 +1,20 @@
+package config
+
+// This file exposes the unexported environment parsing helpers to
+// the external config_test package so each helper can be covered by
+// its own table-driven test without weakening the package API.
+
+// EnvBoolForTest exposes envBool.
+func EnvBoolForTest(key string, defaultValue bool) (bool, error) {
+	return envBool(key, defaultValue)
+}
+
+// EnvPositiveIntForTest exposes envPositiveInt.
+func EnvPositiveIntForTest(key string, defaultValue int) (int, error) {
+	return envPositiveInt(key, defaultValue)
+}
+
+// EnvPortForTest exposes envPort.
+func EnvPortForTest(key string, defaultValue int) (int, error) {
+	return envPort(key, defaultValue)
+}