feat(config): own PasswordFile type

its possible to unmarshal a PasswordFile path to a read string. this is
nice for docker secret setups. also adds a GetPassword method which
checks if both Password and PasswordFile are declared.

internal/config/config.go

@@ -1,11 +1,48 @@
 package config
 
+import (
+	"encoding"
+	"fmt"
+	"os"
+)
+
 var Cfg Config //nolint:gochecknoglobals
 
 type Config struct {
-	Email        string `env:"EMAIL,required"`
-	Password     string `env:"PASSWORD,expand"`
-	PasswordFile string `env:"PASSWORD_FILE,expand"`
-	CacheDir     string `env:"CACHE_DIR,expand"     envDefault:"/var/cache/glucose_exporter"`
-	Debug        bool   `env:"DEBUG"`
+	Email        string       `env:"EMAIL,required"`
+	Password     string       `env:"PASSWORD,expand"`
+	PasswordFile PasswordFile `env:"PASSWORD_FILE,expand"`
+	CacheDir     string       `env:"CACHE_DIR,expand"     envDefault:"/var/cache/glucose_exporter"`
+	Debug        bool         `env:"DEBUG"`
+}
+
+func (c *Config) GetPassword() (string, error) {
+	if c.PasswordFile != "" && c.Password != "" {
+		return "", ErrTooManyPasswords
+	}
+
+	if c.Password != "" {
+		return c.Password, nil
+	}
+
+	if c.PasswordFile != "" {
+		return string(c.PasswordFile), nil
+	}
+
+	return "", ErrMissingPassword
+}
+
+type PasswordFile string
+
+var _ encoding.TextUnmarshaler = (*PasswordFile)(nil)
+
+func (pf *PasswordFile) UnmarshalText(text []byte) error {
+	b, err := os.ReadFile(string(text))
+	if err != nil {
+		return fmt.Errorf("reading password file: %w", err)
+	}
+
+	*pf = PasswordFile(string(b))
+
+	return nil
 }

internal/config/config_test.go

@@ -0,0 +1,84 @@
+package config_test
+
+import (
+	"errors"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/matryer/is"
+	"go.xsfx.dev/glucose_exporter/internal/config"
+)
+
+func TestPasswordFile(t *testing.T) {
+	is := is.New(t)
+
+	dir := t.TempDir()
+
+	pfPath := path.Join(dir, "foo.txt")
+
+	err := os.WriteFile(pfPath, []byte("f00b4r"), 0o600)
+	is.NoErr(err)
+
+	var pf config.PasswordFile
+
+	err = pf.UnmarshalText([]byte(pfPath))
+	is.NoErr(err)
+
+	is.Equal(string(pf), "f00b4r")
+}
+
+func Test(t *testing.T) {
+	tables := []struct {
+		name     string
+		cfg      config.Config
+		expected string
+		err      error
+	}{
+		{
+			name:     "00",
+			cfg:      config.Config{},
+			expected: "",
+			err:      config.ErrMissingPassword,
+		},
+		{
+			name: "01",
+			cfg: config.Config{
+				Password:     "foo",
+				PasswordFile: "bar",
+			},
+			expected: "",
+			err:      config.ErrTooManyPasswords,
+		},
+		{
+			name: "02",
+			cfg: config.Config{
+				Password: "foo",
+			},
+			expected: "foo",
+			err:      nil,
+		},
+		{
+			name: "03",
+			cfg: config.Config{
+				PasswordFile: "foo",
+			},
+			expected: "foo",
+			err:      nil,
+		},
+	}
+
+	is := is.New(t)
+
+	for _, tt := range tables {
+		t.Run(tt.name, func(_ *testing.T) {
+			pass, err := tt.cfg.GetPassword()
+			if tt.err == nil {
+				is.NoErr(err)
+				is.Equal(pass, tt.expected)
+			} else {
+				is.True(errors.Is(err, tt.err))
+			}
+		})
+	}
+}

internal/config/errors.go

@@ -0,0 +1,8 @@
+package config
+
+import "errors"
+
+var (
+	ErrTooManyPasswords = errors.New("too many passwords")
+	ErrMissingPassword  = errors.New("missing password")
+)

internal/metrics/metrics.go

@@ -26,7 +26,6 @@ func Handler(w http.ResponseWriter, r *http.Request) {
 	vm.WritePrometheus(w, false)
 }
 
-//nolint:funlen
 func glucose(ctx context.Context, w io.Writer) error {
 	c, err := cache.Load()
 	if err != nil {
@@ -37,22 +36,8 @@ func glucose(ctx context.Context, w io.Writer) error {
 	if c.JWT == "" || time.Now().After(time.Time(c.Expires)) {
 		slog.Debug("needs a fresh token")
 
-		token, err := api.Login(
-			ctx,
-			api.BaseURL,
-			config.Cfg.Email,
-			config.Cfg.Password,
-		)
-		if err != nil {
-			return fmt.Errorf("login: %w", err)
-		}
-
-		slog.Debug("got token", "token", token)
-
-		if err := cache.Save(
-			cache.Cache{JWT: token.Data.AuthTicket.Token, Expires: token.Data.AuthTicket.Expires},
-		); err != nil {
-			return fmt.Errorf("saving cache: %w", err)
+		if err := token(ctx); err != nil {
+			return fmt.Errorf("refreshing token: %w", err)
 		}
 	}
 
@@ -101,3 +86,30 @@ func glucose(ctx context.Context, w io.Writer) error {
 
 	return nil
 }
+
+func token(ctx context.Context) error {
+	pass, err := config.Cfg.GetPassword()
+	if err != nil {
+		return fmt.Errorf("getting password from config: %w", err)
+	}
+
+	token, err := api.Login(
+		ctx,
+		api.BaseURL,
+		config.Cfg.Email,
+		pass,
+	)
+	if err != nil {
+		return fmt.Errorf("login: %w", err)
+	}
+
+	slog.Debug("got token", "token", token)
+
+	if err := cache.Save(
+		cache.Cache{JWT: token.Data.AuthTicket.Token, Expires: token.Data.AuthTicket.Expires},
+	); err != nil {
+		return fmt.Errorf("saving cache: %w", err)
+	}
+
+	return nil
+}