fix(config): isolate environment overrides

pkg/cmd/root.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"log/slog"
 	"os"
+	"strings"
 
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -14,6 +15,8 @@ var (
 	edmLoggerLevel *slog.LevelVar
 )
 
+const envPrefix = "DNSTAPIR_EDM"
+
 // rootCmd represents the base command when called without any subcommands
 var rootCmd = &cobra.Command{
 	Use:   "dnstapir-edm",
@@ -67,7 +70,7 @@ func initConfig() {
 		viper.SetConfigName(".dnstapir-edm")
 	}
 
-	viper.AutomaticEnv() // read in environment variables that match
+	configureEnv()
 
 	// If a config file is found, read it in.
 	if err := viper.ReadInConfig(); err == nil {
@@ -77,3 +80,9 @@ func initConfig() {
 	// Make it so we can detect changes to the cryptopan secret in the config
 	viper.WatchConfig()
 }
+
+func configureEnv() {
+	viper.SetEnvPrefix(envPrefix)
+	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
+	viper.AutomaticEnv() // read in environment variables that match
+}

pkg/cmd/root_test.go

@@ -0,0 +1,67 @@
+package cmd
+
+import (
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/viper"
+)
+
+func TestInitConfigIgnoresUnprefixedEnv(t *testing.T) {
+	initConfigForTest(t, "debug = false\n")
+	t.Setenv("DEBUG", "release")
+
+	initConfig()
+
+	var conf struct {
+		Debug bool `mapstructure:"debug"`
+	}
+	if err := viper.UnmarshalExact(&conf); err != nil {
+		t.Fatalf("unprefixed DEBUG should not affect config unmarshalling: %s", err)
+	}
+	if conf.Debug {
+		t.Fatal("unprefixed DEBUG unexpectedly overrode config debug=false")
+	}
+}
+
+func TestInitConfigUsesPrefixedEnv(t *testing.T) {
+	initConfigForTest(t, "debug = false\n")
+	t.Setenv("DEBUG", "release")
+	debugEnv := envPrefix + "_DEBUG"
+	t.Setenv(debugEnv, "true")
+
+	initConfig()
+
+	var conf struct {
+		Debug bool `mapstructure:"debug"`
+	}
+	if err := viper.UnmarshalExact(&conf); err != nil {
+		t.Fatalf("prefixed debug env should unmarshal cleanly: %s", err)
+	}
+	if !conf.Debug {
+		t.Fatalf("%s=true did not override config debug=false", debugEnv)
+	}
+}
+
+func initConfigForTest(t *testing.T, configData string) {
+	t.Helper()
+
+	viper.Reset()
+	oldCfgFile := cfgFile
+	oldLogger := edmLogger
+	t.Cleanup(func() {
+		cfgFile = oldCfgFile
+		edmLogger = oldLogger
+		viper.Reset()
+	})
+
+	configFile := filepath.Join(t.TempDir(), "dnstapir-edm.toml")
+	if err := os.WriteFile(configFile, []byte(configData), 0o600); err != nil {
+		t.Fatalf("unable to write test config: %s", err)
+	}
+	cfgFile = configFile
+	edmLogger = slog.New(slog.NewTextHandler(io.Discard, nil))
+}