Allow prefixing env vars to avoid clashes

Author: kevinmcconnell

README.md

@@ -49,7 +49,13 @@ $ SSL_DOMAIN=myapp.example.com thrust bin/rails server
 ## Custom configuration
 
 Thruster provides a number of environment variables that can be used to
-customize its behavior:
+customize its behavior.
+
+To prevent naming clashes with your application's own environment variables,
+Thruster's environment variables can optionally be prefixed with `THRUSTER_`.
+For example, `SSL_DOMAIN` can also be set as `THRUSTER_SSL_DOMAIN`. Whenever a
+prefixed variable is set, Thruster will use it in preference to the unprefixed
+version.
 
 | Variable Name         | Description                                                                     | Default Value |
 |-----------------------|---------------------------------------------------------------------------------|---------------|

internal/config.go

@@ -12,6 +12,8 @@ const (
 	KB = 1024
 	MB = 1024 * KB
 
+	ENV_PREFIX = "THRUSTER_"
+
 	defaultTargetPort = 3000
 
 	defaultCacheSize             = 64 * MB
@@ -73,7 +75,7 @@ func NewConfig() (*Config, error) {
 		XSendfileEnabled:      getEnvBool("X_SENDFILE_ENABLED", true),
 		MaxRequestBody:        getEnvInt("MAX_REQUEST_BODY", defaultMaxRequestBody),
 
-		SSLDomain:      os.Getenv("SSL_DOMAIN"),
+		SSLDomain:      getEnvString("SSL_DOMAIN", ""),
 		StoragePath:    getEnvString("STORAGE_PATH", defaultStoragePath),
 		BadGatewayPage: getEnvString("BAD_GATEWAY_PAGE", defaultBadGatewayPage),
 
@@ -87,18 +89,32 @@ func NewConfig() (*Config, error) {
 	}, nil
 }
 
+func findEnv(key string) (string, bool) {
+	value, ok := os.LookupEnv(ENV_PREFIX + key)
+	if ok {
+		return value, true
+	}
+
+	value, ok = os.LookupEnv(key)
+	if ok {
+		return value, true
+	}
+
+	return "", false
+}
+
 func getEnvString(key, defaultValue string) string {
-	value := os.Getenv(key)
-	if value == "" {
-		return defaultValue
+	value, ok := findEnv(key)
+	if ok {
+		return value
 	}
 
-	return value
+	return defaultValue
 }
 
 func getEnvInt(key string, defaultValue int) int {
-	value := os.Getenv(key)
-	if value == "" {
+	value, ok := findEnv(key)
+	if !ok {
 		return defaultValue
 	}
 
@@ -111,8 +127,8 @@ func getEnvInt(key string, defaultValue int) int {
 }
 
 func getEnvDuration(key string, defaultValue time.Duration) time.Duration {
-	value := os.Getenv(key)
-	if value == "" {
+	value, ok := findEnv(key)
+	if !ok {
 		return defaultValue
 	}
 
@@ -125,8 +141,8 @@ func getEnvDuration(key string, defaultValue time.Duration) time.Duration {
 }
 
 func getEnvBool(key string, defaultValue bool) bool {
-	value := os.Getenv(key)
-	if value == "" {
+	value, ok := findEnv(key)
+	if !ok {
 		return defaultValue
 	}
 

internal/config_test.go

@@ -39,6 +39,35 @@ func TestConfig_override_defaults_with_env_vars(t *testing.T) {
 	assert.Equal(t, slog.LevelDebug, c.LogLevel)
 }
 
+func TestConfig_override_defaults_with_env_vars_using_prefix(t *testing.T) {
+	usingProgramArgs(t, "thruster", "echo", "hello")
+	usingEnvVar(t, "THRUSTER_TARGET_PORT", "4000")
+	usingEnvVar(t, "THRUSTER_CACHE_SIZE", "256")
+	usingEnvVar(t, "THRUSTER_HTTP_READ_TIMEOUT", "5")
+	usingEnvVar(t, "THRUSTER_X_SENDFILE_ENABLED", "0")
+	usingEnvVar(t, "THRUSTER_DEBUG", "1")
+
+	c, err := NewConfig()
+	require.NoError(t, err)
+
+	assert.Equal(t, 4000, c.TargetPort)
+	assert.Equal(t, 256, c.CacheSizeBytes)
+	assert.Equal(t, 5*time.Second, c.HttpReadTimeout)
+	assert.Equal(t, false, c.XSendfileEnabled)
+	assert.Equal(t, slog.LevelDebug, c.LogLevel)
+}
+
+func TestConfig_prefixed_variables_take_precedence_over_non_prefixed(t *testing.T) {
+	usingProgramArgs(t, "thruster", "echo", "hello")
+	usingEnvVar(t, "TARGET_PORT", "3000")
+	usingEnvVar(t, "THRUSTER_TARGET_PORT", "4000")
+
+	c, err := NewConfig()
+	require.NoError(t, err)
+
+	assert.Equal(t, 4000, c.TargetPort)
+}
+
 func TestConfig_return_error_when_no_upstream_command(t *testing.T) {
 	usingProgramArgs(t, "thruster")