Refactor config package

cmd/after-lock/after-lock.go

@@ -18,11 +18,11 @@ import (
 
 
 type afterLockConfig struct {
-	INITIAL_DELAY int
-	LOOP_DELAY int
-	LOCK_PATH string
+	INITIAL_DELAY int `optional`
+	LOOP_DELAY int `optional`
+	LOCK_PATH string `optional`
 	LOG_PATH string
-	PRINT_STACKTRACES bool
+	PRINT_STACKTRACES bool `optional`
 }
 
 var configuration = afterLockConfig{
@@ -46,7 +46,7 @@ func init() {
 
 func main() {
 	defer handleErrors()
-	err := config.Build("AFL", &configuration)
+	err := config.NewBuilder().Build("AFL_", &configuration)
 	if err != nil {
 		panic(err)
 	}

config/config.go

@@ -1,99 +1,95 @@
 package config
 
 import (
-	"os"
-	"strings"
 	"fmt"
+	"os"
 	"reflect"
-	"errors"
 	"strconv"
+	"strings"
 )
 
 
-var ConfigFetchMethod = os.Environ
+type ConfigBuilder struct {
+	ConfigFetchMethod func()[]string
+	typeParsers map[reflect.Kind]func(string)(interface{}, error)
+}
 
+func NewBuilder() *ConfigBuilder {
+	return &ConfigBuilder{
+		ConfigFetchMethod: os.Environ,
+		typeParsers: map[reflect.Kind]func(string)(interface{}, error) {
+			reflect.String: func(value string) (interface{}, error) {
+				return value, nil
+			},
+			reflect.Int: func(value string) (interface{}, error) {
+				i, err := strconv.Atoi(value)
+				if err != nil {
+					return nil, err
+				}
+				return i, nil
+			},
+			reflect.Bool: func(value string) (interface{}, error) {
+				b, err := strconv.ParseBool(value)
+				if err != nil {
+					return nil, err
+				}
+				return b, nil
+			},
+		},
+	}
+}
 
-func Build(prefix string, configStruct interface{}) (err error) {
-	defer func() {
-		if e := recover(); e != nil {
-			switch r := e.(type) {
-			case string:
-				err = errors.New(r)
-			case error:
-				err = r
-			default:
-				err = errors.New("Undefined panic")
-			}
-		}
-	}()
+func (cb *ConfigBuilder) Build(prefix string, configStruct interface{}) error {
 	assertIsPtr(configStruct)
 
 	fieldNames := getConfigStructFieldNames(configStruct)
-	config := loadConfig(prefix)
-
+	config := cb.loadConfig(prefix)
 	structRef := reflect.ValueOf(configStruct)
+
 	for _, fieldName := range fieldNames {
 		value, ok := config[fieldName]
 		if !ok {
-			// no such field loaded, avoid overwriting default
-			continue
+			// no such field loaded, avoid overwriting default if field is optional
+			field, _ := reflect.TypeOf(configStruct).Elem().FieldByName(fieldName)
+			if strings.Contains(string(field.Tag), "optional") {
+				continue
+			}
+			return fmt.Errorf("no config found for required field '%s'", fieldName)
 		}
 		field := reflect.Indirect(structRef).FieldByName(fieldName)
 		typeRef := field.Type()
-		ret, err := tryParseString(value, typeRef.Kind())
+		typedValue, err := cb.tryParseString(value, typeRef.Kind())
 		if err != nil {
 			return err
 		}
-		field.Set(reflect.ValueOf(ret).Convert(typeRef))
+		field.Set(reflect.ValueOf(typedValue).Convert(typeRef))
 	}
 
 	return nil
 }
 
-func tryParseString(what string, toType reflect.Kind) (interface{}, error) {
-	switch toType {
-	case reflect.String:
-		return what, nil
-	case reflect.Int:
-		i, err := strconv.Atoi(what)
-		if err != nil {
-			return nil, err
-		}
-		return i, nil
-	case reflect.Bool:
-		b, err := strconv.ParseBool(what)
-		if err != nil {
-			return nil, err
-		}
-		return b, nil
-	default:
-		return nil, fmt.Errorf("Failed to parse value %v", what)
-	}
-}
-
-func assertIsPtr(what interface{}) {
-	r := reflect.ValueOf(what)
+func assertIsPtr(configStruct interface{}) {
+	r := reflect.ValueOf(configStruct)
 	if r.Kind() != reflect.Ptr {
-		panic(fmt.Errorf("Supplied value is not a pointer to a struct"))
+		panic(fmt.Errorf("supplied value is not a pointer to a struct"))
 	}
 }
 
 func getConfigStructFieldNames(configStruct interface{}) []string {
 	configFields := []string{}
+	structValue := reflect.ValueOf(configStruct).Elem()
 
-	val := reflect.ValueOf(configStruct).Elem()
-	for i := 0; i < val.NumField(); i++ {
-		configFields = append(configFields, val.Type().Field(i).Name)
+	for i := 0; i < structValue.NumField(); i++ {
+		configFields = append(configFields, structValue.Type().Field(i).Name)
 	}
 
 	return configFields
 }
 
-func loadConfig(prefix string) map[string]string {
-	prefix = fmt.Sprintf("%s_", prefix)
-
+func (cb *ConfigBuilder) loadConfig(prefix string) map[string]string {
 	config := map[string]string{}
-	for _, env := range ConfigFetchMethod() {
+
+	for _, env := range cb.ConfigFetchMethod() {
 		parts := strings.SplitN(env, "=", 2)
 		key, value := parts[0], parts[1]
 		if strings.HasPrefix(key, prefix) {
@@ -101,15 +97,22 @@ func loadConfig(prefix string) map[string]string {
 			config[key] = value
 		}
 	}
+
 	return config
 }
 
-// CheckKeysExist returns an error if not all keys are present in config map
-func CheckKeysExist(config map[string]string, keys ...string) error {
-	for _, key := range keys {
-		if _, ok := config[key]; ok {
-			return fmt.Errorf("Config key '%s' is not set", key)
-		}
+func (cb *ConfigBuilder) tryParseString(value string, toType reflect.Kind) (interface{}, error) {
+	parser, ok := cb.typeParsers[toType]
+	if !ok {
+		return nil, fmt.Errorf("no parser found for type %v", toType)
 	}
-	return nil
+	parsed_val, err := parser(value)
+	if err != nil {
+		return nil, err
+	}
+	return parsed_val, nil
+}
+
+func (cb *ConfigBuilder) RegisterParser(toType reflect.Kind, parser func(string)(interface{}, error)) {
+	cb.typeParsers[toType] = parser
 }

config/config_test.go

@@ -1,9 +1,11 @@
 package config_test
 
 import (
-	"testing"
-
 	"kdelsd/config"
+	"reflect"
+	"strings"
+	"strconv"
+	"testing"
 )
 
 
@@ -11,39 +13,96 @@ type TestConfig struct {
 	INT int
 	BOOL bool
 	STR string
-	OTHER_STR string
+	OTHER_STR string `optional`
+	COMPLEX complex64 `optional`
 }
 
-var testConfigInstance = TestConfig{
+var testConfigReference = TestConfig{
 	INT: 42,
 	BOOL: true,
 	STR: "sajtok",
 	OTHER_STR: "default-value",
 }
 
-var testEnv = []string {
+var testEnv = []string{
 	"TEST_INT=42",
 	"TEST_BOOL=true",
 	"TEST_STR=sajtok",
 }
 
-func setup() {
-	config.ConfigFetchMethod = func() []string {
+func configBuilder() *config.ConfigBuilder {
+	cb := config.NewBuilder()
+	cb.ConfigFetchMethod = func()[]string {
 		return testEnv
 	}
+
+	return cb
 }
 
-func TestBuildConfig(t *testing.T) {
-	setup()
+
+func TestConfigBuilder(t *testing.T) {
 	c := TestConfig{}
-	c.OTHER_STR = testConfigInstance.OTHER_STR
+	c.OTHER_STR = testConfigReference.OTHER_STR
+	builder := configBuilder()
 
-	err := config.Build("TEST", &c)
+	err := builder.Build("TEST_", &c)
 	if err != nil {
-		panic(err)
+		t.Fatalf("Config building should not fail\n")
 	}
 
-	if c != testConfigInstance {
-		t.Errorf("%v != %v", c, testConfigInstance)
+	if c != testConfigReference {
+		t.Fatalf("Parsed config shoudl equal reference config\n%v != %v\n", c, testConfigReference)
+	}
+}
+
+func TestConfigBuilderParsers(t *testing.T) {
+	c := TestConfig{}
+	builder := configBuilder()
+	builder.ConfigFetchMethod = func()[]string {
+		return append(testEnv, "TEST_COMPLEX=42+42i")
+	}
+
+	err := builder.Build("TEST_", &c)
+	if err == nil {
+		t.Fatalf("CONFIG should not be parseable, since type has no default parser\n")
+	}
+	if !strings.Contains(err.Error(), "complex64") {
+		t.Fatalf("Error should contain the type that failed to parse\n")
+	}
+
+	builder.RegisterParser(reflect.Complex64, func(value string)(interface{}, error) {
+		num, err := strconv.ParseComplex(value, 64)
+		if err != nil {
+			return nil, err
+		}
+		return num, nil
+	})
+	err = builder.Build("TEST_", &c)
+	if err != nil {
+		t.Fatalf("Parsing type should not fail after registering a parser for it\n")
+	}
+}
+
+func TestConfigBuilderOptional(t *testing.T) {
+	type RequiredConfig struct {
+		REQUIRED_STR string
+	}
+	c := RequiredConfig{}
+	builder := config.NewBuilder()
+
+	err := builder.Build("TEST_", &c)
+	if err == nil {
+		t.Fatalf("Fields not marked with the `optional` tag should be mandatory\n")
+	}
+	if !strings.Contains(err.Error(), "REQUIRED_STR") {
+		t.Fatalf("Error should contain the name of the field\n")
+	}
+
+	builder.ConfigFetchMethod = func()[]string {
+		return append(testEnv, "TEST_REQUIRED_STR=prrrr")
+	}
+	err = builder.Build("TEST_", &c)
+	if err != nil {
+		t.Fatalf("Config building should not fail after providing the mandatory field\n")
 	}
 }