feat: add default config handling (#6)

Signed-off-by: Tronje Krop <[email protected]>

README.md

@@ -71,7 +71,7 @@ type Config struct {
 ```
 
 As usual in [Viper][viper], you can now create your config using the reader
-that allows to create multiple configuration while applying the default setup
+that allows creating multiple configuration while applying the default setup
 mechanisms using the following convenience functions:
 
 ```go
@@ -86,17 +86,32 @@ mechanisms using the following convenience functions:
 The defaults provided have via different options are overwriting each other in
 the following order:
 
-1. First the values provided via the `default`-tags are applied.
-2. Second the values provided by [Viper][viper] setup calls are applied.
-3. Third the values provided in the `<app>[-env].yaml`-file are applied.
-4. And finally the values provided via environment variables are applied
+1. First, the values provided via the `default`-tags are applied.
+2. Second the values provided by the config prototype instance are applied.
+3. Third the values provided by [Viper][viper] custom setup calls are applied.
+   This also includes the convenient methods provided in this package.
+4. Forth the values provided in the `<app>[-env].yaml`-file are applied.
+5. And finally the values provided via environment variables are applied
    taking the highest precedence.
 
 **Note**: While yo declare the reader with a default config structure, it is
 still possible to customize the reader arbitrarily, e.g. with flag support, and
 setup any other config structure by using the original [Viper][viper] interface
 functions.
 
+A special feature provided by `go-config` is to set up the defaults using a
+partial or complete prototype config. You can provide a complete prototype in
+the `New` constructor as well as any sub-prototype in the `SetSubDefaults`
+method as follows:
+
+```go
+    reader := config.New("TEST", "test", &config.Config{
+            Env: "prod",
+        }).SetSubDefaults("log", &log.Config{
+            Level: "debug",
+        }, false).
+```
+
 
 ## Logger setup
 

VERSION

@@ -1 +1 @@
-0.0.2
+0.0.3

config/config.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"github.com/spf13/viper"
+
 	"github.com/tkrop/go-config/info"
 	"github.com/tkrop/go-config/internal/reflect"
 	"github.com/tkrop/go-config/log"
@@ -25,8 +26,8 @@ type Config struct {
 	Log *log.Config
 }
 
-// ConfigReader common config reader based on viper.
-type ConfigReader[C any] struct {
+// Reader common config reader based on viper.
+type Reader[C any] struct {
 	*viper.Viper
 }
 
@@ -42,90 +43,104 @@ func GetEnvName(prefix string, name string) string {
 	return name
 }
 
-// New creates a new config reader with the given prefix, name, and pointer to
-// a config struct. The config struct is used to evaluate the default config
-// values and names from the `default`-tags.
+// New creates a new config reader with the given prefix, name, and config
+// struct. The config struct is evaluate for default config tags and available
+// config values to initialize the map. The `default` tags are only used, if
+// the config values are zero.
 func New[C any](
 	prefix, name string, config *C,
-) *ConfigReader[C] {
-	c := &ConfigReader[C]{
+) *Reader[C] {
+	r := &Reader[C]{
 		Viper: viper.New(),
 	}
 
-	c.SetConfigName(GetEnvName(prefix, name))
-	c.SetConfigType("yaml")
-	c.AddConfigPath(".")
-	c.SetEnvPrefix(prefix)
-	c.AutomaticEnv()
-	c.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
-	c.AllowEmptyEnv(true)
+	r.SetConfigName(GetEnvName(prefix, name))
+	r.SetConfigType("yaml")
+	r.AddConfigPath(".")
+	r.SetEnvPrefix(prefix)
+	r.AutomaticEnv()
+	r.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+	r.AllowEmptyEnv(true)
+
+	r.SetSubDefaults("", config, true)
 
 	// Determine parent directory of this code file.
 	if _, filename, _, ok := runtime.Caller(1); ok {
 		filepath := path.Join(path.Dir(filename), "../..")
-		c.AddConfigPath(filepath)
+		r.AddConfigPath(filepath)
 	}
 
-	// Set default values from config type.
-	reflect.NewTagWalker("default", nil).
-		Walk(config, "", c.setConfigDefault)
-
-	return c
-}
-
-// setConfigDefault sets the default value for the given path using the default
-// tag value.
-func (c *ConfigReader[C]) setConfigDefault(
-	_ reflect.Value, path, tag string,
-) {
-	c.SetDefault(path, tag)
+	return r
 }
 
 // SetDefaults is a convenience method to configure the reader with defaults
 // and standard values. It is also calling the provide function to customize
 // values and add more defaults.
-func (c *ConfigReader[C]) SetDefaults(
-	setup func(*ConfigReader[C]),
-) *ConfigReader[C] {
-	info := info.GetDefault()
-	c.SetDefault("info.path", info.Path)
-	c.SetDefault("info.version", info.Version)
-	c.SetDefault("info.revision", info.Revision)
-	c.SetDefault("info.build", info.Build)
-	c.SetDefault("info.commit", info.Commit)
-	c.SetDefault("info.dirty", info.Dirty)
-	c.SetDefault("info.go", info.Go)
-	c.SetDefault("info.platform", info.Platform)
-	c.SetDefault("info.compiler", info.Compiler)
-
+func (r *Reader[C]) SetDefaults(
+	setup func(*Reader[C]),
+) *Reader[C] {
 	if setup != nil {
-		setup(c)
+		setup(r)
 	}
 
-	return c
+	return r
+}
+
+// SetSubDefaults is a convenience method to update the default values of a
+// sub-section configured in the reader by using the given config struct. The
+// config struct is scanned for `default`-tags and values to set the defaults.
+// Depending on the `zero` flag the default values are either include setting
+// zero values or ignoring them.
+func (r *Reader[C]) SetSubDefaults(
+	key string, config any, zero bool,
+) *Reader[C] {
+	info := info.GetDefault()
+	r.SetDefault("info.path", info.Path)
+	r.SetDefault("info.version", info.Version)
+	r.SetDefault("info.revision", info.Revision)
+	r.SetDefault("info.build", info.Build)
+	r.SetDefault("info.commit", info.Commit)
+	r.SetDefault("info.dirty", info.Dirty)
+	r.SetDefault("info.go", info.Go)
+	r.SetDefault("info.platform", info.Platform)
+	r.SetDefault("info.compiler", info.Compiler)
+
+	reflect.NewTagWalker("default", "mapstructure", zero).
+		Walk(key, config, r.SetDefault)
+
+	return r
+}
+
+// SetDefault is a convenience method to set the default value for the given
+// key in the config reader and return the config reader.
+//
+// *Note:* This method is primarily kept to simplify debugging and testing.
+// Currently, it contains no additional logic.
+func (r *Reader[C]) SetDefault(key string, value any) {
+	r.Viper.SetDefault(key, value)
 }
 
 // ReadConfig is a convenience method to read the environment specific config
 // file to extend the default config. The context is used to distinguish
 // different calls in case of a panic by failures while loading the config
 // file.
-func (c *ConfigReader[C]) ReadConfig(context string) *ConfigReader[C] {
-	err := c.ReadInConfig()
+func (r *Reader[C]) ReadConfig(context string) *Reader[C] {
+	err := r.ReadInConfig()
 	if err != nil {
 		log.WithError(err).Errorf("failed to load config [%s]", context)
 		panic(fmt.Errorf("failed to load config [%s]: %w", context, err))
 	}
 
-	return c
+	return r
 }
 
 // GetConfig is a convenience method to return the config without loading the
 // environment specific config file. The context is used to distinguish
 // different calls in case of a panic created by failures while unmarschalling
 // the config.
-func (c *ConfigReader[C]) GetConfig(context string) *C {
+func (r *Reader[C]) GetConfig(context string) *C {
 	config := new(C)
-	err := c.Unmarshal(config)
+	err := r.Unmarshal(config)
 	if err != nil {
 		log.WithError(err).Errorf("failed to unmarshal config [%s]", context)
 		panic(fmt.Errorf("failed to unmarshal config [%s]: %w", context, err))
@@ -142,6 +157,6 @@ func (c *ConfigReader[C]) GetConfig(context string) *C {
 // file and returns the config. The context is used to distinguish different
 // calls in case of a panic created by failures while loading the config file
 // and umarshalling the config.
-func (c *ConfigReader[C]) LoadConfig(context string) *C {
-	return c.ReadConfig(context).GetConfig(context)
+func (r *Reader[C]) LoadConfig(context string) *C {
+	return r.ReadConfig(context).GetConfig(context)
 }

config/config_test.go

@@ -15,8 +15,8 @@ func TestReadConfig(t *testing.T) {
 
 	// Given
 	reader := config.New("TC", "test", &config.Config{}).
-		SetDefaults(func(c *config.ConfigReader[config.Config]) {
-			c.AddConfigPath("../fixtures")
+		SetDefaults(func(c *config.Reader[config.Config]) {
+			c.AddConfigPath("fixtures")
 		})
 
 	// When
@@ -29,6 +29,7 @@ func TestReadConfig(t *testing.T) {
 
 func TestReadConfig_UnmarshalFailure(t *testing.T) {
 	t.Parallel()
+
 	type Config struct {
 		config.Config `mapstructure:",squash"`
 		Content       int
@@ -37,8 +38,8 @@ func TestReadConfig_UnmarshalFailure(t *testing.T) {
 	// Given
 	defer func() { _ = recover() }()
 	reader := config.New("TC", "test", &Config{}).
-		SetDefaults(func(c *config.ConfigReader[Config]) {
-			c.AddConfigPath("../fixtures")
+		SetDefaults(func(c *config.Reader[Config]) {
+			c.AddConfigPath("fixtures")
 		})
 
 	// When
@@ -53,8 +54,8 @@ func TestReadConfig_FileNotFound(t *testing.T) {
 	defer func() { _ = recover() }()
 	t.Setenv("TC_ENV", "other")
 	reader := config.New("TC", "test", &config.Config{}).
-		SetDefaults(func(c *config.ConfigReader[config.Config]) {
-			c.AddConfigPath("../fixtures")
+		SetDefaults(func(c *config.Reader[config.Config]) {
+			c.AddConfigPath("fixtures")
 		})
 
 	// When
@@ -68,8 +69,8 @@ func TestReadConfig_OverridingEnv(t *testing.T) {
 	// Given
 	t.Setenv("TC_LOG_LEVEL", "trace")
 	reader := config.New("TC", "test", &config.Config{}).
-		SetDefaults(func(c *config.ConfigReader[config.Config]) {
-			c.AddConfigPath("../fixtures")
+		SetDefaults(func(c *config.Reader[config.Config]) {
+			c.AddConfigPath("fixtures")
 		})
 
 	// When
@@ -85,7 +86,7 @@ func TestReadConfig_OverridingFunc(t *testing.T) {
 
 	// Given
 	reader := config.New("TC", "test", &config.Config{}).
-		SetDefaults(func(c *config.ConfigReader[config.Config]) {
+		SetDefaults(func(c *config.Reader[config.Config]) {
 			c.SetDefault("log.level", "trace")
 		})
 

fixtures/test.yaml → config/fixtures/test.yaml

@@ -2,5 +2,8 @@ log:
   level: info
   caller: false
 
+info:
+  path: github.com/tkrop/go-config
+
 content: |
   Hello, World!

go.mod

@@ -3,6 +3,7 @@ module github.com/tkrop/go-config
 go 1.23.1
 
 require (
+	github.com/golang/mock v1.6.0
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/viper v1.19.0
 	github.com/stretchr/testify v1.9.0
@@ -13,7 +14,6 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/fsnotify/fsnotify v1.7.0 // indirect
-	github.com/golang/mock v1.6.0 // indirect
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/magiconair/properties v1.8.7 // indirect
 	github.com/mitchellh/mapstructure v1.5.0 // indirect