Support customising mapstructure.DecoderConfig for Unmarshal

* Added a new `DecoderConfigOption` type allowing the user to write custom
  functions that can override the default mapstructure.DecoderConfig
  settings

* Added a new `DecodeHook` function which returns
  a `DecoderConfigOption`. This allows the user to easily set their own
  Decode hooks when Unmarshaling

* Updated Unmarshal, UnmarshalKey and defaultDecoderConfig to support variadic
  trailing `DecoderConfigOption` functions to allow for customisation of
  the default  mapstructure.DecoderConfig

* Added a test case with example usage

.travis.yml

@@ -2,9 +2,8 @@ go_import_path: github.com/spf13/viper
 
 language: go
 go:
-  - 1.7.x
-  - 1.8.x
   - 1.9.x
+  - 1.10.x
   - tip
 
 os:

README.md

@@ -191,7 +191,7 @@ _When working with ENV variables, it’s important to recognize that Viper
 treats ENV variables as case sensitive._
 
 Viper provides a mechanism to try to ensure that ENV variables are unique. By
-using `SetEnvPrefix`, you can tell Viper to use add a prefix while reading from
+using `SetEnvPrefix`, you can tell Viper to use a prefix while reading from
 the environment variables. Both `BindEnv` and `AutomaticEnv` will use this
 prefix.
 
@@ -437,6 +437,7 @@ The following functions and methods exist:
  * `GetTime(key string) : time.Time`
  * `GetDuration(key string) : time.Duration`
  * `IsSet(key string) : bool`
+ * `AllSettings() : map[string]interface{}`
 
 One important thing to recognize is that each Get function will return a zero
 value if it’s not found. To check if a given key exists, the `IsSet()` method
@@ -590,6 +591,27 @@ if err != nil {
 }
 ```
 
+### Marshalling to string
+
+You may need to marhsal all the settings held in viper into a string rather than write them to a file. 
+You can use your favorite format's marshaller with the config returned by `AllSettings()`.
+
+```go
+import (
+    yaml "gopkg.in/yaml.v2"
+    // ...
+) 
+
+func yamlStringSettings() string {
+    c := viper.AllSettings()
+	bs, err := yaml.Marshal(c)
+	if err != nil {
+        t.Fatalf("unable to marshal config to YAML: %v", err)
+    }
+	return string(bs)
+}
+```
+
 ## Viper or Vipers?
 
 Viper comes ready to use out of the box. There is no configuration or

viper.go

@@ -113,6 +113,23 @@ func (fnfe ConfigFileNotFoundError) Error() string {
 	return fmt.Sprintf("Config File %q Not Found in %q", fnfe.name, fnfe.locations)
 }
 
+// A DecoderConfigOption can be passed to viper.Unmarshal to configure
+// mapstructure.DecoderConfig options
+type DecoderConfigOption func(*mapstructure.DecoderConfig)
+
+// DecodeHook returns a DecoderConfigOption which overrides the default
+// DecoderConfig.DecodeHook value, the default is:
+//
+//  mapstructure.ComposeDecodeHookFunc(
+//		mapstructure.StringToTimeDurationHookFunc(),
+//		mapstructure.StringToSliceHookFunc(","),
+//	)
+func DecodeHook(hook mapstructure.DecodeHookFunc) DecoderConfigOption {
+	return func(c *mapstructure.DecoderConfig) {
+		c.DecodeHook = hook
+	}
+}
+
 // Viper is a prioritized configuration registry. It
 // maintains a set of configuration sources, fetches
 // values to populate those, and provides them according
@@ -268,7 +285,7 @@ func (v *Viper) WatchConfig() {
 		defer watcher.Close()
 
 		// we have to watch the entire directory to pick up renames/atomic saves in a cross-platform way
-		filename, err := v.GetConfigFile()
+		filename, err := v.getConfigFile()
 		if err != nil {
 			log.Println("error:", err)
 			return
@@ -682,6 +699,12 @@ func (v *Viper) GetInt(key string) int {
 	return cast.ToInt(v.Get(key))
 }
 
+// GetInt32 returns the value associated with the key as an integer.
+func GetInt32(key string) int32 { return v.GetInt32(key) }
+func (v *Viper) GetInt32(key string) int32 {
+	return cast.ToInt32(v.Get(key))
+}
+
 // GetInt64 returns the value associated with the key as an integer.
 func GetInt64(key string) int64 { return v.GetInt64(key) }
 func (v *Viper) GetInt64(key string) int64 {
@@ -739,9 +762,11 @@ func (v *Viper) GetSizeInBytes(key string) uint {
 }
 
 // UnmarshalKey takes a single key and unmarshals it into a Struct.
-func UnmarshalKey(key string, rawVal interface{}) error { return v.UnmarshalKey(key, rawVal) }
-func (v *Viper) UnmarshalKey(key string, rawVal interface{}) error {
-	err := decode(v.Get(key), defaultDecoderConfig(rawVal))
+func UnmarshalKey(key string, rawVal interface{}, opts ...DecoderConfigOption) error {
+	return v.UnmarshalKey(key, rawVal, opts...)
+}
+func (v *Viper) UnmarshalKey(key string, rawVal interface{}, opts ...DecoderConfigOption) error {
+	err := decode(v.Get(key), defaultDecoderConfig(rawVal, opts...))
 
 	if err != nil {
 		return err
@@ -754,9 +779,11 @@ func (v *Viper) UnmarshalKey(key string, rawVal interface{}) error {
 
 // Unmarshal unmarshals the config into a Struct. Make sure that the tags
 // on the fields of the structure are properly set.
-func Unmarshal(rawVal interface{}) error { return v.Unmarshal(rawVal) }
-func (v *Viper) Unmarshal(rawVal interface{}) error {
-	err := decode(v.AllSettings(), defaultDecoderConfig(rawVal))
+func Unmarshal(rawVal interface{}, opts ...DecoderConfigOption) error {
+	return v.Unmarshal(rawVal, opts...)
+}
+func (v *Viper) Unmarshal(rawVal interface{}, opts ...DecoderConfigOption) error {
+	err := decode(v.AllSettings(), defaultDecoderConfig(rawVal, opts...))
 
 	if err != nil {
 		return err
@@ -769,8 +796,8 @@ func (v *Viper) Unmarshal(rawVal interface{}) error {
 
 // defaultDecoderConfig returns default mapsstructure.DecoderConfig with suppot
 // of time.Duration values & string slices
-func defaultDecoderConfig(output interface{}) *mapstructure.DecoderConfig {
-	return &mapstructure.DecoderConfig{
+func defaultDecoderConfig(output interface{}, opts ...DecoderConfigOption) *mapstructure.DecoderConfig {
+	c := &mapstructure.DecoderConfig{
 		Metadata:         nil,
 		Result:           output,
 		WeaklyTypedInput: true,
@@ -779,6 +806,10 @@ func defaultDecoderConfig(output interface{}) *mapstructure.DecoderConfig {
 			mapstructure.StringToSliceHookFunc(","),
 		),
 	}
+	for _, opt := range opts {
+		opt(c)
+	}
+	return c
 }
 
 // A wrapper around mapstructure.Decode that mimics the WeakDecode functionality
@@ -1131,7 +1162,7 @@ func (v *Viper) Set(key string, value interface{}) {
 func ReadInConfig() error { return v.ReadInConfig() }
 func (v *Viper) ReadInConfig() error {
 	jww.INFO.Println("Attempting to read in config file")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1161,7 +1192,7 @@ func (v *Viper) ReadInConfig() error {
 func MergeInConfig() error { return v.MergeInConfig() }
 func (v *Viper) MergeInConfig() error {
 	jww.INFO.Println("Attempting to merge in config file")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1203,7 +1234,7 @@ func (v *Viper) MergeConfig(in io.Reader) error {
 // WriteConfig writes the current configuration to a file.
 func WriteConfig() error { return v.WriteConfig() }
 func (v *Viper) WriteConfig() error {
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1213,7 +1244,7 @@ func (v *Viper) WriteConfig() error {
 // SafeWriteConfig writes current configuration to file only if the file does not exist.
 func SafeWriteConfig() error { return v.SafeWriteConfig() }
 func (v *Viper) SafeWriteConfig() error {
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1705,7 +1736,7 @@ func (v *Viper) getConfigType() string {
 		return v.configType
 	}
 
-	cf, err := v.GetConfigFile()
+	cf, err := v.getConfigFile()
 	if err != nil {
 		return ""
 	}
@@ -1719,7 +1750,7 @@ func (v *Viper) getConfigType() string {
 	return ""
 }
 
-func (v *Viper) GetConfigFile() (string, error) {
+func (v *Viper) getConfigFile() (string, error) {
 	if v.configFile == "" {
 		cf, err := v.findConfigFile()
 		if err != nil {

viper_test.go

@@ -7,6 +7,7 @@ package viper
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -18,6 +19,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/afero"
 	"github.com/spf13/cast"
 
@@ -244,7 +246,7 @@ func (s *stringValue) String() string {
 
 func TestBasics(t *testing.T) {
 	SetConfigFile("/tmp/config.yaml")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	assert.Equal(t, "/tmp/config.yaml", filename)
 	assert.NoError(t, err)
 }
@@ -503,6 +505,42 @@ func TestUnmarshal(t *testing.T) {
 	assert.Equal(t, &config{Name: "Steve", Port: 1234, Duration: time.Second + time.Millisecond}, &C)
 }
 
+func TestUnmarshalWithDecoderOptions(t *testing.T) {
+	Set("credentials", "{\"foo\":\"bar\"}")
+
+	opt := DecodeHook(mapstructure.ComposeDecodeHookFunc(
+		mapstructure.StringToTimeDurationHookFunc(),
+		mapstructure.StringToSliceHookFunc(","),
+		// Custom Decode Hook Function
+		func(rf reflect.Kind, rt reflect.Kind, data interface{}) (interface{}, error) {
+			if rf != reflect.String || rt != reflect.Map {
+				return data, nil
+			}
+			m := map[string]string{}
+			raw := data.(string)
+			if raw == "" {
+				return m, nil
+			}
+			return m, json.Unmarshal([]byte(raw), &m)
+		},
+	))
+
+	type config struct {
+		Credentials map[string]string
+	}
+
+	var C config
+
+	err := Unmarshal(&C, opt)
+	if err != nil {
+		t.Fatalf("unable to decode into struct, %v", err)
+	}
+
+	assert.Equal(t, &config{
+		Credentials: map[string]string{"foo": "bar"},
+	}, &C)
+}
+
 func TestBindPFlags(t *testing.T) {
 	v := New() // create independent Viper object
 	flagSet := pflag.NewFlagSet("test", pflag.ContinueOnError)
@@ -1068,6 +1106,10 @@ func TestMergeConfig(t *testing.T) {
 		t.Fatalf("lagrenum != 765432101234567, = %d", pop)
 	}
 
+	if pop := v.GetInt32("hello.pop"); pop != int32(37890) {
+		t.Fatalf("pop != 37890, = %d", pop)
+	}
+
 	if pop := v.GetInt64("hello.lagrenum"); pop != int64(765432101234567) {
 		t.Fatalf("int64 lagrenum != 765432101234567, = %d", pop)
 	}
@@ -1092,6 +1134,10 @@ func TestMergeConfig(t *testing.T) {
 		t.Fatalf("lagrenum != 7654321001234567, = %d", pop)
 	}
 
+	if pop := v.GetInt32("hello.pop"); pop != int32(45000) {
+		t.Fatalf("pop != 45000, = %d", pop)
+	}
+
 	if pop := v.GetInt64("hello.lagrenum"); pop != int64(7654321001234567) {
 		t.Fatalf("int64 lagrenum != 7654321001234567, = %d", pop)
 	}
@@ -1177,7 +1223,7 @@ func TestUnmarshalingWithAliases(t *testing.T) {
 func TestSetConfigNameClearsFileCache(t *testing.T) {
 	SetConfigFile("/tmp/config.yaml")
 	SetConfigName("default")
-	f, err := v.GetConfigFile()
+	f, err := v.getConfigFile()
 	if err == nil {
 		t.Fatalf("config file cache should have been cleared")
 	}