Make the map in MergeConfigMap case insensitive

Fixes #605

.gitignore

@@ -21,4 +21,9 @@ _testmain.go
 
 *.exe
 *.test
-*.bench
+*.bench
+
+.vscode
+
+# exclude dependencies in the `/vendor` folder
+vendor

.travis.yml

@@ -1,10 +1,13 @@
 go_import_path: github.com/spf13/viper
 
 language: go
+
+env:
+  global:
+  - GO111MODULE="on"
+
 go:
-  - 1.7.x
-  - 1.8.x
-  - 1.9.x
+  - 1.11.x
   - tip
 
 os:

README.md

@@ -179,19 +179,20 @@ viper.GetBool("verbose") // true
 ### Working with Environment Variables
 
 Viper has full support for environment variables. This enables 12 factor
-applications out of the box. There are four methods that exist to aid working
+applications out of the box. There are five methods that exist to aid working
 with ENV:
 
  * `AutomaticEnv()`
  * `BindEnv(string...) : error`
  * `SetEnvPrefix(string)`
  * `SetEnvKeyReplacer(string...) *strings.Replacer`
+  * `AllowEmptyEnvVar(bool)`
 
 _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.
 
@@ -217,6 +218,10 @@ keys to an extent. This is useful if you want to use `-` or something in your
 `Get()` calls, but want your environmental variables to use `_` delimiters. An
 example of using it can be found in `viper_test.go`.
 
+By default empty environment variables are considered unset and will fall back to
+the next configuration source. To treat empty environment variables as set, use
+the `AllowEmptyEnv` method.
+
 #### Env example
 
 ```go
@@ -373,12 +378,33 @@ how to use Consul.
 
 ### Remote Key/Value Store Example - Unencrypted
 
+#### etcd
 ```go
 viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001","/config/hugo.json")
 viper.SetConfigType("json") // because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop"
 err := viper.ReadRemoteConfig()
 ```
 
+#### Consul
+You need to set a key to Consul key/value storage with JSON value containing your desired config.  
+For example, create a Consul key/value store key `MY_CONSUL_KEY` with value:
+
+```json
+{
+    "port": 8080,
+    "hostname": "myhostname.com"
+}
+```
+
+```go
+viper.AddRemoteProvider("consul", "localhost:8500", "MY_CONSUL_KEY")
+viper.SetConfigType("json") // Need to explicitly set this to json
+err := viper.ReadRemoteConfig()
+
+fmt.Println(viper.Get("port")) // 8080
+fmt.Println(viper.Get("hostname")) // myhostname.com
+```
+
 ### Remote Key/Value Store Example - Encrypted
 
 ```go
@@ -437,6 +463,7 @@ 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 +617,27 @@ 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

go.mod

@@ -0,0 +1,24 @@
+module github.com/spf13/viper
+
+require (
+	github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6 // indirect
+	github.com/coreos/etcd v3.3.10+incompatible // indirect
+	github.com/coreos/go-etcd v2.0.0+incompatible // indirect
+	github.com/coreos/go-semver v0.2.0 // indirect
+	github.com/fsnotify/fsnotify v1.4.7
+	github.com/hashicorp/hcl v1.0.0
+	github.com/magiconair/properties v1.8.0
+	github.com/mitchellh/mapstructure v1.1.2
+	github.com/pelletier/go-toml v1.2.0
+	github.com/spf13/afero v1.1.2
+	github.com/spf13/cast v1.3.0
+	github.com/spf13/jwalterweatherman v1.0.0
+	github.com/spf13/pflag v1.0.3
+	github.com/stretchr/testify v1.2.2
+	github.com/ugorji/go/codec v0.0.0-20181204163529-d75b2dcb6bc8 // indirect
+	github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77
+	golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9 // indirect
+	golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a // indirect
+	golang.org/x/text v0.3.0 // indirect
+	gopkg.in/yaml.v2 v2.2.2
+)

go.sum

@@ -0,0 +1,51 @@
+github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6 h1:G1bPvciwNyF7IUmKXNt9Ak3m6u9DE1rF+RmtIkBpVdA=
+github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8=
+github.com/coreos/etcd v3.3.10+incompatible h1:KjVWqrZ5U0wa3CxY2AxlH6/UcB+PK2td1DcsYhA+HRs=
+github.com/coreos/etcd v3.3.10+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc32PjwdhPthX9715RE=
+github.com/coreos/go-etcd v2.0.0+incompatible h1:bXhRBIXoTm9BYHS3gE0TtQuyNZyeEMux2sDi4oo5YOo=
+github.com/coreos/go-etcd v2.0.0+incompatible/go.mod h1:Jez6KQU2B/sWsbdaef3ED8NzMklzPG4d5KIOhIy30Tk=
+github.com/coreos/go-semver v0.2.0 h1:3Jm3tLmsgAYcjC+4Up7hJrFBPr+n7rAqYeSw/SZazuY=
+github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.4.7 h1:IXs+QLmnXW2CcXuY+8Mzv/fWEsPGWxqefPtCP5CnV9I=
+github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
+github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=
+github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
+github.com/magiconair/properties v1.8.0 h1:LLgXmsheXeRoUOBOjtwPQCWIYqM/LU1ayDtDePerRcY=
+github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
+github.com/mitchellh/mapstructure v1.1.2 h1:fmNYVwqnSfB9mZU6OS2O6GsXM+wcskZDuKQzvN1EDeE=
+github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
+github.com/pelletier/go-toml v1.2.0 h1:T5zMGML61Wp+FlcbWjRDT7yAxhJNAiPPLOFECq181zc=
+github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/spf13/afero v1.1.2 h1:m8/z1t7/fwjysjQRYbP0RD+bUIF/8tJwPdEZsI83ACI=
+github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
+github.com/spf13/cast v1.3.0 h1:oget//CVOEoFewqQxwr0Ej5yjygnqGkvggSE/gB35Q8=
+github.com/spf13/cast v1.3.0/go.mod h1:Qx5cxh0v+4UWYiBimWS+eyWzqEqokIECu5etghLkUJE=
+github.com/spf13/jwalterweatherman v1.0.0 h1:XHEdyB+EcvlqZamSM4ZOMGlc93t6AcsBEu9Gc1vn7yk=
+github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
+github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
+github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
+github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.2.3-0.20181014000028-04af85275a5c h1:03OmljzZYsezlgAfa+f/cY8E8XXPiFh5bgANMhUlDI4=
+github.com/stretchr/testify v1.2.3-0.20181014000028-04af85275a5c/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.2.3-0.20181115233458-8019298d9fa5 h1:ixuBiBNIIQ3RKRSZy9B0DgaqreXG6NDHrbwAFGg8Mwk=
+github.com/stretchr/testify v1.2.3-0.20181115233458-8019298d9fa5/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/ugorji/go/codec v0.0.0-20181204163529-d75b2dcb6bc8 h1:3SVOIvH7Ae1KRYyQWRjXWJEA9sS/c/pjvH++55Gr648=
+github.com/ugorji/go/codec v0.0.0-20181204163529-d75b2dcb6bc8/go.mod h1:VFNgLljTbGfSG7qAOspJ7OScBnGdDN/yBr0sguwnwf0=
+github.com/xordataexchange/crypt v0.0.2 h1:VBfFXTpEwLq2hzs42qCHOyKw5AqEm9DYGqBuINmzUZY=
+github.com/xordataexchange/crypt v0.0.2/go.mod h1:aYKd//L2LvnjZzWKhF00oedf4jCCReLcmhLdhm1A27Q=
+github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77 h1:ESFSdwYZvkeru3RtdrYueztKhOBCSAAzS4Gf+k0tEow=
+github.com/xordataexchange/crypt v0.0.3-0.20170626215501-b2862e3d0a77/go.mod h1:aYKd//L2LvnjZzWKhF00oedf4jCCReLcmhLdhm1A27Q=
+golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9 h1:mKdxBk7AujPs8kU4m80U72y/zjbZ3UcXC7dClwKbUI0=
+golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a h1:1n5lsVfiQW3yfsRGu98756EH1YthsFqr/5mxHduZW2A=
+golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

viper.go

@@ -30,6 +30,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"strings"
+	"sync"
 	"time"
 
 	yaml "gopkg.in/yaml.v2"
@@ -113,6 +114,23 @@ 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
@@ -169,6 +187,7 @@ type Viper struct {
 
 	automaticEnvApplied bool
 	envKeyReplacer      *strings.Replacer
+	allowEmptyEnv       bool
 
 	config         map[string]interface{}
 	override       map[string]interface{}
@@ -259,48 +278,73 @@ func (v *Viper) OnConfigChange(run func(in fsnotify.Event)) {
 }
 
 func WatchConfig() { v.WatchConfig() }
+
 func (v *Viper) WatchConfig() {
+	initWG := sync.WaitGroup{}
+	initWG.Add(1)
 	go func() {
 		watcher, err := fsnotify.NewWatcher()
 		if err != nil {
 			log.Fatal(err)
 		}
 		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)
+			log.Printf("error: %v\n", err)
 			return
 		}
 
 		configFile := filepath.Clean(filename)
 		configDir, _ := filepath.Split(configFile)
+		realConfigFile, _ := filepath.EvalSymlinks(filename)
 
-		done := make(chan bool)
+		eventsWG := sync.WaitGroup{}
+		eventsWG.Add(1)
 		go func() {
 			for {
 				select {
-				case event := <-watcher.Events:
-					// we only care about the config file
-					if filepath.Clean(event.Name) == configFile {
-						if event.Op&fsnotify.Write == fsnotify.Write || event.Op&fsnotify.Create == fsnotify.Create {
-							err := v.ReadInConfig()
-							if err != nil {
-								log.Println("error:", err)
-							}
+				case event, ok := <-watcher.Events:
+					if !ok { // 'Events' channel is closed
+						eventsWG.Done()
+						return
+					}
+					currentConfigFile, _ := filepath.EvalSymlinks(filename)
+					// we only care about the config file with the following cases:
+					// 1 - if the config file was modified or created
+					// 2 - if the real path to the config file changed (eg: k8s ConfigMap replacement)
+					const writeOrCreateMask = fsnotify.Write | fsnotify.Create
+					if (filepath.Clean(event.Name) == configFile &&
+						event.Op&writeOrCreateMask != 0) ||
+						(currentConfigFile != "" && currentConfigFile != realConfigFile) {
+						realConfigFile = currentConfigFile
+						err := v.ReadInConfig()
+						if err != nil {
+							log.Printf("error reading config file: %v\n", err)
+						}
+						if v.onConfigChange != nil {
 							v.onConfigChange(event)
 						}
+					} else if filepath.Clean(event.Name) == configFile &&
+						event.Op&fsnotify.Remove&fsnotify.Remove != 0 {
+						eventsWG.Done()
+						return
 					}
-				case err := <-watcher.Errors:
-					log.Println("error:", err)
+
+				case err, ok := <-watcher.Errors:
+					if ok { // 'Errors' channel is not closed
+						log.Printf("watcher error: %v\n", err)
+					}
+					eventsWG.Done()
+					return
 				}
 			}
 		}()
-
 		watcher.Add(configDir)
-		<-done
+		initWG.Done()   // done initalizing the watch in this go routine, so the parent routine can move on...
+		eventsWG.Wait() // now, wait for event loop to end in this go-routine...
 	}()
+	initWG.Wait() // make sure that the go routine above fully ended before returning
 }
 
 // SetConfigFile explicitly defines the path, name and extension of the config file.
@@ -330,6 +374,14 @@ func (v *Viper) mergeWithEnvPrefix(in string) string {
 	return strings.ToUpper(in)
 }
 
+// AllowEmptyEnv tells Viper to consider set,
+// but empty environment variables as valid values instead of falling back.
+// For backward compatibility reasons this is false by default.
+func AllowEmptyEnv(allowEmptyEnv bool) { v.AllowEmptyEnv(allowEmptyEnv) }
+func (v *Viper) AllowEmptyEnv(allowEmptyEnv bool) {
+	v.allowEmptyEnv = allowEmptyEnv
+}
+
 // TODO: should getEnv logic be moved into find(). Can generalize the use of
 // rewriting keys many things, Ex: Get('someKey') -> some_key
 // (camel case to snake case for JSON keys perhaps)
@@ -337,11 +389,14 @@ func (v *Viper) mergeWithEnvPrefix(in string) string {
 // getEnv is a wrapper around os.Getenv which replaces characters in the original
 // key. This allows env vars which have different keys than the config object
 // keys.
-func (v *Viper) getEnv(key string) string {
+func (v *Viper) getEnv(key string) (string, bool) {
 	if v.envKeyReplacer != nil {
 		key = v.envKeyReplacer.Replace(key)
 	}
-	return os.Getenv(key)
+
+	val, ok := os.LookupEnv(key)
+
+	return val, ok && (v.allowEmptyEnv || val != "")
 }
 
 // ConfigFileUsed returns the file used to populate the config registry.
@@ -568,10 +623,9 @@ func (v *Viper) isPathShadowedInFlatMap(path []string, mi interface{}) string {
 //       "foo.bar.baz" in a lower-priority map
 func (v *Viper) isPathShadowedInAutoEnv(path []string) string {
 	var parentKey string
-	var val string
 	for i := 1; i < len(path); i++ {
 		parentKey = strings.Join(path[0:i], v.keyDelim)
-		if val = v.getEnv(v.mergeWithEnvPrefix(parentKey)); val != "" {
+		if _, ok := v.getEnv(v.mergeWithEnvPrefix(parentKey)); ok {
 			return parentKey
 		}
 	}
@@ -631,8 +685,10 @@ func (v *Viper) Get(key string) interface{} {
 			return cast.ToBool(val)
 		case string:
 			return cast.ToString(val)
-		case int64, int32, int16, int8, int:
+		case int32, int16, int8, int:
 			return cast.ToInt(val)
+		case int64:
+			return cast.ToInt64(val)
 		case float64, float32:
 			return cast.ToFloat64(val)
 		case time.Time:
@@ -682,6 +738,12 @@ 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 +801,11 @@ 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 +818,11 @@ 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 +835,8 @@ 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 +845,10 @@ 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
@@ -934,7 +1004,7 @@ func (v *Viper) find(lcaseKey string) interface{} {
 	if v.automaticEnvApplied {
 		// even if it hasn't been registered, if automaticEnv is used,
 		// check any Get request
-		if val = v.getEnv(v.mergeWithEnvPrefix(lcaseKey)); val != "" {
+		if val, ok := v.getEnv(v.mergeWithEnvPrefix(lcaseKey)); ok {
 			return val
 		}
 		if nested && v.isPathShadowedInAutoEnv(path) != "" {
@@ -943,7 +1013,7 @@ func (v *Viper) find(lcaseKey string) interface{} {
 	}
 	envkey, exists := v.env[lcaseKey]
 	if exists {
-		if val = v.getEnv(envkey); val != "" {
+		if val, ok := v.getEnv(envkey); ok {
 			return val
 		}
 	}
@@ -1108,7 +1178,7 @@ func (v *Viper) SetDefault(key string, value interface{}) {
 	deepestMap[lastKey] = value
 }
 
-// Set sets the value for the key in the override regiser.
+// Set sets the value for the key in the override register.
 // Set is case-insensitive for a key.
 // Will be used instead of values obtained via
 // flags, config file, ENV, default, or key/value store.
@@ -1131,7 +1201,7 @@ 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 +1231,7 @@ 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
 	}
@@ -1189,13 +1259,21 @@ func (v *Viper) ReadConfig(in io.Reader) error {
 // MergeConfig merges a new configuration with an existing config.
 func MergeConfig(in io.Reader) error { return v.MergeConfig(in) }
 func (v *Viper) MergeConfig(in io.Reader) error {
-	if v.config == nil {
-		v.config = make(map[string]interface{})
-	}
 	cfg := make(map[string]interface{})
 	if err := v.unmarshalReader(in, cfg); err != nil {
 		return err
 	}
+	return v.MergeConfigMap(cfg)
+}
+
+// MergeConfigMap merges the configuration from the map given with an existing config.
+// Note that the map given may be modified.
+func MergeConfigMap(cfg map[string]interface{}) error { return v.MergeConfigMap(cfg) }
+func (v *Viper) MergeConfigMap(cfg map[string]interface{}) error {
+	if v.config == nil {
+		v.config = make(map[string]interface{})
+	}
+	insensitiviseMap(cfg)
 	mergeMaps(cfg, v.config, nil)
 	return nil
 }
@@ -1203,7 +1281,7 @@ 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 +1291,7 @@ 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 +1783,7 @@ func (v *Viper) getConfigType() string {
 		return v.configType
 	}
 
-	cf, err := v.GetConfigFile()
+	cf, err := v.getConfigFile()
 	if err != nil {
 		return ""
 	}
@@ -1719,7 +1797,7 @@ 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

@@ -7,22 +7,29 @@ package viper
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
+	"os/exec"
 	"path"
 	"reflect"
+	"runtime"
 	"sort"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
+	"github.com/fsnotify/fsnotify"
+	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/afero"
 	"github.com/spf13/cast"
 
 	"github.com/spf13/pflag"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 var yamlExample = []byte(`Hacker: true
@@ -244,7 +251,7 @@ 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)
 }
@@ -381,6 +388,36 @@ func TestEnv(t *testing.T) {
 
 }
 
+func TestEmptyEnv(t *testing.T) {
+	initJSON()
+
+	BindEnv("type") // Empty environment variable
+	BindEnv("name") // Bound, but not set environment variable
+
+	os.Clearenv()
+
+	os.Setenv("TYPE", "")
+
+	assert.Equal(t, "donut", Get("type"))
+	assert.Equal(t, "Cake", Get("name"))
+}
+
+func TestEmptyEnv_Allowed(t *testing.T) {
+	initJSON()
+
+	AllowEmptyEnv(true)
+
+	BindEnv("type") // Empty environment variable
+	BindEnv("name") // Bound, but not set environment variable
+
+	os.Clearenv()
+
+	os.Setenv("TYPE", "")
+
+	assert.Equal(t, "", Get("type"))
+	assert.Equal(t, "Cake", Get("name"))
+}
+
 func TestEnvPrefix(t *testing.T) {
 	initJSON()
 
@@ -503,6 +540,42 @@ 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)
@@ -540,24 +613,28 @@ func TestBindPFlags(t *testing.T) {
 }
 
 func TestBindPFlagsStringSlice(t *testing.T) {
-	for _, testValue := range []struct {
+	tests := []struct {
 		Expected []string
 		Value    string
 	}{
-		{[]string{}, ""},
+		{nil, ""},
 		{[]string{"jeden"}, "jeden"},
 		{[]string{"dwa", "trzy"}, "dwa,trzy"},
-		{[]string{"cztery", "piec , szesc"}, "cztery,\"piec , szesc\""}} {
+		{[]string{"cztery", "piec , szesc"}, "cztery,\"piec , szesc\""},
+	}
+
+	v := New() // create independent Viper object
+	defaultVal := []string{"default"}
+	v.SetDefault("stringslice", defaultVal)
+
+	for _, testValue := range tests {
+		flagSet := pflag.NewFlagSet("test", pflag.ContinueOnError)
+		flagSet.StringSlice("stringslice", testValue.Expected, "test")
 
 		for _, changed := range []bool{true, false} {
-			v := New() // create independent Viper object
-			flagSet := pflag.NewFlagSet("test", pflag.ContinueOnError)
-			flagSet.StringSlice("stringslice", testValue.Expected, "test")
-			flagSet.Visit(func(f *pflag.Flag) {
-				if len(testValue.Value) > 0 {
-					f.Value.Set(testValue.Value)
-					f.Changed = changed
-				}
+			flagSet.VisitAll(func(f *pflag.Flag) {
+				f.Value.Set(testValue.Value)
+				f.Changed = changed
 			})
 
 			err := v.BindPFlags(flagSet)
@@ -572,7 +649,11 @@ func TestBindPFlagsStringSlice(t *testing.T) {
 			if err := v.Unmarshal(val); err != nil {
 				t.Fatalf("%+#v cannot unmarshal: %s", testValue.Value, err)
 			}
-			assert.Equal(t, testValue.Expected, val.StringSlice)
+			if changed {
+				assert.Equal(t, testValue.Expected, val.StringSlice)
+			} else {
+				assert.Equal(t, defaultVal, val.StringSlice)
+			}
 		}
 	}
 }
@@ -1064,8 +1145,8 @@ func TestMergeConfig(t *testing.T) {
 		t.Fatalf("pop != 37890, = %d", pop)
 	}
 
-	if pop := v.GetInt("hello.lagrenum"); pop != 765432101234567 {
-		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) {
@@ -1088,8 +1169,8 @@ func TestMergeConfig(t *testing.T) {
 		t.Fatalf("pop != 45000, = %d", pop)
 	}
 
-	if pop := v.GetInt("hello.lagrenum"); pop != 7654321001234567 {
-		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) {
@@ -1149,6 +1230,48 @@ func TestMergeConfigNoMerge(t *testing.T) {
 	}
 }
 
+func TestMergeConfigMap(t *testing.T) {
+	v := New()
+	v.SetConfigType("yml")
+	if err := v.ReadConfig(bytes.NewBuffer(yamlMergeExampleTgt)); err != nil {
+		t.Fatal(err)
+	}
+
+	assert := func(i int) {
+		large := v.GetInt("hello.lagrenum")
+		pop := v.GetInt("hello.pop")
+		if large != 765432101234567 {
+			t.Fatal("Got large num:", large)
+		}
+
+		if pop != i {
+			t.Fatal("Got pop:", pop)
+		}
+	}
+
+	assert(37890)
+
+	update := map[string]interface{}{
+		"Hello": map[string]interface{}{
+			"Pop": 1234,
+		},
+		"World": map[interface{}]interface{}{
+			"Rock": 345,
+		},
+	}
+
+	if err := v.MergeConfigMap(update); err != nil {
+		t.Fatal(err)
+	}
+
+	if rock := v.GetInt("world.rock"); rock != 345 {
+		t.Fatal("Got rock:", rock)
+	}
+
+	assert(1234)
+
+}
+
 func TestUnmarshalingWithAliases(t *testing.T) {
 	v := New()
 	v.SetDefault("ID", 1)
@@ -1177,7 +1300,7 @@ 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")
 	}
@@ -1368,6 +1491,111 @@ func doTestCaseInsensitive(t *testing.T, typ, config string) {
 
 }
 
+func newViperWithConfigFile(t *testing.T) (*Viper, string, func()) {
+	watchDir, err := ioutil.TempDir("", "")
+	require.Nil(t, err)
+	configFile := path.Join(watchDir, "config.yaml")
+	err = ioutil.WriteFile(configFile, []byte("foo: bar\n"), 0640)
+	require.Nil(t, err)
+	cleanup := func() {
+		os.RemoveAll(watchDir)
+	}
+	v := New()
+	v.SetConfigFile(configFile)
+	err = v.ReadInConfig()
+	require.Nil(t, err)
+	require.Equal(t, "bar", v.Get("foo"))
+	return v, configFile, cleanup
+}
+
+func newViperWithSymlinkedConfigFile(t *testing.T) (*Viper, string, string, func()) {
+	watchDir, err := ioutil.TempDir("", "")
+	require.Nil(t, err)
+	dataDir1 := path.Join(watchDir, "data1")
+	err = os.Mkdir(dataDir1, 0777)
+	require.Nil(t, err)
+	realConfigFile := path.Join(dataDir1, "config.yaml")
+	t.Logf("Real config file location: %s\n", realConfigFile)
+	err = ioutil.WriteFile(realConfigFile, []byte("foo: bar\n"), 0640)
+	require.Nil(t, err)
+	cleanup := func() {
+		os.RemoveAll(watchDir)
+	}
+	// now, symlink the tm `data1` dir to `data` in the baseDir
+	os.Symlink(dataDir1, path.Join(watchDir, "data"))
+	// and link the `<watchdir>/datadir1/config.yaml` to `<watchdir>/config.yaml`
+	configFile := path.Join(watchDir, "config.yaml")
+	os.Symlink(path.Join(watchDir, "data", "config.yaml"), configFile)
+	t.Logf("Config file location: %s\n", path.Join(watchDir, "config.yaml"))
+	// init Viper
+	v := New()
+	v.SetConfigFile(configFile)
+	err = v.ReadInConfig()
+	require.Nil(t, err)
+	require.Equal(t, "bar", v.Get("foo"))
+	return v, watchDir, configFile, cleanup
+}
+
+func TestWatchFile(t *testing.T) {
+	if runtime.GOOS == "linux" {
+		// TODO(bep) FIX ME
+		t.Skip("Skip test on Linux ...")
+	}
+
+	t.Run("file content changed", func(t *testing.T) {
+		// given a `config.yaml` file being watched
+		v, configFile, cleanup := newViperWithConfigFile(t)
+		defer cleanup()
+		_, err := os.Stat(configFile)
+		require.NoError(t, err)
+		t.Logf("test config file: %s\n", configFile)
+		wg := sync.WaitGroup{}
+		wg.Add(1)
+		v.OnConfigChange(func(in fsnotify.Event) {
+			t.Logf("config file changed")
+			wg.Done()
+		})
+		v.WatchConfig()
+		// when overwriting the file and waiting for the custom change notification handler to be triggered
+		err = ioutil.WriteFile(configFile, []byte("foo: baz\n"), 0640)
+		wg.Wait()
+		// then the config value should have changed
+		require.Nil(t, err)
+		assert.Equal(t, "baz", v.Get("foo"))
+	})
+
+	t.Run("link to real file changed (à la Kubernetes)", func(t *testing.T) {
+		// skip if not executed on Linux
+		if runtime.GOOS != "linux" {
+			t.Skipf("Skipping test as symlink replacements don't work on non-linux environment...")
+		}
+		v, watchDir, _, _ := newViperWithSymlinkedConfigFile(t)
+		// defer cleanup()
+		wg := sync.WaitGroup{}
+		v.WatchConfig()
+		v.OnConfigChange(func(in fsnotify.Event) {
+			t.Logf("config file changed")
+			wg.Done()
+		})
+		wg.Add(1)
+		// when link to another `config.yaml` file
+		dataDir2 := path.Join(watchDir, "data2")
+		err := os.Mkdir(dataDir2, 0777)
+		require.Nil(t, err)
+		configFile2 := path.Join(dataDir2, "config.yaml")
+		err = ioutil.WriteFile(configFile2, []byte("foo: baz\n"), 0640)
+		require.Nil(t, err)
+		// change the symlink using the `ln -sfn` command
+		err = exec.Command("ln", "-sfn", dataDir2, path.Join(watchDir, "data")).Run()
+		require.Nil(t, err)
+		wg.Wait()
+		// then
+		require.Nil(t, err)
+		assert.Equal(t, "baz", v.Get("foo"))
+	})
+
+}
+
 func BenchmarkGetBool(b *testing.B) {
 	key := "BenchmarkGetBool"
 	v = New()