Add viper.SetKeysCaseSensitive() to disable automatic key lowercasing.

YAML, TOML, and JSON dictate keys to be case-sensitive. Viper's default
behaviour of lowercasing the keys for key insensitivity is incompatible
with these standards and has the side effect of making it difficult for
use cases such as case sensitive API credentials in configuration.
For eg: MyApiKey=MySecret (in TOML).

See #131, #260, #293, #371, #373

This commit adds a global function `viper.SetKeysCaseSensitive()` that
enables this behaviour to be turned off, after which, all keys, irrespective
of nesting, retain their cases. This respects all configuration operations
including getting, setting, and merging.

README.md

@@ -62,7 +62,8 @@ item below it:
  * key/value store
  * default
 
-Viper configuration keys are case insensitive.
+Viper configuration keys are case insensitive by default. They can be made case
+sensitive with `viper.SetKeyCaseSensitivity(true)`.
 
 ## Putting Values into Viper
 

viper.go

@@ -188,6 +188,7 @@ type Viper struct {
 	automaticEnvApplied bool
 	envKeyReplacer      *strings.Replacer
 	allowEmptyEnv       bool
+	caseSensitiveKeys   bool
 
 	config         map[string]interface{}
 	override       map[string]interface{}
@@ -489,7 +490,6 @@ func (v *Viper) providerPathExists(p *defaultRemoteProvider) bool {
 
 // searchMap recursively searches for a value for path in source map.
 // Returns nil if not found.
-// Note: This assumes that the path entries and map keys are lower cased.
 func (v *Viper) searchMap(source map[string]interface{}, path []string) interface{} {
 	if len(path) == 0 {
 		return source
@@ -536,7 +536,7 @@ func (v *Viper) searchMapWithPathPrefixes(source map[string]interface{}, path []
 
 	// search for path prefixes, starting from the longest one
 	for i := len(path); i > 0; i-- {
-		prefixKey := strings.ToLower(strings.Join(path[0:i], v.keyDelim))
+		prefixKey := v.caseKey(strings.Join(path[0:i], v.keyDelim))
 
 		next, ok := source[prefixKey]
 		if ok {
@@ -657,7 +657,7 @@ func GetViper() *Viper {
 }
 
 // Get can retrieve any value given the key to use.
-// Get is case-insensitive for a key.
+// Get's case-sensitivity for key is determined by viper.keyCaseSensitivity.
 // Get has the behavior of returning the value associated with the first
 // place from where it is set. Viper will check in the following order:
 // override, flag, env, config file, key/value store, default
@@ -665,8 +665,8 @@ func GetViper() *Viper {
 // Get returns an interface. For a specific value use one of the Get____ methods.
 func Get(key string) interface{} { return v.Get(key) }
 func (v *Viper) Get(key string) interface{} {
-	lcaseKey := strings.ToLower(key)
+	casedKey := v.caseKey(key)
-	val := v.find(lcaseKey)
+	val := v.find(casedKey)
 	if val == nil {
 		return nil
 	}
@@ -674,7 +674,7 @@ func (v *Viper) Get(key string) interface{} {
 	if v.typeByDefValue {
 		// TODO(bep) this branch isn't covered by a single test.
 		valType := val
-		path := strings.Split(lcaseKey, v.keyDelim)
+		path := strings.Split(casedKey, v.keyDelim)
 		defVal := v.searchMap(v.defaults, path)
 		if defVal != nil {
 			valType = defVal
@@ -704,7 +704,7 @@ func (v *Viper) Get(key string) interface{} {
 }
 
 // Sub returns new Viper instance representing a sub tree of this instance.
-// Sub is case-insensitive for a key.
+// Sub's case-sensitivity for key is determined by viper.keyCaseSensitivity.
 func Sub(key string) *Viper { return v.Sub(key) }
 func (v *Viper) Sub(key string) *Viper {
 	subv := New()
@@ -811,7 +811,9 @@ func (v *Viper) UnmarshalKey(key string, rawVal interface{}, opts ...DecoderConf
 		return err
 	}
 
-	v.insensitiviseMaps()
+	if !v.caseSensitiveKeys {
+		v.insensitiviseMaps()
+	}
 
 	return nil
 }
@@ -828,7 +830,9 @@ func (v *Viper) Unmarshal(rawVal interface{}, opts ...DecoderConfigOption) error
 		return err
 	}
 
-	v.insensitiviseMaps()
+	if !v.caseSensitiveKeys {
+		v.insensitiviseMaps()
+	}
 
 	return nil
 }
@@ -872,8 +876,9 @@ func (v *Viper) UnmarshalExact(rawVal interface{}) error {
 		return err
 	}
 
-	v.insensitiviseMaps()
+	if !v.caseSensitiveKeys {
-
+		v.insensitiviseMaps()
+	}
 	return nil
 }
 
@@ -918,7 +923,7 @@ func (v *Viper) BindFlagValue(key string, flag FlagValue) error {
 	if flag == nil {
 		return fmt.Errorf("flag for %q is nil", key)
 	}
-	v.pflags[strings.ToLower(key)] = flag
+	v.pflags[v.caseKey(key)] = flag
 	return nil
 }
 
@@ -933,7 +938,7 @@ func (v *Viper) BindEnv(input ...string) error {
 		return fmt.Errorf("BindEnv missing key to bind to")
 	}
 
-	key = strings.ToLower(input[0])
+	key = v.caseKey(input[0])
 
 	if len(input) == 1 {
 		envkey = v.mergeWithEnvPrefix(key)
@@ -950,13 +955,14 @@ func (v *Viper) BindEnv(input ...string) error {
 // Viper will check in the following order:
 // flag, env, config file, key/value store, default.
 // Viper will check to see if an alias exists first.
-// Note: this assumes a lower-cased key given.
+// Note: By default, this assumes that a lowercase key is given.
-func (v *Viper) find(lcaseKey string) interface{} {
+// This behavior can be modified with viper.SetKeysCaseSensitive.
+func (v *Viper) find(key string) interface{} {
 
 	var (
 		val    interface{}
 		exists bool
-		path   = strings.Split(lcaseKey, v.keyDelim)
+		path   = strings.Split(key, v.keyDelim)
 		nested = len(path) > 1
 	)
 
@@ -966,8 +972,8 @@ func (v *Viper) find(lcaseKey string) interface{} {
 	}
 
 	// if the requested key is an alias, then return the proper key
-	lcaseKey = v.realKey(lcaseKey)
+	key = v.realKey(key)
-	path = strings.Split(lcaseKey, v.keyDelim)
+	path = strings.Split(key, v.keyDelim)
 	nested = len(path) > 1
 
 	// Set() override first
@@ -980,7 +986,7 @@ func (v *Viper) find(lcaseKey string) interface{} {
 	}
 
 	// PFlag override next
-	flag, exists := v.pflags[lcaseKey]
+	flag, exists := v.pflags[key]
 	if exists && flag.HasChanged() {
 		switch flag.ValueType() {
 		case "int", "int8", "int16", "int32", "int64":
@@ -1004,14 +1010,14 @@ 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, ok := v.getEnv(v.mergeWithEnvPrefix(lcaseKey)); ok {
+		if val, ok := v.getEnv(v.mergeWithEnvPrefix(key)); ok {
 			return val
 		}
 		if nested && v.isPathShadowedInAutoEnv(path) != "" {
 			return nil
 		}
 	}
-	envkey, exists := v.env[lcaseKey]
+	envkey, exists := v.env[key]
 	if exists {
 		if val, ok := v.getEnv(envkey); ok {
 			return val
@@ -1050,7 +1056,7 @@ func (v *Viper) find(lcaseKey string) interface{} {
 
 	// last chance: if no other value is returned and a flag does exist for the value,
 	// get the flag's value even if the flag's value has not changed
-	if flag, exists := v.pflags[lcaseKey]; exists {
+	if flag, exists := v.pflags[key]; exists {
 		switch flag.ValueType() {
 		case "int", "int8", "int16", "int32", "int64":
 			return cast.ToInt(flag.ValueString())
@@ -1080,11 +1086,12 @@ func readAsCSV(val string) ([]string, error) {
 }
 
 // IsSet checks to see if the key has been set in any of the data locations.
-// IsSet is case-insensitive for a key.
+// IsSet is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 func IsSet(key string) bool { return v.IsSet(key) }
 func (v *Viper) IsSet(key string) bool {
-	lcaseKey := strings.ToLower(key)
+	casedKey := v.caseKey(key)
-	val := v.find(lcaseKey)
+	val := v.find(casedKey)
 	return val != nil
 }
 
@@ -1107,11 +1114,11 @@ func (v *Viper) SetEnvKeyReplacer(r *strings.Replacer) {
 // This enables one to change a name without breaking the application
 func RegisterAlias(alias string, key string) { v.RegisterAlias(alias, key) }
 func (v *Viper) RegisterAlias(alias string, key string) {
-	v.registerAlias(alias, strings.ToLower(key))
+	v.registerAlias(alias, v.caseKey(key))
 }
 
 func (v *Viper) registerAlias(alias string, key string) {
-	alias = strings.ToLower(alias)
+	alias = v.caseKey(alias)
 	if alias != key && alias != v.realKey(key) {
 		_, exists := v.aliases[alias]
 
@@ -1162,16 +1169,19 @@ func (v *Viper) InConfig(key string) bool {
 }
 
 // SetDefault sets the default value for this key.
-// SetDefault is case-insensitive for a key.
+// SetDefault is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 // Default only used when no value is provided by the user via flag, config or ENV.
 func SetDefault(key string, value interface{}) { v.SetDefault(key, value) }
 func (v *Viper) SetDefault(key string, value interface{}) {
 	// If alias passed in, then set the proper default
-	key = v.realKey(strings.ToLower(key))
+	key = v.realKey(v.caseKey(key))
-	value = toCaseInsensitiveValue(value)
+	if !v.caseSensitiveKeys {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.caseKey(path[len(path)-1])
 	deepestMap := deepSearch(v.defaults, path[0:len(path)-1])
 
 	// set innermost value
@@ -1179,17 +1189,20 @@ func (v *Viper) SetDefault(key string, value interface{}) {
 }
 
 // Set sets the value for the key in the override register.
-// Set is case-insensitive for a key.
+// Set is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 // Will be used instead of values obtained via
 // flags, config file, ENV, default, or key/value store.
 func Set(key string, value interface{}) { v.Set(key, value) }
 func (v *Viper) Set(key string, value interface{}) {
 	// If alias passed in, then set the proper override
-	key = v.realKey(strings.ToLower(key))
+	key = v.realKey(v.caseKey(key))
-	value = toCaseInsensitiveValue(value)
+	if !v.caseSensitiveKeys {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.caseKey(path[len(path)-1])
 	deepestMap := deepSearch(v.override, path[0:len(path)-1])
 
 	// set innermost value
@@ -1273,7 +1286,9 @@ func (v *Viper) MergeConfigMap(cfg map[string]interface{}) error {
 	if v.config == nil {
 		v.config = make(map[string]interface{})
 	}
-	insensitiviseMap(cfg)
+	if !v.caseSensitiveKeys {
+		insensitiviseMap(cfg)
+	}
 	mergeMaps(cfg, v.config, nil)
 	return nil
 }
@@ -1390,14 +1405,16 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 			value, _ := v.properties.Get(key)
 			// recursively build nested maps
 			path := strings.Split(key, ".")
-			lastKey := strings.ToLower(path[len(path)-1])
+			lastKey := v.caseKey(path[len(path)-1])
 			deepestMap := deepSearch(c, path[0:len(path)-1])
 			// set innermost value
 			deepestMap[lastKey] = value
 		}
 	}
 
-	insensitiviseMap(c)
+	if !v.caseSensitiveKeys {
+		insensitiviseMap(c)
+	}
 	return nil
 }
 
@@ -1468,10 +1485,9 @@ func (v *Viper) marshalWriter(f afero.File, configType string) error {
 }
 
 func keyExists(k string, m map[string]interface{}) string {
-	lk := strings.ToLower(k)
+	ck := v.caseKey(k)
 	for mk := range m {
-		lmk := strings.ToLower(mk)
+		if mk == ck {
-		if lmk == lk {
 			return mk
 		}
 	}
@@ -1701,7 +1717,7 @@ func (v *Viper) flattenAndMergeMap(shadow map[string]bool, m map[string]interfac
 			m2 = cast.ToStringMap(val)
 		default:
 			// immediate value
-			shadow[strings.ToLower(fullKey)] = true
+			shadow[v.caseKey(fullKey)] = true
 			continue
 		}
 		// recursively merge to shadow map
@@ -1727,7 +1743,7 @@ outer:
 			}
 		}
 		// add key
-		shadow[strings.ToLower(k)] = true
+		shadow[v.caseKey(k)] = true
 	}
 	return shadow
 }
@@ -1745,7 +1761,7 @@ func (v *Viper) AllSettings() map[string]interface{} {
 			continue
 		}
 		path := strings.Split(k, v.keyDelim)
-		lastKey := strings.ToLower(path[len(path)-1])
+		lastKey := v.caseKey(path[len(path)-1])
 		deepestMap := deepSearch(m, path[0:len(path)-1])
 		// set innermost value
 		deepestMap[lastKey] = value
@@ -1778,6 +1794,22 @@ func (v *Viper) SetConfigType(in string) {
 	}
 }
 
+// SetKeysCaseSensitive disables the default behaviour of
+// case-insensitivising (lowercasing) keys and preserves the key casing
+// as they are found in the config files. It is important
+// to note that operations such as set and merge when
+// case sensitivity is 'on', and whtn it is turneed 'off',
+// are incompatible. A key that is set when case sentivity
+// is 'on' may not be retrievable when case sensitivity is turned 'off',
+// as the original casing is permanently lost in the former mode.
+// That is ideally, this should only be invoked only once,
+// during initialisation, and the subsequent usage must adhere
+// to the same case sentivity.
+func SetKeysCaseSensitive(on bool) { v.SetKeysCaseSensitive(on) }
+func (v *Viper) SetKeysCaseSensitive(on bool) {
+	v.caseSensitiveKeys = on
+}
+
 func (v *Viper) getConfigType() string {
 	if v.configType != "" {
 		return v.configType
@@ -1821,6 +1853,15 @@ func (v *Viper) searchInPath(in string) (filename string) {
 	return ""
 }
 
+// caseKey cases (preserves sensitivity or lowercases) a
+// given key based on the keyCaseSensitivity config.
+func (v *Viper) caseKey(in string) (filename string) {
+	if v.caseSensitiveKeys {
+		return in
+	}
+	return strings.ToLower(in)
+}
+
 // Search all configPaths for any config file.
 // Returns the first path that exists (and is a config file).
 func (v *Viper) findConfigFile() (string, error) {

viper_test.go

@@ -1389,6 +1389,51 @@ R = 6
 	}
 }
 
+func TestCaseSensitive(t *testing.T) {
+	for _, config := range []struct {
+		typ     string
+		content string
+	}{
+		{"yaml", `
+aBcD: 1
+eF:
+  gH: 2
+  iJk: 3
+  Lm:
+    nO: 4
+    P:
+      Q: 5
+      R: 6
+`},
+		{"json", `{
+  "aBcD": 1,
+  "eF": {
+    "iJk": 3,
+    "Lm": {
+      "P": {
+        "Q": 5,
+        "R": 6
+      },
+      "nO": 4
+    },
+    "gH": 2
+  }
+}`},
+		{"toml", `aBcD = 1
+[eF]
+gH = 2
+iJk = 3
+[eF.Lm]
+nO = 4
+[eF.Lm.P]
+Q = 5
+R = 6
+`},
+	} {
+		doTestCaseSensitive(t, config.typ, config.content)
+	}
+}
+
 func TestCaseInsensitiveSet(t *testing.T) {
 	Reset()
 	m1 := map[string]interface{}{
@@ -1488,6 +1533,32 @@ func doTestCaseInsensitive(t *testing.T, typ, config string) {
 	assert.Equal(t, 3, cast.ToInt(Get("ef.ijk")))
 	assert.Equal(t, 4, cast.ToInt(Get("ef.lm.no")))
 	assert.Equal(t, 5, cast.ToInt(Get("ef.lm.p.q")))
+}
+
+func doTestCaseSensitive(t *testing.T, typ, config string) {
+	Reset()
+	SetConfigType(typ)
+
+	// Turn on case sensitivy.
+	SetKeysCaseSensitive(true)
+	r := strings.NewReader(config)
+	if err := unmarshalReader(r, v.config); err != nil {
+		panic(err)
+	}
+
+	Set("RfD", true)
+	assert.Equal(t, nil, Get("rfd"))
+	assert.Equal(t, true, Get("RfD"))
+	assert.Equal(t, 0, cast.ToInt(Get("abcd")))
+	assert.Equal(t, 1, cast.ToInt(Get("aBcD")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.gh")))
+	assert.Equal(t, 2, cast.ToInt(Get("eF.gH")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.ijk")))
+	assert.Equal(t, 3, cast.ToInt(Get("eF.iJk")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.lm.no")))
+	assert.Equal(t, 4, cast.ToInt(Get("eF.Lm.nO")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.lm.p.q")))
+	assert.Equal(t, 5, cast.ToInt(Get("eF.Lm.P.Q")))
 
 }