Use ristretto to improve find performance

This patch significantly improves `v.find` performance by using
ristretto cache.

Ristretto was chosen because it is a very performant, thread-safe
cache that does not suffer form congestion or long GC pauses.

```
% go test -bench=. .
goos: darwin
goarch: amd64
pkg: github.com/spf13/viper
BenchmarkGetBool-8               5431267               211 ns/op
BenchmarkFind/cache=false-8       289495              4060 ns/op
BenchmarkFind/cache=true-8       6980976               171 ns/op
BenchmarkGet-8                   6332091               193 ns/op
BenchmarkGetBoolFromMap-8       235071828                5.09 ns/op
PASS
```

go.mod

@@ -7,10 +7,12 @@ require (
 	github.com/coreos/bbolt v1.3.2 // indirect
 	github.com/coreos/go-systemd v0.0.0-20190321100706-95778dfbb74e // indirect
 	github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f // indirect
+	github.com/dgraph-io/ristretto v0.0.3
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
 	github.com/fsnotify/fsnotify v1.4.7
 	github.com/gogo/protobuf v1.2.1 // indirect
-	github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef // indirect
+	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
+	github.com/golang/protobuf v1.3.3 // indirect
 	github.com/gorilla/websocket v1.4.2 // indirect
 	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0 // indirect
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
@@ -27,7 +29,7 @@ require (
 	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 v1.3.0
+	github.com/stretchr/testify v1.4.0
 	github.com/subosito/gotenv v1.2.0
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 // indirect
 	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect

go.sum

@@ -20,6 +20,7 @@ dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7
 github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/OneOfOne/xxhash v1.2.2 h1:KMrpdQIwFcEqXDklaen+P1axHaj9BSKzvpUUfnHldSE=
 github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAElWljhcU=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
@@ -33,6 +34,7 @@ github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+Ce
 github.com/bgentry/speakeasy v0.1.0/go.mod h1:+zsyZBPWlz7T6j88CTgSN5bM796AkVf0kBD4zp0CCIs=
 github.com/bketelsen/crypt v0.0.3-0.20200106085610-5cbc8cc4026c h1:+0HFd5KSZ/mm3JmhmrDukiId5iR6w4+BdFtfSy4yWIc=
 github.com/bketelsen/crypt v0.0.3-0.20200106085610-5cbc8cc4026c/go.mod h1:MKsuJmJgSg28kpZDP6UIiPt0e0Oz0kqKNGyRaWEPv84=
+github.com/cespare/xxhash v1.1.0 h1:a6HrQnmkObjyL+Gs60czilIUGqrzKutQD6XZog3p+ko=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/coreos/bbolt v1.3.2 h1:wZwiHHUieZCquLkDL0B8UhzreNWsPHooDAG3q34zk0s=
@@ -48,8 +50,12 @@ github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f/go.mod h1:E3G3o1h8I7cfc
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 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/dgraph-io/ristretto v0.0.3 h1:jh22xisGBjrEVnRZ1DVTpBVQm0Xndu8sMl0CWDzSIBI=
+github.com/dgraph-io/ristretto v0.0.3/go.mod h1:KPxhHT9ZxKefz+PCeOGsrHpl1qZ7i70dGTu2u+Ahh6E=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
+github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2 h1:tdlZCpZ/P9DhczCTSixgIKmwPv6+wP5DGjqLYw5SUiA=
+github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2/go.mod h1:SqUrOPUnsFjfmXRMNPybcSiG0BgUW2AuFH8PAnS2iTw=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
 github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
 github.com/fsnotify/fsnotify v1.4.7 h1:IXs+QLmnXW2CcXuY+8Mzv/fWEsPGWxqefPtCP5CnV9I=
@@ -66,16 +72,16 @@ github.com/gogo/protobuf v1.2.1 h1:/s5zKNz0uPFCZ5hddgPdo2TK2TVrUNMn0OOX8/aZMTE=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
-github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef h1:veQD95Isof8w9/WXiA+pa3tz3fJXkt5B7QaRBrM62gk=
+github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e h1:1r7pUrabqp18hOBcwBwiTsbnFeTZHV9eER/QT5JVZxY=
-github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
+github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/mock v1.2.0/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/mock v1.3.1/go.mod h1:sBzyDLLjw3U8JLTeZvSv8jJB+tU5PVekmnlKIyFUx0Y=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg=
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/golang/protobuf v1.3.2 h1:6nsPYzhq5kReh6QImI3k5qWzO4PEbvbIW2cwSfR/6xs=
 github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.3.3 h1:gyjaxf+svBWX08ZjK86iN9geUJF0H6gp2IRKX6Nf6/I=
+github.com/golang/protobuf v1.3.3/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/btree v1.0.0 h1:0udJVsspx3VBr5FwtLhQQtuAsVc79tTq0ocGIPAU6qo=
 github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
@@ -181,7 +187,6 @@ github.com/pascaldekloe/goe v0.0.0-20180627143212-57f6aae5913c h1:Lgl0gzECD8GnQ5
 github.com/pascaldekloe/goe v0.0.0-20180627143212-57f6aae5913c/go.mod h1:lzWF7FIEvWOWxwDKqyGYQf6ZUaNfKdP144TG7ZOy1lc=
 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/pkg/errors v0.8.0 h1:WdK/asTD0HN+q6hsWO3/vpuAkAr+tw6aNJNDFFf0+qw=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
@@ -214,6 +219,7 @@ github.com/smartystreets/goconvey v1.6.4 h1:fv0U8FUIMPNf1L9lnHLvLhgicrIVChEkdzIK
 github.com/smartystreets/goconvey v1.6.4/go.mod h1:syvi0/a8iFYH4r/RixwvyeAJjdLS9QV7WQ/tjFTllLA=
 github.com/soheilhy/cmux v0.1.4 h1:0HKaf1o97UwFjHH9o5XsHUOF+tqmdA7KEzXLpiyaw0E=
 github.com/soheilhy/cmux v0.1.4/go.mod h1:IM3LyeVVIOuxMH7sFAkER9+bJ4dT7Ms6E4xg4kGIyLM=
+github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72 h1:qLC7fQah7D6K1B0ujays3HV9gkFtllcxhzImRR7ArPQ=
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
 github.com/spf13/afero v1.1.2 h1:m8/z1t7/fwjysjQRYbP0RD+bUIF/8tJwPdEZsI83ACI=
 github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
@@ -225,10 +231,10 @@ github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-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 v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/subosito/gotenv v1.2.0 h1:Slr1R9HxAlEKefgq5jn9U+DnETlIUa6HfgEzj0g5d7s=
 github.com/subosito/gotenv v1.2.0/go.mod h1:N0PQaV/YGNqwC0u51sEeR/aUtSLEXKX9iv69rRypqCw=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 h1:LnC5Kc/wtumK+WB441p7ynQJzVuNRJiqddSIE3IlSEQ=
@@ -248,7 +254,6 @@ go.uber.org/zap v1.10.0 h1:ORx85nbTijNz8ljznvCMR1ZBIPKFn3jQrag10X2AsuM=
 go.uber.org/zap v1.10.0/go.mod h1:vwi/ZaCAaUcBkycHslxD9B2zi4UTXhF60s6SWpuDF0Q=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20181029021203-45a5f77698d3/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2 h1:VklqNMn3ovrHsnt90PveolxSbWFaJdECFbxSq0Mqo2M=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20190605123033-f99c8df09eb5 h1:58fnuSXlxZmFdJyvtTFVmVhcMLU6v5fEb/ok4wyqtNU=
@@ -304,7 +309,6 @@ golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20181026203630-95b1ffbd15a5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -313,7 +317,6 @@ golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20190606165138-5da285871e9c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0 h1:HyfiK1WMnHj5FXFXatD+Qs1A/xC2Run6RzeW1SyHxpc=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
@@ -328,7 +331,6 @@ golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312151545-0bb0c0a6e846/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312170243-e65039ee4138/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
-golang.org/x/tools v0.0.0-20190328211700-ab21143f2384 h1:TFlARGu6Czu1z7q93HTxcP1P+/ZFC/IKythI5RzrnRg=
 golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190425150028-36563e24a262/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 golang.org/x/tools v0.0.0-20190506145303-2d16b83fe98c/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
@@ -352,7 +354,6 @@ google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7
 google.golang.org/appengine v1.5.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
 google.golang.org/appengine v1.6.1 h1:QzqyMA1tlu6CgqCDUtU9V+ZKhLFT2dkJuANu5QaxI3I=
 google.golang.org/appengine v1.6.1/go.mod h1:i06prIuMbXzDqacNJfV5OdTW448YApPu5ww/cMBSeb0=
-google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8 h1:Nw54tB0rB7hY/N0NQvRW8DG4Yk3Q6T9cu9RcFQDu1tc=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
 google.golang.org/genproto v0.0.0-20190307195333-5fe7a883aa19/go.mod h1:VzzqZJRnGkLBvHegQrXjBqPurQTc5/KpmUdxsrq26oE=
 google.golang.org/genproto v0.0.0-20190418145605-e7d98fc518a7/go.mod h1:VzzqZJRnGkLBvHegQrXjBqPurQTc5/KpmUdxsrq26oE=
@@ -368,7 +369,6 @@ google.golang.org/grpc v1.20.1/go.mod h1:10oTOabMzJvdu6/UiuZezV6QK5dSlG84ov/aaiq
 google.golang.org/grpc v1.21.1 h1:j6XxA85m/6txkUCHvzlV5f+HBNl/1r5cZ2A/3IEFOO8=
 google.golang.org/grpc v1.21.1/go.mod h1:oYelfM1adQP15Ek0mdvEgi9Df8B9CZIaU1084ijfRaM=
 gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLkstjWtayDeSgw=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
@@ -378,6 +378,7 @@ gopkg.in/ini.v1 v1.51.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/resty.v1 v1.12.0/go.mod h1:mDo4pnntr5jdWRML875a/NmxYqAlA73dVijT2AXvQQo=
 gopkg.in/yaml.v2 v2.0.0-20170812160011-eb3733d160e7/go.mod h1:JAlM8MvJe8wmxCU4Bli9HhUf9+ttbYbLASfIpnQbh74=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.4 h1:/eiJrUcujPVeJ3xlSWaiNi3uSVmDGBK1pDHUHAnao1I=
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

stub/benchmark.json

@@ -0,0 +1,248 @@
+{
+    "log": {
+        "level": "debug",
+        "format": "json"
+    },
+    "profiling": "cpu",
+    "serve": {
+        "proxy": {
+            "port": 1234,
+            "host": "127.0.0.1",
+            "timeout": {
+                "read": "1s",
+                "write": "2s",
+                "idle": "3s"
+            },
+            "cors": {
+                "enabled": true,
+                "allowed_origins": [
+                    "https://example.com",
+                    "https://*.example.com"
+                ],
+                "allowed_methods": [
+                    "POST",
+                    "GET",
+                    "PUT",
+                    "PATCH",
+                    "DELETE"
+                ],
+                "allowed_headers": [
+                    "Authorization",
+                    "Content-Type"
+                ],
+                "exposed_headers": [
+                    "Content-Type"
+                ],
+                "allow_credentials": true,
+                "max_age": 10,
+                "debug": true
+            },
+            "tls": {
+                "key": {
+                    "path": "/path/to/key.pem",
+                    "base64": "LS0tLS1CRUdJTiBFTkNSWVBURUQgUFJJVkFURSBLRVktLS0tLVxuTUlJRkRqQkFCZ2txaGtpRzl3MEJCUTB3..."
+                },
+                "cert": {
+                    "path": "/path/to/cert.pem",
+                    "base64": "LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0tXG5NSUlEWlRDQ0FrMmdBd0lCQWdJRVY1eE90REFOQmdr..."
+                }
+            }
+        },
+        "api": {
+            "port": 1235,
+            "host": "127.0.0.2",
+            "cors": {
+                "enabled": true,
+                "allowed_origins": [
+                    "https://example.org",
+                    "https://*.example.org"
+                ],
+                "allowed_methods": [
+                    "GET",
+                    "PUT",
+                    "PATCH",
+                    "DELETE"
+                ],
+                "allowed_headers": [
+                    "Authorization",
+                    "Content-Type"
+                ],
+                "exposed_headers": [
+                    "Content-Type"
+                ],
+                "allow_credentials": true,
+                "max_age": 10,
+                "debug": true
+            },
+            "tls": {
+                "key": {
+                    "path": "/path/to/key.pem",
+                    "base64": "LS0tLS1CRUdJTiBFTkNSWVBURUQgUFJJVkFURSBLRVktLS0tLVxuTUlJRkRqQkFCZ2txaGtpRzl3MEJCUTB3..."
+                },
+                "cert": {
+                    "path": "/path/to/cert.pem",
+                    "base64": "LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0tXG5NSUlEWlRDQ0FrMmdBd0lCQWdJRVY1eE90REFOQmdr..."
+                }
+            }
+        }
+    },
+    "access_rules": {
+        "repositories": [
+            "file://path/to/rules.json",
+            "inline://W3siaWQiOiJmb28tcnVsZSIsImF1dGhlbnRpY2F0b3JzIjpbXX1d",
+            "https://path-to-my-rules/rules.json"
+        ],
+        "matching_strategy": "glob"
+    },
+    "errors": {
+        "fallback": [
+            "json"
+        ],
+        "handlers": {
+            "redirect": {
+                "enabled": true,
+                "config": {
+                    "to": "http://path-to/redirect"
+                }
+            },
+            "json": {
+                "enabled": true,
+                "config": {
+                    "verbose": true,
+                    "when": [
+                        {
+                            "error": [
+                                "unauthorized",
+                                "forbidden",
+                                "internal_server_error"
+                            ],
+                            "request": {
+                                "header": {
+                                    "content_type": [
+                                        "application/json"
+                                    ],
+                                    "accept": [
+                                        "application/json"
+                                    ]
+                                },
+                                "cidr": [
+                                    "127.0.0.0/24"
+                                ]
+                            }
+                        }
+                    ]
+                }
+            }
+        }
+    },
+    "authenticators": {
+        "anonymous": {
+            "enabled": true,
+            "config": {
+                "subject": "guest"
+            }
+        },
+        "cookie_session": {
+            "enabled": true,
+            "config": {
+                "check_session_url": "https://session-store-host",
+                "only": [
+                    "sessionid"
+                ]
+            }
+        },
+        "jwt": {
+            "enabled": true,
+            "config": {
+                "jwks_urls": [
+                    "https://my-website.com/.well-known/jwks.json",
+                    "https://my-other-website.com/.well-known/jwks.json",
+                    "file://path/to/local/jwks.json"
+                ],
+                "scope_strategy": "wildcard"
+            }
+        },
+        "noop": {
+            "enabled": true
+        },
+        "oauth2_client_credentials": {
+            "enabled": true,
+            "config": {
+                "token_url": "https://my-website.com/oauth2/token"
+            }
+        },
+        "oauth2_introspection": {
+            "enabled": true,
+            "config": {
+                "introspection_url": "https://my-website.com/oauth2/introspection",
+                "scope_strategy": "exact",
+                "pre_authorization": {
+                    "enabled": true,
+                    "client_id": "some_id",
+                    "client_secret": "some_secret",
+                    "scope": [
+                        "foo",
+                        "bar"
+                    ],
+                    "token_url": "https://my-website.com/oauth2/token"
+                }
+            }
+        },
+        "unauthorized": {
+            "enabled": true
+        }
+    },
+    "authorizers": {
+        "allow": {
+            "enabled": true
+        },
+        "deny": {
+            "enabled": true
+        },
+        "keto_engine_acp_ory": {
+            "enabled": true,
+            "config": {
+                "base_url": "http://my-keto/",
+                "required_action": "unknown",
+                "required_resource": "unknown"
+            }
+        }
+    },
+    "mutators": {
+        "header": {
+            "enabled": false,
+            "config": {
+                "headers": {
+                    "foo": "bar"
+                }
+            }
+        },
+        "cookie": {
+            "enabled": true,
+            "config": {
+                "cookies": {
+                    "foo": "bar"
+                }
+            }
+        },
+        "hydrator": {
+            "enabled": true,
+            "config": {
+                "api": {
+                    "url": "https://some-url/"
+                }
+            }
+        },
+        "id_token": {
+            "enabled": true,
+            "config": {
+                "issuer_url": "https://my-oathkeeper/",
+                "jwks_url": "https://fetch-keys/from/this/location.json",
+                "ttl": "1h"
+            }
+        },
+        "noop": {
+            "enabled": true
+        }
+    }
+}

viper.go

@@ -34,6 +34,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/dgraph-io/ristretto"
 	"github.com/fsnotify/fsnotify"
 	"github.com/hashicorp/hcl"
 	"github.com/hashicorp/hcl/hcl/printer"
@@ -214,6 +215,8 @@ type Viper struct {
 	properties *properties.Properties
 
 	onConfigChange func(fsnotify.Event)
+
+	cache *ristretto.Cache
 }
 
 // New returns an initialized Viper instance.
@@ -231,7 +234,6 @@ func New() *Viper {
 	v.env = make(map[string]string)
 	v.aliases = make(map[string]string)
 	v.typeByDefValue = false
-
 	return v
 }
 
@@ -270,6 +272,15 @@ func EnvKeyReplacer(r StringReplacer) Option {
 	})
 }
 
+// Cache sets Viper's cache (*ristretto.Cache).
+// Using a cache may cause updates to external sources after the value is cached to be ignored,
+// e.g. updating a flag value after the key was initially retrieve does not update the cached value.
+func Cache(c *ristretto.Cache) Option {
+	return optionFunc(func(v *Viper) {
+		v.cache = c
+	})
+}
+
 // NewWithOptions creates a new Viper instance.
 func NewWithOptions(opts ...Option) *Viper {
 	v := New()
@@ -422,6 +433,7 @@ func (v *Viper) SetConfigFile(in string) {
 func SetEnvPrefix(in string) { v.SetEnvPrefix(in) }
 
 func (v *Viper) SetEnvPrefix(in string) {
+	v.cache.Clear()
 	if in != "" {
 		v.envPrefix = in
 	}
@@ -441,6 +453,7 @@ func (v *Viper) mergeWithEnvPrefix(in string) string {
 func AllowEmptyEnv(allowEmptyEnv bool) { v.AllowEmptyEnv(allowEmptyEnv) }
 
 func (v *Viper) AllowEmptyEnv(allowEmptyEnv bool) {
+	v.cache.Clear()
 	v.allowEmptyEnv = allowEmptyEnv
 }
 
@@ -470,6 +483,7 @@ func (v *Viper) ConfigFileUsed() string { return v.configFile }
 func AddConfigPath(in string) { v.AddConfigPath(in) }
 
 func (v *Viper) AddConfigPath(in string) {
+	v.cache.Clear()
 	if in != "" {
 		absin := absPathify(in)
 		jww.INFO.Println("adding", absin, "to paths to search")
@@ -492,6 +506,7 @@ func AddRemoteProvider(provider, endpoint, path string) error {
 }
 
 func (v *Viper) AddRemoteProvider(provider, endpoint, path string) error {
+	v.cache.Clear()
 	if !stringInSlice(provider, SupportedRemoteProviders) {
 		return UnsupportedRemoteProviderError(provider)
 	}
@@ -524,6 +539,7 @@ func AddSecureRemoteProvider(provider, endpoint, path, secretkeyring string) err
 }
 
 func (v *Viper) AddSecureRemoteProvider(provider, endpoint, path, secretkeyring string) error {
+	v.cache.Clear()
 	if !stringInSlice(provider, SupportedRemoteProviders) {
 		return UnsupportedRemoteProviderError(provider)
 	}
@@ -713,6 +729,7 @@ func (v *Viper) isPathShadowedInAutoEnv(path []string) string {
 func SetTypeByDefaultValue(enable bool) { v.SetTypeByDefaultValue(enable) }
 
 func (v *Viper) SetTypeByDefaultValue(enable bool) {
+	v.cache.Clear()
 	v.typeByDefValue = enable
 }
 
@@ -732,7 +749,8 @@ func Get(key string) interface{} { return v.Get(key) }
 
 func (v *Viper) Get(key string) interface{} {
 	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey, true)
+
+	val := v.cachedFind(lcaseKey, true)
 	if val == nil {
 		return nil
 	}
@@ -748,7 +766,7 @@ func (v *Viper) Get(key string) interface{} {
 
 		switch valType.(type) {
 		case bool:
-			return cast.ToBool(val)
+			val = cast.ToBool(val)
 		case string:
 			return cast.ToString(val)
 		case int32, int16, int8, int:
@@ -980,6 +998,7 @@ func (v *Viper) UnmarshalExact(rawVal interface{}, opts ...DecoderConfigOption)
 func BindPFlags(flags *pflag.FlagSet) error { return v.BindPFlags(flags) }
 
 func (v *Viper) BindPFlags(flags *pflag.FlagSet) error {
+	v.cache.Clear()
 	return v.BindFlagValues(pflagValueSet{flags})
 }
 
@@ -992,6 +1011,7 @@ func (v *Viper) BindPFlags(flags *pflag.FlagSet) error {
 func BindPFlag(key string, flag *pflag.Flag) error { return v.BindPFlag(key, flag) }
 
 func (v *Viper) BindPFlag(key string, flag *pflag.Flag) error {
+	v.cache.Clear()
 	return v.BindFlagValue(key, pflagValue{flag})
 }
 
@@ -1000,6 +1020,7 @@ func (v *Viper) BindPFlag(key string, flag *pflag.Flag) error {
 func BindFlagValues(flags FlagValueSet) error { return v.BindFlagValues(flags) }
 
 func (v *Viper) BindFlagValues(flags FlagValueSet) (err error) {
+	v.cache.Clear()
 	flags.VisitAll(func(flag FlagValue) {
 		if err = v.BindFlagValue(flag.Name(), flag); err != nil {
 			return
@@ -1012,6 +1033,7 @@ func (v *Viper) BindFlagValues(flags FlagValueSet) (err error) {
 func BindFlagValue(key string, flag FlagValue) error { return v.BindFlagValue(key, flag) }
 
 func (v *Viper) BindFlagValue(key string, flag FlagValue) error {
+	v.cache.Clear()
 	if flag == nil {
 		return fmt.Errorf("flag for %q is nil", key)
 	}
@@ -1026,6 +1048,7 @@ func (v *Viper) BindFlagValue(key string, flag FlagValue) error {
 func BindEnv(input ...string) error { return v.BindEnv(input...) }
 
 func (v *Viper) BindEnv(input ...string) error {
+	v.cache.Clear()
 	var key, envkey string
 	if len(input) == 0 {
 		return fmt.Errorf("missing key to bind to")
@@ -1044,6 +1067,19 @@ func (v *Viper) BindEnv(input ...string) error {
 	return nil
 }
 
+// cachedFind uses Viper's cache to find a key's value and `v.find` if it is not available
+// in the cache.
+func (v *Viper) cachedFind(lcaseKey string, flagDefault bool) interface{} {
+	realKey := v.realKey(lcaseKey)
+	if value, found := v.cache.Get(realKey); found {
+		return value
+	}
+
+	value := v.find(lcaseKey, flagDefault)
+	v.cache.Set(realKey, value, 0)
+	return value
+}
+
 // Given a key, find the value.
 //
 // Viper will check to see if an alias exists first.
@@ -1226,7 +1262,7 @@ func IsSet(key string) bool { return v.IsSet(key) }
 
 func (v *Viper) IsSet(key string) bool {
 	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey, false)
+	val := v.cachedFind(lcaseKey, false)
 	return val != nil
 }
 
@@ -1235,6 +1271,7 @@ func (v *Viper) IsSet(key string) bool {
 func AutomaticEnv() { v.AutomaticEnv() }
 
 func (v *Viper) AutomaticEnv() {
+	v.cache.Clear()
 	v.automaticEnvApplied = true
 }
 
@@ -1244,6 +1281,7 @@ func (v *Viper) AutomaticEnv() {
 func SetEnvKeyReplacer(r *strings.Replacer) { v.SetEnvKeyReplacer(r) }
 
 func (v *Viper) SetEnvKeyReplacer(r *strings.Replacer) {
+	v.cache.Clear()
 	v.envKeyReplacer = r
 }
 
@@ -1313,6 +1351,9 @@ func (v *Viper) InConfig(key string) bool {
 func SetDefault(key string, value interface{}) { v.SetDefault(key, value) }
 
 func (v *Viper) SetDefault(key string, value interface{}) {
+	// We're clearing the whole cache because nested keys may cause issues if only the key is evicted.
+	v.cache.Clear()
+
 	// If alias passed in, then set the proper default
 	key = v.realKey(strings.ToLower(key))
 	value = toCaseInsensitiveValue(value)
@@ -1332,6 +1373,9 @@ func (v *Viper) SetDefault(key string, value interface{}) {
 func Set(key string, value interface{}) { v.Set(key, value) }
 
 func (v *Viper) Set(key string, value interface{}) {
+	// We're clearing the whole cache because nested keys may cause issues if only the key is evicted.
+	v.cache.Clear()
+
 	// If alias passed in, then set the proper override
 	key = v.realKey(strings.ToLower(key))
 	value = toCaseInsensitiveValue(value)
@@ -1349,6 +1393,7 @@ func (v *Viper) Set(key string, value interface{}) {
 func ReadInConfig() error { return v.ReadInConfig() }
 
 func (v *Viper) ReadInConfig() error {
+	v.cache.Clear()
 	jww.INFO.Println("Attempting to read in config file")
 	filename, err := v.getConfigFile()
 	if err != nil {
@@ -1380,6 +1425,7 @@ func (v *Viper) ReadInConfig() error {
 func MergeInConfig() error { return v.MergeInConfig() }
 
 func (v *Viper) MergeInConfig() error {
+	v.cache.Clear()
 	jww.INFO.Println("Attempting to merge in config file")
 	filename, err := v.getConfigFile()
 	if err != nil {
@@ -1403,6 +1449,7 @@ func (v *Viper) MergeInConfig() error {
 func ReadConfig(in io.Reader) error { return v.ReadConfig(in) }
 
 func (v *Viper) ReadConfig(in io.Reader) error {
+	v.cache.Clear()
 	v.config = make(map[string]interface{})
 	return v.unmarshalReader(in, v.config)
 }
@@ -1411,6 +1458,7 @@ func (v *Viper) ReadConfig(in io.Reader) error {
 func MergeConfig(in io.Reader) error { return v.MergeConfig(in) }
 
 func (v *Viper) MergeConfig(in io.Reader) error {
+	v.cache.Clear()
 	cfg := make(map[string]interface{})
 	if err := v.unmarshalReader(in, cfg); err != nil {
 		return err
@@ -1423,6 +1471,7 @@ func (v *Viper) MergeConfig(in io.Reader) error {
 func MergeConfigMap(cfg map[string]interface{}) error { return v.MergeConfigMap(cfg) }
 
 func (v *Viper) MergeConfigMap(cfg map[string]interface{}) error {
+	v.cache.Clear()
 	if v.config == nil {
 		v.config = make(map[string]interface{})
 	}
@@ -1978,6 +2027,7 @@ func (v *Viper) AllSettings() map[string]interface{} {
 func SetFs(fs afero.Fs) { v.SetFs(fs) }
 
 func (v *Viper) SetFs(fs afero.Fs) {
+	v.cache.Clear()
 	v.fs = fs
 }
 
@@ -1986,6 +2036,7 @@ func (v *Viper) SetFs(fs afero.Fs) {
 func SetConfigName(in string) { v.SetConfigName(in) }
 
 func (v *Viper) SetConfigName(in string) {
+	v.cache.Clear()
 	if in != "" {
 		v.configName = in
 		v.configFile = ""
@@ -1997,6 +2048,7 @@ func (v *Viper) SetConfigName(in string) {
 func SetConfigType(in string) { v.SetConfigType(in) }
 
 func (v *Viper) SetConfigType(in string) {
+	v.cache.Clear()
 	if in != "" {
 		v.configType = in
 	}

viper_test.go

@@ -22,6 +22,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/dgraph-io/ristretto"
 	"github.com/fsnotify/fsnotify"
 	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/afero"
@@ -244,13 +245,16 @@ func initDirs(t *testing.T) (string, string, func()) {
 		testDirs = append(testDirs, `d\d`)
 	}
 
+	wd, err := os.Getwd()
+	require.NoError(t, err, "Unable to get working directory")
+
 	root, err := ioutil.TempDir("", "")
 	require.NoError(t, err, "Failed to create temporary directory")
 
 	cleanup := true
 	defer func() {
 		if cleanup {
-			os.Chdir("..")
+			os.Chdir(wd)
 			os.RemoveAll(root)
 		}
 	}()
@@ -273,7 +277,7 @@ func initDirs(t *testing.T) (string, string, func()) {
 
 	cleanup = false
 	return root, config, func() {
-		os.Chdir("..")
+		os.Chdir(wd)
 		os.RemoveAll(root)
 	}
 }
@@ -2270,6 +2274,60 @@ func BenchmarkGetBool(b *testing.B) {
 	}
 }
 
+func BenchmarkFindCacheDisabled(b *testing.B) {
+	os.Setenv("MUTATORS_HEADER_ENABLED", "true")
+
+	v = New()
+	v.SetConfigFile("stub/benchmark.json")
+	if err := v.ReadInConfig(); err != nil {
+		b.Fatal(err)
+	}
+
+	v.AutomaticEnv()
+	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+
+	keys := v.AllKeys()
+	numKeys := len(keys)
+	var key string
+	for i := 0; i < b.N; i++ {
+		key = keys[i%numKeys]
+		if v.find(key, true) == nil {
+			b.Fatalf("cachedFind returned a nil value for key: %s", key)
+		}
+	}
+}
+
+func BenchmarkFindCacheEnabled(b *testing.B) {
+	os.Setenv("MUTATORS_HEADER_ENABLED", "true")
+
+	cache, err := ristretto.NewCache(&ristretto.Config{
+		NumCounters: 1000,
+		MaxCost:     1 << 20, // 1MB max cache
+		BufferItems: 64,
+	})
+	require.NoError(b, err)
+
+	v = NewWithOptions(Cache(cache))
+	v.SetConfigFile("stub/benchmark.json")
+	if err := v.ReadInConfig(); err != nil {
+		b.Fatal(err)
+	}
+
+	v.AutomaticEnv()
+	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
+
+	keys := v.AllKeys()
+	numKeys := len(keys)
+
+	var key string
+	for i := 0; i < b.N; i++ {
+		key = keys[i%numKeys]
+		if v.cachedFind(key, true) == nil {
+			b.Fatalf("cachedFind returned a nil value for key: %s", key)
+		}
+	}
+}
+
 func BenchmarkGet(b *testing.B) {
 	key := "BenchmarkGet"
 	v = New()