Look for usable on-cluster credentials using k8schain (#243)

* dep ensure and use k8schain

* checkpoint

* fix vendoring, stuff builds

* Use k8schain for pushes too

* Use NewNoClient

* update ggcr dep

* Move k8schain usage to image_util.go

vendor/github.com/google/go-containerregistry/pkg/authn/k8schain/doc.go

@@ -0,0 +1,18 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// package k8schain exposes an implementation of the authn.Keychain interface
+// based on the semantics the Kubelet follows when pulling the images for a
+// Pod in Kubernetes.
+package k8schain

vendor/github.com/google/go-containerregistry/pkg/authn/k8schain/k8schain.go

@@ -0,0 +1,165 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package k8schain
+
+import (
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	"k8s.io/kubernetes/pkg/credentialprovider"
+	credentialprovidersecrets "k8s.io/kubernetes/pkg/credentialprovider/secrets"
+
+	// Credential providers
+	_ "k8s.io/kubernetes/pkg/credentialprovider/aws"
+	_ "k8s.io/kubernetes/pkg/credentialprovider/azure"
+	_ "k8s.io/kubernetes/pkg/credentialprovider/gcp"
+	// TODO(mattmoor): This doesn't seem to build, figure out why `dep ensure`
+	// is not working and add constraints.
+	// _ "k8s.io/kubernetes/pkg/credentialprovider/rancher"
+)
+
+// Options holds configuration data for guiding credential resolution.
+type Options struct {
+	// Namespace holds the namespace inside of which we are resolving the
+	// image reference.  If empty, "default" is assumed.
+	Namespace string
+	// ServiceAccountName holds the serviceaccount as which the container
+	// will run (scoped to Namespace).  If empty, "default" is assumed.
+	ServiceAccountName string
+	// ImagePullSecrets holds the names of the Kubernetes secrets (scoped to
+	// Namespace) containing credential data to use for the image pull.
+	ImagePullSecrets []string
+}
+
+// origKeyRing is a variable so that testing can adjust it.
+var origKeyRing = credentialprovider.NewDockerKeyring()
+
+// New returns a new authn.Keychain suitable for resolving image references as
+// scoped by the provided Options.  It speaks to Kubernetes through the provided
+// client interface.
+func New(client kubernetes.Interface, opt Options) (authn.Keychain, error) {
+	if opt.Namespace == "" {
+		opt.Namespace = "default"
+	}
+	if opt.ServiceAccountName == "" {
+		opt.ServiceAccountName = "default"
+	}
+
+	// Implement a Kubernetes-style authentication keychain.
+	// This needs to support roughly the following kinds of authentication:
+	//  1) The implicit authentication from k8s.io/kubernetes/pkg/credentialprovider
+	//  2) The explicit authentication from imagePullSecrets on Pod
+	//  3) The semi-implicit authentication where imagePullSecrets are on the
+	//    Pod's service account.
+
+	// First, fetch all of the explicitly declared pull secrets
+	var pullSecrets []v1.Secret
+	if client != nil {
+		for _, name := range opt.ImagePullSecrets {
+			ps, err := client.CoreV1().Secrets(opt.Namespace).Get(name, metav1.GetOptions{})
+			if err != nil {
+				return nil, err
+			}
+			pullSecrets = append(pullSecrets, *ps)
+		}
+
+		// Second, fetch all of the pull secrets attached to our service account.
+		sa, err := client.CoreV1().ServiceAccounts(opt.Namespace).Get(opt.ServiceAccountName, metav1.GetOptions{})
+		if err != nil {
+			return nil, err
+		}
+		for _, localObj := range sa.ImagePullSecrets {
+			ps, err := client.CoreV1().Secrets(opt.Namespace).Get(localObj.Name, metav1.GetOptions{})
+			if err != nil {
+				return nil, err
+			}
+			pullSecrets = append(pullSecrets, *ps)
+		}
+	}
+
+	// Third, extend the default keyring with the pull secrets.
+	kr, err := credentialprovidersecrets.MakeDockerKeyring(pullSecrets, origKeyRing)
+	if err != nil {
+		return nil, err
+	}
+	return &keychain{
+		keyring: kr,
+	}, nil
+}
+
+// NewInCluster returns a new authn.Keychain suitable for resolving image references as
+// scoped by the provided Options, constructing a kubernetes.Interface based on in-cluster
+// authentication.
+func NewInCluster(opt Options) (authn.Keychain, error) {
+	clusterConfig, err := rest.InClusterConfig()
+	if err != nil {
+		return nil, err
+	}
+
+	client, err := kubernetes.NewForConfig(clusterConfig)
+	if err != nil {
+		return nil, err
+	}
+	return New(client, opt)
+}
+
+// NewNoClient returns a new authn.Keychain that supports the portions of the K8s keychain
+// that don't read ImagePullSecrets.  This limits it to roughly the Node-identity-based
+// authentication schemes in Kubernetes pkg/credentialprovider.  This version of the
+// k8schain drops the requirement that we run as a K8s serviceaccount with access to all
+// of the on-cluster secrets.  This drop in fidelity also diminishes its value as a stand-in
+// for Kubernetes authentication, but this actually targets a different use-case.  What
+// remains is an interesting sweet spot: this variant can serve as a credential provider
+// for all of the major public clouds, but in library form (vs. an executable you exec).
+func NewNoClient() (authn.Keychain, error) {
+	return New(nil, Options{})
+}
+
+type lazyProvider credentialprovider.LazyAuthConfiguration
+
+// Authorization implements Authenticator.
+func (lp lazyProvider) Authorization() (string, error) {
+	authConfig := credentialprovider.LazyProvide(credentialprovider.LazyAuthConfiguration(lp))
+	if authConfig.Auth != "" {
+		return "Basic " + authConfig.Auth, nil
+	}
+	if authConfig.Username != "" {
+		basic := authn.Basic{
+			Username: authConfig.Username,
+			Password: authConfig.Password,
+		}
+		return basic.Authorization()
+	}
+	return authn.Anonymous.Authorization()
+}
+
+type keychain struct {
+	keyring credentialprovider.DockerKeyring
+}
+
+// Resolve implements authn.Keychain
+func (kc *keychain) Resolve(reg name.Registry) (authn.Authenticator, error) {
+	// TODO(mattmoor): Lookup expects an image reference and we only have a registry,
+	// find something better than this.
+	creds, found := kc.keyring.Lookup(reg.String() + "/foo/bar")
+	if !found || len(creds) < 1 {
+		return authn.Anonymous, nil
+	}
+	// TODO(mattmoor): How to support multiple credentials?
+	return lazyProvider(creds[0]), nil
+}

vendor/github.com/google/go-containerregistry/pkg/authn/keychain.go

@@ -21,7 +21,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
-	"path"
+	"path/filepath"
 	"runtime"
 
 	"github.com/google/go-containerregistry/pkg/name"
@@ -43,7 +43,7 @@ func configDir() (string, error) {
 		return dc, nil
 	}
 	if h := dockerUserHomeDir(); h != "" {
-		return path.Join(dockerUserHomeDir(), ".docker"), nil
+		return filepath.Join(dockerUserHomeDir(), ".docker"), nil
 	}
 	return "", errNoHomeDir
 }
@@ -100,19 +100,19 @@ var (
 func (dk *defaultKeychain) Resolve(reg name.Registry) (Authenticator, error) {
 	dir, err := configDir()
 	if err != nil {
-		log.Printf("Unable to determine config dir, falling back on anonymous: %v", err)
+		log.Printf("Unable to determine config dir: %v", err)
 		return Anonymous, nil
 	}
-	file := path.Join(dir, "config.json")
+	file := filepath.Join(dir, "config.json")
 	content, err := ioutil.ReadFile(file)
 	if err != nil {
-		log.Printf("Unable to read %q, falling back on anonymous: %v", file, err)
+		log.Printf("Unable to read %q: %v", file, err)
 		return Anonymous, nil
 	}
 
 	var cf cfg
 	if err := json.Unmarshal(content, &cf); err != nil {
-		log.Printf("Unable to parse %q, falling back on anonymous: %v", file, err)
+		log.Printf("Unable to parse %q: %v", file, err)
 		return Anonymous, nil
 	}
 
@@ -147,6 +147,6 @@ func (dk *defaultKeychain) Resolve(reg name.Registry) (Authenticator, error) {
 		}
 	}
 
-	log.Printf("No matching credentials found for %v, falling back on anonymous", reg)
+	// Fallback on anonymous.
 	return Anonymous, nil
 }

vendor/github.com/google/go-containerregistry/pkg/authn/multikeychain.go

@@ -0,0 +1,45 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package authn
+
+import (
+	"github.com/google/go-containerregistry/pkg/name"
+)
+
+type multiKeychain struct {
+	keychains []Keychain
+}
+
+// Assert that our multi-keychain implements Keychain.
+var _ (Keychain) = (*multiKeychain)(nil)
+
+// NewMultiKeychain composes a list of keychains into one new keychain.
+func NewMultiKeychain(kcs ...Keychain) Keychain {
+	return &multiKeychain{keychains: kcs}
+}
+
+// Resolve implements Keychain.
+func (mk *multiKeychain) Resolve(reg name.Registry) (Authenticator, error) {
+	for _, kc := range mk.keychains {
+		auth, err := kc.Resolve(reg)
+		if err != nil {
+			return nil, err
+		}
+		if auth != Anonymous {
+			return auth, nil
+		}
+	}
+	return Anonymous, nil
+}

vendor/github.com/google/go-containerregistry/pkg/name/repository.go

@@ -79,7 +79,7 @@ func NewRepository(name string, strict Strictness) (Repository, error) {
 	if len(parts) == 2 && (strings.ContainsRune(parts[0], '.') || strings.ContainsRune(parts[0], ':')) {
 		// The first part of the repository is treated as the registry domain
 		// iff it contains a '.' or ':' character, otherwise it is all repository
-		// and the domain defaults to DockerHub.
+		// and the domain defaults to Docker Hub.
 		registry = parts[0]
 		repo = parts[1]
 	}

vendor/github.com/google/go-containerregistry/pkg/v1/remote/options.go

@@ -15,6 +15,7 @@
 package remote
 
 import (
+	"log"
 	"net/http"
 
 	"github.com/google/go-containerregistry/pkg/authn"
@@ -24,7 +25,8 @@ import (
 // on a remote image
 func WithTransport(t http.RoundTripper) ImageOption {
 	return func(i *imageOpener) error {
-		return i.setTransport(t)
+		i.transport = t
+		return nil
 	}
 }
 
@@ -32,7 +34,8 @@ func WithTransport(t http.RoundTripper) ImageOption {
 // on a remote image
 func WithAuth(auth authn.Authenticator) ImageOption {
 	return func(i *imageOpener) error {
-		return i.setAuth(auth)
+		i.auth = auth
+		return nil
 	}
 }
 
@@ -44,18 +47,10 @@ func WithAuthFromKeychain(keys authn.Keychain) ImageOption {
 		if err != nil {
 			return err
 		}
-		return i.setAuth(auth)
+		if auth == authn.Anonymous {
+			log.Println("No matching credentials were found, falling back on anonymous")
+		}
+		i.auth = auth
+		return nil
 	}
 }
-
-// Set client on image using provided transport, and the default authenticator
-func (i *imageOpener) setTransport(t http.RoundTripper) error {
-	i.transport = t
-	return nil
-}
-
-// Set client on image using provided authenticator, and the default transport
-func (i *imageOpener) setAuth(auth authn.Authenticator) error {
-	i.auth = auth
-	return nil
-}

vendor/github.com/google/gofuzz/LICENSE

@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+
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+      any Contribution intentionally submitted for inclusion in the Work
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+   Unless required by applicable law or agreed to in writing, software
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vendor/github.com/google/gofuzz/doc.go

@@ -0,0 +1,18 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package fuzz is a library for populating go objects with random values.
+package fuzz

vendor/github.com/google/gofuzz/fuzz.go

@@ -0,0 +1,487 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package fuzz
+
+import (
+	"fmt"
+	"math/rand"
+	"reflect"
+	"time"
+)
+
+// fuzzFuncMap is a map from a type to a fuzzFunc that handles that type.
+type fuzzFuncMap map[reflect.Type]reflect.Value
+
+// Fuzzer knows how to fill any object with random fields.
+type Fuzzer struct {
+	fuzzFuncs        fuzzFuncMap
+	defaultFuzzFuncs fuzzFuncMap
+	r                *rand.Rand
+	nilChance        float64
+	minElements      int
+	maxElements      int
+	maxDepth         int
+}
+
+// New returns a new Fuzzer. Customize your Fuzzer further by calling Funcs,
+// RandSource, NilChance, or NumElements in any order.
+func New() *Fuzzer {
+	return NewWithSeed(time.Now().UnixNano())
+}
+
+func NewWithSeed(seed int64) *Fuzzer {
+	f := &Fuzzer{
+		defaultFuzzFuncs: fuzzFuncMap{
+			reflect.TypeOf(&time.Time{}): reflect.ValueOf(fuzzTime),
+		},
+
+		fuzzFuncs:   fuzzFuncMap{},
+		r:           rand.New(rand.NewSource(seed)),
+		nilChance:   .2,
+		minElements: 1,
+		maxElements: 10,
+		maxDepth:    100,
+	}
+	return f
+}
+
+// Funcs adds each entry in fuzzFuncs as a custom fuzzing function.
+//
+// Each entry in fuzzFuncs must be a function taking two parameters.
+// The first parameter must be a pointer or map. It is the variable that
+// function will fill with random data. The second parameter must be a
+// fuzz.Continue, which will provide a source of randomness and a way
+// to automatically continue fuzzing smaller pieces of the first parameter.
+//
+// These functions are called sensibly, e.g., if you wanted custom string
+// fuzzing, the function `func(s *string, c fuzz.Continue)` would get
+// called and passed the address of strings. Maps and pointers will always
+// be made/new'd for you, ignoring the NilChange option. For slices, it
+// doesn't make much sense to  pre-create them--Fuzzer doesn't know how
+// long you want your slice--so take a pointer to a slice, and make it
+// yourself. (If you don't want your map/pointer type pre-made, take a
+// pointer to it, and make it yourself.) See the examples for a range of
+// custom functions.
+func (f *Fuzzer) Funcs(fuzzFuncs ...interface{}) *Fuzzer {
+	for i := range fuzzFuncs {
+		v := reflect.ValueOf(fuzzFuncs[i])
+		if v.Kind() != reflect.Func {
+			panic("Need only funcs!")
+		}
+		t := v.Type()
+		if t.NumIn() != 2 || t.NumOut() != 0 {
+			panic("Need 2 in and 0 out params!")
+		}
+		argT := t.In(0)
+		switch argT.Kind() {
+		case reflect.Ptr, reflect.Map:
+		default:
+			panic("fuzzFunc must take pointer or map type")
+		}
+		if t.In(1) != reflect.TypeOf(Continue{}) {
+			panic("fuzzFunc's second parameter must be type fuzz.Continue")
+		}
+		f.fuzzFuncs[argT] = v
+	}
+	return f
+}
+
+// RandSource causes f to get values from the given source of randomness.
+// Use if you want deterministic fuzzing.
+func (f *Fuzzer) RandSource(s rand.Source) *Fuzzer {
+	f.r = rand.New(s)
+	return f
+}
+
+// NilChance sets the probability of creating a nil pointer, map, or slice to
+// 'p'. 'p' should be between 0 (no nils) and 1 (all nils), inclusive.
+func (f *Fuzzer) NilChance(p float64) *Fuzzer {
+	if p < 0 || p > 1 {
+		panic("p should be between 0 and 1, inclusive.")
+	}
+	f.nilChance = p
+	return f
+}
+
+// NumElements sets the minimum and maximum number of elements that will be
+// added to a non-nil map or slice.
+func (f *Fuzzer) NumElements(atLeast, atMost int) *Fuzzer {
+	if atLeast > atMost {
+		panic("atLeast must be <= atMost")
+	}
+	if atLeast < 0 {
+		panic("atLeast must be >= 0")
+	}
+	f.minElements = atLeast
+	f.maxElements = atMost
+	return f
+}
+
+func (f *Fuzzer) genElementCount() int {
+	if f.minElements == f.maxElements {
+		return f.minElements
+	}
+	return f.minElements + f.r.Intn(f.maxElements-f.minElements+1)
+}
+
+func (f *Fuzzer) genShouldFill() bool {
+	return f.r.Float64() > f.nilChance
+}
+
+// MaxDepth sets the maximum number of recursive fuzz calls that will be made
+// before stopping.  This includes struct members, pointers, and map and slice
+// elements.
+func (f *Fuzzer) MaxDepth(d int) *Fuzzer {
+	f.maxDepth = d
+	return f
+}
+
+// Fuzz recursively fills all of obj's fields with something random.  First
+// this tries to find a custom fuzz function (see Funcs).  If there is no
+// custom function this tests whether the object implements fuzz.Interface and,
+// if so, calls Fuzz on it to fuzz itself.  If that fails, this will see if
+// there is a default fuzz function provided by this package.  If all of that
+// fails, this will generate random values for all primitive fields and then
+// recurse for all non-primitives.
+//
+// This is safe for cyclic or tree-like structs, up to a limit.  Use the
+// MaxDepth method to adjust how deep you need it to recurse.
+//
+// obj must be a pointer. Only exported (public) fields can be set (thanks,
+// golang :/ ) Intended for tests, so will panic on bad input or unimplemented
+// fields.
+func (f *Fuzzer) Fuzz(obj interface{}) {
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		panic("needed ptr!")
+	}
+	v = v.Elem()
+	f.fuzzWithContext(v, 0)
+}
+
+// FuzzNoCustom is just like Fuzz, except that any custom fuzz function for
+// obj's type will not be called and obj will not be tested for fuzz.Interface
+// conformance.  This applies only to obj and not other instances of obj's
+// type.
+// Not safe for cyclic or tree-like structs!
+// obj must be a pointer. Only exported (public) fields can be set (thanks, golang :/ )
+// Intended for tests, so will panic on bad input or unimplemented fields.
+func (f *Fuzzer) FuzzNoCustom(obj interface{}) {
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		panic("needed ptr!")
+	}
+	v = v.Elem()
+	f.fuzzWithContext(v, flagNoCustomFuzz)
+}
+
+const (
+	// Do not try to find a custom fuzz function.  Does not apply recursively.
+	flagNoCustomFuzz uint64 = 1 << iota
+)
+
+func (f *Fuzzer) fuzzWithContext(v reflect.Value, flags uint64) {
+	fc := &fuzzerContext{fuzzer: f}
+	fc.doFuzz(v, flags)
+}
+
+// fuzzerContext carries context about a single fuzzing run, which lets Fuzzer
+// be thread-safe.
+type fuzzerContext struct {
+	fuzzer   *Fuzzer
+	curDepth int
+}
+
+func (fc *fuzzerContext) doFuzz(v reflect.Value, flags uint64) {
+	if fc.curDepth >= fc.fuzzer.maxDepth {
+		return
+	}
+	fc.curDepth++
+	defer func() { fc.curDepth-- }()
+
+	if !v.CanSet() {
+		return
+	}
+
+	if flags&flagNoCustomFuzz == 0 {
+		// Check for both pointer and non-pointer custom functions.
+		if v.CanAddr() && fc.tryCustom(v.Addr()) {
+			return
+		}
+		if fc.tryCustom(v) {
+			return
+		}
+	}
+
+	if fn, ok := fillFuncMap[v.Kind()]; ok {
+		fn(v, fc.fuzzer.r)
+		return
+	}
+	switch v.Kind() {
+	case reflect.Map:
+		if fc.fuzzer.genShouldFill() {
+			v.Set(reflect.MakeMap(v.Type()))
+			n := fc.fuzzer.genElementCount()
+			for i := 0; i < n; i++ {
+				key := reflect.New(v.Type().Key()).Elem()
+				fc.doFuzz(key, 0)
+				val := reflect.New(v.Type().Elem()).Elem()
+				fc.doFuzz(val, 0)
+				v.SetMapIndex(key, val)
+			}
+			return
+		}
+		v.Set(reflect.Zero(v.Type()))
+	case reflect.Ptr:
+		if fc.fuzzer.genShouldFill() {
+			v.Set(reflect.New(v.Type().Elem()))
+			fc.doFuzz(v.Elem(), 0)
+			return
+		}
+		v.Set(reflect.Zero(v.Type()))
+	case reflect.Slice:
+		if fc.fuzzer.genShouldFill() {
+			n := fc.fuzzer.genElementCount()
+			v.Set(reflect.MakeSlice(v.Type(), n, n))
+			for i := 0; i < n; i++ {
+				fc.doFuzz(v.Index(i), 0)
+			}
+			return
+		}
+		v.Set(reflect.Zero(v.Type()))
+	case reflect.Array:
+		if fc.fuzzer.genShouldFill() {
+			n := v.Len()
+			for i := 0; i < n; i++ {
+				fc.doFuzz(v.Index(i), 0)
+			}
+			return
+		}
+		v.Set(reflect.Zero(v.Type()))
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			fc.doFuzz(v.Field(i), 0)
+		}
+	case reflect.Chan:
+		fallthrough
+	case reflect.Func:
+		fallthrough
+	case reflect.Interface:
+		fallthrough
+	default:
+		panic(fmt.Sprintf("Can't handle %#v", v.Interface()))
+	}
+}
+
+// tryCustom searches for custom handlers, and returns true iff it finds a match
+// and successfully randomizes v.
+func (fc *fuzzerContext) tryCustom(v reflect.Value) bool {
+	// First: see if we have a fuzz function for it.
+	doCustom, ok := fc.fuzzer.fuzzFuncs[v.Type()]
+	if !ok {
+		// Second: see if it can fuzz itself.
+		if v.CanInterface() {
+			intf := v.Interface()
+			if fuzzable, ok := intf.(Interface); ok {
+				fuzzable.Fuzz(Continue{fc: fc, Rand: fc.fuzzer.r})
+				return true
+			}
+		}
+		// Finally: see if there is a default fuzz function.
+		doCustom, ok = fc.fuzzer.defaultFuzzFuncs[v.Type()]
+		if !ok {
+			return false
+		}
+	}
+
+	switch v.Kind() {
+	case reflect.Ptr:
+		if v.IsNil() {
+			if !v.CanSet() {
+				return false
+			}
+			v.Set(reflect.New(v.Type().Elem()))
+		}
+	case reflect.Map:
+		if v.IsNil() {
+			if !v.CanSet() {
+				return false
+			}
+			v.Set(reflect.MakeMap(v.Type()))
+		}
+	default:
+		return false
+	}
+
+	doCustom.Call([]reflect.Value{v, reflect.ValueOf(Continue{
+		fc:   fc,
+		Rand: fc.fuzzer.r,
+	})})
+	return true
+}
+
+// Interface represents an object that knows how to fuzz itself.  Any time we
+// find a type that implements this interface we will delegate the act of
+// fuzzing itself.
+type Interface interface {
+	Fuzz(c Continue)
+}
+
+// Continue can be passed to custom fuzzing functions to allow them to use
+// the correct source of randomness and to continue fuzzing their members.
+type Continue struct {
+	fc *fuzzerContext
+
+	// For convenience, Continue implements rand.Rand via embedding.
+	// Use this for generating any randomness if you want your fuzzing
+	// to be repeatable for a given seed.
+	*rand.Rand
+}
+
+// Fuzz continues fuzzing obj. obj must be a pointer.
+func (c Continue) Fuzz(obj interface{}) {
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		panic("needed ptr!")
+	}
+	v = v.Elem()
+	c.fc.doFuzz(v, 0)
+}
+
+// FuzzNoCustom continues fuzzing obj, except that any custom fuzz function for
+// obj's type will not be called and obj will not be tested for fuzz.Interface
+// conformance.  This applies only to obj and not other instances of obj's
+// type.
+func (c Continue) FuzzNoCustom(obj interface{}) {
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		panic("needed ptr!")
+	}
+	v = v.Elem()
+	c.fc.doFuzz(v, flagNoCustomFuzz)
+}
+
+// RandString makes a random string up to 20 characters long. The returned string
+// may include a variety of (valid) UTF-8 encodings.
+func (c Continue) RandString() string {
+	return randString(c.Rand)
+}
+
+// RandUint64 makes random 64 bit numbers.
+// Weirdly, rand doesn't have a function that gives you 64 random bits.
+func (c Continue) RandUint64() uint64 {
+	return randUint64(c.Rand)
+}
+
+// RandBool returns true or false randomly.
+func (c Continue) RandBool() bool {
+	return randBool(c.Rand)
+}
+
+func fuzzInt(v reflect.Value, r *rand.Rand) {
+	v.SetInt(int64(randUint64(r)))
+}
+
+func fuzzUint(v reflect.Value, r *rand.Rand) {
+	v.SetUint(randUint64(r))
+}
+
+func fuzzTime(t *time.Time, c Continue) {
+	var sec, nsec int64
+	// Allow for about 1000 years of random time values, which keeps things
+	// like JSON parsing reasonably happy.
+	sec = c.Rand.Int63n(1000 * 365 * 24 * 60 * 60)
+	c.Fuzz(&nsec)
+	*t = time.Unix(sec, nsec)
+}
+
+var fillFuncMap = map[reflect.Kind]func(reflect.Value, *rand.Rand){
+	reflect.Bool: func(v reflect.Value, r *rand.Rand) {
+		v.SetBool(randBool(r))
+	},
+	reflect.Int:     fuzzInt,
+	reflect.Int8:    fuzzInt,
+	reflect.Int16:   fuzzInt,
+	reflect.Int32:   fuzzInt,
+	reflect.Int64:   fuzzInt,
+	reflect.Uint:    fuzzUint,
+	reflect.Uint8:   fuzzUint,
+	reflect.Uint16:  fuzzUint,
+	reflect.Uint32:  fuzzUint,
+	reflect.Uint64:  fuzzUint,
+	reflect.Uintptr: fuzzUint,
+	reflect.Float32: func(v reflect.Value, r *rand.Rand) {
+		v.SetFloat(float64(r.Float32()))
+	},
+	reflect.Float64: func(v reflect.Value, r *rand.Rand) {
+		v.SetFloat(r.Float64())
+	},
+	reflect.Complex64: func(v reflect.Value, r *rand.Rand) {
+		panic("unimplemented")
+	},
+	reflect.Complex128: func(v reflect.Value, r *rand.Rand) {
+		panic("unimplemented")
+	},
+	reflect.String: func(v reflect.Value, r *rand.Rand) {
+		v.SetString(randString(r))
+	},
+	reflect.UnsafePointer: func(v reflect.Value, r *rand.Rand) {
+		panic("unimplemented")
+	},
+}
+
+// randBool returns true or false randomly.
+func randBool(r *rand.Rand) bool {
+	if r.Int()&1 == 1 {
+		return true
+	}
+	return false
+}
+
+type charRange struct {
+	first, last rune
+}
+
+// choose returns a random unicode character from the given range, using the
+// given randomness source.
+func (r *charRange) choose(rand *rand.Rand) rune {
+	count := int64(r.last - r.first)
+	return r.first + rune(rand.Int63n(count))
+}
+
+var unicodeRanges = []charRange{
+	{' ', '~'},           // ASCII characters
+	{'\u00a0', '\u02af'}, // Multi-byte encoded characters
+	{'\u4e00', '\u9fff'}, // Common CJK (even longer encodings)
+}
+
+// randString makes a random string up to 20 characters long. The returned string
+// may include a variety of (valid) UTF-8 encodings.
+func randString(r *rand.Rand) string {
+	n := r.Intn(20)
+	runes := make([]rune, n)
+	for i := range runes {
+		runes[i] = unicodeRanges[r.Intn(len(unicodeRanges))].choose(r)
+	}
+	return string(runes)
+}
+
+// randUint64 makes random 64 bit numbers.
+// Weirdly, rand doesn't have a function that gives you 64 random bits.
+func randUint64(r *rand.Rand) uint64 {
+	return uint64(r.Uint32())<<32 | uint64(r.Uint32())
+}