Add basic skeleton of libpod runtime

Signed-off-by: Matthew Heon <mheon@redhat.com>

libpod/options.go

@@ -4,14 +4,13 @@ import (
 	"fmt"
 
 	"github.com/containers/storage"
+	"github.com/containers/storage/pkg/idtools"
 	"github.com/kubernetes-incubator/cri-o/libpod/ctr"
 	"github.com/kubernetes-incubator/cri-o/libpod/pod"
 )
 
 var (
-	runtimeNotImplemented = func(rt *Runtime) error {
+	errRuntimeFinalized = fmt.Errorf("runtime has already been finalized")
-		return fmt.Errorf("NOT IMPLEMENTED")
-	}
 	ctrNotImplemented   = func(c *ctr.Container) error {
 		return fmt.Errorf("NOT IMPLEMENTED")
 	}
@@ -37,15 +36,48 @@ const (
 // WithStorageConfig uses the given configuration to set up container storage
 // If this is not specified, the system default configuration will be used
 // instead
-func WithStorageConfig(config *storage.StoreOptions) RuntimeOption {
+func WithStorageConfig(config storage.StoreOptions) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.StorageConfig.RunRoot = config.RunRoot
+		rt.config.StorageConfig.GraphRoot = config.GraphRoot
+		rt.config.StorageConfig.GraphDriverName = config.GraphDriverName
+
+		rt.config.StorageConfig.GraphDriverOptions = make([]string, len(config.GraphDriverOptions))
+		copy(rt.config.StorageConfig.GraphDriverOptions, config.GraphDriverOptions)
+
+		rt.config.StorageConfig.UIDMap = make([]idtools.IDMap, len(config.UIDMap))
+		copy(rt.config.StorageConfig.UIDMap, config.UIDMap)
+
+		rt.config.StorageConfig.GIDMap = make([]idtools.IDMap, len(config.UIDMap))
+		copy(rt.config.StorageConfig.GIDMap, config.GIDMap)
+
+		return nil
+	}
 }
 
 // WithImageConfig uses the given configuration to set up image handling
 // If this is not specified, the system default configuration will be used
 // instead
 func WithImageConfig(defaultTransport string, insecureRegistries, registries []string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.ImageDefaultTransport = defaultTransport
+
+		rt.config.InsecureRegistries = make([]string, len(insecureRegistries))
+		copy(rt.config.InsecureRegistries, insecureRegistries)
+
+		rt.config.Registries = make([]string, len(registries))
+		copy(rt.config.Registries, registries)
+
+		return nil
+	}
 }
 
 // WithSignaturePolicy specifies the path of a file which decides how trust is
@@ -53,52 +85,97 @@ func WithImageConfig(defaultTransport string, insecureRegistries, registries []s
 // If this is not specified, the system default configuration will be used
 // instead
 func WithSignaturePolicy(path string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.SignaturePolicyPath = path
+
+		return nil
+	}
 }
 
 // WithOCIRuntime specifies an OCI runtime to use for running containers
 func WithOCIRuntime(runtimePath string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.RuntimePath = runtimePath
+
+		return nil
+	}
 }
 
 // WithConmonPath specifies the path to the conmon binary which manages the
 // runtime
 func WithConmonPath(path string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.ConmonPath = path
+
+		return nil
+	}
 }
 
 // WithConmonEnv specifies the environment variable list for the conmon process
 func WithConmonEnv(environment []string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.ConmonEnvVars = make([]string, len(environment))
+		copy(rt.config.ConmonEnvVars, environment)
+
+		return nil
+	}
 }
 
 // WithCgroupManager specifies the manager implementation name which is used to
 // handle cgroups for containers
 func WithCgroupManager(manager string) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.CgroupManager = manager
+
+		return nil
+	}
 }
 
 // WithSELinux enables SELinux on the container server
 func WithSELinux() RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
-}
+		if rt.valid {
+			return errRuntimeFinalized
+		}
 
-// WithApparmorProfile specifies the apparmor profile name which will be used as
+		rt.config.SelinuxEnabled = true
-// the default for created containers
-func WithApparmorProfile(profile string) RuntimeOption {
-	return runtimeNotImplemented
-}
 
-// WithSeccompProfile specifies the seccomp profile which will be used as the
+		return nil
-// default for created containers
+	}
-func WithSeccompProfile(profilePath string) RuntimeOption {
-	return runtimeNotImplemented
 }
 
 // WithPidsLimit specifies the maximum number of processes each container is
 // restricted to
 func WithPidsLimit(limit int64) RuntimeOption {
-	return runtimeNotImplemented
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return errRuntimeFinalized
+		}
+
+		rt.config.PidsLimit = limit
+
+		return nil
+	}
 }
 
 // Container Creation Options

libpod/runtime.go

@@ -1,26 +1,135 @@
 package libpod
 
 import (
+	"fmt"
+	"sync"
+
+	"github.com/containers/image/types"
 	"github.com/containers/storage"
 	"github.com/kubernetes-incubator/cri-o/libpod/ctr"
 	"github.com/kubernetes-incubator/cri-o/libpod/pod"
+	"github.com/kubernetes-incubator/cri-o/server/apparmor"
+	"github.com/kubernetes-incubator/cri-o/server/seccomp"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/pkg/errors"
+	"github.com/ulule/deepcopier"
 )
 
-// Runtime API
-
 // A RuntimeOption is a functional option which alters the Runtime created by
 // NewRuntime
 type RuntimeOption func(*Runtime) error
 
 // Runtime is the core libpod runtime
 type Runtime struct {
-	// TODO populate
+	config          *RuntimeConfig
+	store           storage.Store
+	imageContext    *types.SystemContext
+	apparmorEnabled bool
+	seccompEnabled  bool
+	valid           bool
+	lock            sync.RWMutex
 }
 
+// RuntimeConfig contains configuration options used to set up the runtime
+type RuntimeConfig struct {
+	StorageConfig         storage.StoreOptions
+	ImageDefaultTransport string
+	InsecureRegistries    []string
+	Registries            []string
+	SignaturePolicyPath   string
+	RuntimePath           string
+	ConmonPath            string
+	ConmonEnvVars         []string
+	CgroupManager         string
+	SelinuxEnabled        bool
+	PidsLimit             int64
+}
+
+var (
+	defaultRuntimeConfig = RuntimeConfig{
+		// Leave this empty so containers/storage will use its defaults
+		StorageConfig:         storage.StoreOptions{},
+		ImageDefaultTransport: "docker://",
+		RuntimePath:           "/usr/bin/runc",
+		ConmonPath:            "/usr/local/libexec/crio/conmon",
+		ConmonEnvVars: []string{
+			"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+		},
+		CgroupManager:  "cgroupfs",
+		SelinuxEnabled: false,
+		PidsLimit:      1024,
+	}
+)
+
 // NewRuntime creates a new container runtime
+// Options can be passed to override the default configuration for the runtime
 func NewRuntime(options ...RuntimeOption) (*Runtime, error) {
-	return nil, ctr.ErrNotImplemented
+	runtime := new(Runtime)
+	runtime.config = new(RuntimeConfig)
+
+	// Copy the default configuration
+	deepcopier.Copy(defaultRuntimeConfig).To(runtime.config)
+
+	// Overwrite it with user-given configuration options
+	for _, opt := range options {
+		if err := opt(runtime); err != nil {
+			return nil, errors.Wrapf(err, "error configuring runtime")
+		}
+	}
+
+	// Set up containers/storage
+	store, err := storage.GetStore(runtime.config.StorageConfig)
+	if err != nil {
+		return nil, err
+	}
+	runtime.store = store
+
+	// Set up containers/image
+	runtime.imageContext = &types.SystemContext{
+		SignaturePolicyPath: runtime.config.SignaturePolicyPath,
+	}
+
+	runtime.seccompEnabled = seccomp.IsEnabled()
+	runtime.apparmorEnabled = apparmor.IsEnabled()
+
+	// Mark the runtime as valid - ready to be used, cannot be modified
+	// further
+	runtime.valid = true
+
+	return runtime, nil
+}
+
+// GetConfig returns a copy of the configuration used by the runtime
+func (r *Runtime) GetConfig() *RuntimeConfig {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	if !r.valid {
+		return nil
+	}
+
+	config := new(RuntimeConfig)
+
+	// Copy so the caller won't be able to modify the actual config
+	deepcopier.Copy(r.config).To(config)
+
+	return config
+}
+
+// Shutdown shuts down the runtime and associated containers and storage
+// If force is true, containers and mounted storage will be shut down before
+// cleaning up; if force is false, an error will be returned if there are
+// still containers running or mounted
+func (r *Runtime) Shutdown(force bool) error {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	if !r.valid {
+		return fmt.Errorf("runtime has already been shut down")
+	}
+
+	_, err := r.store.Shutdown(force)
+	return err
 }
 
 // Container API

vendor/github.com/ulule/deepcopier/LICENSE

@@ -0,0 +1,22 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Ulule
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+

vendor/github.com/ulule/deepcopier/README.md

@@ -0,0 +1,129 @@
+# Deepcopier
+
+[![Build Status](https://secure.travis-ci.org/ulule/deepcopier.png?branch=master)](http://travis-ci.org/ulule/deepcopier)
+
+This package is meant to make copying of structs to/from others structs a bit easier.
+
+## Installation
+
+```bash
+go get -u github.com/ulule/deepcopier
+```
+
+## Usage
+
+```golang
+// Deep copy instance1 into instance2
+Copy(instance1).To(instance2)
+
+// Deep copy instance1 into instance2 and passes the following context (which
+// is basically a map[string]interface{}) as first argument
+// to methods of instance2 that defined the struct tag "context".
+Copy(instance1).WithContext(map[string]interface{}{"foo": "bar"}).To(instance2)
+
+// Deep copy instance2 into instance1
+Copy(instance1).From(instance2)
+
+// Deep copy instance2 into instance1 and passes the following context (which
+// is basically a map[string]interface{}) as first argument
+// to methods of instance1 that defined the struct tag "context".
+Copy(instance1).WithContext(map[string]interface{}{"foo": "bar"}).From(instance2)
+```
+
+Available options for `deepcopier` struct tag:
+
+| Option    | Description                                                          |
+| --------- | -------------------------------------------------------------------- |
+| `field`   | Field or method name in source instance                              |
+| `skip`    | Ignores the field                                                    |
+| `context` | Takes a `map[string]interface{}` as first argument (for methods)     |
+| `force`   | Set the value of a `sql.Null*` field (instead of copying the struct) |
+
+**Options example:**
+
+```golang
+type Source struct {
+    Name                         string
+    SkipMe                       string
+    SQLNullStringToSQLNullString sql.NullString
+    SQLNullStringToString        sql.NullString
+
+}
+
+func (Source) MethodThatTakesContext(c map[string]interface{}) string {
+    return "whatever"
+}
+
+type Destination struct {
+    FieldWithAnotherNameInSource      string         `deepcopier:"field:Name"`
+    SkipMe                            string         `deepcopier:"skip"`
+    MethodThatTakesContext            string         `deepcopier:"context"`
+    SQLNullStringToSQLNullString      sql.NullString 
+    SQLNullStringToString             string         `deepcopier:"force"`
+}
+
+```
+
+Example:
+
+```golang
+package main
+
+import (
+    "fmt"
+ 
+    "github.com/ulule/deepcopier"
+)
+
+// Model
+type User struct {
+    // Basic string field
+    Name  string
+    // Deepcopier supports https://golang.org/pkg/database/sql/driver/#Valuer
+    Email sql.NullString
+}
+
+func (u *User) MethodThatTakesContext(ctx map[string]interface{}) string {
+    // do whatever you want
+    return "hello from this method"
+}
+
+// Resource
+type UserResource struct {
+    DisplayName            string `deepcopier:"field:Name"`
+    SkipMe                 string `deepcopier:"skip"`
+    MethodThatTakesContext string `deepcopier:"context"`
+    Email                  string `deepcopier:"force"`
+
+}
+
+func main() {
+    user := &User{
+        Name: "gilles",
+        Email: sql.NullString{
+            Valid: true,
+            String: "gilles@example.com",
+        },
+    }
+
+    resource := &UserResource{}
+
+    deepcopier.Copy(user).To(resource)
+
+    fmt.Println(resource.DisplayName)
+    fmt.Println(resource.Email)
+}
+```
+
+Looking for more information about the usage?
+
+We wrote [an introduction article](https://github.com/ulule/deepcopier/blob/master/examples/rest-usage/README.rst).
+Have a look and feel free to give us your feedback.
+
+## Contributing
+
+* Ping us on twitter [@oibafsellig](https://twitter.com/oibafsellig), [@thoas](https://twitter.com/thoas)
+* Fork the [project](https://github.com/ulule/deepcopier)
+* Help us improving and fixing [issues](https://github.com/ulule/deepcopier/issues)
+
+Don't hesitate ;)

vendor/github.com/ulule/deepcopier/deepcopier.go

@@ -0,0 +1,350 @@
+package deepcopier
+
+import (
+	"database/sql/driver"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+const (
+	// TagName is the deepcopier struct tag name.
+	TagName = "deepcopier"
+	// FieldOptionName is the from field option name for struct tag.
+	FieldOptionName = "field"
+	// ContextOptionName is the context option name for struct tag.
+	ContextOptionName = "context"
+	// SkipOptionName is the skip option name for struct tag.
+	SkipOptionName = "skip"
+	// ForceOptionName is the skip option name for struct tag.
+	ForceOptionName = "force"
+)
+
+type (
+	// TagOptions is a map that contains extracted struct tag options.
+	TagOptions map[string]string
+
+	// Options are copier options.
+	Options struct {
+		// Context given to WithContext() method.
+		Context map[string]interface{}
+		// Reversed reverses struct tag checkings.
+		Reversed bool
+	}
+)
+
+// DeepCopier deep copies a struct to/from a struct.
+type DeepCopier struct {
+	dst interface{}
+	src interface{}
+	ctx map[string]interface{}
+}
+
+// Copy sets source or destination.
+func Copy(src interface{}) *DeepCopier {
+	return &DeepCopier{src: src}
+}
+
+// WithContext injects the given context into the builder instance.
+func (dc *DeepCopier) WithContext(ctx map[string]interface{}) *DeepCopier {
+	dc.ctx = ctx
+	return dc
+}
+
+// To sets the destination.
+func (dc *DeepCopier) To(dst interface{}) error {
+	dc.dst = dst
+	return process(dc.dst, dc.src, Options{Context: dc.ctx})
+}
+
+// From sets the given the source as destination and destination as source.
+func (dc *DeepCopier) From(src interface{}) error {
+	dc.dst = dc.src
+	dc.src = src
+	return process(dc.dst, dc.src, Options{Context: dc.ctx, Reversed: true})
+}
+
+// process handles copy.
+func process(dst interface{}, src interface{}, args ...Options) error {
+	var (
+		options        = Options{}
+		srcValue       = reflect.Indirect(reflect.ValueOf(src))
+		dstValue       = reflect.Indirect(reflect.ValueOf(dst))
+		srcFieldNames  = getFieldNames(src)
+		srcMethodNames = getMethodNames(src)
+	)
+
+	if len(args) > 0 {
+		options = args[0]
+	}
+
+	if !dstValue.CanAddr() {
+		return fmt.Errorf("destination %+v is unaddressable", dstValue.Interface())
+	}
+
+	for _, f := range srcFieldNames {
+		var (
+			srcFieldValue               = srcValue.FieldByName(f)
+			srcFieldType, srcFieldFound = srcValue.Type().FieldByName(f)
+			srcFieldName                = srcFieldType.Name
+			dstFieldName                = srcFieldName
+			tagOptions                  TagOptions
+		)
+
+		if !srcFieldFound {
+			continue
+		}
+
+		if options.Reversed {
+			tagOptions = getTagOptions(srcFieldType.Tag.Get(TagName))
+			if v, ok := tagOptions[FieldOptionName]; ok && v != "" {
+				dstFieldName = v
+			}
+		} else {
+			if name, opts := getRelatedField(dst, srcFieldName); name != "" {
+				dstFieldName, tagOptions = name, opts
+			}
+		}
+
+		if _, ok := tagOptions[SkipOptionName]; ok {
+			continue
+		}
+
+		var (
+			dstFieldType, dstFieldFound = dstValue.Type().FieldByName(dstFieldName)
+			dstFieldValue               = dstValue.FieldByName(dstFieldName)
+		)
+
+		if !dstFieldFound {
+			continue
+		}
+
+		// Force option for empty interfaces and nullable types
+		_, force := tagOptions[ForceOptionName]
+
+		// Valuer -> ptr
+		if isNullableType(srcFieldType.Type) && dstFieldValue.Kind() == reflect.Ptr && force {
+			v, _ := srcFieldValue.Interface().(driver.Valuer).Value()
+			if v == nil {
+				continue
+			}
+
+			valueType := reflect.TypeOf(v)
+
+			ptr := reflect.New(valueType)
+			ptr.Elem().Set(reflect.ValueOf(v))
+
+			if valueType.AssignableTo(dstFieldType.Type.Elem()) {
+				dstFieldValue.Set(ptr)
+			}
+
+			continue
+		}
+
+		// Valuer -> value
+		if isNullableType(srcFieldType.Type) {
+			if force {
+				v, _ := srcFieldValue.Interface().(driver.Valuer).Value()
+				if v == nil {
+					continue
+				}
+
+				rv := reflect.ValueOf(v)
+				if rv.Type().AssignableTo(dstFieldType.Type) {
+					dstFieldValue.Set(rv)
+				}
+			}
+
+			continue
+		}
+
+		if dstFieldValue.Kind() == reflect.Interface {
+			if force {
+				dstFieldValue.Set(srcFieldValue)
+			}
+			continue
+		}
+
+		// Ptr -> Value
+		if srcFieldType.Type.Kind() == reflect.Ptr && !srcFieldValue.IsNil() && dstFieldType.Type.Kind() != reflect.Ptr {
+			indirect := reflect.Indirect(srcFieldValue)
+
+			if indirect.Type().AssignableTo(dstFieldType.Type) {
+				dstFieldValue.Set(indirect)
+				continue
+			}
+		}
+
+		// Other types
+		if srcFieldType.Type.AssignableTo(dstFieldType.Type) {
+			dstFieldValue.Set(srcFieldValue)
+		}
+	}
+
+	for _, m := range srcMethodNames {
+		name, opts := getRelatedField(dst, m)
+		if name == "" {
+			continue
+		}
+
+		if _, ok := opts[SkipOptionName]; ok {
+			continue
+		}
+
+		method := reflect.ValueOf(src).MethodByName(m)
+		if !method.IsValid() {
+			return fmt.Errorf("method %s is invalid", m)
+		}
+
+		var (
+			dstFieldType, _ = dstValue.Type().FieldByName(name)
+			dstFieldValue   = dstValue.FieldByName(name)
+			_, withContext  = opts[ContextOptionName]
+			_, force        = opts[ForceOptionName]
+		)
+
+		args := []reflect.Value{}
+		if withContext {
+			args = []reflect.Value{reflect.ValueOf(options.Context)}
+		}
+
+		var (
+			result          = method.Call(args)[0]
+			resultInterface = result.Interface()
+			resultValue     = reflect.ValueOf(resultInterface)
+			resultType      = resultValue.Type()
+		)
+
+		// Value -> Ptr
+		if dstFieldValue.Kind() == reflect.Ptr && force {
+			ptr := reflect.New(resultType)
+			ptr.Elem().Set(resultValue)
+
+			if ptr.Type().AssignableTo(dstFieldType.Type) {
+				dstFieldValue.Set(ptr)
+			}
+
+			continue
+		}
+
+		// Ptr -> value
+		if resultValue.Kind() == reflect.Ptr && force {
+			if resultValue.Elem().Type().AssignableTo(dstFieldType.Type) {
+				dstFieldValue.Set(resultValue.Elem())
+			}
+
+			continue
+		}
+
+		if resultType.AssignableTo(dstFieldType.Type) && result.IsValid() {
+			dstFieldValue.Set(result)
+		}
+	}
+
+	return nil
+}
+
+// getTagOptions parses deepcopier tag field and returns options.
+func getTagOptions(value string) TagOptions {
+	options := TagOptions{}
+
+	for _, opt := range strings.Split(value, ";") {
+		o := strings.Split(opt, ":")
+
+		// deepcopier:"keyword; without; value;"
+		if len(o) == 1 {
+			options[o[0]] = ""
+		}
+
+		// deepcopier:"key:value; anotherkey:anothervalue"
+		if len(o) == 2 {
+			options[strings.TrimSpace(o[0])] = strings.TrimSpace(o[1])
+		}
+	}
+
+	return options
+}
+
+// getRelatedField returns first matching field.
+func getRelatedField(instance interface{}, name string) (string, TagOptions) {
+	var (
+		value      = reflect.Indirect(reflect.ValueOf(instance))
+		fieldName  string
+		tagOptions TagOptions
+	)
+
+	for i := 0; i < value.NumField(); i++ {
+		var (
+			vField     = value.Field(i)
+			tField     = value.Type().Field(i)
+			tagOptions = getTagOptions(tField.Tag.Get(TagName))
+		)
+
+		if tField.Type.Kind() == reflect.Struct && tField.Anonymous {
+			if n, o := getRelatedField(vField.Interface(), name); n != "" {
+				return n, o
+			}
+		}
+
+		if v, ok := tagOptions[FieldOptionName]; ok && v == name {
+			return tField.Name, tagOptions
+		}
+
+		if tField.Name == name {
+			return tField.Name, tagOptions
+		}
+	}
+
+	return fieldName, tagOptions
+}
+
+// getMethodNames returns instance's method names.
+func getMethodNames(instance interface{}) []string {
+	var methods []string
+
+	t := reflect.TypeOf(instance)
+	for i := 0; i < t.NumMethod(); i++ {
+		methods = append(methods, t.Method(i).Name)
+	}
+
+	return methods
+}
+
+// getFieldNames returns instance's field names.
+func getFieldNames(instance interface{}) []string {
+	var (
+		fields []string
+		v      = reflect.Indirect(reflect.ValueOf(instance))
+		t      = v.Type()
+	)
+
+	if t.Kind() != reflect.Struct {
+		return nil
+	}
+
+	for i := 0; i < v.NumField(); i++ {
+		var (
+			vField = v.Field(i)
+			tField = v.Type().Field(i)
+		)
+
+		// Is exportable?
+		if tField.PkgPath != "" {
+			continue
+		}
+
+		if tField.Type.Kind() == reflect.Struct && tField.Anonymous {
+			fields = append(fields, getFieldNames(vField.Interface())...)
+			continue
+		}
+
+		fields = append(fields, tField.Name)
+	}
+
+	return fields
+}
+
+// isNullableType returns true if the given type is a nullable one.
+func isNullableType(t reflect.Type) bool {
+	return t.ConvertibleTo(reflect.TypeOf((*driver.Valuer)(nil)).Elem())
+}