vendor files

vendor/k8s.io/apimachinery/pkg/conversion/converter.go

@@ -0,0 +1,898 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+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 conversion
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type typePair struct {
+	source reflect.Type
+	dest   reflect.Type
+}
+
+type typeNamePair struct {
+	fieldType reflect.Type
+	fieldName string
+}
+
+// DebugLogger allows you to get debugging messages if necessary.
+type DebugLogger interface {
+	Logf(format string, args ...interface{})
+}
+
+type NameFunc func(t reflect.Type) string
+
+var DefaultNameFunc = func(t reflect.Type) string { return t.Name() }
+
+type GenericConversionFunc func(a, b interface{}, scope Scope) (bool, error)
+
+// Converter knows how to convert one type to another.
+type Converter struct {
+	// Map from the conversion pair to a function which can
+	// do the conversion.
+	conversionFuncs          ConversionFuncs
+	generatedConversionFuncs ConversionFuncs
+
+	// genericConversions are called during normal conversion to offer a "fast-path"
+	// that avoids all reflection. These methods are not called outside of the .Convert()
+	// method.
+	genericConversions []GenericConversionFunc
+
+	// Set of conversions that should be treated as a no-op
+	ignoredConversions map[typePair]struct{}
+
+	// This is a map from a source field type and name, to a list of destination
+	// field type and name.
+	structFieldDests map[typeNamePair][]typeNamePair
+
+	// Allows for the opposite lookup of structFieldDests. So that SourceFromDest
+	// copy flag also works. So this is a map of destination field name, to potential
+	// source field name and type to look for.
+	structFieldSources map[typeNamePair][]typeNamePair
+
+	// Map from an input type to a function which can apply a key name mapping
+	inputFieldMappingFuncs map[reflect.Type]FieldMappingFunc
+
+	// Map from an input type to a set of default conversion flags.
+	inputDefaultFlags map[reflect.Type]FieldMatchingFlags
+
+	// If non-nil, will be called to print helpful debugging info. Quite verbose.
+	Debug DebugLogger
+
+	// nameFunc is called to retrieve the name of a type; this name is used for the
+	// purpose of deciding whether two types match or not (i.e., will we attempt to
+	// do a conversion). The default returns the go type name.
+	nameFunc func(t reflect.Type) string
+}
+
+// NewConverter creates a new Converter object.
+func NewConverter(nameFn NameFunc) *Converter {
+	c := &Converter{
+		conversionFuncs:          NewConversionFuncs(),
+		generatedConversionFuncs: NewConversionFuncs(),
+		ignoredConversions:       make(map[typePair]struct{}),
+		nameFunc:                 nameFn,
+		structFieldDests:         make(map[typeNamePair][]typeNamePair),
+		structFieldSources:       make(map[typeNamePair][]typeNamePair),
+
+		inputFieldMappingFuncs: make(map[reflect.Type]FieldMappingFunc),
+		inputDefaultFlags:      make(map[reflect.Type]FieldMatchingFlags),
+	}
+	c.RegisterConversionFunc(Convert_Slice_byte_To_Slice_byte)
+	return c
+}
+
+// AddGenericConversionFunc adds a function that accepts the ConversionFunc call pattern
+// (for two conversion types) to the converter. These functions are checked first during
+// a normal conversion, but are otherwise not called. Use AddConversionFuncs when registering
+// typed conversions.
+func (c *Converter) AddGenericConversionFunc(fn GenericConversionFunc) {
+	c.genericConversions = append(c.genericConversions, fn)
+}
+
+// WithConversions returns a Converter that is a copy of c but with the additional
+// fns merged on top.
+func (c *Converter) WithConversions(fns ConversionFuncs) *Converter {
+	copied := *c
+	copied.conversionFuncs = c.conversionFuncs.Merge(fns)
+	return &copied
+}
+
+// DefaultMeta returns the conversion FieldMappingFunc and meta for a given type.
+func (c *Converter) DefaultMeta(t reflect.Type) (FieldMatchingFlags, *Meta) {
+	return c.inputDefaultFlags[t], &Meta{
+		KeyNameMapping: c.inputFieldMappingFuncs[t],
+	}
+}
+
+// Convert_Slice_byte_To_Slice_byte prevents recursing into every byte
+func Convert_Slice_byte_To_Slice_byte(in *[]byte, out *[]byte, s Scope) error {
+	if *in == nil {
+		*out = nil
+		return nil
+	}
+	*out = make([]byte, len(*in))
+	copy(*out, *in)
+	return nil
+}
+
+// Scope is passed to conversion funcs to allow them to continue an ongoing conversion.
+// If multiple converters exist in the system, Scope will allow you to use the correct one
+// from a conversion function--that is, the one your conversion function was called by.
+type Scope interface {
+	// Call Convert to convert sub-objects. Note that if you call it with your own exact
+	// parameters, you'll run out of stack space before anything useful happens.
+	Convert(src, dest interface{}, flags FieldMatchingFlags) error
+
+	// DefaultConvert performs the default conversion, without calling a conversion func
+	// on the current stack frame. This makes it safe to call from a conversion func.
+	DefaultConvert(src, dest interface{}, flags FieldMatchingFlags) error
+
+	// SrcTags and DestTags contain the struct tags that src and dest had, respectively.
+	// If the enclosing object was not a struct, then these will contain no tags, of course.
+	SrcTag() reflect.StructTag
+	DestTag() reflect.StructTag
+
+	// Flags returns the flags with which the conversion was started.
+	Flags() FieldMatchingFlags
+
+	// Meta returns any information originally passed to Convert.
+	Meta() *Meta
+}
+
+// FieldMappingFunc can convert an input field value into different values, depending on
+// the value of the source or destination struct tags.
+type FieldMappingFunc func(key string, sourceTag, destTag reflect.StructTag) (source string, dest string)
+
+func NewConversionFuncs() ConversionFuncs {
+	return ConversionFuncs{fns: make(map[typePair]reflect.Value)}
+}
+
+type ConversionFuncs struct {
+	fns map[typePair]reflect.Value
+}
+
+// Add adds the provided conversion functions to the lookup table - they must have the signature
+// `func(type1, type2, Scope) error`. Functions are added in the order passed and will override
+// previously registered pairs.
+func (c ConversionFuncs) Add(fns ...interface{}) error {
+	for _, fn := range fns {
+		fv := reflect.ValueOf(fn)
+		ft := fv.Type()
+		if err := verifyConversionFunctionSignature(ft); err != nil {
+			return err
+		}
+		c.fns[typePair{ft.In(0).Elem(), ft.In(1).Elem()}] = fv
+	}
+	return nil
+}
+
+// Merge returns a new ConversionFuncs that contains all conversions from
+// both other and c, with other conversions taking precedence.
+func (c ConversionFuncs) Merge(other ConversionFuncs) ConversionFuncs {
+	merged := NewConversionFuncs()
+	for k, v := range c.fns {
+		merged.fns[k] = v
+	}
+	for k, v := range other.fns {
+		merged.fns[k] = v
+	}
+	return merged
+}
+
+// Meta is supplied by Scheme, when it calls Convert.
+type Meta struct {
+	// KeyNameMapping is an optional function which may map the listed key (field name)
+	// into a source and destination value.
+	KeyNameMapping FieldMappingFunc
+	// Context is an optional field that callers may use to pass info to conversion functions.
+	Context interface{}
+}
+
+// scope contains information about an ongoing conversion.
+type scope struct {
+	converter *Converter
+	meta      *Meta
+	flags     FieldMatchingFlags
+
+	// srcStack & destStack are separate because they may not have a 1:1
+	// relationship.
+	srcStack  scopeStack
+	destStack scopeStack
+}
+
+type scopeStackElem struct {
+	tag   reflect.StructTag
+	value reflect.Value
+	key   string
+}
+
+type scopeStack []scopeStackElem
+
+func (s *scopeStack) pop() {
+	n := len(*s)
+	*s = (*s)[:n-1]
+}
+
+func (s *scopeStack) push(e scopeStackElem) {
+	*s = append(*s, e)
+}
+
+func (s *scopeStack) top() *scopeStackElem {
+	return &(*s)[len(*s)-1]
+}
+
+func (s scopeStack) describe() string {
+	desc := ""
+	if len(s) > 1 {
+		desc = "(" + s[1].value.Type().String() + ")"
+	}
+	for i, v := range s {
+		if i < 2 {
+			// First layer on stack is not real; second is handled specially above.
+			continue
+		}
+		if v.key == "" {
+			desc += fmt.Sprintf(".%v", v.value.Type())
+		} else {
+			desc += fmt.Sprintf(".%v", v.key)
+		}
+	}
+	return desc
+}
+
+// Formats src & dest as indices for printing.
+func (s *scope) setIndices(src, dest int) {
+	s.srcStack.top().key = fmt.Sprintf("[%v]", src)
+	s.destStack.top().key = fmt.Sprintf("[%v]", dest)
+}
+
+// Formats src & dest as map keys for printing.
+func (s *scope) setKeys(src, dest interface{}) {
+	s.srcStack.top().key = fmt.Sprintf(`["%v"]`, src)
+	s.destStack.top().key = fmt.Sprintf(`["%v"]`, dest)
+}
+
+// Convert continues a conversion.
+func (s *scope) Convert(src, dest interface{}, flags FieldMatchingFlags) error {
+	return s.converter.Convert(src, dest, flags, s.meta)
+}
+
+// DefaultConvert continues a conversion, performing a default conversion (no conversion func)
+// for the current stack frame.
+func (s *scope) DefaultConvert(src, dest interface{}, flags FieldMatchingFlags) error {
+	return s.converter.DefaultConvert(src, dest, flags, s.meta)
+}
+
+// SrcTag returns the tag of the struct containing the current source item, if any.
+func (s *scope) SrcTag() reflect.StructTag {
+	return s.srcStack.top().tag
+}
+
+// DestTag returns the tag of the struct containing the current dest item, if any.
+func (s *scope) DestTag() reflect.StructTag {
+	return s.destStack.top().tag
+}
+
+// Flags returns the flags with which the current conversion was started.
+func (s *scope) Flags() FieldMatchingFlags {
+	return s.flags
+}
+
+// Meta returns the meta object that was originally passed to Convert.
+func (s *scope) Meta() *Meta {
+	return s.meta
+}
+
+// describe prints the path to get to the current (source, dest) values.
+func (s *scope) describe() (src, dest string) {
+	return s.srcStack.describe(), s.destStack.describe()
+}
+
+// error makes an error that includes information about where we were in the objects
+// we were asked to convert.
+func (s *scope) errorf(message string, args ...interface{}) error {
+	srcPath, destPath := s.describe()
+	where := fmt.Sprintf("converting %v to %v: ", srcPath, destPath)
+	return fmt.Errorf(where+message, args...)
+}
+
+// Verifies whether a conversion function has a correct signature.
+func verifyConversionFunctionSignature(ft reflect.Type) error {
+	if ft.Kind() != reflect.Func {
+		return fmt.Errorf("expected func, got: %v", ft)
+	}
+	if ft.NumIn() != 3 {
+		return fmt.Errorf("expected three 'in' params, got: %v", ft)
+	}
+	if ft.NumOut() != 1 {
+		return fmt.Errorf("expected one 'out' param, got: %v", ft)
+	}
+	if ft.In(0).Kind() != reflect.Ptr {
+		return fmt.Errorf("expected pointer arg for 'in' param 0, got: %v", ft)
+	}
+	if ft.In(1).Kind() != reflect.Ptr {
+		return fmt.Errorf("expected pointer arg for 'in' param 1, got: %v", ft)
+	}
+	scopeType := Scope(nil)
+	if e, a := reflect.TypeOf(&scopeType).Elem(), ft.In(2); e != a {
+		return fmt.Errorf("expected '%v' arg for 'in' param 2, got '%v' (%v)", e, a, ft)
+	}
+	var forErrorType error
+	// This convolution is necessary, otherwise TypeOf picks up on the fact
+	// that forErrorType is nil.
+	errorType := reflect.TypeOf(&forErrorType).Elem()
+	if ft.Out(0) != errorType {
+		return fmt.Errorf("expected error return, got: %v", ft)
+	}
+	return nil
+}
+
+// RegisterConversionFunc registers a conversion func with the
+// Converter. conversionFunc must take three parameters: a pointer to the input
+// type, a pointer to the output type, and a conversion.Scope (which should be
+// used if recursive conversion calls are desired).  It must return an error.
+//
+// Example:
+// c.RegisterConversionFunc(
+//         func(in *Pod, out *v1.Pod, s Scope) error {
+//                 // conversion logic...
+//                 return nil
+//          })
+func (c *Converter) RegisterConversionFunc(conversionFunc interface{}) error {
+	return c.conversionFuncs.Add(conversionFunc)
+}
+
+// Similar to RegisterConversionFunc, but registers conversion function that were
+// automatically generated.
+func (c *Converter) RegisterGeneratedConversionFunc(conversionFunc interface{}) error {
+	return c.generatedConversionFuncs.Add(conversionFunc)
+}
+
+// RegisterIgnoredConversion registers a "no-op" for conversion, where any requested
+// conversion between from and to is ignored.
+func (c *Converter) RegisterIgnoredConversion(from, to interface{}) error {
+	typeFrom := reflect.TypeOf(from)
+	typeTo := reflect.TypeOf(to)
+	if reflect.TypeOf(from).Kind() != reflect.Ptr {
+		return fmt.Errorf("expected pointer arg for 'from' param 0, got: %v", typeFrom)
+	}
+	if typeTo.Kind() != reflect.Ptr {
+		return fmt.Errorf("expected pointer arg for 'to' param 1, got: %v", typeTo)
+	}
+	c.ignoredConversions[typePair{typeFrom.Elem(), typeTo.Elem()}] = struct{}{}
+	return nil
+}
+
+// IsConversionIgnored returns true if the specified objects should be dropped during
+// conversion.
+func (c *Converter) IsConversionIgnored(inType, outType reflect.Type) bool {
+	_, found := c.ignoredConversions[typePair{inType, outType}]
+	return found
+}
+
+func (c *Converter) HasConversionFunc(inType, outType reflect.Type) bool {
+	_, found := c.conversionFuncs.fns[typePair{inType, outType}]
+	return found
+}
+
+func (c *Converter) ConversionFuncValue(inType, outType reflect.Type) (reflect.Value, bool) {
+	value, found := c.conversionFuncs.fns[typePair{inType, outType}]
+	return value, found
+}
+
+// SetStructFieldCopy registers a correspondence. Whenever a struct field is encountered
+// which has a type and name matching srcFieldType and srcFieldName, it wil be copied
+// into the field in the destination struct matching destFieldType & Name, if such a
+// field exists.
+// May be called multiple times, even for the same source field & type--all applicable
+// copies will be performed.
+func (c *Converter) SetStructFieldCopy(srcFieldType interface{}, srcFieldName string, destFieldType interface{}, destFieldName string) error {
+	st := reflect.TypeOf(srcFieldType)
+	dt := reflect.TypeOf(destFieldType)
+	srcKey := typeNamePair{st, srcFieldName}
+	destKey := typeNamePair{dt, destFieldName}
+	c.structFieldDests[srcKey] = append(c.structFieldDests[srcKey], destKey)
+	c.structFieldSources[destKey] = append(c.structFieldSources[destKey], srcKey)
+	return nil
+}
+
+// RegisterInputDefaults registers a field name mapping function, used when converting
+// from maps to structs. Inputs to the conversion methods are checked for this type and a mapping
+// applied automatically if the input matches in. A set of default flags for the input conversion
+// may also be provided, which will be used when no explicit flags are requested.
+func (c *Converter) RegisterInputDefaults(in interface{}, fn FieldMappingFunc, defaultFlags FieldMatchingFlags) error {
+	fv := reflect.ValueOf(in)
+	ft := fv.Type()
+	if ft.Kind() != reflect.Ptr {
+		return fmt.Errorf("expected pointer 'in' argument, got: %v", ft)
+	}
+	c.inputFieldMappingFuncs[ft] = fn
+	c.inputDefaultFlags[ft] = defaultFlags
+	return nil
+}
+
+// FieldMatchingFlags contains a list of ways in which struct fields could be
+// copied. These constants may be | combined.
+type FieldMatchingFlags int
+
+const (
+	// Loop through destination fields, search for matching source
+	// field to copy it from. Source fields with no corresponding
+	// destination field will be ignored. If SourceToDest is
+	// specified, this flag is ignored. If neither is specified,
+	// or no flags are passed, this flag is the default.
+	DestFromSource FieldMatchingFlags = 0
+	// Loop through source fields, search for matching dest field
+	// to copy it into. Destination fields with no corresponding
+	// source field will be ignored.
+	SourceToDest FieldMatchingFlags = 1 << iota
+	// Don't treat it as an error if the corresponding source or
+	// dest field can't be found.
+	IgnoreMissingFields
+	// Don't require type names to match.
+	AllowDifferentFieldTypeNames
+)
+
+// IsSet returns true if the given flag or combination of flags is set.
+func (f FieldMatchingFlags) IsSet(flag FieldMatchingFlags) bool {
+	if flag == DestFromSource {
+		// The bit logic doesn't work on the default value.
+		return f&SourceToDest != SourceToDest
+	}
+	return f&flag == flag
+}
+
+// Convert will translate src to dest if it knows how. Both must be pointers.
+// If no conversion func is registered and the default copying mechanism
+// doesn't work on this type pair, an error will be returned.
+// Read the comments on the various FieldMatchingFlags constants to understand
+// what the 'flags' parameter does.
+// 'meta' is given to allow you to pass information to conversion functions,
+// it is not used by Convert() other than storing it in the scope.
+// Not safe for objects with cyclic references!
+func (c *Converter) Convert(src, dest interface{}, flags FieldMatchingFlags, meta *Meta) error {
+	if len(c.genericConversions) > 0 {
+		// TODO: avoid scope allocation
+		s := &scope{converter: c, flags: flags, meta: meta}
+		for _, fn := range c.genericConversions {
+			if ok, err := fn(src, dest, s); ok {
+				return err
+			}
+		}
+	}
+	return c.doConversion(src, dest, flags, meta, c.convert)
+}
+
+// DefaultConvert will translate src to dest if it knows how. Both must be pointers.
+// No conversion func is used. If the default copying mechanism
+// doesn't work on this type pair, an error will be returned.
+// Read the comments on the various FieldMatchingFlags constants to understand
+// what the 'flags' parameter does.
+// 'meta' is given to allow you to pass information to conversion functions,
+// it is not used by DefaultConvert() other than storing it in the scope.
+// Not safe for objects with cyclic references!
+func (c *Converter) DefaultConvert(src, dest interface{}, flags FieldMatchingFlags, meta *Meta) error {
+	return c.doConversion(src, dest, flags, meta, c.defaultConvert)
+}
+
+type conversionFunc func(sv, dv reflect.Value, scope *scope) error
+
+func (c *Converter) doConversion(src, dest interface{}, flags FieldMatchingFlags, meta *Meta, f conversionFunc) error {
+	dv, err := EnforcePtr(dest)
+	if err != nil {
+		return err
+	}
+	if !dv.CanAddr() && !dv.CanSet() {
+		return fmt.Errorf("can't write to dest")
+	}
+	sv, err := EnforcePtr(src)
+	if err != nil {
+		return err
+	}
+	s := &scope{
+		converter: c,
+		flags:     flags,
+		meta:      meta,
+	}
+	// Leave something on the stack, so that calls to struct tag getters never fail.
+	s.srcStack.push(scopeStackElem{})
+	s.destStack.push(scopeStackElem{})
+	return f(sv, dv, s)
+}
+
+// callCustom calls 'custom' with sv & dv. custom must be a conversion function.
+func (c *Converter) callCustom(sv, dv, custom reflect.Value, scope *scope) error {
+	if !sv.CanAddr() {
+		sv2 := reflect.New(sv.Type())
+		sv2.Elem().Set(sv)
+		sv = sv2
+	} else {
+		sv = sv.Addr()
+	}
+	if !dv.CanAddr() {
+		if !dv.CanSet() {
+			return scope.errorf("can't addr or set dest.")
+		}
+		dvOrig := dv
+		dv := reflect.New(dvOrig.Type())
+		defer func() { dvOrig.Set(dv) }()
+	} else {
+		dv = dv.Addr()
+	}
+	args := []reflect.Value{sv, dv, reflect.ValueOf(scope)}
+	ret := custom.Call(args)[0].Interface()
+	// This convolution is necessary because nil interfaces won't convert
+	// to errors.
+	if ret == nil {
+		return nil
+	}
+	return ret.(error)
+}
+
+// convert recursively copies sv into dv, calling an appropriate conversion function if
+// one is registered.
+func (c *Converter) convert(sv, dv reflect.Value, scope *scope) error {
+	dt, st := dv.Type(), sv.Type()
+	pair := typePair{st, dt}
+
+	// ignore conversions of this type
+	if _, ok := c.ignoredConversions[pair]; ok {
+		if c.Debug != nil {
+			c.Debug.Logf("Ignoring conversion of '%v' to '%v'", st, dt)
+		}
+		return nil
+	}
+
+	// Convert sv to dv.
+	if fv, ok := c.conversionFuncs.fns[pair]; ok {
+		if c.Debug != nil {
+			c.Debug.Logf("Calling custom conversion of '%v' to '%v'", st, dt)
+		}
+		return c.callCustom(sv, dv, fv, scope)
+	}
+	if fv, ok := c.generatedConversionFuncs.fns[pair]; ok {
+		if c.Debug != nil {
+			c.Debug.Logf("Calling generated conversion of '%v' to '%v'", st, dt)
+		}
+		return c.callCustom(sv, dv, fv, scope)
+	}
+
+	return c.defaultConvert(sv, dv, scope)
+}
+
+// defaultConvert recursively copies sv into dv. no conversion function is called
+// for the current stack frame (but conversion functions may be called for nested objects)
+func (c *Converter) defaultConvert(sv, dv reflect.Value, scope *scope) error {
+	dt, st := dv.Type(), sv.Type()
+
+	if !dv.CanSet() {
+		return scope.errorf("Cannot set dest. (Tried to deep copy something with unexported fields?)")
+	}
+
+	if !scope.flags.IsSet(AllowDifferentFieldTypeNames) && c.nameFunc(dt) != c.nameFunc(st) {
+		return scope.errorf(
+			"type names don't match (%v, %v), and no conversion 'func (%v, %v) error' registered.",
+			c.nameFunc(st), c.nameFunc(dt), st, dt)
+	}
+
+	switch st.Kind() {
+	case reflect.Map, reflect.Ptr, reflect.Slice, reflect.Interface, reflect.Struct:
+		// Don't copy these via assignment/conversion!
+	default:
+		// This should handle all simple types.
+		if st.AssignableTo(dt) {
+			dv.Set(sv)
+			return nil
+		}
+		if st.ConvertibleTo(dt) {
+			dv.Set(sv.Convert(dt))
+			return nil
+		}
+	}
+
+	if c.Debug != nil {
+		c.Debug.Logf("Trying to convert '%v' to '%v'", st, dt)
+	}
+
+	scope.srcStack.push(scopeStackElem{value: sv})
+	scope.destStack.push(scopeStackElem{value: dv})
+	defer scope.srcStack.pop()
+	defer scope.destStack.pop()
+
+	switch dv.Kind() {
+	case reflect.Struct:
+		return c.convertKV(toKVValue(sv), toKVValue(dv), scope)
+	case reflect.Slice:
+		if sv.IsNil() {
+			// Don't make a zero-length slice.
+			dv.Set(reflect.Zero(dt))
+			return nil
+		}
+		dv.Set(reflect.MakeSlice(dt, sv.Len(), sv.Cap()))
+		for i := 0; i < sv.Len(); i++ {
+			scope.setIndices(i, i)
+			if err := c.convert(sv.Index(i), dv.Index(i), scope); err != nil {
+				return err
+			}
+		}
+	case reflect.Ptr:
+		if sv.IsNil() {
+			// Don't copy a nil ptr!
+			dv.Set(reflect.Zero(dt))
+			return nil
+		}
+		dv.Set(reflect.New(dt.Elem()))
+		switch st.Kind() {
+		case reflect.Ptr, reflect.Interface:
+			return c.convert(sv.Elem(), dv.Elem(), scope)
+		default:
+			return c.convert(sv, dv.Elem(), scope)
+		}
+	case reflect.Map:
+		if sv.IsNil() {
+			// Don't copy a nil ptr!
+			dv.Set(reflect.Zero(dt))
+			return nil
+		}
+		dv.Set(reflect.MakeMap(dt))
+		for _, sk := range sv.MapKeys() {
+			dk := reflect.New(dt.Key()).Elem()
+			if err := c.convert(sk, dk, scope); err != nil {
+				return err
+			}
+			dkv := reflect.New(dt.Elem()).Elem()
+			scope.setKeys(sk.Interface(), dk.Interface())
+			// TODO:  sv.MapIndex(sk) may return a value with CanAddr() == false,
+			// because a map[string]struct{} does not allow a pointer reference.
+			// Calling a custom conversion function defined for the map value
+			// will panic. Example is PodInfo map[string]ContainerStatus.
+			if err := c.convert(sv.MapIndex(sk), dkv, scope); err != nil {
+				return err
+			}
+			dv.SetMapIndex(dk, dkv)
+		}
+	case reflect.Interface:
+		if sv.IsNil() {
+			// Don't copy a nil interface!
+			dv.Set(reflect.Zero(dt))
+			return nil
+		}
+		tmpdv := reflect.New(sv.Elem().Type()).Elem()
+		if err := c.convert(sv.Elem(), tmpdv, scope); err != nil {
+			return err
+		}
+		dv.Set(reflect.ValueOf(tmpdv.Interface()))
+		return nil
+	default:
+		return scope.errorf("couldn't copy '%v' into '%v'; didn't understand types", st, dt)
+	}
+	return nil
+}
+
+var stringType = reflect.TypeOf("")
+
+func toKVValue(v reflect.Value) kvValue {
+	switch v.Kind() {
+	case reflect.Struct:
+		return structAdaptor(v)
+	case reflect.Map:
+		if v.Type().Key().AssignableTo(stringType) {
+			return stringMapAdaptor(v)
+		}
+	}
+
+	return nil
+}
+
+// kvValue lets us write the same conversion logic to work with both maps
+// and structs. Only maps with string keys make sense for this.
+type kvValue interface {
+	// returns all keys, as a []string.
+	keys() []string
+	// Will just return "" for maps.
+	tagOf(key string) reflect.StructTag
+	// Will return the zero Value if the key doesn't exist.
+	value(key string) reflect.Value
+	// Maps require explicit setting-- will do nothing for structs.
+	// Returns false on failure.
+	confirmSet(key string, v reflect.Value) bool
+}
+
+type stringMapAdaptor reflect.Value
+
+func (a stringMapAdaptor) len() int {
+	return reflect.Value(a).Len()
+}
+
+func (a stringMapAdaptor) keys() []string {
+	v := reflect.Value(a)
+	keys := make([]string, v.Len())
+	for i, v := range v.MapKeys() {
+		if v.IsNil() {
+			continue
+		}
+		switch t := v.Interface().(type) {
+		case string:
+			keys[i] = t
+		}
+	}
+	return keys
+}
+
+func (a stringMapAdaptor) tagOf(key string) reflect.StructTag {
+	return ""
+}
+
+func (a stringMapAdaptor) value(key string) reflect.Value {
+	return reflect.Value(a).MapIndex(reflect.ValueOf(key))
+}
+
+func (a stringMapAdaptor) confirmSet(key string, v reflect.Value) bool {
+	return true
+}
+
+type structAdaptor reflect.Value
+
+func (a structAdaptor) len() int {
+	v := reflect.Value(a)
+	return v.Type().NumField()
+}
+
+func (a structAdaptor) keys() []string {
+	v := reflect.Value(a)
+	t := v.Type()
+	keys := make([]string, t.NumField())
+	for i := range keys {
+		keys[i] = t.Field(i).Name
+	}
+	return keys
+}
+
+func (a structAdaptor) tagOf(key string) reflect.StructTag {
+	v := reflect.Value(a)
+	field, ok := v.Type().FieldByName(key)
+	if ok {
+		return field.Tag
+	}
+	return ""
+}
+
+func (a structAdaptor) value(key string) reflect.Value {
+	v := reflect.Value(a)
+	return v.FieldByName(key)
+}
+
+func (a structAdaptor) confirmSet(key string, v reflect.Value) bool {
+	return true
+}
+
+// convertKV can convert things that consist of key/value pairs, like structs
+// and some maps.
+func (c *Converter) convertKV(skv, dkv kvValue, scope *scope) error {
+	if skv == nil || dkv == nil {
+		// TODO: add keys to stack to support really understandable error messages.
+		return fmt.Errorf("Unable to convert %#v to %#v", skv, dkv)
+	}
+
+	lister := dkv
+	if scope.flags.IsSet(SourceToDest) {
+		lister = skv
+	}
+
+	var mapping FieldMappingFunc
+	if scope.meta != nil && scope.meta.KeyNameMapping != nil {
+		mapping = scope.meta.KeyNameMapping
+	}
+
+	for _, key := range lister.keys() {
+		if found, err := c.checkField(key, skv, dkv, scope); found {
+			if err != nil {
+				return err
+			}
+			continue
+		}
+		stag := skv.tagOf(key)
+		dtag := dkv.tagOf(key)
+		skey := key
+		dkey := key
+		if mapping != nil {
+			skey, dkey = scope.meta.KeyNameMapping(key, stag, dtag)
+		}
+
+		df := dkv.value(dkey)
+		sf := skv.value(skey)
+		if !df.IsValid() || !sf.IsValid() {
+			switch {
+			case scope.flags.IsSet(IgnoreMissingFields):
+				// No error.
+			case scope.flags.IsSet(SourceToDest):
+				return scope.errorf("%v not present in dest", dkey)
+			default:
+				return scope.errorf("%v not present in src", skey)
+			}
+			continue
+		}
+		scope.srcStack.top().key = skey
+		scope.srcStack.top().tag = stag
+		scope.destStack.top().key = dkey
+		scope.destStack.top().tag = dtag
+		if err := c.convert(sf, df, scope); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// checkField returns true if the field name matches any of the struct
+// field copying rules. The error should be ignored if it returns false.
+func (c *Converter) checkField(fieldName string, skv, dkv kvValue, scope *scope) (bool, error) {
+	replacementMade := false
+	if scope.flags.IsSet(DestFromSource) {
+		df := dkv.value(fieldName)
+		if !df.IsValid() {
+			return false, nil
+		}
+		destKey := typeNamePair{df.Type(), fieldName}
+		// Check each of the potential source (type, name) pairs to see if they're
+		// present in sv.
+		for _, potentialSourceKey := range c.structFieldSources[destKey] {
+			sf := skv.value(potentialSourceKey.fieldName)
+			if !sf.IsValid() {
+				continue
+			}
+			if sf.Type() == potentialSourceKey.fieldType {
+				// Both the source's name and type matched, so copy.
+				scope.srcStack.top().key = potentialSourceKey.fieldName
+				scope.destStack.top().key = fieldName
+				if err := c.convert(sf, df, scope); err != nil {
+					return true, err
+				}
+				dkv.confirmSet(fieldName, df)
+				replacementMade = true
+			}
+		}
+		return replacementMade, nil
+	}
+
+	sf := skv.value(fieldName)
+	if !sf.IsValid() {
+		return false, nil
+	}
+	srcKey := typeNamePair{sf.Type(), fieldName}
+	// Check each of the potential dest (type, name) pairs to see if they're
+	// present in dv.
+	for _, potentialDestKey := range c.structFieldDests[srcKey] {
+		df := dkv.value(potentialDestKey.fieldName)
+		if !df.IsValid() {
+			continue
+		}
+		if df.Type() == potentialDestKey.fieldType {
+			// Both the dest's name and type matched, so copy.
+			scope.srcStack.top().key = fieldName
+			scope.destStack.top().key = potentialDestKey.fieldName
+			if err := c.convert(sf, df, scope); err != nil {
+				return true, err
+			}
+			dkv.confirmSet(potentialDestKey.fieldName, df)
+			replacementMade = true
+		}
+	}
+	return replacementMade, nil
+}