open-consul/vendor/github.com/hashicorp/go-memdb/index.go

884 lines
24 KiB
Go

package memdb
import (
"encoding/binary"
"encoding/hex"
"errors"
"fmt"
"reflect"
"strings"
)
// Indexer is an interface used for defining indexes. Indexes are used
// for efficient lookup of objects in a MemDB table. An Indexer must also
// implement one of SingleIndexer or MultiIndexer.
//
// Indexers are primarily responsible for returning the lookup key as
// a byte slice. The byte slice is the key data in the underlying data storage.
type Indexer interface {
// FromArgs is called to build the exact index key from a list of arguments.
FromArgs(args ...interface{}) ([]byte, error)
}
// SingleIndexer is an interface used for defining indexes that generate a
// single value per object
type SingleIndexer interface {
// FromObject extracts the index value from an object. The return values
// are whether the index value was found, the index value, and any error
// while extracting the index value, respectively.
FromObject(raw interface{}) (bool, []byte, error)
}
// MultiIndexer is an interface used for defining indexes that generate
// multiple values per object. Each value is stored as a seperate index
// pointing to the same object.
//
// For example, an index that extracts the first and last name of a person
// and allows lookup based on eitherd would be a MultiIndexer. The FromObject
// of this example would split the first and last name and return both as
// values.
type MultiIndexer interface {
// FromObject extracts index values from an object. The return values
// are the same as a SingleIndexer except there can be multiple index
// values.
FromObject(raw interface{}) (bool, [][]byte, error)
}
// PrefixIndexer is an optional interface on top of an Indexer that allows
// indexes to support prefix-based iteration.
type PrefixIndexer interface {
// PrefixFromArgs is the same as FromArgs for an Indexer except that
// the index value returned should return all prefix-matched values.
PrefixFromArgs(args ...interface{}) ([]byte, error)
}
// StringFieldIndex is used to extract a field from an object
// using reflection and builds an index on that field.
type StringFieldIndex struct {
Field string
Lowercase bool
}
func (s *StringFieldIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(s.Field)
isPtr := fv.Kind() == reflect.Ptr
fv = reflect.Indirect(fv)
if !isPtr && !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid %v ", s.Field, obj, isPtr)
}
if isPtr && !fv.IsValid() {
val := ""
return false, []byte(val), nil
}
val := fv.String()
if val == "" {
return false, nil, nil
}
if s.Lowercase {
val = strings.ToLower(val)
}
// Add the null character as a terminator
val += "\x00"
return true, []byte(val), nil
}
func (s *StringFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
arg, ok := args[0].(string)
if !ok {
return nil, fmt.Errorf("argument must be a string: %#v", args[0])
}
if s.Lowercase {
arg = strings.ToLower(arg)
}
// Add the null character as a terminator
arg += "\x00"
return []byte(arg), nil
}
func (s *StringFieldIndex) PrefixFromArgs(args ...interface{}) ([]byte, error) {
val, err := s.FromArgs(args...)
if err != nil {
return nil, err
}
// Strip the null terminator, the rest is a prefix
n := len(val)
if n > 0 {
return val[:n-1], nil
}
return val, nil
}
// StringSliceFieldIndex builds an index from a field on an object that is a
// string slice ([]string). Each value within the string slice can be used for
// lookup.
type StringSliceFieldIndex struct {
Field string
Lowercase bool
}
func (s *StringSliceFieldIndex) FromObject(obj interface{}) (bool, [][]byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(s.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", s.Field, obj)
}
if fv.Kind() != reflect.Slice || fv.Type().Elem().Kind() != reflect.String {
return false, nil, fmt.Errorf("field '%s' is not a string slice", s.Field)
}
length := fv.Len()
vals := make([][]byte, 0, length)
for i := 0; i < fv.Len(); i++ {
val := fv.Index(i).String()
if val == "" {
continue
}
if s.Lowercase {
val = strings.ToLower(val)
}
// Add the null character as a terminator
val += "\x00"
vals = append(vals, []byte(val))
}
if len(vals) == 0 {
return false, nil, nil
}
return true, vals, nil
}
func (s *StringSliceFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
arg, ok := args[0].(string)
if !ok {
return nil, fmt.Errorf("argument must be a string: %#v", args[0])
}
if s.Lowercase {
arg = strings.ToLower(arg)
}
// Add the null character as a terminator
arg += "\x00"
return []byte(arg), nil
}
func (s *StringSliceFieldIndex) PrefixFromArgs(args ...interface{}) ([]byte, error) {
val, err := s.FromArgs(args...)
if err != nil {
return nil, err
}
// Strip the null terminator, the rest is a prefix
n := len(val)
if n > 0 {
return val[:n-1], nil
}
return val, nil
}
// StringMapFieldIndex is used to extract a field of type map[string]string
// from an object using reflection and builds an index on that field.
//
// Note that although FromArgs in theory supports using either one or
// two arguments, there is a bug: FromObject only creates an index
// using key/value, and does not also create an index using key. This
// means a lookup using one argument will never actually work.
//
// It is currently left as-is to prevent backwards compatibility
// issues.
//
// TODO: Fix this in the next major bump.
type StringMapFieldIndex struct {
Field string
Lowercase bool
}
var MapType = reflect.MapOf(reflect.TypeOf(""), reflect.TypeOf("")).Kind()
func (s *StringMapFieldIndex) FromObject(obj interface{}) (bool, [][]byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(s.Field)
if !fv.IsValid() {
return false, nil, fmt.Errorf("field '%s' for %#v is invalid", s.Field, obj)
}
if fv.Kind() != MapType {
return false, nil, fmt.Errorf("field '%s' is not a map[string]string", s.Field)
}
length := fv.Len()
vals := make([][]byte, 0, length)
for _, key := range fv.MapKeys() {
k := key.String()
if k == "" {
continue
}
val := fv.MapIndex(key).String()
if s.Lowercase {
k = strings.ToLower(k)
val = strings.ToLower(val)
}
// Add the null character as a terminator
k += "\x00" + val + "\x00"
vals = append(vals, []byte(k))
}
if len(vals) == 0 {
return false, nil, nil
}
return true, vals, nil
}
// WARNING: Because of a bug in FromObject, this function will never return
// a value when using the single-argument version.
func (s *StringMapFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) > 2 || len(args) == 0 {
return nil, fmt.Errorf("must provide one or two arguments")
}
key, ok := args[0].(string)
if !ok {
return nil, fmt.Errorf("argument must be a string: %#v", args[0])
}
if s.Lowercase {
key = strings.ToLower(key)
}
// Add the null character as a terminator
key += "\x00"
if len(args) == 2 {
val, ok := args[1].(string)
if !ok {
return nil, fmt.Errorf("argument must be a string: %#v", args[1])
}
if s.Lowercase {
val = strings.ToLower(val)
}
// Add the null character as a terminator
key += val + "\x00"
}
return []byte(key), nil
}
// IntFieldIndex is used to extract an int field from an object using
// reflection and builds an index on that field.
type IntFieldIndex struct {
Field string
}
func (i *IntFieldIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(i.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", i.Field, obj)
}
// Check the type
k := fv.Kind()
size, ok := IsIntType(k)
if !ok {
return false, nil, fmt.Errorf("field %q is of type %v; want an int", i.Field, k)
}
// Get the value and encode it
val := fv.Int()
buf := make([]byte, size)
binary.PutVarint(buf, val)
return true, buf, nil
}
func (i *IntFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
v := reflect.ValueOf(args[0])
if !v.IsValid() {
return nil, fmt.Errorf("%#v is invalid", args[0])
}
k := v.Kind()
size, ok := IsIntType(k)
if !ok {
return nil, fmt.Errorf("arg is of type %v; want a int", k)
}
val := v.Int()
buf := make([]byte, size)
binary.PutVarint(buf, val)
return buf, nil
}
// IsIntType returns whether the passed type is a type of int and the number
// of bytes needed to encode the type.
func IsIntType(k reflect.Kind) (size int, okay bool) {
switch k {
case reflect.Int:
return binary.MaxVarintLen64, true
case reflect.Int8:
return 2, true
case reflect.Int16:
return binary.MaxVarintLen16, true
case reflect.Int32:
return binary.MaxVarintLen32, true
case reflect.Int64:
return binary.MaxVarintLen64, true
default:
return 0, false
}
}
// UintFieldIndex is used to extract a uint field from an object using
// reflection and builds an index on that field.
type UintFieldIndex struct {
Field string
}
func (u *UintFieldIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(u.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", u.Field, obj)
}
// Check the type
k := fv.Kind()
size, ok := IsUintType(k)
if !ok {
return false, nil, fmt.Errorf("field %q is of type %v; want a uint", u.Field, k)
}
// Get the value and encode it
val := fv.Uint()
buf := make([]byte, size)
binary.PutUvarint(buf, val)
return true, buf, nil
}
func (u *UintFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
v := reflect.ValueOf(args[0])
if !v.IsValid() {
return nil, fmt.Errorf("%#v is invalid", args[0])
}
k := v.Kind()
size, ok := IsUintType(k)
if !ok {
return nil, fmt.Errorf("arg is of type %v; want a uint", k)
}
val := v.Uint()
buf := make([]byte, size)
binary.PutUvarint(buf, val)
return buf, nil
}
// IsUintType returns whether the passed type is a type of uint and the number
// of bytes needed to encode the type.
func IsUintType(k reflect.Kind) (size int, okay bool) {
switch k {
case reflect.Uint:
return binary.MaxVarintLen64, true
case reflect.Uint8:
return 2, true
case reflect.Uint16:
return binary.MaxVarintLen16, true
case reflect.Uint32:
return binary.MaxVarintLen32, true
case reflect.Uint64:
return binary.MaxVarintLen64, true
default:
return 0, false
}
}
// BoolFieldIndex is used to extract an boolean field from an object using
// reflection and builds an index on that field.
type BoolFieldIndex struct {
Field string
}
func (i *BoolFieldIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(i.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", i.Field, obj)
}
// Check the type
k := fv.Kind()
if k != reflect.Bool {
return false, nil, fmt.Errorf("field %q is of type %v; want a bool", i.Field, k)
}
// Get the value and encode it
buf := make([]byte, 1)
if fv.Bool() {
buf[0] = 1
}
return true, buf, nil
}
func (i *BoolFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
return fromBoolArgs(args)
}
// UUIDFieldIndex is used to extract a field from an object
// using reflection and builds an index on that field by treating
// it as a UUID. This is an optimization to using a StringFieldIndex
// as the UUID can be more compactly represented in byte form.
type UUIDFieldIndex struct {
Field string
}
func (u *UUIDFieldIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(u.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", u.Field, obj)
}
val := fv.String()
if val == "" {
return false, nil, nil
}
buf, err := u.parseString(val, true)
return true, buf, err
}
func (u *UUIDFieldIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
switch arg := args[0].(type) {
case string:
return u.parseString(arg, true)
case []byte:
if len(arg) != 16 {
return nil, fmt.Errorf("byte slice must be 16 characters")
}
return arg, nil
default:
return nil,
fmt.Errorf("argument must be a string or byte slice: %#v", args[0])
}
}
func (u *UUIDFieldIndex) PrefixFromArgs(args ...interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
switch arg := args[0].(type) {
case string:
return u.parseString(arg, false)
case []byte:
return arg, nil
default:
return nil,
fmt.Errorf("argument must be a string or byte slice: %#v", args[0])
}
}
// parseString parses a UUID from the string. If enforceLength is false, it will
// parse a partial UUID. An error is returned if the input, stripped of hyphens,
// is not even length.
func (u *UUIDFieldIndex) parseString(s string, enforceLength bool) ([]byte, error) {
// Verify the length
l := len(s)
if enforceLength && l != 36 {
return nil, fmt.Errorf("UUID must be 36 characters")
} else if l > 36 {
return nil, fmt.Errorf("Invalid UUID length. UUID have 36 characters; got %d", l)
}
hyphens := strings.Count(s, "-")
if hyphens > 4 {
return nil, fmt.Errorf(`UUID should have maximum of 4 "-"; got %d`, hyphens)
}
// The sanitized length is the length of the original string without the "-".
sanitized := strings.Replace(s, "-", "", -1)
sanitizedLength := len(sanitized)
if sanitizedLength%2 != 0 {
return nil, fmt.Errorf("Input (without hyphens) must be even length")
}
dec, err := hex.DecodeString(sanitized)
if err != nil {
return nil, fmt.Errorf("Invalid UUID: %v", err)
}
return dec, nil
}
// FieldSetIndex is used to extract a field from an object using reflection and
// builds an index on whether the field is set by comparing it against its
// type's nil value.
type FieldSetIndex struct {
Field string
}
func (f *FieldSetIndex) FromObject(obj interface{}) (bool, []byte, error) {
v := reflect.ValueOf(obj)
v = reflect.Indirect(v) // Dereference the pointer if any
fv := v.FieldByName(f.Field)
if !fv.IsValid() {
return false, nil,
fmt.Errorf("field '%s' for %#v is invalid", f.Field, obj)
}
if fv.Interface() == reflect.Zero(fv.Type()).Interface() {
return true, []byte{0}, nil
}
return true, []byte{1}, nil
}
func (f *FieldSetIndex) FromArgs(args ...interface{}) ([]byte, error) {
return fromBoolArgs(args)
}
// ConditionalIndex builds an index based on a condition specified by a passed
// user function. This function may examine the passed object and return a
// boolean to encapsulate an arbitrarily complex conditional.
type ConditionalIndex struct {
Conditional ConditionalIndexFunc
}
// ConditionalIndexFunc is the required function interface for a
// ConditionalIndex.
type ConditionalIndexFunc func(obj interface{}) (bool, error)
func (c *ConditionalIndex) FromObject(obj interface{}) (bool, []byte, error) {
// Call the user's function
res, err := c.Conditional(obj)
if err != nil {
return false, nil, fmt.Errorf("ConditionalIndexFunc(%#v) failed: %v", obj, err)
}
if res {
return true, []byte{1}, nil
}
return true, []byte{0}, nil
}
func (c *ConditionalIndex) FromArgs(args ...interface{}) ([]byte, error) {
return fromBoolArgs(args)
}
// fromBoolArgs is a helper that expects only a single boolean argument and
// returns a single length byte array containing either a one or zero depending
// on whether the passed input is true or false respectively.
func fromBoolArgs(args []interface{}) ([]byte, error) {
if len(args) != 1 {
return nil, fmt.Errorf("must provide only a single argument")
}
if val, ok := args[0].(bool); !ok {
return nil, fmt.Errorf("argument must be a boolean type: %#v", args[0])
} else if val {
return []byte{1}, nil
}
return []byte{0}, nil
}
// CompoundIndex is used to build an index using multiple sub-indexes
// Prefix based iteration is supported as long as the appropriate prefix
// of indexers support it. All sub-indexers are only assumed to expect
// a single argument.
type CompoundIndex struct {
Indexes []Indexer
// AllowMissing results in an index based on only the indexers
// that return data. If true, you may end up with 2/3 columns
// indexed which might be useful for an index scan. Otherwise,
// the CompoundIndex requires all indexers to be satisfied.
AllowMissing bool
}
func (c *CompoundIndex) FromObject(raw interface{}) (bool, []byte, error) {
var out []byte
for i, idxRaw := range c.Indexes {
idx, ok := idxRaw.(SingleIndexer)
if !ok {
return false, nil, fmt.Errorf("sub-index %d error: %s", i, "sub-index must be a SingleIndexer")
}
ok, val, err := idx.FromObject(raw)
if err != nil {
return false, nil, fmt.Errorf("sub-index %d error: %v", i, err)
}
if !ok {
if c.AllowMissing {
break
} else {
return false, nil, nil
}
}
out = append(out, val...)
}
return true, out, nil
}
func (c *CompoundIndex) FromArgs(args ...interface{}) ([]byte, error) {
if len(args) != len(c.Indexes) {
return nil, fmt.Errorf("non-equivalent argument count and index fields")
}
var out []byte
for i, arg := range args {
val, err := c.Indexes[i].FromArgs(arg)
if err != nil {
return nil, fmt.Errorf("sub-index %d error: %v", i, err)
}
out = append(out, val...)
}
return out, nil
}
func (c *CompoundIndex) PrefixFromArgs(args ...interface{}) ([]byte, error) {
if len(args) > len(c.Indexes) {
return nil, fmt.Errorf("more arguments than index fields")
}
var out []byte
for i, arg := range args {
if i+1 < len(args) {
val, err := c.Indexes[i].FromArgs(arg)
if err != nil {
return nil, fmt.Errorf("sub-index %d error: %v", i, err)
}
out = append(out, val...)
} else {
prefixIndexer, ok := c.Indexes[i].(PrefixIndexer)
if !ok {
return nil, fmt.Errorf("sub-index %d does not support prefix scanning", i)
}
val, err := prefixIndexer.PrefixFromArgs(arg)
if err != nil {
return nil, fmt.Errorf("sub-index %d error: %v", i, err)
}
out = append(out, val...)
}
}
return out, nil
}
// CompoundMultiIndex is used to build an index using multiple
// sub-indexes.
//
// Unlike CompoundIndex, CompoundMultiIndex can have both
// SingleIndexer and MultiIndexer sub-indexers. However, each
// MultiIndexer adds considerable overhead/complexity in terms of
// the number of indexes created under-the-hood. It is not suggested
// to use more than one or two, if possible.
//
// Another change from CompoundIndexer is that if AllowMissing is
// set, not only is it valid to have empty index fields, but it will
// still create index values up to the first empty index. This means
// that if you have a value with an empty field, rather than using a
// prefix for lookup, you can simply pass in less arguments. As an
// example, if {Foo, Bar} is indexed but Bar is missing for a value
// and AllowMissing is set, an index will still be created for {Foo}
// and it is valid to do a lookup passing in only Foo as an argument.
// Note that the ordering isn't guaranteed -- it's last-insert wins,
// but this is true if you have two objects that have the same
// indexes not using AllowMissing anyways.
//
// Because StringMapFieldIndexers can take a varying number of args,
// it is currently a requirement that whenever it is used, two
// arguments must _always_ be provided for it. In theory we only
// need one, except a bug in that indexer means the single-argument
// version will never work. You can leave the second argument nil,
// but it will never produce a value. We support this for whenever
// that bug is fixed, likely in a next major version bump.
//
// Prefix-based indexing is not currently supported.
type CompoundMultiIndex struct {
Indexes []Indexer
// AllowMissing results in an index based on only the indexers
// that return data. If true, you may end up with 2/3 columns
// indexed which might be useful for an index scan. Otherwise,
// CompoundMultiIndex requires all indexers to be satisfied.
AllowMissing bool
}
func (c *CompoundMultiIndex) FromObject(raw interface{}) (bool, [][]byte, error) {
// At each entry, builder is storing the results from the next index
builder := make([][][]byte, 0, len(c.Indexes))
// Start with something higher to avoid resizing if possible
out := make([][]byte, 0, len(c.Indexes)^3)
forloop:
// This loop goes through each indexer and adds the value(s) provided to the next
// entry in the slice. We can then later walk it like a tree to construct the indices.
for i, idxRaw := range c.Indexes {
switch idx := idxRaw.(type) {
case SingleIndexer:
ok, val, err := idx.FromObject(raw)
if err != nil {
return false, nil, fmt.Errorf("single sub-index %d error: %v", i, err)
}
if !ok {
if c.AllowMissing {
break forloop
} else {
return false, nil, nil
}
}
builder = append(builder, [][]byte{val})
case MultiIndexer:
ok, vals, err := idx.FromObject(raw)
if err != nil {
return false, nil, fmt.Errorf("multi sub-index %d error: %v", i, err)
}
if !ok {
if c.AllowMissing {
break forloop
} else {
return false, nil, nil
}
}
// Add each of the new values to each of the old values
builder = append(builder, vals)
default:
return false, nil, fmt.Errorf("sub-index %d does not satisfy either SingleIndexer or MultiIndexer", i)
}
}
// We are walking through the builder slice essentially in a depth-first fashion,
// building the prefix and leaves as we go. If AllowMissing is false, we only insert
// these full paths to leaves. Otherwise, we also insert each prefix along the way.
// This allows for lookup in FromArgs when AllowMissing is true that does not contain
// the full set of arguments. e.g. for {Foo, Bar} where an object has only the Foo
// field specified as "abc", it is valid to call FromArgs with just "abc".
var walkVals func([]byte, int)
walkVals = func(currPrefix []byte, depth int) {
if depth == len(builder)-1 {
// These are the "leaves", so append directly
for _, v := range builder[depth] {
out = append(out, append(currPrefix, v...))
}
return
}
for _, v := range builder[depth] {
nextPrefix := append(currPrefix, v...)
if c.AllowMissing {
out = append(out, nextPrefix)
}
walkVals(nextPrefix, depth+1)
}
}
walkVals(nil, 0)
return true, out, nil
}
func (c *CompoundMultiIndex) FromArgs(args ...interface{}) ([]byte, error) {
var stringMapCount int
var argCount int
for _, index := range c.Indexes {
if argCount >= len(args) {
break
}
if _, ok := index.(*StringMapFieldIndex); ok {
// We require pairs for StringMapFieldIndex, but only got one
if argCount+1 >= len(args) {
return nil, errors.New("invalid number of arguments")
}
stringMapCount++
argCount += 2
} else {
argCount++
}
}
argCount = 0
switch c.AllowMissing {
case true:
if len(args) > len(c.Indexes)+stringMapCount {
return nil, errors.New("too many arguments")
}
default:
if len(args) != len(c.Indexes)+stringMapCount {
return nil, errors.New("number of arguments does not equal number of indexers")
}
}
var out []byte
var val []byte
var err error
for i, idx := range c.Indexes {
if argCount >= len(args) {
// We're done; should only hit this if AllowMissing
break
}
if _, ok := idx.(*StringMapFieldIndex); ok {
if args[argCount+1] == nil {
val, err = idx.FromArgs(args[argCount])
} else {
val, err = idx.FromArgs(args[argCount : argCount+2]...)
}
argCount += 2
} else {
val, err = idx.FromArgs(args[argCount])
argCount++
}
if err != nil {
return nil, fmt.Errorf("sub-index %d error: %v", i, err)
}
out = append(out, val...)
}
return out, nil
}