lang: core: Simplify list and map lookup functions
This commit is contained in:
James Shubin
@@ -34,191 +34,39 @@ import (
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"fmt"
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"math"
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"github.com/purpleidea/mgmt/lang/funcs"
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"github.com/purpleidea/mgmt/lang/interfaces"
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"github.com/purpleidea/mgmt/lang/funcs/simple"
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"github.com/purpleidea/mgmt/lang/types"
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"github.com/purpleidea/mgmt/util/errwrap"
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)
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const (
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// ListLookupFuncName is the name this function is registered as.
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ListLookupFuncName = "list_lookup"
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// arg names...
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listLookupArgNameList = "list"
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listLookupArgNameIndex = "index"
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)
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func init() {
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funcs.Register(ListLookupFuncName, func() interfaces.Func { return &ListLookupFunc{} }) // must register the func and name
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simple.Register(ListLookupFuncName, &simple.Scaffold{
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T: types.NewType("func(list []?1, index int) ?1"),
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F: ListLookup,
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})
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}
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var _ interfaces.BuildableFunc = &ListLookupFunc{} // ensure it meets this expectation
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// ListLookup returns the value corresponding to the input index in the list.
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func ListLookup(ctx context.Context, input []types.Value) (types.Value, error) {
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l := input[0].(*types.ListValue)
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index := input[1].Int()
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zero := l.Type().Val.New() // the zero value
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// ListLookupFunc is a list index lookup function. If you provide a negative
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// index, then it will return the zero value for that type.
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type ListLookupFunc struct {
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Type *types.Type // Kind == List, that is used as the list we lookup in
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// TODO: should we handle overflow by returning zero?
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if index > math.MaxInt { // max int size varies by arch
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return nil, fmt.Errorf("list index overflow, got: %d, max is: %d", index, math.MaxInt)
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}
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if index < 0 { // lists can't have negative indexes (for now)
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return nil, fmt.Errorf("list index negative, got: %d", index)
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}
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init *interfaces.Init
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last types.Value // last value received to use for diff
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result types.Value // last calculated output
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}
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// String returns a simple name for this function. This is needed so this struct
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// can satisfy the pgraph.Vertex interface.
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func (obj *ListLookupFunc) String() string {
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return ListLookupFuncName
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}
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// ArgGen returns the Nth arg name for this function.
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func (obj *ListLookupFunc) ArgGen(index int) (string, error) {
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seq := []string{listLookupArgNameList, listLookupArgNameIndex}
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if l := len(seq); index >= l {
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return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
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}
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return seq[index], nil
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}
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// helper
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func (obj *ListLookupFunc) sig() *types.Type {
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// func(list []?1, index int, default ?1) ?1
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v := "?1"
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if obj.Type != nil { // don't panic if called speculatively
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v = obj.Type.Val.String()
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}
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return types.NewType(fmt.Sprintf(
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"func(%s []%s, %s int) %s",
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listLookupArgNameList, v,
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listLookupArgNameIndex,
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v,
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))
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}
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// Build is run to turn the polymorphic, undetermined function, into the
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// specific statically typed version. It is usually run after Unify completes,
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// and must be run before Info() and any of the other Func interface methods are
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// used. This function is idempotent, as long as the arg isn't changed between
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// runs.
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func (obj *ListLookupFunc) Build(typ *types.Type) (*types.Type, error) {
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// typ is the KindFunc signature we're trying to build...
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if typ.Kind != types.KindFunc {
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return nil, fmt.Errorf("input type must be of kind func")
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}
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if len(typ.Ord) != 2 {
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return nil, fmt.Errorf("the listlookup function needs exactly two args")
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}
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if typ.Out == nil {
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return nil, fmt.Errorf("return type of function must be specified")
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}
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if typ.Map == nil {
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return nil, fmt.Errorf("invalid input type")
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}
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tList, exists := typ.Map[typ.Ord[0]]
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if !exists || tList == nil {
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return nil, fmt.Errorf("first arg must be specified")
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}
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tIndex, exists := typ.Map[typ.Ord[1]]
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if !exists || tIndex == nil {
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return nil, fmt.Errorf("second arg must be specified")
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}
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if tIndex != nil && tIndex.Kind != types.KindInt {
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return nil, fmt.Errorf("index must be int kind")
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}
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if err := tList.Val.Cmp(typ.Out); err != nil {
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return nil, errwrap.Wrapf(err, "return type must match list val type")
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}
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obj.Type = tList // list type
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return obj.sig(), nil
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}
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// Validate tells us if the input struct takes a valid form.
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func (obj *ListLookupFunc) Validate() error {
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if obj.Type == nil { // build must be run first
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return fmt.Errorf("type is still unspecified")
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}
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if obj.Type.Kind != types.KindList {
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return fmt.Errorf("type must be a kind of list")
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}
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return nil
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}
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// Info returns some static info about itself. Build must be called before this
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// will return correct data.
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func (obj *ListLookupFunc) Info() *interfaces.Info {
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return &interfaces.Info{
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Pure: true,
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Memo: false,
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Sig: obj.sig(), // helper
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Err: obj.Validate(),
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}
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}
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// Init runs some startup code for this function.
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func (obj *ListLookupFunc) Init(init *interfaces.Init) error {
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obj.init = init
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return nil
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}
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// Stream returns the changing values that this func has over time.
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func (obj *ListLookupFunc) Stream(ctx context.Context) error {
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defer close(obj.init.Output) // the sender closes
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for {
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select {
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case input, ok := <-obj.init.Input:
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if !ok {
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return nil // can't output any more
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}
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//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
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// return errwrap.Wrapf(err, "wrong function input")
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//}
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if obj.last != nil && input.Cmp(obj.last) == nil {
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continue // value didn't change, skip it
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}
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obj.last = input // store for next
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l := (input.Struct()[listLookupArgNameList]).(*types.ListValue)
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index := input.Struct()[listLookupArgNameIndex].Int()
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zero := l.Type().Val.New() // the zero value
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// TODO: should we handle overflow by returning zero?
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if index > math.MaxInt { // max int size varies by arch
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return fmt.Errorf("list index overflow, got: %d, max is: %d", index, math.MaxInt)
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}
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// negative index values are "not found" here!
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var result types.Value
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val, exists := l.Lookup(int(index))
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if exists {
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result = val
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} else {
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result = zero
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}
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// if previous input was `2 + 4`, but now it
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// changed to `1 + 5`, the result is still the
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// same, so we can skip sending an update...
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if obj.result != nil && result.Cmp(obj.result) == nil {
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continue // result didn't change
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}
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obj.result = result // store new result
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case <-ctx.Done():
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return nil
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}
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select {
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case obj.init.Output <- obj.result: // send
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case <-ctx.Done():
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return nil
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}
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}
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val, exists := l.Lookup(int(index))
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if !exists {
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return zero, nil
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}
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return val, nil
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}
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