5d664855de
This adds the requirement that all function implementations provider a String() string method so that these can be used as vertices in the pgraph library. If we eventually move to generics for the pgraph DAG, then this might not matter, but it's not bad that these have names either.
140 lines
3.9 KiB
Go
140 lines
3.9 KiB
Go
// Mgmt
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// Copyright (C) 2013-2022+ James Shubin and the project contributors
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// Written by James Shubin <james@shubin.ca> and the project contributors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package structs
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import (
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"fmt"
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"github.com/purpleidea/mgmt/lang/interfaces"
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"github.com/purpleidea/mgmt/lang/types"
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)
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const (
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// IfFuncName is the unique name identifier for this function.
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IfFuncName = "if"
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)
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// IfFunc is a function that passes through the value of the correct branch
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// based on the conditional value it gets.
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type IfFunc struct {
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Type *types.Type // this is the type of the if expression output we hold
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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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closeChan chan struct{}
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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 *IfFunc) String() string {
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return IfFuncName
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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 *IfFunc) Validate() error {
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if obj.Type == nil {
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return fmt.Errorf("must specify a type")
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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.
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func (obj *IfFunc) Info() *interfaces.Info {
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var typ *types.Type
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if obj.Type != nil { // don't panic if called speculatively
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typ = &types.Type{
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Kind: types.KindFunc, // function type
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Map: map[string]*types.Type{
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"c": types.TypeBool, // conditional must be a boolean
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"a": obj.Type, // true branch must be this type
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"b": obj.Type, // false branch must be this type too
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},
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Ord: []string{"c", "a", "b"}, // conditional, and two branches
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Out: obj.Type, // result type must match
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}
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}
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return &interfaces.Info{
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Pure: true,
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Memo: false, // TODO: ???
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Sig: typ,
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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 if expression function.
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func (obj *IfFunc) Init(init *interfaces.Init) error {
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obj.init = init
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obj.closeChan = make(chan struct{})
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return nil
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}
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// Stream takes an input struct in the format as described in the Func and Graph
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// methods of the Expr, and returns the actual expected value as a stream based
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// on the changing inputs to that value.
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func (obj *IfFunc) Stream() 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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var result types.Value
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if input.Struct()["c"].Bool() {
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result = input.Struct()["a"] // true branch
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} else {
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result = input.Struct()["b"] // false branch
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}
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// 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 <-obj.closeChan:
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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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// pass
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case <-obj.closeChan:
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return nil
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}
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}
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}
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// Close runs some shutdown code for this function and turns off the stream.
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func (obj *IfFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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