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.
142 lines
4.0 KiB
Go
142 lines
4.0 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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//"github.com/purpleidea/mgmt/util/errwrap"
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)
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const (
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// VarFuncName is the unique name identifier for this function.
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VarFuncName = "var"
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)
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// VarFunc is a function that passes through a function that came from a bind
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// lookup. It exists so that the reactive function engine type checks correctly.
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type VarFunc struct {
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Type *types.Type // this is the type of the var's value that we hold
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Edge string // name of the edge used
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//Func interfaces.Func // this isn't actually used in the Stream :/
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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 *VarFunc) String() string {
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return VarFuncName
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}
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// Validate makes sure we've built our struct properly.
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func (obj *VarFunc) 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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if obj.Edge == "" {
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return fmt.Errorf("must specify an edge name")
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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 *VarFunc) 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{obj.Edge: obj.Type},
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Ord: []string{obj.Edge},
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Out: obj.Type, // this is the output type for the expression
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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 composite function.
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func (obj *VarFunc) 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 *VarFunc) 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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st := input.(*types.StructValue) // must be!
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value, exists := st.Lookup(obj.Edge)
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if !exists {
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return fmt.Errorf("missing expected input argument `%s`", obj.Edge)
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}
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result = value
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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 *VarFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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