5c27a249b7
This adds the first reversible resource (file) and the necessary engine API hooks to make it all work. This allows a special "reversed" resource to be added to the subsequent graph in the stream when an earlier version "disappears". This disappearance can happen if it was previously in an if statement that then becomes false. It might be wise to combine the use of this meta parameter with the use of the `realize` meta parameter to ensure that your reversed resource actually runs at least once, if there's a chance that it might be gone for a while. This patch also adds a new test harness for testing resources. It doesn't test the "live" aspect of resources, as it doesn't run Watch, but it was designed to ensure CheckApply works as intended, and it runs very quickly with a simplified timeline of happenings.
86 lines
3.4 KiB
Go
86 lines
3.4 KiB
Go
// Mgmt
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// Copyright (C) 2013-2019+ 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 engine
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import (
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"fmt"
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)
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// ReversibleRes is an interface that a resource can implement if it wants to
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// have some resource run when it disappears. A disappearance happens when a
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// resource is defined in one instance of the graph, and is gone in the
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// subsequent one. This is helpful for building robust programs with the engine.
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// Default implementations for most of the methods declared in this interface
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// can be obtained for your resource by anonymously adding the traits.Reversible
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// struct to your resource implementation.
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type ReversibleRes interface {
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Res
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// ReversibleMeta lets you get or set meta params for the reversible
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// trait.
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ReversibleMeta() *ReversibleMeta
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// SetReversibleMeta lets you set all of the meta params for the
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// reversible trait in a single call.
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SetReversibleMeta(*ReversibleMeta)
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// Reversed returns the "reverse" or "reciprocal" resource. This is used
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// to "clean" up after a previously defined resource has been removed.
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// Interestingly, this could return the core Res interface instead of a
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// ReversibleRes, because there is no requirement that the reverse of a
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// Res be the same kind of Res, and the reverse might not be reversible!
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// However, in practice, it's nice to use some of the Reversible meta
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// params in the built value, so keep things simple and have this be a
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// reversible res. The Res itself doesn't have to implement Reversed()
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// in a meaningful way, it can just return nil and it will get ignored.
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Reversed() (ReversibleRes, error)
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}
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// ReversibleMeta provides some parameters specific to reversible resources.
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type ReversibleMeta struct {
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// Disabled specifies that reversing should be disabled for this
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// resource.
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Disabled bool
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// Reversal specifies that the resource was built from a reversal. This
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// must be set if the resource was built by a reversal.
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Reversal bool
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// Overwrite specifies that we should overwrite any existing stored
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// reversible resource if one that is pending already exists. If this is
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// false, and a resource with the same name and kind exists, then this
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// will cause an error.
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Overwrite bool
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// TODO: add options here, including whether to reverse edges, etc...
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}
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// Cmp compares two ReversibleMeta structs and determines if they're equivalent.
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func (obj *ReversibleMeta) Cmp(rm *ReversibleMeta) error {
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if obj.Disabled != rm.Disabled {
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return fmt.Errorf("values for Disabled are different")
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}
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if obj.Reversal != rm.Reversal { // TODO: do we want to compare these?
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return fmt.Errorf("values for Reversal are different")
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}
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if obj.Overwrite != rm.Overwrite {
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return fmt.Errorf("values for Overwrite are different")
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}
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return nil
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}
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