lang: Initial implementation of the mgmt language
This is an initial implementation of the mgmt language. It is a declarative (immutable) functional, reactive, domain specific programming language. It is intended to be a language that is: * safe * powerful * easy to reason about With these properties, we hope this language, and the mgmt engine will allow you to model the real-time systems that you'd like to automate. This also includes a number of other associated changes. Sorry for the large size of this patch.
This commit is contained in:
James Shubin
290
lang/funcs/core/template_polyfunc.go
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290
lang/funcs/core/template_polyfunc.go
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// Mgmt
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// Copyright (C) 2013-2018+ 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 core // TODO: should this be in its own individual package?
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import (
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"bytes"
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"fmt"
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"text/template"
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"time"
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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/types"
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errwrap "github.com/pkg/errors"
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)
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func init() {
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funcs.Register("template", func() interfaces.Func { return &TemplateFunc{} })
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}
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// TemplateName is the name of our template as required by the template library.
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const TemplateName = "template"
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// TemplateFunc is a static polymorphic function that compiles a template and
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// returns the output as a string. It bases its output on the values passed in
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// to it. It examines the type of the second argument (the input data vars) at
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// compile time and then determines the static functions signature by including
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// that in the overall signature.
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// XXX: do we need to add events if any of the internal functions change over time?
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type TemplateFunc struct {
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Type *types.Type // type of vars
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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 string // last calculated output
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closeChan chan struct{}
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}
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// Polymorphisms returns the possible type signatures for this template. In this
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// case, since the second argument can be an infinite number of values, it
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// instead returns either the final precise type (if it can be gleamed from the
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// input partials) or if it cannot, it returns a single entry with the complete
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// type but with the variable second argument specified as a `variant` type.
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// If it encounters any partial type specifications which are not possible, then
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// it errors out. This could happen if you specified a non string template arg.
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// XXX: is there a better API than returning a buried `variant` type?
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func (obj *TemplateFunc) Polymorphisms(partialType *types.Type, partialValues []types.Value) ([]*types.Type, error) {
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// TODO: return `variant` as second arg for now -- maybe there's a better way?
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variant := []*types.Type{types.NewType("func(a str, b variant) str")}
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if partialType == nil {
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return variant, nil
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}
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if partialType.Out != nil && partialType.Out.Cmp(types.TypeStr) != nil {
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return nil, fmt.Errorf("return value of template must be str")
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}
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ord := partialType.Ord
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if partialType.Map != nil {
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if len(ord) != 2 {
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return nil, fmt.Errorf("must have exactly two args in template func")
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}
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if t, exists := partialType.Map[ord[0]]; exists && t != nil {
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if t.Cmp(types.TypeStr) != nil {
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return nil, fmt.Errorf("first arg for template must be an str")
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}
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}
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if t, exists := partialType.Map[ord[1]]; exists && t != nil {
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// known vars type! w00t!
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return []*types.Type{types.NewType(fmt.Sprintf("func(a str, b %s) str", t.String()))}, nil
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}
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}
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return variant, nil
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}
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// Build takes the now known function signature and stores it so that this
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// function can appear to be static. It extracts the type of the vars argument,
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// which is the dynamic part which can change. That type is used to build our
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// function statically.
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func (obj *TemplateFunc) Build(typ *types.Type) error {
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if typ.Kind != types.KindFunc {
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return 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 fmt.Errorf("the template function needs exactly two args")
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}
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if typ.Out == nil {
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return fmt.Errorf("return type of function must be specified")
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}
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if typ.Out.Cmp(types.TypeStr) != nil {
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return fmt.Errorf("return type of function must be an str")
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}
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if typ.Map == nil {
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return fmt.Errorf("invalid input type")
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}
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t0, exists := typ.Map[typ.Ord[0]]
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if !exists || t0 == nil {
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return fmt.Errorf("first arg must be specified")
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}
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if t0.Cmp(types.TypeStr) != nil {
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return fmt.Errorf("first arg for template must be an str")
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}
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t1, exists := typ.Map[typ.Ord[1]]
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if !exists || t1 == nil {
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return fmt.Errorf("second arg must be specified")
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}
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obj.Type = t1 // extracted vars type is now known!
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return nil
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}
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// Validate makes sure we've built our struct properly. It is usually unused for
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// normal functions that users can use directly.
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func (obj *TemplateFunc) 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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return nil
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}
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// Info returns some static info about itself.
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func (obj *TemplateFunc) 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: types.NewType(fmt.Sprintf("func(template str, vars %s) str", obj.Type.String())),
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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 fact.
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func (obj *TemplateFunc) 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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// run runs a template and returns the result.
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func (obj *TemplateFunc) run(templateText string, vars types.Value) (string, error) {
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funcMap := map[string]interface{}{
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// XXX: can these functions come from normal funcValue things
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// that we build for the interfaces.Func part?
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// TODO: add a bunch of stdlib-like stuff here...
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"datetimeprint": func(epochDelta int64) string { // TODO: rename
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return time.Unix(epochDelta, 0).String()
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},
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}
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var err error
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tmpl := template.New(TemplateName)
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tmpl = tmpl.Funcs(funcMap)
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tmpl, err = tmpl.Parse(templateText)
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if err != nil {
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return "", errwrap.Wrapf(err, "template: parse error")
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}
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buf := new(bytes.Buffer)
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// NOTE: any objects in here can have their methods called by the template!
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var data interface{} // can be many types, eg a struct!
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v := vars.Copy() // make a copy since we make modifications to it...
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Loop:
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// TODO: simplify with Type.Underlying()
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for {
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switch x := v.Type().Kind; x {
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case types.KindBool:
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fallthrough
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case types.KindStr:
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fallthrough
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case types.KindInt:
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fallthrough
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case types.KindFloat:
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// standalone values can be used in templates with a dot
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data = v.Value()
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break Loop
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case types.KindList:
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// TODO: can we improve on this to expose indexes?
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data = v.Value()
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break Loop
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case types.KindMap:
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if v.Type().Key.Cmp(types.TypeStr) != nil {
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return "", errwrap.Wrapf(err, "template: map keys must be str")
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}
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m := make(map[string]interface{})
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for k, v := range v.Map() { // map[Value]Value
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m[k.Str()] = v.Value()
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}
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data = m
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break Loop
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case types.KindStruct:
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m := make(map[string]interface{})
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for k, v := range v.Struct() { // map[string]Value
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m[k] = v.Value()
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}
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data = m
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break Loop
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// TODO: should we allow functions here?
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//case types.KindFunc:
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case types.KindVariant:
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v = v.(*types.VariantValue).V // un-nest and recurse
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continue Loop
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default:
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return "", fmt.Errorf("can't use `%+v` as vars input", x)
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}
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}
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// run the template
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if err := tmpl.Execute(buf, data); err != nil {
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return "", errwrap.Wrapf(err, "template: execution error")
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}
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return buf.String(), 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 *TemplateFunc) 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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tmpl := input.Struct()["template"].Str()
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vars := input.Struct()["vars"]
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result, err := obj.run(tmpl, vars)
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if err != nil {
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return err // no errwrap needed b/c helper func
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}
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if obj.result == result {
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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 <- &types.StrValue{
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V: obj.result,
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}:
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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 fact and turns off the stream.
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func (obj *TemplateFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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