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topdown.go
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topdown.go
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// Copyright 2016 The OPA Authors. All rights reserved.
// Use of this source code is governed by an Apache2
// license that can be found in the LICENSE file.
package topdown
import (
"context"
"fmt"
"strings"
"sync"
"github.com/open-policy-agent/opa/ast"
"github.com/open-policy-agent/opa/metrics"
"github.com/open-policy-agent/opa/storage"
"github.com/pkg/errors"
)
// Topdown stores the state of the evaluation process and contains context
// needed to evaluate queries.
type Topdown struct {
Query ast.Body
Compiler *ast.Compiler
Input ast.Value
Index int
Previous *Topdown
Store *storage.Storage
Tracer Tracer
Context context.Context
txn storage.Transaction
locals *ast.ValueMap
refs *valueMapStack
cache *contextcache
qid uint64
redos *redoStack
}
// ResetQueryIDs resets the query ID generator. This is only for test purposes.
func ResetQueryIDs() {
qidFactory.Reset()
}
type queryIDFactory struct {
next uint64
mtx sync.Mutex
}
func (f *queryIDFactory) Next() uint64 {
f.mtx.Lock()
defer f.mtx.Unlock()
next := f.next
f.next++
return next
}
func (f *queryIDFactory) Reset() {
f.mtx.Lock()
defer f.mtx.Unlock()
f.next = uint64(1)
}
var qidFactory = &queryIDFactory{
next: uint64(1),
}
type redoStack struct {
events []*redoStackElement
}
type redoStackElement struct {
t *Topdown
evt *Event
}
// New returns a new Topdown object without any bindings.
func New(ctx context.Context, query ast.Body, compiler *ast.Compiler, store *storage.Storage, txn storage.Transaction) *Topdown {
return &Topdown{
Context: ctx,
Query: query,
Compiler: compiler,
Store: store,
refs: newValueMapStack(),
txn: txn,
cache: newContextCache(),
qid: qidFactory.Next(),
redos: &redoStack{},
}
}
// Vars represents a set of var bindings.
type Vars map[ast.Var]ast.Value
// Diff returns the var bindings in vs that are not in other.
func (vs Vars) Diff(other Vars) Vars {
result := Vars{}
for k := range vs {
if _, ok := other[k]; !ok {
result[k] = vs[k]
}
}
return result
}
// Equal returns true if vs is equal to other.
func (vs Vars) Equal(other Vars) bool {
return len(vs.Diff(other)) == 0 && len(other.Diff(vs)) == 0
}
// Vars returns bindings for the vars in the current query
func (t *Topdown) Vars() map[ast.Var]ast.Value {
result := map[ast.Var]ast.Value{}
t.locals.Iter(func(k, v ast.Value) bool {
if k, ok := k.(ast.Var); ok {
result[k] = v
}
return false
})
return result
}
// Binding returns the value bound to the given key.
func (t *Topdown) Binding(k ast.Value) ast.Value {
if _, ok := k.(ast.Ref); ok {
return t.refs.Binding(k)
}
return t.locals.Get(k)
}
// Undo represents a binding that can be undone.
type Undo struct {
Key ast.Value
Value ast.Value
Prev *Undo
}
// Bind updates t to include a binding from the key to the value. The return
// value is used to return t to the state before the binding was added.
func (t *Topdown) Bind(key ast.Value, value ast.Value, prev *Undo) *Undo {
if _, ok := key.(ast.Ref); ok {
return t.refs.Bind(key, value, prev)
}
o := t.locals.Get(key)
if t.locals == nil {
t.locals = ast.NewValueMap()
}
t.locals.Put(key, value)
return &Undo{key, o, prev}
}
// Unbind updates t by removing the binding represented by the undo.
func (t *Topdown) Unbind(undo *Undo) {
if undo == nil {
return
}
if _, ok := undo.Key.(ast.Ref); ok {
for u := undo; u != nil; u = u.Prev {
t.refs.Unbind(u)
}
} else {
for u := undo; u != nil; u = u.Prev {
if u.Value != nil {
t.locals.Put(u.Key, u.Value)
} else {
t.locals.Delete(u.Key)
}
}
}
}
// Closure returns a new Topdown object to evaluate query with bindings from t.
func (t *Topdown) Closure(query ast.Body) *Topdown {
cpy := *t
cpy.Query = query
cpy.Previous = t
cpy.Index = 0
cpy.qid = qidFactory.Next()
return &cpy
}
// Child returns a new Topdown object to evaluate query without bindings from t.
func (t *Topdown) Child(query ast.Body) *Topdown {
cpy := t.Closure(query)
cpy.locals = nil
cpy.refs = newValueMapStack()
return cpy
}
// Current returns the current expression to evaluate.
func (t *Topdown) Current() *ast.Expr {
return t.Query[t.Index]
}
// Resolve returns the native Go value referred to by the ref.
func (t *Topdown) Resolve(ref ast.Ref) (interface{}, error) {
if ref.IsNested() {
cpy := make(ast.Ref, len(ref))
for i := range ref {
switch v := ref[i].Value.(type) {
case ast.Ref:
r, err := lookupValue(t, v)
if err != nil {
return nil, err
}
cpy[i] = ast.NewTerm(r)
default:
cpy[i] = ref[i]
}
}
ref = cpy
}
path, err := storage.NewPathForRef(ref)
if err != nil {
return nil, err
}
doc, err := t.Store.Read(t.Context, t.txn, path)
if err != nil {
return nil, err
}
// When the root document is queried we hide the SystemDocumentKey.
if len(path) == 0 {
obj := doc.(map[string]interface{})
tmp := map[string]interface{}{}
for k := range obj {
if k != string(ast.SystemDocumentKey) {
tmp[k] = obj[k]
}
}
doc = tmp
}
return doc, nil
}
// Step returns a new Topdown object to evaluate the next expression.
func (t *Topdown) Step() *Topdown {
cpy := *t
cpy.Index++
return &cpy
}
// WithInput returns a new Topdown object that has the input document set.
func (t *Topdown) WithInput(input ast.Value) *Topdown {
cpy := *t
cpy.Input = input
return &cpy
}
// WithTracer returns a new Topdown object that has a tracer set.
func (t *Topdown) WithTracer(tracer Tracer) *Topdown {
cpy := *t
cpy.Tracer = tracer
return &cpy
}
// currentLocation returns the current expression's location or the first
// fallback that has a location set, otherwise nil.
func (t *Topdown) currentLocation(fallback ...ast.Statement) *ast.Location {
curr := t.Current().Location
if curr != nil {
return curr
}
for i := range fallback {
curr = fallback[i].Loc()
if curr != nil {
return curr
}
}
return nil
}
func (t *Topdown) traceEnter(node interface{}) {
if t.tracingEnabled() {
evt := t.makeEvent(EnterOp, node)
t.flushRedos(evt)
t.Tracer.Trace(t, evt)
}
}
func (t *Topdown) traceExit(node interface{}) {
if t.tracingEnabled() {
evt := t.makeEvent(ExitOp, node)
t.flushRedos(evt)
t.Tracer.Trace(t, evt)
}
}
func (t *Topdown) traceEval(node interface{}) {
if t.tracingEnabled() {
evt := t.makeEvent(EvalOp, node)
t.flushRedos(evt)
t.Tracer.Trace(t, evt)
}
}
func (t *Topdown) traceRedo(node interface{}) {
if t.tracingEnabled() {
evt := t.makeEvent(RedoOp, node)
t.saveRedo(evt)
}
}
func (t *Topdown) traceFail(node interface{}) {
if t.tracingEnabled() {
evt := t.makeEvent(FailOp, node)
t.flushRedos(evt)
t.Tracer.Trace(t, evt)
}
}
func (t *Topdown) tracingEnabled() bool {
return t.Tracer != nil && t.Tracer.Enabled()
}
func (t *Topdown) saveRedo(evt *Event) {
buf := &redoStackElement{
t: t,
evt: evt,
}
// Search stack for redo that this (redo) event should follow.
for len(t.redos.events) > 0 {
idx := len(t.redos.events) - 1
top := t.redos.events[idx]
// Expression redo should follow rule/body redo from the same query.
if evt.HasExpr() {
if top.evt.QueryID == evt.QueryID && (top.evt.HasBody() || top.evt.HasRule()) {
break
}
}
// Rule/body redo should follow expression redo from the parent query.
if evt.HasRule() || evt.HasBody() {
if top.evt.QueryID == evt.ParentID && top.evt.HasExpr() {
break
}
}
// Top of stack can be discarded. This indicates the search terminated
// without producing any more events.
t.redos.events = t.redos.events[:idx]
}
t.redos.events = append(t.redos.events, buf)
}
func (t *Topdown) flushRedos(evt *Event) {
idx := len(t.redos.events) - 1
if idx != -1 {
top := t.redos.events[idx]
if top.evt.QueryID == evt.QueryID {
for _, buf := range t.redos.events {
t.Tracer.Trace(buf.t, buf.evt)
}
}
t.redos.events = nil
}
}
func (t *Topdown) makeEvent(op Op, node interface{}) *Event {
evt := Event{
Op: op,
Node: node,
QueryID: t.qid,
Locals: t.locals.Copy(),
}
if t.Previous != nil {
evt.ParentID = t.Previous.qid
}
return &evt
}
// contextcache stores the result of rule evaluation for a query. The
// contextcache is inherited by child contexts. The contextcache is consulted
// when virtual document references are evaluated. If a miss occurs, the virtual
// document is generated and the contextcache is updated.
type contextcache struct {
partialobjs partialObjDocCache
complete completeDocCache
}
type partialObjDocCache map[*ast.Rule]map[ast.Value]ast.Value
type completeDocCache map[*ast.Rule]ast.Value
func newContextCache() *contextcache {
return &contextcache{
partialobjs: partialObjDocCache{},
complete: completeDocCache{},
}
}
func (c *contextcache) Invalidate() {
c.partialobjs = partialObjDocCache{}
c.complete = completeDocCache{}
}
// Iterator is the interface for processing evaluation results.
type Iterator func(*Topdown) error
// Continue binds key to value in t and calls the iterator. This is a helper
// function for simple cases where a single value (e.g., a variable) needs to be
// bound to a value in order for the evaluation the proceed.
func Continue(t *Topdown, key, value ast.Value, iter Iterator) error {
undo := t.Bind(key, value, nil)
err := iter(t)
t.Unbind(undo)
return err
}
// Eval evaluates the query in t and calls iter once for each set of bindings
// that satisfy all of the expressions in the query.
func Eval(t *Topdown, iter Iterator) error {
t.traceEnter(t.Query)
return eval(t, func(t *Topdown) error {
t.traceExit(t.Query)
if err := iter(t); err != nil {
return err
}
t.traceRedo(t.Query)
return nil
})
}
// Binding defines the interface used to apply term bindings to terms,
// expressions, etc.
type Binding func(ast.Value) ast.Value
// PlugHead returns a copy of head with bound terms substituted for the binding.
func PlugHead(head *ast.Head, binding Binding) *ast.Head {
plugged := *head
if plugged.Key != nil {
plugged.Key = PlugTerm(plugged.Key, binding)
}
if plugged.Value != nil {
plugged.Value = PlugTerm(plugged.Value, binding)
}
return &plugged
}
// PlugExpr returns a copy of expr with bound terms substituted for the binding.
func PlugExpr(expr *ast.Expr, binding Binding) *ast.Expr {
plugged := *expr
switch ts := plugged.Terms.(type) {
case []*ast.Term:
var buf []*ast.Term
buf = append(buf, ts[0])
for _, term := range ts[1:] {
buf = append(buf, PlugTerm(term, binding))
}
plugged.Terms = buf
case *ast.Term:
plugged.Terms = PlugTerm(ts, binding)
default:
panic(fmt.Sprintf("illegal argument: %v", ts))
}
return &plugged
}
// PlugTerm returns a copy of term with bound terms substituted for the binding.
func PlugTerm(term *ast.Term, binding Binding) *ast.Term {
switch v := term.Value.(type) {
case ast.Var:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
case ast.Ref:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
case ast.Array:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
case ast.Object:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
case *ast.Set:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
case *ast.ArrayComprehension:
plugged := *term
plugged.Value = PlugValue(v, binding)
return &plugged
default:
if !term.IsGround() {
panic("unreachable")
}
return term
}
}
// PlugValue returns a copy of v with bound terms substituted for the binding.
func PlugValue(v ast.Value, binding func(ast.Value) ast.Value) ast.Value {
switch v := v.(type) {
case ast.Var:
if b := binding(v); b != nil {
return PlugValue(b, binding)
}
return v
case *ast.ArrayComprehension:
b := binding(v)
if b == nil {
return v
}
return b
case ast.Ref:
if b := binding(v); b != nil {
return PlugValue(b, binding)
}
buf := make(ast.Ref, len(v))
buf[0] = v[0]
for i, p := range v[1:] {
buf[i+1] = PlugTerm(p, binding)
}
if b := binding(buf); b != nil {
return PlugValue(b, binding)
}
return buf
case ast.Array:
buf := make(ast.Array, len(v))
for i, e := range v {
buf[i] = PlugTerm(e, binding)
}
return buf
case ast.Object:
buf := make(ast.Object, len(v))
for i, e := range v {
k := PlugTerm(e[0], binding)
v := PlugTerm(e[1], binding)
buf[i] = [...]*ast.Term{k, v}
}
return buf
case *ast.Set:
buf := &ast.Set{}
for _, e := range *v {
buf.Add(PlugTerm(e, binding))
}
return buf
case nil:
return nil
default:
if !v.IsGround() {
panic(fmt.Sprintf("illegal value: %v", v))
}
return v
}
}
// QueryParams defines input parameters for the query interface.
type QueryParams struct {
Context context.Context
Compiler *ast.Compiler
Store *storage.Storage
Transaction storage.Transaction
Input ast.Value
Tracer Tracer
Metrics metrics.Metrics
Path ast.Ref
}
// NewQueryParams returns a new QueryParams.
func NewQueryParams(ctx context.Context, compiler *ast.Compiler, store *storage.Storage, txn storage.Transaction, input ast.Value, path ast.Ref) *QueryParams {
return &QueryParams{
Context: ctx,
Compiler: compiler,
Store: store,
Transaction: txn,
Input: input,
Path: path,
}
}
// NewTopdown returns a new Topdown object.
//
// This function will not propagate optional values such as the tracer, input
// document, etc. Those must be set by the caller.
func (q *QueryParams) NewTopdown(query ast.Body) *Topdown {
return New(q.Context, query, q.Compiler, q.Store, q.Transaction)
}
// QueryResult represents a single query result.
type QueryResult struct {
Result interface{} // Result contains the document referred to by the params Path.
Bindings map[string]interface{} // Bindings contains values for variables in the params Input.
}
func (qr *QueryResult) String() string {
return fmt.Sprintf("[%v %v]", qr.Result, qr.Bindings)
}
// QueryResultSet represents a collection of query results.
type QueryResultSet []*QueryResult
// Undefined returns true if the query did not find any results.
func (qrs QueryResultSet) Undefined() bool {
return len(qrs) == 0
}
// Add inserts a result into the query result set.
func (qrs *QueryResultSet) Add(qr *QueryResult) {
*qrs = append(*qrs, qr)
}
// Query returns the value of the document referred to by the params' path. If
// the params' input contains non-ground terms, there may be multiple query
// results.
func Query(params *QueryParams) (QueryResultSet, error) {
if params.Metrics == nil {
params.Metrics = metrics.New()
}
t, resultVar, requestVars, err := makeTopdown(params)
if err != nil {
return nil, err
}
qrs := QueryResultSet{}
params.Metrics.Timer(metrics.RegoQueryEval).Start()
err = Eval(t, func(t *Topdown) error {
// Gather bindings for vars from the request.
bindings := map[string]interface{}{}
for v := range requestVars {
binding, err := ast.ValueToInterface(PlugValue(v, t.Binding), t)
if err != nil {
return err
}
bindings[v.String()] = binding
}
// Gather binding for result var.
val, err := ast.ValueToInterface(PlugValue(resultVar, t.Binding), t)
if err != nil {
return err
}
// Aggregate results.
qrs.Add(&QueryResult{val, bindings})
return nil
})
params.Metrics.Timer(metrics.RegoQueryEval).Stop()
return qrs, err
}
func makeTopdown(params *QueryParams) (*Topdown, ast.Var, ast.VarSet, error) {
inputVar := ast.VarTerm(ast.WildcardPrefix + "0")
pathVar := ast.VarTerm(ast.WildcardPrefix + "1")
var query ast.Body
params.Metrics.Timer(metrics.RegoQueryCompile).Start()
if params.Input == nil {
query = ast.NewBody(ast.Equality.Expr(ast.NewTerm(params.Path), pathVar))
} else {
// <input> = $0,
// <path> = $1 with input as $0
inputExpr := ast.Equality.Expr(ast.NewTerm(params.Input), inputVar)
pathExpr := ast.Equality.Expr(ast.NewTerm(params.Path), pathVar).
IncludeWith(ast.NewTerm(ast.InputRootRef), inputVar)
query = ast.NewBody(inputExpr, pathExpr)
}
compiled, err := params.Compiler.QueryCompiler().Compile(query)
if err != nil {
return nil, "", nil, err
}
params.Metrics.Timer(metrics.RegoQueryCompile).Stop()
vis := ast.NewVarVisitor().WithParams(ast.VarVisitorParams{
SkipRefHead: true,
SkipClosures: true,
})
ast.Walk(vis, params.Input)
t := params.NewTopdown(compiled).
WithTracer(params.Tracer)
return t, pathVar.Value.(ast.Var), vis.Vars(), nil
}
// Resolver defines the interface for resolving references to base documents to
// native Go values. The native Go value types map to JSON types.
type Resolver interface {
Resolve(ref ast.Ref) (value interface{}, err error)
}
type resolver struct {
context context.Context
store *storage.Storage
txn storage.Transaction
}
func (r resolver) Resolve(ref ast.Ref) (interface{}, error) {
path, err := storage.NewPathForRef(ref)
if err != nil {
return nil, err
}
return r.store.Read(r.context, r.txn, path)
}
// ResolveRefs returns the value obtained by resolving references to base
// documents.
func ResolveRefs(v ast.Value, t *Topdown) (ast.Value, error) {
result, err := ast.TransformRefs(v, func(r ast.Ref) (ast.Value, error) {
return lookupValue(t, r)
})
if err != nil {
return nil, err
}
return result.(ast.Value), nil
}
// ResolveRefsTerm returns a copy of term obtained by resolving references to
// base documents.
func ResolveRefsTerm(term *ast.Term, t *Topdown) (*ast.Term, error) {
cpy := *term
var err error
cpy.Value, err = ResolveRefs(term.Value, t)
if err != nil {
return nil, err
}
return &cpy, nil
}
func eval(t *Topdown, iter Iterator) error {
if t.Index >= len(t.Query) {
return iter(t)
}
if len(t.Current().With) > 0 {
return evalWith(t, iter)
}
return evalStep(t, func(t *Topdown) error {
t = t.Step()
return eval(t, iter)
})
}
func evalStep(t *Topdown, iter Iterator) error {
if t.Current().Negated {
return evalNot(t, iter)
}
t.traceEval(t.Current())
// isRedo indicates if the expression's terms are defined at least once. If
// any of the terms are undefined, then the closure below will not run (but
// a Fail event still needs to be emitted).
isRedo := false
err := evalTerms(t, func(t *Topdown) error {
isRedo = true
// isTrue indicates if the expression is true and is used to determine
// if a Fail event should be emitted below.
isTrue := false
err := evalExpr(t, func(t *Topdown) error {
isTrue = true
return iter(t)
})
if err != nil {
return err
}
if !isTrue {
t.traceFail(t.Current())
}
t.traceRedo(t.Current())
return nil
})
if err != nil {
return err
}
if !isRedo {
t.traceFail(t.Current())
}
return nil
}
func evalNot(t *Topdown, iter Iterator) error {
negation := ast.NewBody(t.Current().Complement().NoWith())
child := t.Closure(negation)
t.traceEval(t.Current())
isTrue := false
err := Eval(child, func(*Topdown) error {
isTrue = true
return nil
})
if err != nil {
return err
}
if !isTrue {
return iter(t)
}
t.traceFail(t.Current())
return nil
}
func evalWith(t *Topdown, iter Iterator) error {
curr := t.Current()
pairs := make([][2]*ast.Term, len(curr.With))
for i := range curr.With {
plugged := PlugTerm(curr.With[i].Value, t.Binding)
resolved, err := ResolveRefsTerm(plugged, t)
if err != nil {
return err
}
pairs[i] = [...]*ast.Term{curr.With[i].Target, resolved}
}
input, err := MakeInput(pairs)
if err != nil {
return &Error{
Code: ConflictErr,
Location: curr.Location,
Message: err.Error(),
}
}
cpy := t.WithInput(input)
// All ref bindings added during evaluation of this expression must be
// discarded before moving to the next expression. Push a new binding map
// onto the stack that will be popped below before continuing. Similarly,
// the document caches must be invalidated before continuing.
//
// TODO(tsandall): analyze queries and invalidate only affected caches.
cpy.refs.Push(ast.NewValueMap())
err = evalStep(cpy, func(next *Topdown) error {
next.refs.Pop()
next.cache.Invalidate()
next = next.Step()
return eval(next, iter)
})
if err != nil {
return err
}
if vm := cpy.refs.Peek(); vm != nil {
cpy.refs.Pop()
}
cpy.cache.Invalidate()
return nil
}
func evalExpr(t *Topdown, iter Iterator) error {
expr := PlugExpr(t.Current(), t.Binding)
switch tt := expr.Terms.(type) {
case []*ast.Term:
builtin, ok := builtinFunctions[tt[0].Value.(ast.String)]
if !ok {
return unsupportedBuiltinErr(expr.Location)
}
return builtin(t, expr, iter)
case *ast.Term:
v := tt.Value
if r, ok := v.(ast.Ref); ok {
var err error
v, err = lookupValue(t, r)
if err != nil {
return err
}
}
if !v.Equal(ast.Boolean(false)) {
if v.IsGround() {
return iter(t)
}
}
return nil
default:
panic(fmt.Sprintf("illegal argument: %v", tt))
}
}
// evalRef evaluates the reference and invokes the iterator for each instance of
// the reference that is defined. The iterator is invoked with bindings for (1)
// all variables found in the reference and (2) the reference itself if that
// reference refers to a virtual document (ditto for nested references).
func evalRef(t *Topdown, ref, path ast.Ref, iter Iterator) error {
// If ref is already bound then invoke iterator immediately. No further
// evaluation has to be done.
if len(path) == 0 && t.Binding(ref) != nil {
return iter(t)
}
if len(ref) == 0 {
if path.HasPrefix(ast.DefaultRootRef) {
return evalRefRec(t, path, iter)
}
if path.HasPrefix(ast.InputRootRef) {
// If no input was supplied, then any references to the input
// are undefined.
if t.Input == nil {
return nil
}
return evalRefRuleResult(t, path, path[1:], t.Input, iter)
}
if v := t.Binding(path[0].Value); v != nil {
return evalRefRuleResult(t, path, path[1:], v, iter)
}
// This should not be reachable.
return fmt.Errorf("unbound ref head: %v", path)
}
head, tail := ref[0], ref[1:]
n, ok := head.Value.(ast.Ref)
if !ok {
path = append(path, head)
return evalRef(t, tail, path, iter)
}
return evalRef(t, n, ast.Ref{}, func(t *Topdown) error {
var undo *Undo
// Add a binding for the nested reference 'n' if one does not exist. If
// 'n' referred to a virtual document the binding would already exist.
// We bind nested references so that when the overall expression is
// evaluated, it will not contain any nested references.
if b := t.Binding(n); b == nil {
var err error
var v ast.Value
switch p := PlugValue(n, t.Binding).(type) {
case ast.Ref:
v, err = lookupValue(t, p)
if err != nil {
return err
}
default:
v = p
}
undo = t.Bind(n, v, nil)
}
tmp := append(path, head)