Add link conditions for 'stop-at' expression in ExploreRecursive selector

traversal/selector/condition.go

@@ -0,0 +1,74 @@
+package selector
+
+import (
+	"fmt"
+
+	ipld "github.com/ipld/go-ipld-prime"
+	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
+)
+
+// Condition provides a mechanism for matching and limiting matching and
+// exploration of selectors.
+// Not all types of conditions which are imagined in the selector specification
+// are encoded at present, instead we currently only implement a subset that
+// is sufficient for initial pressing use cases.
+type Condition struct {
+	mode  ConditionMode
+	match ipld.Node
+}
+
+// A ConditionMode is the keyed representation for the union that is the condition
+type ConditionMode string
+
+const (
+	ConditionMode_Link ConditionMode = "/"
+)
+
+// Match decides if a given ipld.Node matches the condition.
+func (c *Condition) Match(n ipld.Node) bool {
+	switch c.mode {
+	case ConditionMode_Link:
+		if n.Kind() != ipld.Kind_Link {
+			return false
+		}
+		lnk, err := n.AsLink()
+		if err != nil {
+			return false
+		}
+		match, err := c.match.AsLink()
+		if err != nil {
+			return false
+		}
+		cidlnk, ok := lnk.(cidlink.Link)
+		cidmatch, ok2 := match.(cidlink.Link)
+		if ok && ok2 {
+			return cidmatch.Equals(cidlnk.Cid)
+		}
+		return match.String() == lnk.String()
+	default:
+		return false
+	}
+}
+
+// ParseCondition assembles a Condition from a condition selector node
+func (pc ParseContext) ParseCondition(n ipld.Node) (Condition, error) {
+	if n.Kind() != ipld.Kind_Map {
+		return Condition{}, fmt.Errorf("selector spec parse rejected: condition body must be a map")
+	}
+	if n.Length() != 1 {
+		return Condition{}, fmt.Errorf("selector spec parse rejected: condition is a keyed union and thus must be single-entry map")
+	}
+	kn, v, _ := n.MapIterator().Next()
+	kstr, _ := kn.AsString()
+	// Switch over the single key to determine which condition body comes next.
+	//  (This switch is where the keyed union discriminators concretely happen.)
+	switch ConditionMode(kstr) {
+	case ConditionMode_Link:
+		if _, err := v.AsLink(); err != nil {
+			return Condition{}, fmt.Errorf("selector spec parse rejected: condition_link must be a link")
+		}
+		return Condition{mode: ConditionMode_Link, match: v}, nil
+	default:
+		return Condition{}, fmt.Errorf("selector spec parse rejected: %q is not a known member of the condition union", kstr)
+	}
+}

traversal/selector/condition_test.go

@@ -0,0 +1,44 @@
+package selector
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/ipfs/go-cid"
+	. "github.com/warpfork/go-wish"
+
+	"github.com/ipld/go-ipld-prime/fluent"
+	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
+	basicnode "github.com/ipld/go-ipld-prime/node/basic"
+)
+
+func TestParseCondition(t *testing.T) {
+	t.Run("parsing non map node should error", func(t *testing.T) {
+		sn := basicnode.NewInt(0)
+		_, err := ParseContext{}.ParseCondition(sn)
+		Wish(t, err, ShouldEqual, fmt.Errorf("selector spec parse rejected: condition body must be a map"))
+	})
+	t.Run("parsing map node without field should error", func(t *testing.T) {
+		sn := fluent.MustBuildMap(basicnode.Prototype__Map{}, 0, func(na fluent.MapAssembler) {})
+		_, err := ParseContext{}.ParseCondition(sn)
+		Wish(t, err, ShouldEqual, fmt.Errorf("selector spec parse rejected: condition is a keyed union and thus must be single-entry map"))
+	})
+
+	t.Run("parsing map node keyed to invalid type should error", func(t *testing.T) {
+		sn := fluent.MustBuildMap(basicnode.Prototype__Map{}, 1, func(na fluent.MapAssembler) {
+			na.AssembleEntry(string(ConditionMode_Link)).AssignInt(0)
+		})
+		_, err := ParseContext{}.ParseCondition(sn)
+		Wish(t, err, ShouldEqual, fmt.Errorf("selector spec parse rejected: condition_link must be a link"))
+	})
+	t.Run("parsing map node with condition field with valid selector node should parse", func(t *testing.T) {
+		lnk := cidlink.Link{Cid: cid.Undef}
+		sn := fluent.MustBuildMap(basicnode.Prototype__Map{}, 1, func(na fluent.MapAssembler) {
+			na.AssembleEntry(string(ConditionMode_Link)).AssignLink(lnk)
+		})
+		s, err := ParseContext{}.ParseCondition(sn)
+		Wish(t, err, ShouldEqual, nil)
+		lnkNode := basicnode.NewLink(lnk)
+		Wish(t, s, ShouldEqual, Condition{mode: ConditionMode_Link, match: lnkNode})
+	})
+}

traversal/selector/exploreRecursive.go

@@ -35,6 +35,7 @@ type ExploreRecursive struct {
 	sequence Selector       // selector for element we're interested in
 	current  Selector       // selector to apply to the current node
 	limit    RecursionLimit // the limit for this recursive selector
+	stopAt   *Condition     // a condition for not exploring the node or children
 }
 
 // RecursionLimit_Mode is an enum that represents the type of a recursion limit
@@ -86,23 +87,27 @@ func (s ExploreRecursive) Interests() []ipld.PathSegment {
 
 // Explore returns the node's selector for all fields
 func (s ExploreRecursive) Explore(n ipld.Node, p ipld.PathSegment) Selector {
+	if s.stopAt != nil && s.stopAt.Match(n) {
+		return nil
+	}
+
 	nextSelector := s.current.Explore(n, p)
 	limit := s.limit
 
 	if nextSelector == nil {
 		return nil
 	}
 	if !s.hasRecursiveEdge(nextSelector) {
-		return ExploreRecursive{s.sequence, nextSelector, limit}
+		return ExploreRecursive{s.sequence, nextSelector, limit, s.stopAt}
 	}
 	switch limit.mode {
 	case RecursionLimit_Depth:
 		if limit.depth < 2 {
 			return s.replaceRecursiveEdge(nextSelector, nil)
 		}
-		return ExploreRecursive{s.sequence, s.replaceRecursiveEdge(nextSelector, s.sequence), RecursionLimit{RecursionLimit_Depth, limit.depth - 1}}
+		return ExploreRecursive{s.sequence, s.replaceRecursiveEdge(nextSelector, s.sequence), RecursionLimit{RecursionLimit_Depth, limit.depth - 1}, s.stopAt}
 	case RecursionLimit_None:
-		return ExploreRecursive{s.sequence, s.replaceRecursiveEdge(nextSelector, s.sequence), limit}
+		return ExploreRecursive{s.sequence, s.replaceRecursiveEdge(nextSelector, s.sequence), limit, s.stopAt}
 	default:
 		panic("Unsupported recursion limit type")
 	}
@@ -149,7 +154,7 @@ func (s ExploreRecursive) replaceRecursiveEdge(nextSelector Selector, replacemen
 	return nextSelector
 }
 
-// Decide always returns false because this is not a matcher
+// Decide if a node directly matches
 func (s ExploreRecursive) Decide(n ipld.Node) bool {
 	return s.current.Decide(n)
 }
@@ -192,7 +197,16 @@ func (pc ParseContext) ParseExploreRecursive(n ipld.Node) (Selector, error) {
 	if erc.edgesFound == 0 {
 		return nil, fmt.Errorf("selector spec parse rejected: ExploreRecursive must have at least one ExploreRecursiveEdge")
 	}
-	return ExploreRecursive{selector, selector, limit}, nil
+	var stopCondition *Condition
+	stop, err := n.LookupByString(SelectorKey_StopAt)
+	if err == nil {
+		condition, err := pc.ParseCondition(stop)
+		if err != nil {
+			return nil, err
+		}
+		stopCondition = &condition
+	}
+	return ExploreRecursive{selector, selector, limit, stopCondition}, nil
 }
 
 func parseLimit(n ipld.Node) (RecursionLimit, error) {