pkg/client: return error for unindexed attr search

Calling 'GetPermanodesWithAttr', as currently written, will return an
empty list for any unindexed parameters.

Rather than always returning an empty list if the user asks for a
unindexed attribute, error out.

Also add documentation of this potential foot-gun for users of the
client.

Change-Id: Iadc1b5a00aa709584affb89a1397e82aaffb692f

pkg/client/client.go

@@ -716,6 +716,10 @@ func (c *Client) GetRecentPermanodes(ctx context.Context, req *search.RecentRequ
 	return res, nil
 }
 
+// GetPermanodesWithAttr searches for permanodes that match the given search request.
+// The Fuzzy option in the request must not be set, and the Attribute option
+// must be set.
+// Only indexed attributes may be queried.
 func (c *Client) GetPermanodesWithAttr(ctx context.Context, req *search.WithAttrRequest) (*search.WithAttrResponse, error) {
 	sr, err := c.SearchRoot()
 	if err != nil {

pkg/index/index.go

@@ -1031,6 +1031,9 @@ func (x *Index) SearchPermanodesWithAttr(ctx context.Context, dest chan<- blob.R
 	if request.Attribute == "" {
 		return errors.New("index: missing Attribute in SearchPermanodesWithAttr")
 	}
+	if !IsIndexedAttribute(request.Attribute) {
+		return fmt.Errorf("SearchPermanodesWithAttr: called with a non-indexed attribute %q", request.Attribute)
+	}
 
 	keyId, err := x.KeyId(ctx, request.Signer)
 	if err == sorted.ErrNotFound {

pkg/index/indextest/tests.go

@@ -317,6 +317,7 @@ func Index(t *testing.T, initIdx func() *index.Index) {
 	t.Logf("set attribute %q", rootClaim)
 
 	pnChild := id.NewPermanode()
+	id.SetAttribute(pnChild, "unindexed", "lost in time and space")
 	br3 := id.SetAttribute(pnChild, "tag", "bar")
 	br3Time := id.LastTime()
 	t.Logf("set attribute %q", br3)
@@ -536,6 +537,50 @@ func Index(t *testing.T, initIdx func() *index.Index) {
 		}
 	}
 
+	// SearchPermanodesWithAttr - match none with attr type "tag=nosuchtag"
+	{
+		ch := make(chan blob.Ref, 10)
+		req := &camtypes.PermanodeByAttrRequest{
+			Signer:    id.SignerBlobRef,
+			Attribute: "tag",
+			Query:     "nosuchtag",
+		}
+		err := id.Index.SearchPermanodesWithAttr(ctx, ch, req)
+		if err != nil {
+			t.Fatalf("SearchPermanodesWithAttr = %v", err)
+		}
+		var got []blob.Ref
+		for r := range ch {
+			got = append(got, r)
+		}
+		want := []blob.Ref{}
+		if len(got) != len(want) {
+			t.Errorf("SearchPermanodesWithAttr results differ.\n got: %q\nwant: %q",
+				got, want)
+		}
+	}
+	// SearchPermanodesWithAttr - error for unindexed attr
+	{
+		ch := make(chan blob.Ref, 10)
+		req := &camtypes.PermanodeByAttrRequest{
+			Signer:    id.SignerBlobRef,
+			Attribute: "unindexed",
+		}
+		err := id.Index.SearchPermanodesWithAttr(ctx, ch, req)
+		if err != nil {
+			t.Fatalf("SearchPermanodesWithAttr = %v", err)
+		}
+		var got []blob.Ref
+		for r := range ch {
+			got = append(got, r)
+		}
+		want := []blob.Ref{}
+		if len(got) != len(want) {
+			t.Errorf("SearchPermanodesWithAttr results differ.\n got: %q\nwant: %q",
+				got, want)
+		}
+	}
+
 	// Delete value "pony" of type "title" (which does not actually exist) for pn
 	br4 := id.DelAttribute(pn, "title", "pony")
 	br4Time := id.LastTime()