Merge pull request #421 from kubeshop/feat/first-last-selectors

feat: support :first and :last pseudo classes
kubeshop · May 4, 2022 · 9ab8e38 · 9ab8e38
2 parents afa9a8a + a35231e
commit 9ab8e38
Show file tree

Hide file tree

Showing 4 changed files with 39 additions and 4 deletions.
diff --git a/server/assertions/selectors/builder.go b/server/assertions/selectors/builder.go
@@ -128,6 +128,10 @@ func createPseudoClass(parserPseudoClass parserPseudoClass) (PseudoClass, error)
 		return &NthChildPseudoClass{
 			N: *parserPseudoClass.Value.Int,
 		}, nil
+	case "first":
+		return &FirstPseudoClass{}, nil
+	case "last":
+		return &LastPseudoClass{}, nil
 	case "":
 		// No pseudoClass
 		return nil, nil

diff --git a/server/assertions/selectors/parser.go b/server/assertions/selectors/parser.go
@@ -30,8 +30,8 @@ type parserValue struct {
 }
 
 type parserPseudoClass struct {
-	Type  string       `":" @("nth_child")`
-	Value *parserValue `"(" @@* ")"`
+	Type  string       `":" @("nth_child" | "first" | "last")`
+	Value *parserValue `("(" @@* ")")*`
 }
 
 func CreateParser() (*participle.Parser, error) {

diff --git a/server/assertions/selectors/pseudo_classes.go b/server/assertions/selectors/pseudo_classes.go
@@ -13,9 +13,30 @@ type NthChildPseudoClass struct {
 }
 
 func (nc NthChildPseudoClass) Filter(spans []traces.Span) []traces.Span {
-	if len(spans) < int(nc.N) {
+	if int(nc.N) < 1 || int(nc.N) > len(spans) {
 		return []traces.Span{}
 	}
 
 	return []traces.Span{spans[int(nc.N-1)]}
 }
+
+type FirstPseudoClass struct{}
+
+func (fpc FirstPseudoClass) Filter(spans []traces.Span) []traces.Span {
+	if len(spans) == 0 {
+		return []traces.Span{}
+	}
+
+	return []traces.Span{spans[0]}
+}
+
+type LastPseudoClass struct{}
+
+func (lpc LastPseudoClass) Filter(spans []traces.Span) []traces.Span {
+	length := len(spans)
+	if length == 0 {
+		return []traces.Span{}
+	}
+
+	return []traces.Span{spans[length-1]}
+}
diff --git a/server/assertions/selectors/selector_test.go b/server/assertions/selectors/selector_test.go
@@ -92,7 +92,17 @@ func TestSelector(t *testing.T) {
 			ExpectedSpanIds: []trace.SpanID{updatePokemonDatabaseSpanID},
 		},
 		{
-			Name:            "Selector with pseudo class",
+			Name:            "Selector with first pseudo class",
+			Expression:      "span[tracetest.span.type=\"db\"]:first",
+			ExpectedSpanIds: []trace.SpanID{insertPokemonDatabaseSpanID},
+		},
+		{
+			Name:            "Selector with first pseudo class",
+			Expression:      "span[tracetest.span.type=\"db\"]:last",
+			ExpectedSpanIds: []trace.SpanID{updatePokemonDatabaseSpanID},
+		},
+		{
+			Name:            "Selector with nth_child pseudo class",
 			Expression:      "span[tracetest.span.type=\"db\"]:nth_child(2)",
 			ExpectedSpanIds: []trace.SpanID{updatePokemonDatabaseSpanID},
 		},