net/http: add a benchmark for multi indexing

We don't index multis, so a corpus full of them will take quadratic
time to check for conflicts. How slow is that going to be in practice?

This benchmark indexes and checks a thousand multi patterns, all disjoint.
It runs in about 35ms.

Change-Id: Id27940ab19ad003627bd5c43c53466e01456b796
Reviewed-on: https://go-review.googlesource.com/c/go/+/529477
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

src/net/http/pattern_test.go

@@ -159,11 +159,11 @@ func TestIsValidHTTPToken(t *testing.T) {
 	}
 }
 
-func mustParsePattern(t *testing.T, s string) *pattern {
-	t.Helper()
+func mustParsePattern(tb testing.TB, s string) *pattern {
+	tb.Helper()
 	p, err := parsePattern(s)
 	if err != nil {
-		t.Fatal(err)
+		tb.Fatal(err)
 	}
 	return p
 }

src/net/http/routing_index_test.go

@@ -151,3 +151,29 @@ func genStar(max int, g generator) generator {
 		}
 	}
 }
+
+func BenchmarkMultiConflicts(b *testing.B) {
+	// How fast is indexing if the corpus is all multis?
+	const nMultis = 1000
+	var pats []*pattern
+	for i := 0; i < nMultis; i++ {
+		pats = append(pats, mustParsePattern(b, fmt.Sprintf("/a/b/{x}/d%d/", i)))
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		var idx routingIndex
+		for _, p := range pats {
+			got := indexConflicts(p, &idx)
+			if len(got) != 0 {
+				b.Fatalf("got %d conflicts, want 0", len(got))
+			}
+			idx.addPattern(p)
+		}
+		if i == 0 {
+			// Confirm that all the multis ended up where they belong.
+			if g, w := len(idx.multis), nMultis; g != w {
+				b.Fatalf("got %d multis, want %d", g, w)
+			}
+		}
+	}
+}