From 0bcf73f5c969d9ae35f1ed986ab27fbb37a58ff2 Mon Sep 17 00:00:00 2001
From: Olivier Poitrey <rs@rhapsodyk.net>
Date: Sat, 10 Feb 2024 00:34:16 +0100
Subject: [PATCH] Update benchmark

Also initialize the response headers with the default header in
benchmarks as all reponse at least have one header. This removes the
single allocation that should not be attributed to this library.

Also add a micro-optimization on the critical path.
---
 README.md     | 16 ++++++++--------
 bench_test.go |  4 +++-
 cors.go       |  6 +++---
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index f92e8e6..6bc95a5 100644
--- a/README.md
+++ b/README.md
@@ -106,15 +106,15 @@ See [API documentation](http://godoc.org/github.com/rs/cors) for more info.
 goos: darwin
 goarch: arm64
 pkg: github.com/rs/cors
-BenchmarkWithout-10             352671961       3.317 ns/op       0 B/op       0 allocs/op
-BenchmarkDefault-10              18261723       65.63 ns/op       0 B/op       0 allocs/op
-BenchmarkAllowedOrigin-10        13309591       90.21 ns/op       0 B/op       0 allocs/op
-BenchmarkPreflight-10             7247728       166.9 ns/op       0 B/op       0 allocs/op
-BenchmarkPreflightHeader-10       5915437       202.9 ns/op       0 B/op       0 allocs/op
-BenchmarkWildcard/match-10      250336476       4.784 ns/op       0 B/op       0 allocs/op
-BenchmarkWildcard/too_short-10 1000000000       0.6354 ns/op       0 B/op       0 allocs/op
+BenchmarkWithout-10            	135325480	         8.124 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDefault-10            	24082140	        51.40 ns/op	       0 B/op	       0 allocs/op
+BenchmarkAllowedOrigin-10      	16424518	        88.25 ns/op	       0 B/op	       0 allocs/op
+BenchmarkPreflight-10          	 8010259	       147.3 ns/op	       0 B/op	       0 allocs/op
+BenchmarkPreflightHeader-10    	 6850962	       175.0 ns/op	       0 B/op	       0 allocs/op
+BenchmarkWildcard/match-10     	253275342	         4.714 ns/op	       0 B/op	       0 allocs/op
+BenchmarkWildcard/too_short-10 	1000000000	         0.6235 ns/op	       0 B/op	       0 allocs/op
 PASS
-ok  	github.com/rs/cors	9.613s
+ok  	github.com/rs/cors	99.131s
 ```
 
 ## Licenses
diff --git a/bench_test.go b/bench_test.go
index d8eeac0..6859382 100644
--- a/bench_test.go
+++ b/bench_test.go
@@ -100,7 +100,9 @@ func BenchmarkPreflightHeader(b *testing.B) {
 func makeFakeResponses(n int) []*FakeResponse {
 	resps := make([]*FakeResponse, n)
 	for i := 0; i < n; i++ {
-		resps[i] = &FakeResponse{http.Header{}}
+		resps[i] = &FakeResponse{http.Header{
+			"Content-Type": []string{"text/plain"},
+		}}
 	}
 	return resps
 }
diff --git a/cors.go b/cors.go
index 9a8b419..e084128 100644
--- a/cors.go
+++ b/cors.go
@@ -394,10 +394,10 @@ func (c *Cors) handleActualRequest(w http.ResponseWriter, r *http.Request) {
 	allowed, additionalVaryHeaders := c.isOriginAllowed(r, origin)
 
 	// Always set Vary, see https://github.com/rs/cors/issues/10
-	if vary, found := headers["Vary"]; found {
-		headers["Vary"] = append(vary, headerVaryOrigin[0])
-	} else {
+	if vary := headers["Vary"]; vary == nil {
 		headers["Vary"] = headerVaryOrigin
+	} else {
+		headers["Vary"] = append(vary, headerVaryOrigin[0])
 	}
 	if len(additionalVaryHeaders) > 0 {
 		headers.Add("Vary", strings.Join(convert(additionalVaryHeaders, http.CanonicalHeaderKey), ", "))