Part 1: Optimize using compiler's inliner (#2687)

* optimized functions for inlining

* added note regarding ResponseWriterWrapper

* optimzed browseWrite* methods for FileServer

* created benchmarks for comparison

* creating browseListing instance in each function

* created benchmarks for openResponseWriter

* removed benchmarks of old implementations

* implemented sync.Pool for byte buffers

* using global sync.Pool for writing JSON/HTML

2 files changed, 27 insertions, 6 deletions

diff --git a/modules/caddyhttp/encode/encode.go b/modules/caddyhttp/encode/encode.go
index c78ccb9..b2c1327 100644
--- a/modules/caddyhttp/encode/encode.go
+++ b/modules/caddyhttp/encode/encode.go
@@ -93,14 +93,23 @@ func (enc *Encode) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyh
 // encode the response with encodingName. The returned response writer MUST
 // be closed after the handler completes.
 func (enc *Encode) openResponseWriter(encodingName string, w http.ResponseWriter) *responseWriter {
+	var rw responseWriter
+	return enc.initResponseWriter(&rw, encodingName, w)
+}
+
+// initResponseWriter initializes the responseWriter instance
+// allocated in openResponseWriter, enabling mid-stack inlining.
+func (enc *Encode) initResponseWriter(rw *responseWriter, encodingName string, wrappedRW http.ResponseWriter) *responseWriter {
 	buf := bufPool.Get().(*bytes.Buffer)
 	buf.Reset()
-	return &responseWriter{
-		ResponseWriterWrapper: &caddyhttp.ResponseWriterWrapper{ResponseWriter: w},
-		encodingName:          encodingName,
-		buf:                   buf,
-		config:                enc,
-	}
+
+	// The allocation of ResponseWriterWrapper might be optimized as well.
+	rw.ResponseWriterWrapper = &caddyhttp.ResponseWriterWrapper{ResponseWriter: wrappedRW}
+	rw.encodingName = encodingName
+	rw.buf = buf
+	rw.config = enc
+
+	return rw
 }
 
 // responseWriter writes to an underlying response writer
diff --git a/modules/caddyhttp/encode/encode_test.go b/modules/caddyhttp/encode/encode_test.go
new file mode 100644
index 0000000..79eae3c
--- /dev/null
+++ b/modules/caddyhttp/encode/encode_test.go
@@ -0,0 +1,12 @@
+package encode
+
+import (
+	"testing"
+)
+
+func BenchmarkOpenResponseWriter(b *testing.B) {
+	enc := new(Encode)
+	for n := 0; n < b.N; n++ {
+		enc.openResponseWriter("test", nil)
+	}
+}