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

6 files changed, 104 insertions, 10 deletions

diff --git a/caddy.go b/caddy.go
index 5a5349e99..c30eccf77 100644
--- a/caddy.go
+++ b/caddy.go
@@ -208,8 +208,16 @@ func (d *Duration) UnmarshalJSON(b []byte) error {
 // If no version information is available, a non-nil
 // value will still be returned, but with an
 // unknown version.
-func GoModule() debug.Module {
-	mod := debug.Module{Version: "unknown"}
+func GoModule() *debug.Module {
+	var mod debug.Module
+	return goModule(&mod)
+}
+
+// goModule holds the actual implementation of GoModule.
+// Allocating debug.Module in GoModule() and passing a
+// reference to goModule enables mid-stack inlining.
+func goModule(mod *debug.Module) *debug.Module {
+	mod.Version = "unknown"
 	bi, ok := debug.ReadBuildInfo()
 	if ok {
 		mod.Path = bi.Main.Path
diff --git a/modules/caddyhttp/encode/encode.go b/modules/caddyhttp/encode/encode.go
index c78ccb906..b2c132717 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 000000000..79eae3c56
--- /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)
+	}
+}
diff --git a/modules/caddyhttp/fileserver/browse.go b/modules/caddyhttp/fileserver/browse.go
index e0e6de2c2..91ebcd5c0 100644
--- a/modules/caddyhttp/fileserver/browse.go
+++ b/modules/caddyhttp/fileserver/browse.go
@@ -133,14 +133,16 @@ func (fsrv *FileServer) browseApplyQueryParams(w http.ResponseWriter, r *http.Re
 }
 
 func (fsrv *FileServer) browseWriteJSON(listing browseListing) (*bytes.Buffer, error) {
-	buf := new(bytes.Buffer)
+	buf := bufPool.Get().(*bytes.Buffer)
 	err := json.NewEncoder(buf).Encode(listing.Items)
+	bufPool.Put(buf)
 	return buf, err
 }
 
 func (fsrv *FileServer) browseWriteHTML(listing browseListing) (*bytes.Buffer, error) {
-	buf := new(bytes.Buffer)
+	buf := bufPool.Get().(*bytes.Buffer)
 	err := fsrv.Browse.template.Execute(buf, listing)
+	bufPool.Put(buf)
 	return buf, err
 }
 
diff --git a/modules/caddyhttp/fileserver/browse_test.go b/modules/caddyhttp/fileserver/browse_test.go
new file mode 100644
index 000000000..b1f7092bf
--- /dev/null
+++ b/modules/caddyhttp/fileserver/browse_test.go
@@ -0,0 +1,54 @@
+package fileserver
+
+import (
+	"html/template"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func BenchmarkBrowseWriteJSON(b *testing.B) {
+	fsrv := new(FileServer)
+	fsrv.Provision(caddy.Context{})
+	listing := browseListing{
+		Name:           "test",
+		Path:           "test",
+		CanGoUp:        false,
+		Items:          make([]fileInfo, 100),
+		NumDirs:        42,
+		NumFiles:       420,
+		Sort:           "",
+		Order:          "",
+		ItemsLimitedTo: 42,
+	}
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		fsrv.browseWriteJSON(listing)
+	}
+}
+
+func BenchmarkBrowseWriteHTML(b *testing.B) {
+	fsrv := new(FileServer)
+	fsrv.Provision(caddy.Context{})
+	fsrv.Browse = &Browse{
+		TemplateFile: "",
+		template:     template.New("test"),
+	}
+	listing := browseListing{
+		Name:           "test",
+		Path:           "test",
+		CanGoUp:        false,
+		Items:          make([]fileInfo, 100),
+		NumDirs:        42,
+		NumFiles:       420,
+		Sort:           "",
+		Order:          "",
+		ItemsLimitedTo: 42,
+	}
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		fsrv.browseWriteHTML(listing)
+	}
+}
diff --git a/modules/caddyhttp/fileserver/staticfiles.go b/modules/caddyhttp/fileserver/staticfiles.go
index 761dfc3cb..a66b75324 100644
--- a/modules/caddyhttp/fileserver/staticfiles.go
+++ b/modules/caddyhttp/fileserver/staticfiles.go
@@ -15,6 +15,7 @@
 package fileserver
 
 import (
+	"bytes"
 	"fmt"
 	"html/template"
 	weakrand "math/rand"
@@ -25,6 +26,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/caddyserver/caddy/v2"
@@ -46,6 +48,7 @@ type FileServer struct {
 	Hide       []string `json:"hide,omitempty"`
 	IndexNames []string `json:"index_names,omitempty"`
 	Browse     *Browse  `json:"browse,omitempty"`
+
 	// TODO: Content negotiation
 }
 
@@ -301,6 +304,12 @@ func calculateEtag(d os.FileInfo) string {
 
 var defaultIndexNames = []string{"index.html"}
 
+var bufPool = sync.Pool{
+	New: func() interface{} {
+		return new(bytes.Buffer)
+	},
+}
+
 const minBackoff, maxBackoff = 2, 5
 
 // Interface guards