accesslog: add CSV format

relative to: https://github.com/kataras/iris/issues/1601

middleware/accesslog/template.go

@@ -0,0 +1,65 @@
+package accesslog
+
+import (
+	"io"
+	"sync"
+	"text/template"
+)
+
+// Template is a Formatter.
+// It's used to print the Log in a text/template way.
+// The caller has full control over the printable result;
+// certain fields can be ignored, change the display order and e.t.c.
+type Template struct {
+	// Custom template source.
+	// Use this or `Tmpl/TmplName` fields.
+	Text string
+	// Custom template funcs to used when `Text` is not empty.
+	Funcs template.FuncMap
+
+	// Custom template to use, overrides the `Text` and `Funcs` fields.
+	Tmpl *template.Template
+	// If not empty then this named template/block renders the log line.
+	TmplName string
+
+	dest io.Writer
+	mu   sync.Mutex
+}
+
+// SetOutput creates the default template if missing
+// when this formatter is registered.
+func (f *Template) SetOutput(dest io.Writer) {
+	if f.Tmpl == nil {
+		tmpl := template.New("")
+
+		text := f.Text
+		if text != "" {
+			tmpl.Funcs(f.Funcs)
+		} else {
+			text = defaultTmplText
+		}
+
+		f.Tmpl = template.Must(tmpl.Parse(text))
+	}
+
+	f.dest = dest
+}
+
+const defaultTmplText = "{{.Now.Format .TimeFormat}}|{{.Latency}}|{{.Code}}|{{.Method}}|{{.Path}}|{{.IP}}|{{.RequestValuesLine}}|{{.BytesReceivedLine}}|{{.BytesSentLine}}|{{.Request}}|{{.Response}}|\n"
+
+// Format prints the logs in text/template format.
+func (f *Template) Format(log *Log) (bool, error) {
+	var err error
+
+	// A template may be executed safely in parallel, although if parallel
+	// executions share a Writer the output may be interleaved.
+	f.mu.Lock()
+	if f.TmplName != "" {
+		err = f.Tmpl.ExecuteTemplate(f.dest, f.TmplName, log)
+	} else {
+		err = f.Tmpl.Execute(f.dest, log)
+	}
+	f.mu.Unlock()
+
+	return true, err
+}