accesslog: add CSV format

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

middleware/accesslog/json.go

@@ -0,0 +1,54 @@
+package accesslog
+
+import (
+	"encoding/json"
+	"io"
+	"sync"
+)
+
+// JSON is a Formatter type for JSON logs.
+type JSON struct {
+	Prefix, Indent string
+	EscapeHTML     bool
+
+	enc         *json.Encoder
+	mu          sync.Mutex
+	lockEncoder bool
+}
+
+// SetOutput creates the json encoder writes to the "dest".
+// It's called automatically by the middleware when this Formatter is used.
+func (f *JSON) SetOutput(dest io.Writer) {
+	if dest == nil {
+		return
+	}
+
+	// All logs share the same accesslog's writer and it cannot change during serve-time.
+	enc := json.NewEncoder(dest)
+	enc.SetEscapeHTML(f.EscapeHTML)
+	enc.SetIndent(f.Prefix, f.Indent)
+	f.lockEncoder = f.Prefix != "" || f.Indent != ""
+	f.enc = enc
+}
+
+// Format prints the logs in JSON format.
+// Writes to the destination directly,
+// locks on each Format call.
+func (f *JSON) Format(log *Log) (bool, error) {
+	// f.mu.Lock()
+	// ^ This lock is not required as the writer is
+	// protected with mutex if necessary or configurated to do so.
+	// However, if we navigate through the
+	// internal encoding's source code we'll see that it
+	// uses a field for its indent buffer,
+	// therefore it's only useful when Prefix or Indent was not empty.
+	if f.lockEncoder {
+		f.mu.Lock()
+	}
+	err := f.enc.Encode(log)
+	if f.lockEncoder {
+		f.mu.Unlock()
+	}
+
+	return true, err
+}