gzip for v3 #153 (#183)

Co-authored-by: Кирилл Горбунов <kirya_gorbunov_2015@mail.ru>
Co-committed-by: Кирилл Горбунов <kirya_gorbunov_2015@mail.ru>

handler/meter/meter.go

@@ -2,13 +2,36 @@ package meter // import "go.unistack.org/micro-server-http/v3/handler/meter"
 
 import (
 	"bytes"
+	"compress/gzip"
 	"context"
+	"io"
+	"strings"
+	"sync"
 
 	codecpb "go.unistack.org/micro-proto/v3/codec"
 	"go.unistack.org/micro/v3/errors"
+	"go.unistack.org/micro/v3/logger"
+	"go.unistack.org/micro/v3/metadata"
 	"go.unistack.org/micro/v3/meter"
 )
 
+const (
+	contentEncodingHeader = "Content-Encoding"
+	acceptEncodingHeader  = "Accept-Encoding"
+)
+
+var gzipPool = sync.Pool{
+	New: func() interface{} {
+		return gzip.NewWriter(nil)
+	},
+}
+
+var bufPool = sync.Pool{
+	New: func() interface{} {
+		return bytes.NewBuffer(nil)
+	},
+}
+
 // guard to fail early
 var _ MeterServiceServer = &Handler{}
 
@@ -56,12 +79,46 @@ func NewHandler(opts ...Option) *Handler {
 }
 
 func (h *Handler) Metrics(ctx context.Context, req *codecpb.Frame, rsp *codecpb.Frame) error {
-	buf := bytes.NewBuffer(nil)
-	if err := h.opts.Meter.Write(buf, h.opts.MeterOptions...); err != nil {
-		return errors.InternalServerError(h.opts.Name, "%v", err)
+	log, ok := logger.FromContext(ctx)
+	if !ok {
+		log = logger.DefaultLogger()
+	}
+
+	buf := bufPool.Get().(*bytes.Buffer)
+	defer bufPool.Put(buf)
+	buf.Reset()
+
+	w := io.Writer(buf)
+
+	if md, ok := metadata.FromIncomingContext(ctx); gzipAccepted(md) && ok {
+		md.Set(contentEncodingHeader, "gzip")
+		gz := gzipPool.Get().(*gzip.Writer)
+		defer gzipPool.Put(gz)
+
+		gz.Reset(w)
+		defer gz.Close()
+
+		w = gz
+	}
+
+	if err := h.opts.Meter.Write(w, h.opts.MeterOptions...); err != nil {
+		log.Error(ctx, errors.InternalServerError(h.opts.Name, "%v", err))
+		return nil
 	}
 
 	rsp.Data = buf.Bytes()
 
 	return nil
 }
+
+// gzipAccepted returns whether the client will accept gzip-encoded content.
+func gzipAccepted(md metadata.Metadata) bool {
+	a, ok := md.Get(acceptEncodingHeader)
+	if !ok {
+		return false
+	}
+	if strings.Contains(a, "gzip") {
+		return true
+	}
+	return false
+}