Add GZIP compression to collector endpoint (#95)

* Add GZIP compression to collector endpoint

* Check 'Accept-Encoding' header

collector/collector.go

@@ -1,6 +1,7 @@
 package collector
 
 import (
+	"compress/gzip"
 	"context"
 	"encoding/binary"
 	"fmt"
@@ -22,6 +23,11 @@ import (
 	"github.com/castai/egressd/pb"
 )
 
+var (
+	acceptEncoding  = http.CanonicalHeaderKey("Accept-Encoding")
+	contentEncoding = http.CanonicalHeaderKey("Content-Encoding")
+)
+
 func CurrentTimeGetter() func() time.Time {
 	return func() time.Time {
 		return time.Now()
@@ -139,10 +145,20 @@ func (c *Collector) GetRawNetworkMetricsHandler(w http.ResponseWriter, req *http
 		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}
-	if _, err := w.Write(batchBytes); err != nil {
-		c.log.Errorf("write batch: %v", err)
-		return
+
+	enc := req.Header.Get(acceptEncoding)
+	if strings.Contains(strings.ToLower(enc), "gzip") {
+		if err := c.writeGzipBody(w, batchBytes); err != nil {
+			c.log.Errorf("write batch %v", err)
+			return
+		}
+	} else {
+		if err := c.writePlainBody(w, batchBytes); err != nil {
+			c.log.Errorf("write batch %v", err)
+			return
+		}
 	}
+
 	if c.cfg.SendTrafficDelta {
 		// reset metric tx/rx values, so only delta numbers will be sent with the next batch
 		for _, m := range c.podMetrics {
@@ -154,6 +170,32 @@ func (c *Collector) GetRawNetworkMetricsHandler(w http.ResponseWriter, req *http
 	}
 }
 
+func (c *Collector) writeGzipBody(w http.ResponseWriter, body []byte) error {
+	writer, err := gzip.NewWriterLevel(w, gzip.BestCompression)
+	if err != nil {
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return fmt.Errorf("cannot create gzip writer: %w", err)
+	}
+	defer writer.Close()
+
+	w.Header().Add(contentEncoding, "gzip")
+
+	if _, err := writer.Write(body); err != nil {
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return err
+	}
+
+	return nil
+}
+
+func (c *Collector) writePlainBody(w http.ResponseWriter, body []byte) error {
+	if _, err := w.Write(body); err != nil {
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return err
+	}
+	return nil
+}
+
 // collect aggregates conntract records into reduced pod metrics.
 func (c *Collector) collect() error {
 	start := time.Now()

collector/collector_test.go

@@ -1,6 +1,8 @@
 package collector
 
 import (
+	"compress/gzip"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"sort"
@@ -420,11 +422,19 @@ func TestCollector__GetRawNetworkMetricsHandler(t *testing.T) {
 
 		w := httptest.NewRecorder()
 		// scrape pods metrics and prepare them to be sent
-		coll.GetRawNetworkMetricsHandler(w, &http.Request{})
+		coll.GetRawNetworkMetricsHandler(w, &http.Request{Header: http.Header{
+			"Accept-Encoding": []string{"gzip"},
+		}})
 		r.Equal(200, w.Code)
 
 		batch := &pb.RawNetworkMetricBatch{}
-		err := proto.Unmarshal(w.Body.Bytes(), batch)
+		gzreader, err := gzip.NewReader(w.Body)
+		r.NoError(err)
+
+		body, err := io.ReadAll(gzreader)
+		r.NoError(err)
+
+		err = proto.Unmarshal(body, batch)
 		r.NoError(err)
 		r.Len(batch.Items, 2)
 		sort.Slice(batch.Items, func(i, j int) bool {
@@ -507,11 +517,20 @@ func TestCollector__GetRawNetworkMetricsHandler(t *testing.T) {
 
 		w := httptest.NewRecorder()
 		// scrape pods metrics and prepare them to be sent
-		coll.GetRawNetworkMetricsHandler(w, &http.Request{})
+		coll.GetRawNetworkMetricsHandler(w, &http.Request{Header: http.Header{
+			"Accept-Encoding": []string{"gzip"},
+		}})
 		r.Equal(200, w.Code)
 
 		batch := &pb.RawNetworkMetricBatch{}
-		err := proto.Unmarshal(w.Body.Bytes(), batch)
+
+		gzreader, err := gzip.NewReader(w.Body)
+		r.NoError(err)
+
+		body, err := io.ReadAll(gzreader)
+		r.NoError(err)
+
+		err = proto.Unmarshal(body, batch)
 		r.NoError(err)
 		r.Len(batch.Items, 2)
 		sort.Slice(batch.Items, func(i, j int) bool {