x-pack/filebeat/input/websocket: do minor clean-up in main loop (#40145)

* remove unneeded goroutine
* fix logging: The body was previously not being logged since an io.ReadCloser
  is not a JSON-serialisable type.

x-pack/filebeat/input/websocket/input.go

@@ -5,15 +5,18 @@
 package websocket
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"net/url"
 	"reflect"
 	"time"
 
 	"github.com/google/cel-go/cel"
 	"github.com/gorilla/websocket"
+	"go.uber.org/zap/zapcore"
 	"google.golang.org/protobuf/types/known/structpb"
 
 	v2 "github.com/elastic/beats/v7/filebeat/input/v2"
@@ -109,7 +112,15 @@ func (i input) run(env v2.Context, src *source, cursor map[string]interface{}, p
 	headers := formHeader(cfg)
 	c, resp, err := websocket.DefaultDialer.DialContext(ctx, url, headers)
 	if resp != nil && resp.Body != nil {
-		log.Debugw("websocket connection response", "body", resp.Body)
+		var buf bytes.Buffer
+		if log.Core().Enabled(zapcore.DebugLevel) {
+			const limit = 1e4
+			io.CopyN(&buf, resp.Body, limit)
+		}
+		if n, _ := io.Copy(io.Discard, resp.Body); n != 0 && buf.Len() != 0 {
+			buf.WriteString("... truncated")
+		}
+		log.Debugw("websocket connection response", "body", &buf)
 		resp.Body.Close()
 	}
 	if err != nil {
@@ -119,41 +130,26 @@ func (i input) run(env v2.Context, src *source, cursor map[string]interface{}, p
 	}
 	defer c.Close()
 
-	done := make(chan error)
-
-	go func() {
-		defer close(done)
-		for {
-			_, message, err := c.ReadMessage()
-			if err != nil {
-				metrics.errorsTotal.Inc()
-				if websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway) {
-					log.Errorw("websocket connection closed", "error", err)
-				} else {
-					log.Errorw("failed to read websocket data", "error", err)
-				}
-				done <- err
-				return
-			}
-			metrics.receivedBytesTotal.Add(uint64(len(message)))
-			state["response"] = message
-			log.Debugw("received websocket message", logp.Namespace("websocket"), string(message))
-			err = i.processAndPublishData(ctx, metrics, prg, ast, state, cursor, pub, log)
-			if err != nil {
-				metrics.errorsTotal.Inc()
-				log.Errorw("failed to process and publish data", "error", err)
-				done <- err
-				return
+	for {
+		_, message, err := c.ReadMessage()
+		if err != nil {
+			metrics.errorsTotal.Inc()
+			if websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway) {
+				log.Errorw("websocket connection closed", "error", err)
+			} else {
+				log.Errorw("failed to read websocket data", "error", err)
 			}
+			return err
+		}
+		metrics.receivedBytesTotal.Add(uint64(len(message)))
+		state["response"] = message
+		log.Debugw("received websocket message", logp.Namespace("websocket"), string(message))
+		err = i.processAndPublishData(ctx, metrics, prg, ast, state, cursor, pub, log)
+		if err != nil {
+			metrics.errorsTotal.Inc()
+			log.Errorw("failed to process and publish data", "error", err)
+			return err
 		}
-	}()
-
-	// blocks until done is closed, context is cancelled or an error is received
-	select {
-	case err := <-done:
-		return err
-	case <-ctx.Done():
-		return ctx.Err()
 	}
 }