[8.13](backport #39455) x-pack/filebeat/input/internal/httplog: improve req/resp logging

CHANGELOG.next.asciidoc

@@ -129,6 +129,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Add setup option `--force-enable-module-filesets`, that will act as if all filesets have been enabled in a module during setup. {issue}30915[30915] {pull}99999[99999]
 - Made Azure Blob Storage input GA and updated docs accordingly. {pull}37128[37128]
 - Made GCS input GA and updated docs accordingly. {pull}37127[37127]
+- Improve logging of request and response with request trace logging in error conditions. {pull}39455[39455]
 
 *Auditbeat*
 

x-pack/filebeat/input/internal/httplog/roundtripper.go

@@ -109,14 +109,13 @@ func (rt *LoggingRoundTripper) RoundTrip(req *http.Request) (*http.Response, err
 	resp.Body, body, err = copyBody(resp.Body)
 	if err != nil {
 		errorsMessages = append(errorsMessages, fmt.Sprintf("failed to read response body: %s", err))
-	} else {
-		respParts = append(respParts,
-			zap.ByteString("http.response.body.content", body[:min(len(body), rt.maxBodyLen)]),
-			zap.Bool("http.response.body.truncated", rt.maxBodyLen < len(body)),
-			zap.Int("http.response.body.bytes", len(body)),
-			zap.String("http.response.mime_type", resp.Header.Get("Content-Type")),
-		)
 	}
+	respParts = append(respParts,
+		zap.ByteString("http.response.body.content", body[:min(len(body), rt.maxBodyLen)]),
+		zap.Bool("http.response.body.truncated", rt.maxBodyLen < len(body)),
+		zap.Int("http.response.body.bytes", len(body)),
+		zap.String("http.response.mime_type", resp.Header.Get("Content-Type")),
+	)
 	message, err := httputil.DumpResponse(resp, false)
 	if err != nil {
 		errorsMessages = append(errorsMessages, fmt.Sprintf("failed to dump response: %s", err))
@@ -178,14 +177,13 @@ func logRequest(log *zap.Logger, req *http.Request, maxBodyLen int, extra ...zap
 	req.Body, body, err = copyBody(req.Body)
 	if err != nil {
 		errorsMessages = append(errorsMessages, fmt.Sprintf("failed to read request body: %s", err))
-	} else {
-		reqParts = append(reqParts,
-			zap.ByteString("http.request.body.content", body[:min(len(body), maxBodyLen)]),
-			zap.Bool("http.request.body.truncated", maxBodyLen < len(body)),
-			zap.Int("http.request.body.bytes", len(body)),
-			zap.String("http.request.mime_type", req.Header.Get("Content-Type")),
-		)
 	}
+	reqParts = append(reqParts,
+		zap.ByteString("http.request.body.content", body[:min(len(body), maxBodyLen)]),
+		zap.Bool("http.request.body.truncated", maxBodyLen < len(body)),
+		zap.Int("http.request.body.bytes", len(body)),
+		zap.String("http.request.mime_type", req.Header.Get("Content-Type")),
+	)
 	message, err := httputil.DumpRequestOut(req, false)
 	if err != nil {
 		errorsMessages = append(errorsMessages, fmt.Sprintf("failed to dump request: %s", err))
@@ -204,6 +202,13 @@ func logRequest(log *zap.Logger, req *http.Request, maxBodyLen int, extra ...zap
 	return req, reqParts[:0], errorsMessages
 }
 
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
 // TxID returns the current transaction.id value. If rt is nil, the empty string is returned.
 func (rt *LoggingRoundTripper) TxID() string {
 	if rt == nil {