x-pack/filebeat/input/internal/httplog: improve req/resp logging

Attempt to log the request and response bodies and other details even
when copying the body has been reported to have failed.

CHANGELOG.next.asciidoc

@@ -262,6 +262,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - added benchmark input {pull}37437[37437]
 - added benchmark input and discard output {pull}37437[37437]
 - Ensure all responses sent by HTTP Endpoint are HTML-escaped. {pull}39329[39329]
+- 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

@@ -115,14 +115,13 @@ 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))
@@ -184,14 +183,13 @@ 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))