fix #79: remove compatibility header

pkg/cfg/cluster.go

@@ -189,6 +189,7 @@ func (cluster *Cluster) getDefaultOptions() []elasticsearch.Option {
 			cluster.getTransport(),
 			elastictransport.WithHeader(headers),
 		),
+		elasticsearch.WithCompatibilityMode(),
 	}
 }
 
@@ -203,7 +204,9 @@ func (cluster *Cluster) getTransport() elastictransport.Option {
 		)
 	}
 
-	return elastictransport.WithTransport(transport)
+	return elastictransport.WithTransport(
+		&CompatibilityTransport{Transport: transport},
+	)
 }
 
 func (conf *Config) SetupES() error {

pkg/cfg/transport.go

@@ -53,6 +53,11 @@ func (t *DebugTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 		contentline = buf.String()
 	}
 
+	if req.Header.Get("Accept") != "" {
+		req.Header.Del("Accept")
+		req.Header.Add("Accept", "application/json")
+	}
+
 	slog.Info("req", "host", req.URL.Host, "uri", req.URL.Path,
 		"body", content, "bodyline", contentline,
 		"headers", req.Header,
@@ -60,3 +65,21 @@ func (t *DebugTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 
 	return t.Transport.RoundTrip(req)
 }
+
+// Fixes https://codeberg.org/scip/esctl/issues/79:
+// the API client has this Accept header hardcoded everywhere:
+// req.Header.Set("Accept", "application/vnd.elasticsearch+json;compatible-with=9")
+// While this works pretty well with ES9, it doesn't with ES8. So, we replace
+// this header with a new one without the compatibility part.
+type CompatibilityTransport struct {
+	Transport http.RoundTripper
+}
+
+func (t *CompatibilityTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if req.Header.Get("Accept") != "" {
+		req.Header.Del("Accept")
+		req.Header.Add("Accept", "application/json")
+	}
+
+	return t.Transport.RoundTrip(req)
+}