Check if datasource exists before querying (#84)

Author: ioanarm

tools/datasources.go

@@ -77,6 +77,10 @@ func getDatasourceByUID(ctx context.Context, args GetDatasourceByUIDParams) (*mo
 	c := mcpgrafana.GrafanaClientFromContext(ctx)
 	datasource, err := c.Datasources.GetDataSourceByUID(args.UID)
 	if err != nil {
+		// Check if it's a 404 Not Found Error
+		if strings.Contains(err.Error(), "404") {
+			return nil, fmt.Errorf("datasource with UID '%s' not found. Please check if the datasource exists and is accessible", args.UID)
+		}
 		return nil, fmt.Errorf("get datasource by uid %s: %w", args.UID, err)
 	}
 	return datasource.Payload, nil

tools/datasources_test.go

@@ -74,6 +74,16 @@ func TestDatasourcesTools(t *testing.T) {
 		assert.Equal(t, "Prometheus", result.Name)
 	})
 
+	t.Run("get datasource by uid - not found", func(t *testing.T) {
+		ctx := newTestContext()
+		result, err := getDatasourceByUID(ctx, GetDatasourceByUIDParams{
+			UID: "non-existent-datasource",
+		})
+		require.Error(t, err)
+		require.Nil(t, result)
+		assert.Contains(t, err.Error(), "not found")
+	})
+
 	t.Run("get datasource by name", func(t *testing.T) {
 		ctx := newTestContext()
 		result, err := getDatasourceByName(ctx, GetDatasourceByNameParams{

tools/loki.go

@@ -44,6 +44,12 @@ type Stats struct {
 }
 
 func newLokiClient(ctx context.Context, uid string) (*Client, error) {
+	// First check if the datasource exists
+	_, err := getDatasourceByUID(ctx, GetDatasourceByUIDParams{UID: uid})
+	if err != nil {
+		return nil, err
+	}
+
 	grafanaURL, apiKey := mcpgrafana.GrafanaURLFromContext(ctx), mcpgrafana.GrafanaAPIKeyFromContext(ctx)
 	url := fmt.Sprintf("%s/api/datasources/proxy/uid/%s", strings.TrimRight(grafanaURL, "/"), uid)
 

tools/prometheus.go

@@ -27,6 +27,12 @@ var (
 )
 
 func promClientFromContext(ctx context.Context, uid string) (promv1.API, error) {
+	// First check if the datasource exists
+	_, err := getDatasourceByUID(ctx, GetDatasourceByUIDParams{UID: uid})
+	if err != nil {
+		return nil, err
+	}
+
 	grafanaURL, apiKey := mcpgrafana.GrafanaURLFromContext(ctx), mcpgrafana.GrafanaAPIKeyFromContext(ctx)
 	url := fmt.Sprintf("%s/api/datasources/proxy/uid/%s", strings.TrimRight(grafanaURL, "/"), uid)
 	rt := api.DefaultRoundTripper
@@ -42,6 +48,7 @@ func promClientFromContext(ctx context.Context, uid string) (promv1.API, error)
 	if err != nil {
 		return nil, fmt.Errorf("creating Prometheus client: %w", err)
 	}
+
 	return promv1.NewAPI(c), nil
 }