Fix callback URL rewrite

backend/handlers/onlyoffice.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"git.elijahkuntz.com/Elijah/drive/config"
 	"git.elijahkuntz.com/Elijah/drive/middleware"
@@ -48,8 +49,15 @@ func (h *OnlyOfficeHandler) Callback(c *fiber.Ctx) error {
 			return c.Status(400).JSON(fiber.Map{"error": "url required"})
 		}
 
+		// If the server cannot resolve the public URL due to hairpin NAT,
+		// we can rewrite it to use the internal Docker IP
+		downloadUrl := req.Url
+		if strings.HasPrefix(downloadUrl, "https://office.elijahkuntz.com") {
+			downloadUrl = strings.Replace(downloadUrl, "https://office.elijahkuntz.com", "http://192.168.50.81:8084", 1)
+		}
+
 		// Download modified file from Document Server
-		resp, err := http.Get(req.Url)
+		resp, err := http.Get(downloadUrl)
 		if err != nil {
 			return c.Status(500).JSON(fiber.Map{"error": "failed to download file"})
 		}