feat: configurable OPDS download folder and filename format (#2571)

src/activities/browser/OpdsBookBrowserActivity.cpp

@@ -2,11 +2,13 @@
 
 #include <Arduino.h>
 #include <GfxRenderer.h>
+#include <HalStorage.h>
 #include <I18n.h>
 #include <Logging.h>
 #include <OpdsStream.h>
 #include <WiFi.h>
 
+#include "CrossPointSettings.h"
 #include "MappedInputManager.h"
 #include "SilentRestart.h"
 #include "activities/network/WifiSelectionActivity.h"
@@ -15,6 +17,7 @@
 #include "fontIds.h"
 #include "network/HttpDownloader.h"
 #include "util/BookCacheUtils.h"
+#include "util/OpdsFilename.h"
 #include "util/StringUtils.h"
 #include "util/UrlUtils.h"
 
@@ -279,8 +282,26 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
   // Build full download URL relative to the current feed, not the root server URL
   const std::string feedUrl = UrlUtils::buildUrl(server.url, currentPath);
   std::string downloadUrl = UrlUtils::buildUrl(feedUrl, book.href);
-  std::string filename =
-      "/" + StringUtils::sanitizeFilename((book.author.empty() ? "" : book.author + " - ") + book.title) + ".epub";
+  // opdsDownloadFolder is already a null-terminated char[64]; use it directly —
+  // no std::string copy. exists()/mkdir() take const char*.
+  const char* folder = SETTINGS.opdsDownloadFolder;  // "" => SD root
+  bool haveFolder = folder[0] != '\0';
+  if (haveFolder && !Storage.exists(folder) && !Storage.mkdir(folder)) {
+    // exists()-guard first: mkdir's return-on-existing is unconfirmed, and every
+    // existing caller checks exists() before mkdir. On real failure, fall back
+    // to SD root so the download is never lost.
+    LOG_ERR("OPDS", "mkdir failed for %s, using SD root", folder);
+    haveFolder = false;
+  }
+
+  // downloadToFile() needs a std::string, and titles are unbounded (a fixed
+  // char[] would truncate). Cold path (a multi-second download follows), so one
+  // reserve'd, in-place-appended owning string is the right call.
+  std::string filename;
+  filename.reserve(96);
+  if (haveFolder) filename += folder;
+  filename += '/';
+  filename += opdsBookFilename(book.author, book.title, static_cast<OpdsFilenameFormat>(SETTINGS.opdsFilenameFormat));
   LOG_DBG("OPDS", "Downloading: %s -> %s", downloadUrl.c_str(), filename.c_str());
 
   int lastRenderedPercent = -1;