fix: use HTTPClient::writeToStream for downloading files from OPDS (#1207)

## Summary

* Refactored `HttpDownloader::downloadToFile` to use `FileWriteStream`
and `HTTPClient::writeToStream`, removing manual chunked downloading
logic, which was error-prone.
* Fixes
https://github.com/crosspoint-reader/crosspoint-reader/issues/632

## Additional Context

* Tested downloading files from OPDS with a size up to 10 mb.

---

### AI Usage

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please be transparent about their usage as it
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Did you use AI tools to help write this code? _**< YES >**_

src/activities/browser/OpdsBookBrowserActivity.cpp

@@ -171,7 +171,10 @@ void OpdsBookBrowserActivity::render(RenderLock&&) {
 
   if (state == BrowserState::DOWNLOADING) {
     renderer.drawCenteredText(UI_10_FONT_ID, pageHeight / 2 - 40, tr(STR_DOWNLOADING));
-    renderer.drawCenteredText(UI_10_FONT_ID, pageHeight / 2 - 10, statusMessage.c_str());
+    const auto maxWidth = pageWidth - 40;
+    // Trim long titles to keep them within the screen bounds.
+    auto title = renderer.truncatedText(UI_10_FONT_ID, statusMessage.c_str(), maxWidth);
+    renderer.drawCenteredText(UI_10_FONT_ID, pageHeight / 2 - 10, title.c_str());
     if (downloadTotal > 0) {
       const int barWidth = pageWidth - 100;
       constexpr int barHeight = 20;

src/network/HttpDownloader.cpp

@@ -9,10 +9,49 @@
 
 #include <cstring>
 #include <memory>
+#include <utility>
 
 #include "CrossPointSettings.h"
 #include "util/UrlUtils.h"
 
+namespace {
+class FileWriteStream final : public Stream {
+ public:
+  FileWriteStream(FsFile& file, size_t total, HttpDownloader::ProgressCallback progress)
+      : file_(file), total_(total), progress_(std::move(progress)) {}
+
+  size_t write(uint8_t byte) override { return write(&byte, 1); }
+
+  size_t write(const uint8_t* buffer, size_t size) override {
+    // Write-through stream for HTTPClient::writeToStream with progress tracking.
+    const size_t written = file_.write(buffer, size);
+    if (written != size) {
+      writeOk_ = false;
+    }
+    downloaded_ += written;
+    if (progress_ && total_ > 0) {
+      progress_(downloaded_, total_);
+    }
+    return written;
+  }
+
+  int available() override { return 0; }
+  int read() override { return -1; }
+  int peek() override { return -1; }
+  void flush() override { file_.flush(); }
+
+  size_t downloaded() const { return downloaded_; }
+  bool ok() const { return writeOk_; }
+
+ private:
+  FsFile& file_;
+  size_t total_;
+  size_t downloaded_ = 0;
+  bool writeOk_ = true;
+  HttpDownloader::ProgressCallback progress_;
+};
+}  // namespace
+
 bool HttpDownloader::fetchUrl(const std::string& url, Stream& outContent) {
   // Use NetworkClientSecure for HTTPS, regular NetworkClient for HTTP
   std::unique_ptr<NetworkClient> client;
@@ -96,8 +135,13 @@ HttpDownloader::DownloadError HttpDownloader::downloadToFile(const std::string&
     return HTTP_ERROR;
   }
 
-  const size_t contentLength = http.getSize();
+  const int64_t reportedLength = http.getSize();
+  const size_t contentLength = reportedLength > 0 ? static_cast<size_t>(reportedLength) : 0;
+  if (contentLength > 0) {
     LOG_DBG("HTTP", "Content-Length: %zu", contentLength);
+  } else {
+    LOG_DBG("HTTP", "Content-Length: unknown");
+  }
 
   // Remove existing file if present
   if (Storage.exists(destPath.c_str())) {
@@ -112,55 +156,34 @@ HttpDownloader::DownloadError HttpDownloader::downloadToFile(const std::string&
     return FILE_ERROR;
   }
 
-  // Get the stream for chunked reading
-  NetworkClient* stream = http.getStreamPtr();
-  if (!stream) {
-    LOG_ERR("HTTP", "Failed to get stream");
+  // Let HTTPClient handle chunked decoding and stream body bytes into the file.
+  FileWriteStream fileStream(file, contentLength, progress);
+  const int writeResult = http.writeToStream(&fileStream);
+
   file.close();
-    Storage.remove(destPath.c_str());
   http.end();
+
+  if (writeResult < 0) {
+    LOG_ERR("HTTP", "writeToStream error: %d", writeResult);
+    Storage.remove(destPath.c_str());
     return HTTP_ERROR;
   }
 
-  // Download in chunks
-  uint8_t buffer[DOWNLOAD_CHUNK_SIZE];
-  size_t downloaded = 0;
-  const size_t total = contentLength > 0 ? contentLength : 0;
+  const size_t downloaded = fileStream.downloaded();
+  LOG_DBG("HTTP", "Downloaded %zu bytes", downloaded);
 
-  while (http.connected() && (contentLength == 0 || downloaded < contentLength)) {
-    const size_t available = stream->available();
-    if (available == 0) {
-      delay(1);
-      continue;
-    }
-
-    const size_t toRead = available < DOWNLOAD_CHUNK_SIZE ? available : DOWNLOAD_CHUNK_SIZE;
-    const size_t bytesRead = stream->readBytes(buffer, toRead);
-
-    if (bytesRead == 0) {
-      break;
-    }
-
-    const size_t written = file.write(buffer, bytesRead);
-    if (written != bytesRead) {
-      LOG_ERR("HTTP", "Write failed: wrote %zu of %zu bytes", written, bytesRead);
-      file.close();
+  // Guard against partial writes even if HTTPClient completes.
+  if (!fileStream.ok()) {
+    LOG_ERR("HTTP", "Write failed during download");
     Storage.remove(destPath.c_str());
-      http.end();
     return FILE_ERROR;
   }
 
-    downloaded += bytesRead;
-
-    if (progress && total > 0) {
-      progress(downloaded, total);
+  if (contentLength == 0 && downloaded == 0) {
+    LOG_ERR("HTTP", "Download failed: no data received");
+    Storage.remove(destPath.c_str());
+    return HTTP_ERROR;
   }
-  }
-
-  file.close();
-  http.end();
-
-  LOG_DBG("HTTP", "Downloaded %zu bytes", downloaded);
 
   // Verify download size if known
   if (contentLength > 0 && downloaded != contentLength) {

src/network/HttpDownloader.h

@@ -38,7 +38,4 @@ class HttpDownloader {
    */
   static DownloadError downloadToFile(const std::string& url, const std::string& destPath,
                                       ProgressCallback progress = nullptr);
-
- private:
-  static constexpr size_t DOWNLOAD_CHUNK_SIZE = 1024;
 };