feat(downloader): report release download progress via listener

Stream the release asset in chunks and notify a DownloadProgressListener
with bytes read and total size, so clients can render a real progress bar
instead of an indefinite spinner. The existing downloadIfNeeded overload
keeps working via a no-op listener.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CXTAaR4opi34idMG7ZZ8BV

Author: claude

src/main/java/com/github/_1c_syntax/utils/downloader/BslLanguageServerDownloader.java

@@ -148,6 +148,24 @@ public Optional<String> installedVersion() {
    * @throws IOException если сервер не установлен и его не удалось скачать
    */
   public Path downloadIfNeeded(BslLanguageServerReleaseChannel channel) throws IOException {
+    return downloadIfNeeded(channel, DownloadProgressListener.NONE);
+  }
+
+  /**
+   * Скачивает сервер при необходимости и возвращает путь к его исполняемому файлу, сообщая о
+   * прогрессе скачивания ассета.
+   *
+   * <p>Поведение совпадает с {@link #downloadIfNeeded(BslLanguageServerReleaseChannel)}; отличие —
+   * в передаче {@code progressListener}, который вызывается по мере вычитывания тела ответа
+   * (только когда действительно происходит скачивание новой версии).
+   *
+   * @param channel          канал релизов (стабильный / pre-release)
+   * @param progressListener слушатель прогресса скачивания ассета
+   * @return путь к исполняемому файлу сервера
+   * @throws IOException если сервер не установлен и его не удалось скачать
+   */
+  public Path downloadIfNeeded(BslLanguageServerReleaseChannel channel,
+                               DownloadProgressListener progressListener) throws IOException {
     var installed = installedVersion().orElse(null);
 
     if (installed != null && !checkIntervalElapsed()) {
@@ -173,7 +191,7 @@ public Path downloadIfNeeded(BslLanguageServerReleaseChannel channel) throws IOE
     if (installed == null || compareVersions(latestVersion, installed) > 0) {
       LOGGER.info("Downloading BSL Language Server {}", latestVersion);
       try {
-        downloadAndExtract(release, latestVersion);
+        downloadAndExtract(release, latestVersion, progressListener);
         cleanupOtherVersions(latestVersion);
         installed = latestVersion;
       } catch (IOException e) {
@@ -234,7 +252,8 @@ private GHRelease latestRelease(BslLanguageServerReleaseChannel channel) throws
     return release;
   }
 
-  private void downloadAndExtract(GHRelease release, String version) throws IOException {
+  private void downloadAndExtract(GHRelease release, String version,
+                                  DownloadProgressListener progressListener) throws IOException {
     var assetName = assetName();
     var downloadUrl = release.listAssets().toList().stream()
       .filter(asset -> asset.getName().equals(assetName))
@@ -248,15 +267,16 @@ private void downloadAndExtract(GHRelease release, String version) throws IOExce
     var versionDir = installDir.resolve(version);
 
     try {
-      download(downloadUrl, archive);
+      download(downloadUrl, archive, progressListener);
       deleteRecursively(versionDir);
       extract(archive, versionDir);
     } finally {
       Files.deleteIfExists(archive);
     }
   }
 
-  private void download(String url, Path destination) throws IOException {
+  private void download(String url, Path destination, DownloadProgressListener progressListener)
+    throws IOException {
     var client = HttpClient.newBuilder()
       .followRedirects(HttpClient.Redirect.NORMAL)
       .connectTimeout(CONNECT_TIMEOUT)
@@ -267,16 +287,35 @@ private void download(String url, Path destination) throws IOException {
       .GET()
       .build();
     try {
-      var response = client.send(request, HttpResponse.BodyHandlers.ofFile(destination));
+      var response = client.send(request, HttpResponse.BodyHandlers.ofInputStream());
       if (response.statusCode() != 200) {
-        throw new IOException("Failed to download " + url + ": HTTP " + response.statusCode());
+        try (var ignored = response.body()) {
+          throw new IOException("Failed to download " + url + ": HTTP " + response.statusCode());
+        }
       }
+      var totalBytes = response.headers().firstValueAsLong("Content-Length").orElse(-1L);
+      copyToFile(response.body(), destination, totalBytes, progressListener);
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
       throw new IOException("BSL Language Server download was interrupted", e);
     }
   }
 
+  static void copyToFile(InputStream source, Path destination, long totalBytes,
+                         DownloadProgressListener progressListener) throws IOException {
+    var buffer = new byte[16 * 1024];
+    long readTotal = 0;
+    progressListener.onProgress(0, totalBytes);
+    try (var input = source; var output = Files.newOutputStream(destination)) {
+      int read;
+      while ((read = input.read(buffer)) != -1) {
+        output.write(buffer, 0, read);
+        readTotal += read;
+        progressListener.onProgress(readTotal, totalBytes);
+      }
+    }
+  }
+
   private static void extract(Path archive, Path targetDir) throws IOException {
     Files.createDirectories(targetDir);
     try (var zip = ZipFile.builder().setPath(archive).get()) {

src/main/java/com/github/_1c_syntax/utils/downloader/DownloadProgressListener.java

@@ -0,0 +1,49 @@
+/*
+ * This file is a part of 1c-syntax utils.
+ *
+ * Copyright (c) 2018-2026
+ * Alexey Sosnoviy <labotamy@gmail.com>, Nikita Fedkin <nixel2007@gmail.com> and contributors
+ *
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * 1c-syntax utils is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3.0 of the License, or (at your option) any later version.
+ *
+ * 1c-syntax utils is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with 1c-syntax utils.
+ */
+package com.github._1c_syntax.utils.downloader;
+
+/**
+ * Слушатель прогресса скачивания ассета релиза.
+ *
+ * <p>Вызывается загрузчиком по мере вычитывания тела ответа: сначала один раз с нулём вычитанных
+ * байт, затем после каждого прочитанного блока. Позволяет клиенту (например, IntelliJ-плагину)
+ * рисовать прогресс-бар вместо неопределённого «крутящегося» индикатора.
+ *
+ * <p>Реализация может бросить {@link RuntimeException} (в частности, для отмены операции) —
+ * исключение пробрасывается наружу через вызов загрузки, а частично скачанный файл удаляется.
+ */
+@FunctionalInterface
+public interface DownloadProgressListener {
+
+  /**
+   * Слушатель, ничего не делающий — значение по умолчанию, когда прогресс не нужен.
+   */
+  DownloadProgressListener NONE = (bytesRead, totalBytes) -> {
+    // no-op
+  };
+
+  /**
+   * @param bytesRead  сколько байт ассета уже скачано
+   * @param totalBytes полный размер ассета в байтах или {@code -1}, если сервер его не сообщил
+   */
+  void onProgress(long bytesRead, long totalBytes);
+}

src/test/java/com/github/_1c_syntax/utils/downloader/BslLanguageServerDownloaderTest.java

@@ -26,9 +26,13 @@
 import org.junit.jupiter.api.condition.OS;
 import org.junit.jupiter.api.io.TempDir;
 
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -82,6 +86,40 @@ void installedBinaryResolvesLinuxLauncher(@TempDir Path installDir) throws IOExc
     assertThat(downloader.installedBinary()).contains(binary);
   }
 
+  @Test
+  void copyToFileWritesContentAndReportsProgress(@TempDir Path installDir) throws IOException {
+    var payload = "bsl-language-server".getBytes(StandardCharsets.UTF_8);
+    var destination = installDir.resolve("asset.bin");
+    var progress = new ArrayList<long[]>();
+
+    BslLanguageServerDownloader.copyToFile(
+      new ByteArrayInputStream(payload),
+      destination,
+      payload.length,
+      (bytesRead, totalBytes) -> progress.add(new long[]{bytesRead, totalBytes}));
+
+    assertThat(Files.readAllBytes(destination)).isEqualTo(payload);
+    assertThat(progress).isNotEmpty();
+    assertThat(progress.get(0)).containsExactly(0, payload.length);
+    var last = progress.get(progress.size() - 1);
+    assertThat(last).containsExactly(payload.length, payload.length);
+    assertThat(last[0]).isLessThanOrEqualTo(last[1]);
+  }
+
+  @Test
+  void copyToFilePropagatesUnknownTotalSize(@TempDir Path installDir) throws IOException {
+    var destination = installDir.resolve("asset.bin");
+    List<Long> totals = new ArrayList<>();
+
+    BslLanguageServerDownloader.copyToFile(
+      new ByteArrayInputStream(new byte[]{1, 2, 3}),
+      destination,
+      -1,
+      (bytesRead, totalBytes) -> totals.add(totalBytes));
+
+    assertThat(totals).isNotEmpty().allMatch(total -> total == -1);
+  }
+
   private static void writeServerInfo(Path installDir, String version) throws IOException {
     Files.createDirectories(installDir);
     Files.writeString(installDir.resolve("SERVER-INFO"),