feat(update-service,file-service): 下载页对已丢失的历史APK显示"无法下载"

新增 file-service GET /api/file/{hash}/exists 轻量存在性检查（不读取文件内容），
下载页为每个历史版本调用该接口确认文件是否真实存在；若已丢失（如本次修复之前
就已被 30 天回收任务误删），不再展示会 404 的下载按钮，改为显示"无法下载"提示。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

file-service/src/main/java/com/xuqm/file/config/SecurityConfig.java

@@ -38,6 +38,7 @@ public class SecurityConfig {
                 .requestMatchers(new AntPathRequestMatcher("/**", "OPTIONS")).permitAll()
                 .requestMatchers(new AntPathRequestMatcher("/api/file/upload", "POST")).permitAll()
                 .requestMatchers(new AntPathRequestMatcher("/api/file/*/thumbnail", "GET")).permitAll()
+                .requestMatchers(new AntPathRequestMatcher("/api/file/*/exists", "GET")).permitAll()
                 .requestMatchers(new AntPathRequestMatcher("/api/file/*", "GET")).permitAll()
                 .requestMatchers(new AntPathRequestMatcher("/api/file/*/pin", "POST")).permitAll()
                 // DELETE is permitAll at the Spring Security layer but enforces its own

file-service/src/main/java/com/xuqm/file/controller/FileController.java

@@ -51,6 +51,16 @@ public class FileController {
         serveFromPath(entity.getStoragePath(), entity.getMimeType(), entity.getOriginalName(), response);
     }
 
+    /**
+     * Lightweight existence check — does not read/stream file content. Used by other
+     * services (e.g. update-service's public download page) to avoid exposing dead
+     * download links for files already lost to reclaim.
+     */
+    @GetMapping("/{hash}/exists")
+    public ApiResponse<Boolean> exists(@PathVariable String hash) {
+        return ApiResponse.success(fileStorageService.exists(hash));
+    }
+
     /**
      * Mark a file as permanently retained, excluding it from the 30-day unused-file reclaim job.
      * Called by other services (e.g. update-service) for files that must stay downloadable

file-service/src/main/java/com/xuqm/file/service/FileStorageService.java

@@ -167,6 +167,14 @@ public class FileStorageService {
         return entity;
     }
 
+    /** Lightweight existence check — no file content read, used by other services to avoid dead download links. */
+    @Transactional(readOnly = true)
+    public boolean exists(String hash) {
+        return fileRepository.findByHash(hash)
+                .map(e -> Files.exists(Paths.get(e.getStoragePath())))
+                .orElse(false);
+    }
+
     @Transactional
     public void pin(String hash) {
         FileEntity entity = fileRepository.findByHash(hash)

update-service/src/main/java/com/xuqm/update/controller/PublicDownloadController.java

@@ -6,6 +6,7 @@ import com.xuqm.update.entity.AppStoreConfigEntity;
 import com.xuqm.update.entity.AppVersionEntity;
 import com.xuqm.update.repository.AppVersionRepository;
 import com.xuqm.update.service.AppStoreService;
+import com.xuqm.update.service.UpdateAssetService;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -28,12 +29,14 @@ public class PublicDownloadController {
     private final AppVersionRepository versionRepository;
     private final AppStoreService appStoreService;
     private final ObjectMapper objectMapper;
+    private final UpdateAssetService updateAssetService;
 
     public PublicDownloadController(AppVersionRepository versionRepository, AppStoreService appStoreService,
-                                     ObjectMapper objectMapper) {
+                                     ObjectMapper objectMapper, UpdateAssetService updateAssetService) {
         this.versionRepository = versionRepository;
         this.appStoreService = appStoreService;
         this.objectMapper = objectMapper;
+        this.updateAssetService = updateAssetService;
     }
 
     @GetMapping("/download-info")
@@ -84,10 +87,31 @@ public class PublicDownloadController {
             return null;
         }
         AppVersionEntity latest = versions.get(0);
+
+        List<Map<String, Object>> history = new ArrayList<>();
+        for (AppVersionEntity v : versions) {
+            // Retention cleanup already clears downloadUrl for evicted versions; for the
+            // rest, confirm the file is still actually there — some historical APKs were
+            // reclaimed by file-service before the pin-on-upload fix shipped.
+            boolean hasUrl = v.getDownloadUrl() != null && !v.getDownloadUrl().isBlank();
+            boolean available = hasUrl && updateAssetService.downloadUrlExists(v.getDownloadUrl());
+            Map<String, Object> h = new LinkedHashMap<>();
+            h.put("versionName", v.getVersionName());
+            h.put("versionCode", v.getVersionCode());
+            h.put("downloadUrl", available ? v.getDownloadUrl() : "");
+            h.put("available", available);
+            h.put("changeLog", v.getChangeLog() != null ? v.getChangeLog() : "");
+            h.put("publishedAt", v.getCreatedAt() != null ? v.getCreatedAt().toString() : "");
+            h.put("current", v.getId().equals(latest.getId()));
+            history.add(h);
+        }
+        Map<String, Object> latestEntry = history.get(0);
+
         Map<String, Object> info = new LinkedHashMap<>();
         info.put("versionName", latest.getVersionName());
         info.put("versionCode", latest.getVersionCode());
-        info.put("downloadUrl", latest.getDownloadUrl() != null ? latest.getDownloadUrl() : "");
+        info.put("downloadUrl", latestEntry.get("downloadUrl"));
+        info.put("available", latestEntry.get("available"));
         info.put("changeLog", latest.getChangeLog() != null ? latest.getChangeLog() : "");
         info.put("publishedAt", latest.getCreatedAt() != null ? latest.getCreatedAt().toString() : "");
 
@@ -100,18 +124,6 @@ public class PublicDownloadController {
             }
         }
         info.put("storeLinks", storeLinks);
-
-        List<Map<String, Object>> history = new ArrayList<>();
-        for (AppVersionEntity v : versions) {
-            Map<String, Object> h = new LinkedHashMap<>();
-            h.put("versionName", v.getVersionName());
-            h.put("versionCode", v.getVersionCode());
-            h.put("downloadUrl", v.getDownloadUrl() != null ? v.getDownloadUrl() : "");
-            h.put("changeLog", v.getChangeLog() != null ? v.getChangeLog() : "");
-            h.put("publishedAt", v.getCreatedAt() != null ? v.getCreatedAt().toString() : "");
-            h.put("current", v.getId().equals(latest.getId()));
-            history.add(h);
-        }
         info.put("history", history);
         return info;
     }

update-service/src/main/java/com/xuqm/update/service/UpdateAssetService.java

@@ -486,6 +486,48 @@ public class UpdateAssetService {
         }
     }
 
+    /**
+     * Whether a version's downloadUrl still resolves to an actual file, without downloading
+     * its content. Used by the public download page so it can show "无法下载" instead of a
+     * dead link for historical versions whose APK was already lost (e.g. reclaimed by
+     * file-service before the pin-on-upload fix shipped). Fails open (assumes it still
+     * exists) on transient check errors, so a network blip never hides a good link.
+     */
+    public boolean downloadUrlExists(String downloadUrl) {
+        if (downloadUrl == null || downloadUrl.isBlank()) {
+            return false;
+        }
+        if (isFileServiceUrl(downloadUrl)) {
+            try {
+                String existsUrl = rewriteToInternalUrl(downloadUrl) + "/exists";
+                HttpURLConnection connection = (HttpURLConnection) new URL(existsUrl).openConnection();
+                connection.setConnectTimeout(8_000);
+                connection.setReadTimeout(10_000);
+                int status = connection.getResponseCode();
+                if (status >= 400) {
+                    return true;
+                }
+                try (InputStream in = connection.getInputStream()) {
+                    JsonNode root = objectMapper.readTree(in);
+                    return root.path("data").asBoolean(true);
+                }
+            } catch (Exception e) {
+                log.warn("Failed to check existence for {}: {}", downloadUrl, e.getMessage());
+                return true;
+            }
+        }
+        if (downloadUrl.startsWith(baseUrl)) {
+            String prefix = "/files/apk/";
+            int idx = downloadUrl.indexOf(prefix);
+            if (idx >= 0) {
+                String filename = downloadUrl.substring(idx + prefix.length());
+                return Files.exists(Paths.get(uploadDir, "apk", filename));
+            }
+        }
+        // Externally-hosted URL of unknown origin — can't check, assume it's fine.
+        return true;
+    }
+
     private RemotePackage downloadRemotePackage(String packageUrl, boolean tempFile) throws IOException {
         String internalUrl = rewriteToInternalUrl(packageUrl);
         HttpURLConnection connection = (HttpURLConnection) new URL(internalUrl).openConnection();