feat: sync moves to a plugin, desktop gets multiple accounts (#1580, #1654)

src/backend/sync/provider.ts

@@ -0,0 +1,80 @@
+/**
+ * The sync provider: a plugin that answers /sync/v2 and /sync/link through
+ * ctx.sync.provide. Core only forwards. With no provider the paths answer 404,
+ * so a server without it looks like one that never had sync.
+ */
+
+import type { NextFunction, Request, RequestHandler, Response } from "express";
+import type { PluginSyncProvider } from "@termix-ssh/plugin-sdk/backend";
+import { syncLogger } from "../utils/logger.js";
+
+interface Entry {
+  pluginId: string;
+  provider: PluginSyncProvider;
+}
+
+const providers = new Map<symbol, Entry>();
+
+export function provideSync(
+  pluginId: string,
+  provider: PluginSyncProvider,
+): () => void {
+  const key = Symbol(pluginId);
+  providers.set(key, { pluginId, provider });
+  return () => {
+    providers.delete(key);
+  };
+}
+
+/** Test seam. */
+export function clearSyncProviders(): void {
+  providers.clear();
+}
+
+export function hasSyncProvider(): boolean {
+  return providers.size > 0;
+}
+
+/** Sends the request to the first provider that does not pass. */
+export const syncForwarder: RequestHandler = (
+  req: Request,
+  res: Response,
+  next: NextFunction,
+) => {
+  const entries = [...providers.values()];
+  const run = (index: number): void => {
+    const entry = entries[index];
+    if (!entry) {
+      next();
+      return;
+    }
+    const pass = (error?: unknown): void => {
+      if (error) next(error);
+      else run(index + 1);
+    };
+    try {
+      const result = entry.provider.handle(req, res, pass);
+      if (result && typeof result.catch === "function") {
+        result.catch((error: unknown) => fail(entry, error, res, next));
+      }
+    } catch (error) {
+      fail(entry, error, res, next);
+    }
+  };
+  run(0);
+};
+
+function fail(
+  entry: Entry,
+  error: unknown,
+  res: Response,
+  next: NextFunction,
+): void {
+  syncLogger.warn("Sync provider failed", {
+    operation: "sync_provider",
+    pluginId: entry.pluginId,
+    error: error instanceof Error ? error.message : String(error),
+  });
+  if (res.headersSent) next(error);
+  else res.status(500).json({ error: "Sync is not available right now" });
+}