fix(xo-server): limit number of VDI exports (#2673)

Fixes #2672

packages/xo-server/src/xapi/index.js

@@ -869,13 +869,8 @@ export default class Xapi extends XapiBase {
             ...vdi,
             $SR$uuid: vdi.$SR.uuid,
           }
-      const stream = (streams[`${vdiRef}.vhd`] = this._exportVdi(
+      streams[`${vdiRef}.vhd`] = () =>
-        $cancelToken,
+        this._exportVdi($cancelToken, vdi, baseVdi, VDI_FORMAT_VHD)
-        vdi,
-        baseVdi,
-        VDI_FORMAT_VHD
-      ))
-      $defer.onFailure(stream.cancel)
     })
 
     const vifs = {}
@@ -905,7 +900,7 @@ export default class Xapi extends XapiBase {
       },
       'streams',
       {
-        value: await streams::pAll(),
+        value: streams,
       }
     )
   }
@@ -1029,7 +1024,10 @@ export default class Xapi extends XapiBase {
 
       // Import VDI contents.
       asyncMap(newVdis, async (vdi, id) => {
-        for (const stream of ensureArray(streams[`${id}.vhd`])) {
+        for (let stream of ensureArray(streams[`${id}.vhd`])) {
+          if (typeof stream === 'function') {
+            stream = await stream()
+          }
           await this._importVdiContent(vdi, stream, VDI_FORMAT_VHD)
         }
       }),
@@ -1847,6 +1845,7 @@ export default class Xapi extends XapiBase {
     return snap
   }
 
+  @concurrency(12, stream => stream.then(stream => fromEvent(stream, 'end')))
   @cancellable
   _exportVdi ($cancelToken, vdi, base, format = VDI_FORMAT_VHD) {
     const host = vdi.$SR.$PBDs[0].$host

packages/xo-server/src/xo-mixins/backups.js

@@ -652,6 +652,10 @@ export default class {
     xapi,
     { vdiParent, isFull, handler, stream, dir, retention }
   ) {
+    if (typeof stream === 'function') {
+      stream = await stream()
+    }
+
     const backupDirectory = `vdi_${vdiParent.uuid}`
     dir = `${dir}/${backupDirectory}`