fix(xo-server/rest-api): VDI export via NBD

CHANGELOG.unreleased.md

@@ -13,6 +13,8 @@
 
 > Users must be able to say: “I had this issue, happy to know it's fixed”
 
+- [REST API] Fix VDI export when NBD is enabled
+
 ### Packages to release
 
 > When modifying a package, add it here with its release type.
@@ -32,6 +34,7 @@
 - @xen-orchestra/backups minor
 - @xen-orchestra/xapi major
 - complex-matcher patch
+- xo-server patch
 - xo-web minor
 
 <!--packages-end-->

packages/xo-server/src/xo-mixins/rest-api.mjs

@@ -371,9 +371,18 @@ export default class RestApi {
       wrap(async (req, res) => {
         const stream = await req.xapiObject.$exportContent({ format: req.params.format })
 
-        stream.headers['content-disposition'] = 'attachment'
-        res.writeHead(stream.statusCode, stream.statusMessage != null ? stream.statusMessage : '', stream.headers)
+        // stream can be an HTTP response, in this case, extract interesting data
+        const { headers = {}, length, statusCode = 200, statusMessage = 'OK' } = stream
 
+        // Set the correct disposition
+        headers['content-disposition'] = 'attachment'
+
+        // expose the stream length if known
+        if (headers['content-length'] === undefined && length !== undefined) {
+          headers['content-length'] = length
+        }
+
+        res.writeHead(statusCode, statusMessage, headers)
         await pipeline(stream, res)
       })
     )