feat(backups/_forkStreamUnpipe): add more debug

@xen-orchestra/backups/_forkStreamUnpipe.js

@@ -3,6 +3,8 @@
 const eos = require('end-of-stream')
 const { PassThrough } = require('stream')
 
+const { debug } = require('@xen-orchestra/log').createLogger('xo:backups:forkStreamUnpipe')
+
 // create a new readable stream from an existing one which may be piped later
 //
 // in case of error in the new readable stream, it will simply be unpiped
@@ -11,18 +13,23 @@ exports.forkStreamUnpipe = function forkStreamUnpipe(stream) {
   const { forks = 0 } = stream
   stream.forks = forks + 1
 
+  debug('forking', { forks: stream.forks })
+
   const proxy = new PassThrough()
   stream.pipe(proxy)
   eos(stream, error => {
     if (error !== undefined) {
+      debug('error on original stream, destroying fork', { error })
       proxy.destroy(error)
     }
   })
-  eos(proxy, _ => {
-    stream.forks--
+  eos(proxy, error => {
+    debug('end of stream, unpiping', { error, forks: --stream.forks })
+
     stream.unpipe(proxy)
 
     if (stream.forks === 0) {
+      debug('no more forks, destroying original stream')
       stream.destroy(new Error('no more consumers for this stream'))
     }
   })