Expect exit status code in spring client

In the previous commit I fixed a scenario where Spring Server failed to pass the application exit code through to Spring Client. Should similar thing happen in future, this can also be detected in Spring Client. It should expect to read some integer and not default to 0 when read nil.

This commit introduces such assertion in Spring Client.

Also fixes #676.

@see 3a8e609

Author: zygzagZ

lib/spring/client/run.rb

@@ -184,11 +184,16 @@ def run_command(client, application)
           suspend_resume_on_tstp_cont(pid)
 
           forward_signals(application)
-          status = application.read.to_i
+          status = application.read
+          log "got exit status #{status.inspect}"
 
-          log "got exit status #{status}"
+          # Status should always be an integer. If it is empty, something unexpected must have happened to the server.
+          if status.to_s.strip.empty?
+            log "unexpected empty exit status, app crashed?"
+            exit 1
+          end
 
-          exit status
+          exit status.to_i
         else
           log "got no pid"
           exit 1