Fix potential deadlocks with talosctl config validation

Since we never flushed the stdout/stderr buffers before checking exit code we could hang indefinitely in case the output was large enough.

Author: dbackeus

app/models/cluster.rb

@@ -68,10 +68,9 @@ def validate_secrets_yaml
 
     cmd = "talosctl gen config -o - --output-types controlplane --with-secrets #{random_tmp_file} test https://host:6443"
 
-    Open3.popen3(cmd) do |_stdin, _stdout, stderr, wait_thread|
-      break if wait_thread.value.success?
-
-      errors.add(:secrets, stderr.read)
+    _stdout, stderr, status = Open3.capture3(cmd)
+    unless status.success?
+      errors.add(:secrets, stderr.presence || "talosctl gen config failed")
     end
   ensure
     FileUtils.rm_f(random_tmp_file)

app/models/machine_config.rb

@@ -71,22 +71,18 @@ def generate_config(output_type: server.talos_type)
         #{server.cluster.endpoint}
     )
 
-    config = Open3.popen3(command) do |_stdin, stdout, stderr, wait_thread|
-      if wait_thread.value.success?
-        stdout.read
-      else
-        output = stderr.read
-        message = "Failed to generate talos configuration.\nCommand:#{command}\nOutput: #{output}"
-        raise InvalidConfigError.new(message, output)
-      end
+    stdout, stderr, status = Open3.capture3(command)
+    unless status.success?
+      message = "Failed to generate talos configuration.\nCommand:#{command}\nOutput: #{stderr}"
+      raise InvalidConfigError.new(message, stderr)
     end
 
     File.delete(secrets_file)
     File.delete(patch_file)
     File.delete(patch_control_plane_file)
     File.delete(patch_worker_file)
 
-    talosconfig = YAML.safe_load(config)
+    talosconfig = YAML.safe_load(stdout)
 
     # Initially talosconfig is generated with an endpoint of 127.0.0.1 and no nodes.
     # Hence we add the first control plane IP as both enpoint and node.