station_server: provide history handlers

While the history handlers do need to match what has been saved on disk,
the project provides MfgEvent protobuffer writers out of the box, and
no-others, so at least let the out of box experience function as
expected, even if you would want to change this in your own
implementations.

To enable the (built in) writers, something like this is required in
your station server.

```

if __name__ == '__main__':
	openhtf.util.conf.load(station_server_port='4444')

	interface = mfg_inspector.MfgInspector()
	interface.set_converter(mfg_event_from_test_record)

	with station_server.StationServer(history_path="somepath") as server:
		while 1:
			test = .... #your tests here
			test.add_output_callbacks(server.publish_final_state)
			# explicitly match hardcoded pattern in HistoryListHandler
			test.add_output_callbacks(interface.save_to_disk("somepath/mfg_event_{dut_id}_{start_time_millis}.pb"))
			test.execute(test_start=user_input.prompt_for_test_start())
```

Signed-off-by: Karl Palsson <[email protected]>

openhtf/output/servers/station_server.py

@@ -21,6 +21,8 @@
 
 import openhtf
 from openhtf.output.callbacks import mfg_inspector
+from openhtf.output.proto import mfg_event_converter
+from openhtf.output.proto import mfg_event_pb2
 from openhtf.output.servers import pub_sub
 from openhtf.output.servers import web_gui_server
 from openhtf.util import conf
@@ -461,10 +463,25 @@ class HistoryItemHandler(BaseHistoryHandler):
   """GET endpoint for a test record from the history."""
 
   def get(self, file_name):
-    # TODO(Kenadia): Implement the history item handler. The implementation
-    # depends on the format used to store test records on disk.
-    self.write('Not implemented.')
-    self.set_status(500)
+    # The "Out of the box" disk format is fixed, subclasses/alternative
+    # implementations need to be sure their implementation matches their
+    # recorder
+
+    fn = os.path.join(self.history_path, file_name)
+    if not os.path.isfile(fn):
+      self.write('Not found')
+      self.set_status(404)
+      return
+
+    with open(fn, mode='rb') as f:
+      me = mfg_event_pb2.MfgEvent()
+      me.ParseFromString(f.read())
+      tr = mfg_event_converter.test_record_from_mfg_event(me)
+      test_record_dict = data.convert_to_base_types(tr)
+      test_state_dict = _test_state_from_record(test_record_dict,
+                                                StationPubSub._last_execution_uid)
+      self.set_status(200)
+      self.write(test_state_dict)
 
 
 class HistoryAttachmentsHandler(BaseHistoryHandler):
@@ -477,10 +494,25 @@ class HistoryAttachmentsHandler(BaseHistoryHandler):
   """
 
   def get(self, file_name, attachment_name):
-    # TODO(Kenadia): Implement the history item handler. The implementation
-    # depends on the format used to store test records on disk.
-    self.write('Not implemented.')
-    self.set_status(500)
+    # The implementation depends on the format used to store
+    # test records on disk.
+    fn = os.path.join(self.history_path, file_name)
+    if not os.path.isfile(fn):
+      self.write('Not found')
+      self.set_status(404)
+      return
+
+    with open(fn, mode='rb') as f:
+      me = mfg_event_pb2.MfgEvent()
+      me.ParseFromString(f.read())
+      # TODO: could use sha1 here to check?
+      desired_real = [a for a in me.attachment if a.name == attachment_name]
+      if len(desired_real) > 0:
+        self.write(desired_real[0].value_binary)
+        self.set_status(200)
+      else:
+        self.write('Attachment not found in test')
+        self.set_status(404)
 
 
 class StationMulticast(multicast.MulticastListener):