From 3c202a87ba83958c7f04b272a9792285e482ed19 Mon Sep 17 00:00:00 2001
From: Matthew Richards <matthew.richards@stfc.ac.uk>
Date: Mon, 15 Mar 2021 11:55:43 +0000
Subject: [PATCH]  #209: Make login() use client cache

- Extra attention should be paid to the flushing of session ID on the client object to previous users being logged out the next time backend.login() is called
---
 datagateway_api/common/icat/backend.py | 10 +++++++++-
 datagateway_api/common/icat/helpers.py |  8 ++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/datagateway_api/common/icat/backend.py b/datagateway_api/common/icat/backend.py
index 2770f190..6b436c24 100644
--- a/datagateway_api/common/icat/backend.py
+++ b/datagateway_api/common/icat/backend.py
@@ -9,6 +9,7 @@
     create_client,
     create_entities,
     delete_entity_by_id,
+    get_cached_client,
     get_count_with_filters,
     get_entity_by_id,
     get_entity_with_filters,
@@ -39,7 +40,9 @@ def __init__(self):
 
     def login(self, credentials):
         log.info("Logging in to get session ID")
-        client = create_client()
+        # There is no session ID required for this endpoint, a client object will be
+        # fetched from cache with a blank `sessionId` attribute
+        client = get_cached_client(None)
 
         # Syntax for Python ICAT
         login_details = {
@@ -48,6 +51,11 @@ def login(self, credentials):
         }
         try:
             session_id = client.login(credentials["mechanism"], login_details)
+            # Flushing client's session ID so the session ID returned in this request
+            # won't be logged out next time `client.login()` is used in this function.
+            # `login()` calls `self.logout()` if `sessionId` is set
+            client.sessionId = None
+
             return session_id
         except ICATSessionError:
             raise AuthenticationError("User credentials are incorrect")
diff --git a/datagateway_api/common/icat/helpers.py b/datagateway_api/common/icat/helpers.py
index 51d9d7f2..7cc5bb1d 100644
--- a/datagateway_api/common/icat/helpers.py
+++ b/datagateway_api/common/icat/helpers.py
@@ -77,9 +77,13 @@ def get_cached_client(session_id):
     """
     TODO - Add docstring
     """
-    log.debug(f"Caching, session ID: {session_id}")
     client = create_client()
-    client.sessionId = session_id
+
+    # `session_id` of None suggests this function is being called from an endpoint that
+    # doesn't use the `requires_session_id` decorator (e.g. POST /sessions)
+    log.info("Caching, session ID: %s", session_id)
+    if session_id:
+        client.sessionId = session_id
 
     return client