Fix logic to not re-download existing files when force=no (#45495)

* Fix logic to not re-download existing files when force=no. Fixes #45491

* Reduce logic complexity

changelogs/fragments/get-url-fix-idempotency.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+- get_url - Don't re-download files unnecessarily when force=no (https://github.com/ansible/ansible/issues/45491)

lib/ansible/modules/net_tools/basics/get_url.py

@@ -482,7 +482,11 @@ def main():
         if not force and checksum != '':
             destination_checksum = module.digest_from_file(dest, algorithm)
 
-            if checksum == destination_checksum:
+            if checksum != destination_checksum:
+                checksum_mismatch = True
+
+        # Not forcing redownload, unless checksum does not match
+        if not force and not checksum_mismatch:
             # Not forcing redownload, unless checksum does not match
             # allow file attribute changes
             module.params['path'] = dest
@@ -493,8 +497,6 @@ def main():
                 module.exit_json(msg="file already exists but file attributes changed", **result)
             module.exit_json(msg="file already exists", **result)
 
-            checksum_mismatch = True
-
         # If the file already exists, prepare the last modified time for the
         # request.
         mtime = os.path.getmtime(dest)

test/integration/targets/get_url/tasks/main.yml

@@ -241,7 +241,7 @@
 # https://github.com/ansible/ansible/issues/29614
 - name: Change mode on an already downloaded file and specify checksum
   get_url:
-    url: 'https://{{ httpbin_host }}/'
+    url: 'https://{{ httpbin_host }}/get'
     dest: '{{ output_dir }}/test'
     checksum: 'sha256:7036ede810fad2b5d2e7547ec703cae8da61edbba43c23f9d7203a0239b765c4.'
     mode: '0775'
@@ -257,6 +257,17 @@
       - result is changed
       - "stat_result.stat.mode == '0775'"
 
+- name: Get a file that already exists
+  get_url:
+    url: 'https://{{ httpbin_host }}/get'
+    dest: '{{ output_dir }}/test'
+  register: result
+
+- name: Assert that we didn't re-download unnecessarily
+  assert:
+    that:
+      - result is not changed
+
 # https://github.com/ansible/ansible/issues/27617
 
 - name: set role facts