Adds cache control header and updates all existing headers to be lowercase for HTTP/2 (GoogleCloudPlatform#1155)

Author: gguuss

iot/api-client/http_example/cloudiot_http_example.py

@@ -69,6 +69,37 @@ def create_jwt(project_id, private_key_file, algorithm):
     return jwt.encode(token, private_key, algorithm=algorithm)
 
 
+def publish_message(
+        message, message_type, base_url, project_id, cloud_region, registry_id,
+        device_id, jwt_token):
+    headers = {
+            'authorization': 'Bearer {}'.format(jwt_token),
+            'content-type': 'application/json',
+            'cache-control': 'no-cache'
+    }
+
+    # Publish to the events or state topic based on the flag.
+    url_suffix = 'publishEvent' if message_type == 'event' else 'setState'
+
+    publish_url = (
+        '{}/projects/{}/locations/{}/registries/{}/devices/{}:{}').format(
+            base_url, project_id, cloud_region, registry_id, device_id,
+            url_suffix)
+
+    body = None
+    if message_type == 'event':
+        body = {'binary_data': base64.urlsafe_b64encode(message)}
+    else:
+        body = {
+          'state': {'binary_data': base64.urlsafe_b64encode(message)}
+        }
+
+    resp = requests.post(
+            publish_url, data=json.dumps(body), headers=headers)
+
+    return resp
+
+
 def parse_command_line_args():
     """Parse command line arguments."""
     parser = argparse.ArgumentParser(description=(
@@ -117,38 +148,20 @@ def parse_command_line_args():
 def main():
     args = parse_command_line_args()
 
-    # Publish to the events or state topic based on the flag.
-    url_suffix = 'publishEvent' if args.message_type == 'event' else 'setState'
-
-    publish_url = (
-        '{}/projects/{}/locations/{}/registries/{}/devices/{}:{}').format(
-            args.base_url, args.project_id, args.cloud_region,
-            args.registry_id, args.device_id, url_suffix)
-
     jwt_token = create_jwt(
             args.project_id, args.private_key_file, args.algorithm)
 
-    headers = {
-            'Authorization': 'Bearer {}'.format(jwt_token),
-            'Content-Type': 'application/json'
-    }
-
     # Publish num_messages mesages to the HTTP bridge once per second.
     for i in range(1, args.num_messages + 1):
         payload = '{}/{}-payload-{}'.format(
                 args.registry_id, args.device_id, i)
+
         print('Publishing message {}/{}: \'{}\''.format(
                 i, args.num_messages, payload))
-        body = None
-        if args.message_type == 'event':
-            body = {'binary_data': base64.urlsafe_b64encode(payload)}
-        else:
-            body = {
-              'state': {'binary_data': base64.urlsafe_b64encode(payload)}
-            }
-
-        resp = requests.post(
-                publish_url, data=json.dumps(body), headers=headers)
+
+        resp = publish_message(
+                payload, args.message_type, args.base_url, args.project_id,
+                args.cloud_region, args.registry_id, args.device_id, jwt_token)
 
         print('HTTP response: ', resp)