management: Extract parse_headers in send_webhook_fixture_message.

This way other devtools such as the integrations development panel
could also use the method.

zerver/management/commands/send_webhook_fixture_message.py

@@ -9,6 +9,20 @@ from django.test import Client
 from zerver.lib.management import ZulipBaseCommand, CommandError
 from zerver.models import get_realm
 
+def parse_headers(custom_headers: Union[None, str]) -> Union[None, Dict[str, str]]:
+    """ The main aim of this method is be to convert regular HTTP headers into a format that
+    Django prefers. Note: This function throws a ValueError and thus it should be used in a
+    try/except block. """
+    headers = {}
+    if not custom_headers:
+        return None
+    custom_headers_dict = ujson.loads(custom_headers)
+    for header in custom_headers_dict:
+        if len(header.split(" ")) > 1:
+            raise ValueError("custom header '%s' contains a space." % (header,))
+        headers["HTTP_" + header.upper().replace("-", "_")] = str(custom_headers_dict[header])
+    return headers
+
 class Command(ZulipBaseCommand):
     help = """
 Create webhook message based on given fixture
@@ -50,16 +64,8 @@ approach shown above.
         self.add_realm_args(parser, help="Specify which realm/subdomain to connect to; default is zulip")
 
     def parse_headers(self, custom_headers: Union[None, str]) -> Union[None, Dict[str, str]]:
-        headers = {}
-        if not custom_headers:
-            return None
         try:
-            custom_headers_dict = ujson.loads(custom_headers)
-            for header in custom_headers_dict:
-                if len(header.split(" ")) > 1:
-                    raise ValueError("custom header '%s' contains a space." % (header,))
-                headers["HTTP_" + header.upper().replace("-", "_")] = str(custom_headers_dict[header])
-            return headers
+            return parse_headers(custom_headers)
         except ValueError as ve:
             raise CommandError('Encountered an error while attempting to parse custom headers: {}\n'
                                'Note: all strings must be enclosed within "" instead of \'\''.format(ve))