We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
[E2503] fails incorrectly when intrinsic function used in Protocol value 
*cfn-lint version: 0.4.2*

*Description of issue.*

This is valid, and conforms to the spec, but rule throws an error:

```yaml
Parameters:
  TestParam:
    Type: String
    Default: TCP
Conditions:
  TestCond: !Equals ['a', 'a']
Resources:
  OpenShiftMasterELB:
    Type: AWS::ElasticLoadBalancing::LoadBalancer
    Properties:
      Subnets:
        - subnet-1234abcd
      SecurityGroups:
        - sg-1234abcd
      Listeners:
        # Fails on Protocol
        - InstancePort: '1'
          InstanceProtocol: !Ref TestParam
          LoadBalancerPort: '1'
          Protocol: !Ref TestParam
        # Also fails on Protocol
        - InstancePort: '2'
          InstanceProtocol: !If [TestCond, TCP, SSL]
          LoadBalancerPort: '2'
          Protocol: !If [TestCond, TCP, SSL]
        # Works
        - InstancePort: '3'
          InstanceProtocol: !If [TestCond, TCP, SSL]
          LoadBalancerPort: '3'
          Protocol: TCP
```

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `src/cfnlint/rules/resources/elb/Elb.py`
Content:
```
1 """
2   Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
3 
4   Permission is hereby granted, free of charge, to any person obtaining a copy of this
5   software and associated documentation files (the "Software"), to deal in the Software
6   without restriction, including without limitation the rights to use, copy, modify,
7   merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
8   permit persons to whom the Software is furnished to do so.
9 
10   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
11   INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
12   PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
13   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
14   OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
15   SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
16 """
17 from cfnlint import CloudFormationLintRule
18 from cfnlint import RuleMatch
19 
20 
21 class Elb(CloudFormationLintRule):
22     """Check if Elb Resource Properties"""
23     id = 'E2503'
24     shortdesc = 'Resource ELB Properties'
25     description = 'See if Elb Resource Properties are set correctly \
26 HTTPS has certificate HTTP has no certificate'
27     source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-elb-listener.html'
28     tags = ['properties', 'elb']
29 
30     def match(self, cfn):
31         """Check ELB Resource Parameters"""
32 
33         matches = list()
34 
35         results = cfn.get_resource_properties(['AWS::ElasticLoadBalancingV2::Listener'])
36         for result in results:
37             protocol = result['Value'].get('Protocol')
38             if protocol:
39                 if protocol not in ['HTTP', 'HTTPS', 'TCP']:
40                     message = 'Protocol is invalid for {0}'
41                     path = result['Path'] + ['Protocol']
42                     matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))
43                 elif protocol in ['HTTPS']:
44                     certificate = result['Value'].get('Certificates')
45                     if not certificate:
46                         message = 'Certificates should be specified when using HTTPS for {0}'
47                         path = result['Path'] + ['Protocol']
48                         matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))
49 
50         results = cfn.get_resource_properties(['AWS::ElasticLoadBalancing::LoadBalancer', 'Listeners'])
51         for result in results:
52             if isinstance(result['Value'], list):
53                 for index, listener in enumerate(result['Value']):
54                     protocol = listener.get('Protocol')
55                     if protocol:
56                         if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL']:
57                             message = 'Protocol is invalid for {0}'
58                             path = result['Path'] + [index, 'Protocol']
59                             matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))
60                         elif protocol in ['HTTPS', 'SSL']:
61                             certificate = listener.get('SSLCertificateId')
62                             if not certificate:
63                                 message = 'Certificates should be specified when using HTTPS for {0}'
64                                 path = result['Path'] + [index, 'Protocol']
65                                 matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))
66 
67         return matches
68
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/src/cfnlint/rules/resources/elb/Elb.py b/src/cfnlint/rules/resources/elb/Elb.py
--- a/src/cfnlint/rules/resources/elb/Elb.py
+++ b/src/cfnlint/rules/resources/elb/Elb.py
@@ -30,13 +30,21 @@
     def match(self, cfn):
         """Check ELB Resource Parameters"""
 
+        def is_intrinsic(input_obj):
+            """Checks if a given input looks like an intrinsic function"""
+
+            if isinstance(input_obj, dict) and len(input_obj) == 1:
+                if list(input_obj.keys())[0] == 'Ref' or list(input_obj.keys())[0].startswith('Fn::'):
+                    return True
+            return False
+
         matches = list()
 
         results = cfn.get_resource_properties(['AWS::ElasticLoadBalancingV2::Listener'])
         for result in results:
             protocol = result['Value'].get('Protocol')
             if protocol:
-                if protocol not in ['HTTP', 'HTTPS', 'TCP']:
+                if protocol not in ['HTTP', 'HTTPS', 'TCP'] and not is_intrinsic(protocol):
                     message = 'Protocol is invalid for {0}'
                     path = result['Path'] + ['Protocol']
                     matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))
@@ -53,7 +61,7 @@
                 for index, listener in enumerate(result['Value']):
                     protocol = listener.get('Protocol')
                     if protocol:
-                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL']:
+                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL'] and not is_intrinsic(protocol):
                             message = 'Protocol is invalid for {0}'
                             path = result['Path'] + [index, 'Protocol']
                             matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))

{"golden_diff": "diff --git a/src/cfnlint/rules/resources/elb/Elb.py b/src/cfnlint/rules/resources/elb/Elb.py\n--- a/src/cfnlint/rules/resources/elb/Elb.py\n+++ b/src/cfnlint/rules/resources/elb/Elb.py\n@@ -30,13 +30,21 @@\n     def match(self, cfn):\n         \"\"\"Check ELB Resource Parameters\"\"\"\n \n+        def is_intrinsic(input_obj):\n+            \"\"\"Checks if a given input looks like an intrinsic function\"\"\"\n+\n+            if isinstance(input_obj, dict) and len(input_obj) == 1:\n+                if list(input_obj.keys())[0] == 'Ref' or list(input_obj.keys())[0].startswith('Fn::'):\n+                    return True\n+            return False\n+\n         matches = list()\n \n         results = cfn.get_resource_properties(['AWS::ElasticLoadBalancingV2::Listener'])\n         for result in results:\n             protocol = result['Value'].get('Protocol')\n             if protocol:\n-                if protocol not in ['HTTP', 'HTTPS', 'TCP']:\n+                if protocol not in ['HTTP', 'HTTPS', 'TCP'] and not is_intrinsic(protocol):\n                     message = 'Protocol is invalid for {0}'\n                     path = result['Path'] + ['Protocol']\n                     matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n@@ -53,7 +61,7 @@\n                 for index, listener in enumerate(result['Value']):\n                     protocol = listener.get('Protocol')\n                     if protocol:\n-                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL']:\n+                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL'] and not is_intrinsic(protocol):\n                             message = 'Protocol is invalid for {0}'\n                             path = result['Path'] + [index, 'Protocol']\n                             matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n", "issue": "[E2503] fails incorrectly when intrinsic function used in Protocol value \n*cfn-lint version: 0.4.2*\r\n\r\n*Description of issue.*\r\n\r\nThis is valid, and conforms to the spec, but rule throws an error:\r\n\r\n```yaml\r\nParameters:\r\n  TestParam:\r\n    Type: String\r\n    Default: TCP\r\nConditions:\r\n  TestCond: !Equals ['a', 'a']\r\nResources:\r\n  OpenShiftMasterELB:\r\n    Type: AWS::ElasticLoadBalancing::LoadBalancer\r\n    Properties:\r\n      Subnets:\r\n        - subnet-1234abcd\r\n      SecurityGroups:\r\n        - sg-1234abcd\r\n      Listeners:\r\n        # Fails on Protocol\r\n        - InstancePort: '1'\r\n          InstanceProtocol: !Ref TestParam\r\n          LoadBalancerPort: '1'\r\n          Protocol: !Ref TestParam\r\n        # Also fails on Protocol\r\n        - InstancePort: '2'\r\n          InstanceProtocol: !If [TestCond, TCP, SSL]\r\n          LoadBalancerPort: '2'\r\n          Protocol: !If [TestCond, TCP, SSL]\r\n        # Works\r\n        - InstancePort: '3'\r\n          InstanceProtocol: !If [TestCond, TCP, SSL]\r\n          LoadBalancerPort: '3'\r\n          Protocol: TCP\r\n```\n", "before_files": [{"content": "\"\"\"\n  Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.\n\n  Permission is hereby granted, free of charge, to any person obtaining a copy of this\n  software and associated documentation files (the \"Software\"), to deal in the Software\n  without restriction, including without limitation the rights to use, copy, modify,\n  merge, publish, distribute, sublicense, and/or sell copies of the Software, and to\n  permit persons to whom the Software is furnished to do so.\n\n  THE SOFTWARE IS PROVIDED \"AS IS\", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,\n  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A\n  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT\n  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION\n  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE\n  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.\n\"\"\"\nfrom cfnlint import CloudFormationLintRule\nfrom cfnlint import RuleMatch\n\n\nclass Elb(CloudFormationLintRule):\n    \"\"\"Check if Elb Resource Properties\"\"\"\n    id = 'E2503'\n    shortdesc = 'Resource ELB Properties'\n    description = 'See if Elb Resource Properties are set correctly \\\nHTTPS has certificate HTTP has no certificate'\n    source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-elb-listener.html'\n    tags = ['properties', 'elb']\n\n    def match(self, cfn):\n        \"\"\"Check ELB Resource Parameters\"\"\"\n\n        matches = list()\n\n        results = cfn.get_resource_properties(['AWS::ElasticLoadBalancingV2::Listener'])\n        for result in results:\n            protocol = result['Value'].get('Protocol')\n            if protocol:\n                if protocol not in ['HTTP', 'HTTPS', 'TCP']:\n                    message = 'Protocol is invalid for {0}'\n                    path = result['Path'] + ['Protocol']\n                    matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n                elif protocol in ['HTTPS']:\n                    certificate = result['Value'].get('Certificates')\n                    if not certificate:\n                        message = 'Certificates should be specified when using HTTPS for {0}'\n                        path = result['Path'] + ['Protocol']\n                        matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n\n        results = cfn.get_resource_properties(['AWS::ElasticLoadBalancing::LoadBalancer', 'Listeners'])\n        for result in results:\n            if isinstance(result['Value'], list):\n                for index, listener in enumerate(result['Value']):\n                    protocol = listener.get('Protocol')\n                    if protocol:\n                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL']:\n                            message = 'Protocol is invalid for {0}'\n                            path = result['Path'] + [index, 'Protocol']\n                            matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n                        elif protocol in ['HTTPS', 'SSL']:\n                            certificate = listener.get('SSLCertificateId')\n                            if not certificate:\n                                message = 'Certificates should be specified when using HTTPS for {0}'\n                                path = result['Path'] + [index, 'Protocol']\n                                matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n\n        return matches\n", "path": "src/cfnlint/rules/resources/elb/Elb.py"}], "after_files": [{"content": "\"\"\"\n  Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.\n\n  Permission is hereby granted, free of charge, to any person obtaining a copy of this\n  software and associated documentation files (the \"Software\"), to deal in the Software\n  without restriction, including without limitation the rights to use, copy, modify,\n  merge, publish, distribute, sublicense, and/or sell copies of the Software, and to\n  permit persons to whom the Software is furnished to do so.\n\n  THE SOFTWARE IS PROVIDED \"AS IS\", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,\n  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A\n  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT\n  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION\n  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE\n  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.\n\"\"\"\nfrom cfnlint import CloudFormationLintRule\nfrom cfnlint import RuleMatch\n\n\nclass Elb(CloudFormationLintRule):\n    \"\"\"Check if Elb Resource Properties\"\"\"\n    id = 'E2503'\n    shortdesc = 'Resource ELB Properties'\n    description = 'See if Elb Resource Properties are set correctly \\\nHTTPS has certificate HTTP has no certificate'\n    source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-elb-listener.html'\n    tags = ['properties', 'elb']\n\n    def match(self, cfn):\n        \"\"\"Check ELB Resource Parameters\"\"\"\n\n        def is_intrinsic(input_obj):\n            \"\"\"Checks if a given input looks like an intrinsic function\"\"\"\n\n            if isinstance(input_obj, dict) and len(input_obj) == 1:\n                if list(input_obj.keys())[0] == 'Ref' or list(input_obj.keys())[0].startswith('Fn::'):\n                    return True\n            return False\n\n        matches = list()\n\n        results = cfn.get_resource_properties(['AWS::ElasticLoadBalancingV2::Listener'])\n        for result in results:\n            protocol = result['Value'].get('Protocol')\n            if protocol:\n                if protocol not in ['HTTP', 'HTTPS', 'TCP'] and not is_intrinsic(protocol):\n                    message = 'Protocol is invalid for {0}'\n                    path = result['Path'] + ['Protocol']\n                    matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n                elif protocol in ['HTTPS']:\n                    certificate = result['Value'].get('Certificates')\n                    if not certificate:\n                        message = 'Certificates should be specified when using HTTPS for {0}'\n                        path = result['Path'] + ['Protocol']\n                        matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n\n        results = cfn.get_resource_properties(['AWS::ElasticLoadBalancing::LoadBalancer', 'Listeners'])\n        for result in results:\n            if isinstance(result['Value'], list):\n                for index, listener in enumerate(result['Value']):\n                    protocol = listener.get('Protocol')\n                    if protocol:\n                        if protocol not in ['HTTP', 'HTTPS', 'TCP', 'SSL'] and not is_intrinsic(protocol):\n                            message = 'Protocol is invalid for {0}'\n                            path = result['Path'] + [index, 'Protocol']\n                            matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n                        elif protocol in ['HTTPS', 'SSL']:\n                            certificate = listener.get('SSLCertificateId')\n                            if not certificate:\n                                message = 'Certificates should be specified when using HTTPS for {0}'\n                                path = result['Path'] + [index, 'Protocol']\n                                matches.append(RuleMatch(path, message.format(('/'.join(result['Path'])))))\n\n        return matches\n", "path": "src/cfnlint/rules/resources/elb/Elb.py"}]}