more pylinting and refactor out common code to a new lambda layer to be included in use by all functions

Author: rpcme

src/layer_utils/__init__.py

@@ -0,0 +1,40 @@
+"""
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: MIT-0
+
+AWS related functions that multiple lambda functions use, here to reduce redundancy
+"""
+from io import BytesIO
+from json import dumps
+from botocore.exceptions import ClientError
+from boto3 import resource, client
+
+# Given a bucket and object, verify its existence and return the resource.
+def s3_object_stream(bucket_name: str, object_name: str):
+    """Retrieve an s3 object and read as stream"""
+    s3res = resource('s3')
+    res = s3res.Object(bucket_name=bucket_name, key=object_name)
+    try:
+        fs = BytesIO()
+        res.download_fileobj(fs)
+        return fs
+    except ClientError as ce:
+        raise ce
+
+# Given a bucket name and object name, return bytes representing
+# the object content.
+def s3_filebuf_bytes(bucket_name: str, object_name: str):
+    """Flush s3 object stream buffer to string object"""
+    object_stream = s3_object_stream(bucket_name=bucket_name,
+                                     object_name=object_name)
+    return object_stream.getvalue()
+
+def queue_manifest_certificate(identity, certificate, queue_url):
+    """Send the thing name and certificate to sqs queue"""
+    sqs_client = client("sqs")
+    payload = {
+        'thing': identity,
+        'certificate': certificate
+    }
+    sqs_client.send_message( QueueUrl=queue_url,
+                             MessageBody=dumps(payload) )

src/layer_utils/aws_utils.py

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+"""
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: MIT-0
+
+Certificate/manifest related functions that multiple lambda functions use,
+here to reduce redundancy
+"""
+from base64 import b64encode
+from cryptography import x509
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+
+def format_certificate(cert_string):
+    """Encode certificate so that it can safely travel via sqs"""
+    cert_encoded = cert_string.encode('ascii')
+
+    pem_obj = x509.load_pem_x509_certificate(cert_encoded,
+                                             backend=default_backend())
+    block = pem_obj.public_bytes(encoding=serialization.Encoding.PEM).decode('ascii')
+    return str(b64encode(block.encode('ascii')))

src/layer_utils/cert_utils.py

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+"""
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: MIT-0
+
+Utility lambda layer unit testing
+"""
+import os
+import io
+from unittest import TestCase
+from unittest.mock import MagicMock, patch
+import pytest
+from moto import mock_aws, settings
+from botocore.exceptions import ClientError
+from boto3 import resource, client
+
+from aws_utils import s3_object_stream, s3_filebuf_bytes
+from .model_provider_espressif import LambdaS3Class
+
+@mock_aws(config={
+    "core": {
+        "mock_credentials": True,
+        "reset_boto3_session": False,
+        "service_whitelist": None,
+    },
+    'iot': {'use_valid_cert': True}})
+class TestProviderEspressif(TestCase):
+    """Unit tests for the espressif provider module"""
+    def setUp(self):
+        self.test_s3_bucket_name = "unit_test_s3_bucket"
+        self.test_s3_object_content = None
+        os.environ["S3_BUCKET_NAME"] = self.test_s3_bucket_name
+        s3_client = client('s3', region_name="us-east-1")
+        s3_client.create_bucket(Bucket = self.test_s3_bucket_name )
+        with open('./test/artifacts/manifest-espressif.csv', 'rb') as data:
+            s3_client.put_object(Bucket=self.test_s3_bucket_name, Key="manifest.csv", Body=data)
+            self.test_s3_object_content = s3_client.get_object(Bucket=self.test_s3_bucket_name, Key="manifest.csv")['Body']
+        mocked_s3_resource = resource("s3")
+        mocked_s3_resource = { "resource" : resource('s3'),
+                               "bucket_name" : self.test_s3_bucket_name }
+        self.mocked_s3_class = LambdaS3Class(mocked_s3_resource)
+
+    def test_pos_s3_object_resource(self):
+        """Basic pos test case for object resource"""
+        r = s3_object_stream("unit_test_s3_bucket", "manifest.csv")
+        assert isinstance(r, io.BytesIO)
+
+    def test_neg_s3_object_resource(self):
+        """Basic neg test case for object resource"""
+        with pytest.raises(ClientError) as e:
+            # Although this returns a value, no need to define var for it
+            s3_object_stream("unit_test_s3_buckets", "manifest")
+        errstr = "An error occurred (NoSuchBucket) when calling the " \
+                 "HeadObject operation: The specified bucket does not exist"
+        assert str(e.value) == errstr
+
+    def test_pos_s3_filebuf_bytes(self):
+        """Basic pos test case for byte buffer handling"""
+        # The bytes should equal to the object in the bucket
+        v = s3_filebuf_bytes("unit_test_s3_bucket", "manifest.csv")
+        assert v == self.test_s3_object_content.read()