raise an error on attempt to copy s3 object to itself without changing anything (#4838)

moto/s3/exceptions.py

@@ -575,6 +575,16 @@ class BucketMustHaveLockeEnabled(S3ClientError):
         )
 
 
+class CopyObjectMustChangeSomething(S3ClientError):
+    code = 400
+
+    def __init__(self):
+        super().__init__(
+            "InvalidRequest",
+            "This copy request is illegal because it is trying to copy an object to itself without changing the object's metadata, storage class, website redirect location or encryption attributes.",
+        )
+
+
 class InvalidFilterRuleName(InvalidArgumentError):
     code = 400
 

moto/s3/models.py

@@ -37,6 +37,7 @@ from moto.s3.exceptions import (
     AccessDeniedByLock,
     BucketAlreadyExists,
     BucketNeedsToBeNew,
+    CopyObjectMustChangeSomething,
     MissingBucket,
     InvalidBucketName,
     InvalidPart,
@@ -2016,6 +2017,16 @@ class S3Backend(BaseBackend, CloudWatchMetricProvider):
         kms_key_id=None,
         bucket_key_enabled=False,
     ):
+        if (
+            src_key.name == dest_key_name
+            and src_key.bucket_name == dest_bucket_name
+            and storage == src_key.storage_class
+            and acl == src_key.acl
+            and encryption == src_key.encryption
+            and kms_key_id == src_key.kms_key_id
+            and bucket_key_enabled == (src_key.bucket_key_enabled or False)
+        ):
+            raise CopyObjectMustChangeSomething
 
         new_key = self.put_object(
             bucket_name=dest_bucket_name,

tests/test_s3/test_s3.py

@@ -683,6 +683,28 @@ def test_copy_key_replace_metadata_boto3():
     resp["ETag"].should.equal(initial["ETag"])
 
 
+@mock_s3
+def test_copy_key_without_changes_should_error_boto3():
+    client = boto3.client("s3", region_name=DEFAULT_REGION_NAME)
+    bucket_name = "my_bucket"
+    s3 = boto3.resource("s3", region_name=DEFAULT_REGION_NAME)
+    key_name = "my_key"
+    key = s3.Object(bucket_name, key_name)
+
+    s3.create_bucket(Bucket=bucket_name)
+    key.put(Body=b"some value")
+
+    with pytest.raises(ClientError) as e:
+        client.copy_object(
+            Bucket=bucket_name,
+            CopySource="{}/{}".format(bucket_name, key_name),
+            Key=key_name,
+        )
+        e.value.response["Error"]["Message"].should.equal(
+            "This copy request is illegal because it is trying to copy an object to itself without changing the object's metadata, storage class, website redirect location or encryption attributes."
+        )
+
+
 @freeze_time("2012-01-01 12:00:00")
 @mock_s3
 def test_last_modified_boto3():