[v2] Validate multipart download content ranges

.changes/next-release/feature-download-58503.json

@@ -0,0 +1,5 @@
+{
+  "type": "feature",
+  "category": "s3 download",
+  "description": "Validate requested range matches content range in response for multipart downloads"
+}

awscli/s3transfer/download.py

@@ -16,7 +16,11 @@
 
 from botocore.exceptions import ClientError
 from s3transfer.compat import seekable
-from s3transfer.exceptions import RetriesExceededError, S3DownloadFailedError
+from s3transfer.exceptions import (
+    RetriesExceededError,
+    S3DownloadFailedError,
+    S3ValidationError,
+)
 from s3transfer.futures import IN_MEMORY_DOWNLOAD_TAG
 from s3transfer.tasks import SubmissionTask, Task
 from s3transfer.utils import (
@@ -577,6 +581,10 @@ def _main(
                 response = client.get_object(
                     Bucket=bucket, Key=key, **extra_args
                 )
+                self._validate_content_range(
+                    extra_args.get('Range'),
+                    response.get('ContentRange'),
+                )
                 streaming_body = StreamReaderProgress(
                     response['Body'], callbacks
                 )
@@ -634,6 +642,27 @@ def _main(
     def _handle_io(self, download_output_manager, fileobj, chunk, index):
         download_output_manager.queue_file_io_task(fileobj, chunk, index)
 
+    def _validate_content_range(self, requested_range, content_range):
+        if not requested_range or not content_range:
+            return
+        # Unparsed `ContentRange` looks like `bytes 0-8388607/39542919`,
+        # where `0-8388607` is the fetched range and `39542919` is
+        # the total object size.
+        response_range, total_size = content_range.split('/')
+        # Subtract `1` because range is 0-indexed.
+        final_byte = str(int(total_size) - 1)
+        # If it's the last part, the requested range will not include
+        # the final byte, eg `bytes=33554432-`.
+        if requested_range.endswith('-'):
+            requested_range += final_byte
+        # Request looks like `bytes=0-8388607`.
+        # Parsed response looks like `bytes 0-8388607`.
+        if requested_range[6:] != response_range[6:]:
+            raise S3ValidationError(
+                f"Requested range: `{requested_range[6:]}` does not match "
+                f"content range in response: `{response_range[6:]}`"
+            )
+
 
 class ImmediatelyWriteIOGetObjectTask(GetObjectTask):
     """GetObjectTask that immediately writes to the provided file object

awscli/s3transfer/exceptions.py

@@ -39,3 +39,7 @@ class FatalError(CancelledError):
     """A CancelledError raised from an error in the TransferManager"""
 
     pass
+
+
+class S3ValidationError(Exception):
+    pass

tests/functional/s3transfer/test_download.py

@@ -20,7 +20,11 @@
 
 from botocore.exceptions import ClientError
 from s3transfer.compat import SOCKET_ERROR
-from s3transfer.exceptions import RetriesExceededError, S3DownloadFailedError
+from s3transfer.exceptions import (
+    RetriesExceededError,
+    S3DownloadFailedError,
+    S3ValidationError,
+)
 from s3transfer.manager import TransferConfig, TransferManager
 
 from tests import (
@@ -109,7 +113,7 @@ def add_head_object_response(self, expected_params=None):
         self.stubber.add_response(**head_response)
 
     def add_successful_get_object_responses(
-        self, expected_params=None, expected_ranges=None
+        self, expected_params=None, expected_ranges=None, extras=None
     ):
         # Add all get_object responses needed to complete the download.
         # Should account for both ranged and nonranged downloads.
@@ -124,6 +128,8 @@ def add_successful_get_object_responses(
                     stubbed_response['expected_params']['Range'] = (
                         expected_ranges[i]
                     )
+                if extras:
+                    stubbed_response['service_response'].update(extras[i])
             self.stubber.add_response(**stubbed_response)
 
     def add_n_retryable_get_object_responses(self, n, num_reads=0):
@@ -511,9 +517,12 @@ def test_download(self):
             'RequestPayer': 'requester',
         }
         expected_ranges = ['bytes=0-3', 'bytes=4-7', 'bytes=8-']
+        stubbed_ranges = ['bytes 0-3/10', 'bytes 4-7/10', 'bytes 8-9/10']
         self.add_head_object_response(expected_params)
         self.add_successful_get_object_responses(
-            {**expected_params, 'IfMatch': self.etag}, expected_ranges
+            {**expected_params, 'IfMatch': self.etag},
+            expected_ranges,
+            [{"ContentRange": r} for r in stubbed_ranges],
         )
 
         future = self.manager.download(
@@ -547,6 +556,28 @@ def test_download_with_checksum_enabled(self):
         with open(self.filename, 'rb') as f:
             self.assertEqual(self.content, f.read())
 
+    def test_download_raises_if_content_range_mismatch(self):
+        expected_params = {
+            'Bucket': self.bucket,
+            'Key': self.key,
+        }
+        expected_ranges = ['bytes=0-3', 'bytes=4-7', 'bytes=8-']
+        # Note that the final retrieved range should be `bytes 8-9/10`.
+        stubbed_ranges = ['bytes 0-3/10', 'bytes 4-7/10', 'bytes 7-8/10']
+        self.add_head_object_response(expected_params)
+        self.add_successful_get_object_responses(
+            {**expected_params, 'IfMatch': self.etag},
+            expected_ranges,
+            [{"ContentRange": r} for r in stubbed_ranges],
+        )
+
+        future = self.manager.download(
+            self.bucket, self.key, self.filename, self.extra_args
+        )
+        with self.assertRaises(S3ValidationError) as e:
+            future.result()
+        self.assertIn('does not match content range', str(e.exception))
+
     def test_download_raises_if_etag_validation_fails(self):
         expected_params = {
             'Bucket': self.bucket,