Reintroduce case-sensitivity handling to multi-object download operations

.changes/next-release/enhancement-s3-49696.json

@@ -0,0 +1,5 @@
+{
+  "type": "enhancement",
+  "category": "``s3``",
+  "description": "Adds new parameter ``--case-conflict`` that configures how case conflicts are handled on case-insensitive filesystems"
+}

awscli/customizations/s3/filegenerator.py

@@ -94,7 +94,8 @@ def __init__(self, directory, filename):
 class FileStat(object):
     def __init__(self, src, dest=None, compare_key=None, size=None,
                  last_update=None, src_type=None, dest_type=None,
-                 operation_name=None, response_data=None, etag=None):
+                 operation_name=None, response_data=None, etag=None,
+                 case_conflict_submitted=None, case_conflict_key=None,):
         self.src = src
         self.dest = dest
         self.compare_key = compare_key
@@ -105,6 +106,8 @@ def __init__(self, src, dest=None, compare_key=None, size=None,
         self.operation_name = operation_name
         self.response_data = response_data
         self.etag = etag
+        self.case_conflict_submitted = case_conflict_submitted
+        self.case_conflict_key = case_conflict_key
 
 
 class FileGenerator(object):

awscli/customizations/s3/fileinfo.py

@@ -42,7 +42,8 @@ def __init__(self, src, dest=None, compare_key=None, size=None,
                  last_update=None, src_type=None, dest_type=None,
                  operation_name=None, client=None, parameters=None,
                  source_client=None, is_stream=False,
-                 associated_response_data=None, etag=None):
+                 associated_response_data=None, etag=None,
+                 case_conflict_submitted=None, case_conflict_key=None,):
         self.src = src
         self.src_type = src_type
         self.operation_name = operation_name
@@ -60,6 +61,8 @@ def __init__(self, src, dest=None, compare_key=None, size=None,
         self.is_stream = is_stream
         self.associated_response_data = associated_response_data
         self.etag = etag
+        self.case_conflict_submitted = case_conflict_submitted
+        self.case_conflict_key = case_conflict_key
 
     def is_glacier_compatible(self):
         """Determines if a file info object is glacier compatible

awscli/customizations/s3/fileinfobuilder.py

@@ -46,6 +46,12 @@ def _inject_info(self, file_base):
         file_info_attr['is_stream'] = self._is_stream
         file_info_attr['associated_response_data'] = file_base.response_data
         file_info_attr['etag'] = file_base.etag
+        file_info_attr['case_conflict_submitted'] = getattr(
+            file_base, 'case_conflict_submitted', None
+        )
+        file_info_attr['case_conflict_key'] = getattr(
+            file_base, 'case_conflict_key', None
+        )
 
         # This is a bit quirky. The below conditional hinges on the --delete
         # flag being set, which only occurs during a sync command. The source

awscli/customizations/s3/s3handler.py

@@ -47,6 +47,7 @@
 from awscli.customizations.s3.utils import DeleteSourceFileSubscriber
 from awscli.customizations.s3.utils import DeleteSourceObjectSubscriber
 from awscli.customizations.s3.utils import DeleteCopySourceObjectSubscriber
+from awscli.customizations.s3.utils import CaseConflictCleanupSubscriber
 from awscli.compat import get_binary_stdin
 
 
@@ -403,6 +404,13 @@ def _add_additional_subscribers(self, subscribers, fileinfo):
         if self._cli_params.get('is_move', False):
             subscribers.append(DeleteSourceObjectSubscriber(
                 fileinfo.source_client))
+        if fileinfo.case_conflict_submitted is not None:
+            subscribers.append(
+                CaseConflictCleanupSubscriber(
+                    fileinfo.case_conflict_submitted,
+                    fileinfo.case_conflict_key,
+                )
+            )
 
     def _submit_transfer_request(self, fileinfo, extra_args, subscribers):
         bucket, key = find_bucket_key(fileinfo.src)

awscli/customizations/s3/subcommands.py

@@ -34,7 +34,8 @@
     S3PathResolver
 from awscli.customizations.utils import uni_print
 from awscli.customizations.s3.syncstrategy.base import MissingFileSync, \
-    SizeAndLastModifiedSync, NeverSync
+    SizeAndLastModifiedSync, NeverSync, AlwaysSync
+from awscli.customizations.s3.syncstrategy.caseconflict import CaseConflictSync
 from awscli.customizations.s3 import transferconfig
 from awscli.utils import resolve_v2_debug_mode
 
@@ -482,6 +483,33 @@
     )
 }
 
+CASE_CONFLICT = {
+    'name': 'case-conflict',
+    'choices': [
+         'ignore',
+         'skip',
+         'warn',
+         'error',
+    ],
+    'default': 'ignore',
+    'help_text': (
+         "Configures behavior when attempting to download multiple objects "
+         "whose keys differ only by case, which can cause undefined behavior "
+         "on case-insensitive filesystems. "
+         "This parameter only applies for commands that perform multiple S3 "
+         "to local downloads. "
+         f"See <a href='{CaseConflictSync.DOC_URI}'>Handling case "
+         "conflicts</a> for details. Valid values are: "
+         "<ul>"
+         "<li>``error`` - Raise an error and abort downloads.</li>"
+         "<li>``warn`` - Emit a warning and download the object.</li>"
+         "<li>``skip`` - Skip downloading the object.</li>"
+         "<li>``ignore`` - The default value. Ignore the conflict and "
+         "download the object.</li>"
+         "</ul>"
+    ),
+ }
+
 TRANSFER_ARGS = [DRYRUN, QUIET, INCLUDE, EXCLUDE, ACL,
                  FOLLOW_SYMLINKS, NO_FOLLOW_SYMLINKS, NO_GUESS_MIME_TYPE,
                  SSE, SSE_C, SSE_C_KEY, SSE_KMS_KEY_ID, SSE_C_COPY_SOURCE,
@@ -807,7 +835,8 @@ class CpCommand(S3TransferCommand):
             "or <S3Uri> <S3Uri>"
     ARG_TABLE = [{'name': 'paths', 'nargs': 2, 'positional_arg': True,
                   'synopsis': USAGE}] + TRANSFER_ARGS + \
-                [METADATA, METADATA_DIRECTIVE, EXPECTED_SIZE, RECURSIVE]
+                [METADATA, METADATA_DIRECTIVE, EXPECTED_SIZE, RECURSIVE,
+                 CASE_CONFLICT]
 
 
 class MvCommand(S3TransferCommand):
@@ -817,7 +846,8 @@ class MvCommand(S3TransferCommand):
             "or <S3Uri> <S3Uri>"
     ARG_TABLE = [{'name': 'paths', 'nargs': 2, 'positional_arg': True,
                   'synopsis': USAGE}] + TRANSFER_ARGS +\
-                [METADATA, METADATA_DIRECTIVE, RECURSIVE, VALIDATE_SAME_S3_PATHS]
+                [METADATA, METADATA_DIRECTIVE, RECURSIVE, VALIDATE_SAME_S3_PATHS,
+                 CASE_CONFLICT]
 
 
 class RmCommand(S3TransferCommand):
@@ -839,7 +869,7 @@ class SyncCommand(S3TransferCommand):
             "<LocalPath> or <S3Uri> <S3Uri>"
     ARG_TABLE = [{'name': 'paths', 'nargs': 2, 'positional_arg': True,
                   'synopsis': USAGE}] + TRANSFER_ARGS + \
-                [METADATA, METADATA_DIRECTIVE]
+                [METADATA, METADATA_DIRECTIVE, CASE_CONFLICT]
 
 
 class MbCommand(S3Command):
@@ -1004,7 +1034,16 @@ def choose_sync_strategies(self):
         # Set the default strategies.
         sync_strategies['file_at_src_and_dest_sync_strategy'] = \
             SizeAndLastModifiedSync()
-        sync_strategies['file_not_at_dest_sync_strategy'] = MissingFileSync()
+        if self._should_handle_case_conflicts():
+            sync_strategies['file_not_at_dest_sync_strategy'] = (
+                CaseConflictSync(
+                    on_case_conflict=self.parameters['case_conflict']
+                )
+            )
+        else:
+            sync_strategies['file_not_at_dest_sync_strategy'] = (
+                MissingFileSync()
+            )
         sync_strategies['file_not_at_src_sync_strategy'] = NeverSync()
 
         # Determine what strategies to override if any.
@@ -1138,6 +1177,12 @@ def run(self):
                             'filters': [create_filter(self.parameters)],
                             'file_info_builder': [file_info_builder],
                             's3_handler': [s3_transfer_handler]}
+            if self._should_handle_case_conflicts():
+                self._handle_case_conflicts(
+                    command_dict,
+                    rev_files,
+                    rev_generator,
+                )
         elif self.cmd == 'rm':
             command_dict = {'setup': [files],
                             'file_generator': [file_generator],
@@ -1150,6 +1195,12 @@ def run(self):
                             'filters': [create_filter(self.parameters)],
                             'file_info_builder': [file_info_builder],
                             's3_handler': [s3_transfer_handler]}
+            if self._should_handle_case_conflicts():
+                self._handle_case_conflicts(
+                    command_dict,
+                    rev_files,
+                    rev_generator,
+                )
 
         files = command_dict['setup']
         while self.instructions:
@@ -1215,6 +1266,74 @@ def _map_sse_c_params(self, request_parameters, paths_type):
                 }
             )
 
+    def _should_handle_case_conflicts(self):
+        return (
+                self.cmd in {'sync', 'cp', 'mv'}
+                and self.parameters.get('paths_type') == 's3local'
+                and self.parameters['case_conflict'] != 'ignore'
+                and self.parameters.get('dir_op')
+        )
+
+    def _handle_case_conflicts(self, command_dict, rev_files, rev_generator):
+        # Objects are not returned in lexicographical order when
+        # operated on S3 Express directory buckets. This is required
+        # for sync operations to behave correctly, which is what
+        # recursive copies and moves fall back to so potential case
+        # conflicts can be detected and handled.
+        if not is_s3express_bucket(
+                split_s3_bucket_key(self.parameters['src'])[0]
+        ):
+            self._modify_instructions_for_case_conflicts(
+                command_dict, rev_files, rev_generator
+            )
+            return
+        # `skip` and `error` are not valid choices in this case because
+        # it's not possible to detect case conflicts.
+        if self.parameters['case_conflict'] not in {'ignore', 'warn'}:
+            raise ValueError(
+                f"`{self.parameters['case_conflict']}` is not a valid value "
+                "for `--case-conflict` when operating on S3 Express "
+                "directory buckets. Valid values: `warn`, `ignore`."
+            )
+        msg = (
+            "warning: Recursive copies/moves from an S3 Express "
+            "directory bucket to a case-insensitive local filesystem "
+            "may result in undefined behavior if there are "
+            "S3 object key names that differ only by case. To disable "
+            "this warning, set the `--case-conflict` parameter to `ignore`. "
+            f"For more information, see {CaseConflictSync.DOC_URI}."
+        )
+        uni_print(msg, sys.stderr)
+
+    def _modify_instructions_for_case_conflicts(
+            self, command_dict, rev_files, rev_generator
+    ):
+        # Command will perform recursive S3 to local downloads.
+        # Checking for potential case conflicts requires knowledge
+        # of local files. Instead of writing a separate validation
+        # mechanism for recursive downloads, we modify the instructions
+        # to mimic a sync command.
+        sync_strategies = {
+            # Local filename exists with exact case match. Always sync
+            # because it's a copy operation.
+            'file_at_src_and_dest_sync_strategy': AlwaysSync(),
+            # Local filename either doesn't exist or differs only by case.
+            # Let `CaseConflictSync` determine which it is and handle it
+            # according to configured `--case-conflict` parameter.
+            'file_not_at_dest_sync_strategy': CaseConflictSync(
+                on_case_conflict=self.parameters['case_conflict']
+            ),
+            # Copy is one-way so never sync if not at source.
+            'file_not_at_src_sync_strategy': NeverSync(),
+        }
+        command_dict['setup'].append(rev_files)
+        command_dict['file_generator'].append(rev_generator)
+        command_dict['filters'].append(create_filter(self.parameters))
+        command_dict['comparator'] = [Comparator(**sync_strategies)]
+        self.instructions.insert(
+            self.instructions.index('file_info_builder'), 'comparator'
+        )
+
 
 class CommandParameters(object):
     """

awscli/customizations/s3/syncstrategy/base.py

@@ -254,3 +254,12 @@ def determine_should_sync(self, src_file, dest_file):
         LOG.debug("syncing: %s -> %s, file does not exist at destination",
                   src_file.src, src_file.dest)
         return True
+
+
+class AlwaysSync(BaseSync):
+    def __init__(self, sync_type='file_at_src_and_dest'):
+        super(AlwaysSync, self).__init__(sync_type)
+
+    def determine_should_sync(self, src_file, dest_file):
+        LOG.debug(f"syncing: {src_file.src} -> {src_file.dest}")
+        return True

awscli/customizations/s3/syncstrategy/caseconflict.py

@@ -0,0 +1,96 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+import logging
+import os
+import sys
+
+from awscli.customizations.s3.syncstrategy.base import BaseSync
+from awscli.customizations.utils import uni_print
+
+LOG = logging.getLogger(__name__)
+
+
+class CaseConflictException(Exception):
+    pass
+
+
+class CaseConflictSync(BaseSync):
+    DOC_URI = (
+        "https://docs.aws.amazon.com/cli/v1/topic/"
+        "s3-case-insensitivity.html"
+    )
+
+    def __init__(
+            self,
+            sync_type='file_not_at_dest',
+            on_case_conflict='ignore',
+            submitted=None,
+    ):
+        super().__init__(sync_type)
+        self._on_case_conflict = on_case_conflict
+        if submitted is None:
+            submitted = set()
+        self._submitted = submitted
+
+    @property
+    def submitted(self):
+        return self._submitted
+
+    def determine_should_sync(self, src_file, dest_file):
+        # `src_file.compare_key` and `dest_file.compare_key` are not equal.
+        # This could mean that they're completely different or differ
+        # only by case. eg, `/tmp/a` and `/tmp/b` versus `/tmp/a` and `/tmp/A`.
+        # If the source file's destination already exists, that means it
+        # differs only by case and the conflict needs to be handled.
+        should_sync = True
+        # Normalize compare key for case sensitivity.
+        lower_compare_key = src_file.compare_key.lower()
+        if lower_compare_key in self._submitted or os.path.exists(
+                src_file.dest
+        ):
+            handler = getattr(self, f"_handle_{self._on_case_conflict}")
+            should_sync = handler(src_file)
+        if should_sync:
+            LOG.debug(f"syncing: {src_file.src} -> {src_file.dest}")
+            self._submitted.add(lower_compare_key)
+            # Set properties so that a subscriber can be created
+            # that removes the key from the set after download finishes.
+            src_file.case_conflict_submitted = self._submitted
+            src_file.case_conflict_key = lower_compare_key
+        return should_sync
+
+    @staticmethod
+    def _handle_ignore(src_file):
+        return True
+
+    @staticmethod
+    def _handle_skip(src_file):
+        msg = (
+            f"warning: Skipping {src_file.src} -> {src_file.dest} "
+            "because a file whose name differs only by case either exists "
+            "or is being downloaded.\n"
+        )
+        uni_print(msg, sys.stderr)
+        return False
+
+    @staticmethod
+    def _handle_warn(src_file):
+        msg = (
+            f"warning: Downloading {src_file.src} -> {src_file.dest} "
+            "despite a file whose name differs only by case either existing "
+            "or being downloaded. This behavior is not defined on "
+            "case-insensitive filesystems and may result in overwriting "
+            "existing files or race conditions between concurrent downloads. "
+            f"For more information, see {CaseConflictSync.DOC_URI}.\n"
+        )
+        uni_print(msg, sys.stderr)
+        return True
+
+    @staticmethod
+    def _handle_error(src_file):
+        msg = (
+            f"Failed to download {src_file.src} -> {src_file.dest} "
+            "because a file whose name differs only by case either exists "
+            "or is being downloaded."
+        )
+        raise CaseConflictException(msg)