[Storage] az storage blob download: Allow downloading to stdout for pipe support (Azure#22317)

* fix blob download stdout

* fix check

* Update src/azure-cli/azure/cli/command_modules/storage/operations/blob.py

Co-authored-by: Yishi Wang <[email protected]>

Co-authored-by: Yishi Wang <[email protected]>

Author: jonie001

src/azure-cli/azure/cli/command_modules/storage/_help.py

@@ -1193,6 +1193,8 @@
 examples:
   - name: Download a blob.
     text: az storage blob download -f /path/to/file -c mycontainer -n MyBlob
+  - name: Download a blob content to stdout(pipe support).
+    text: az storage blob download -c mycontainer -n myblob --account-name mystorageaccount --account-key myaccountkey
 """
 
 helps['storage blob url'] = """

src/azure-cli/azure/cli/command_modules/storage/_params.py

@@ -1008,7 +1008,8 @@ def load_arguments(self, _):  # pylint: disable=too-many-locals, too-many-statem
         c.register_blob_arguments_track2()
         c.register_precondition_options()
         c.argument('file_path', options_list=('--file', '-f'), type=file_type, completer=FilesCompleter(),
-                   help='Path of file to write out to.', validator=blob_download_file_path_validator)
+                   help='Path of file to write out to. If not specified, stdout will be used '
+                        'and max_connections will be set to 1.', validator=blob_download_file_path_validator)
         c.argument('start_range', type=int,
                    help='Start of byte range to use for downloading a section of the blob. If no end_range is given, '
                         'all bytes after the start_range will be downloaded. The start_range and end_range params are '

src/azure-cli/azure/cli/command_modules/storage/_transformers.py

@@ -218,6 +218,8 @@ def transform_blob_list_output(result):
 
 
 def transform_blob_json_output(result):
+    if result is None:
+        return
     result = todict(result)
     new_result = {
         "content": "",

src/azure-cli/azure/cli/command_modules/storage/_validators.py

@@ -1445,6 +1445,8 @@ def blob_tier_validator_track2(cmd, namespace):
 
 
 def blob_download_file_path_validator(namespace):
+    if namespace.file_path is None:
+        return
     if os.path.isdir(namespace.file_path):
         from azure.cli.core.azclierror import FileOperationError
         raise FileOperationError('File is expected, not a directory: {}'.format(namespace.file_path))

src/azure-cli/azure/cli/command_modules/storage/operations/blob.py

@@ -4,6 +4,7 @@
 # --------------------------------------------------------------------------------------------
 
 import os
+import sys
 from datetime import datetime
 
 from azure.cli.core.profiles import ResourceType, get_sdk
@@ -529,7 +530,6 @@ def transform_blob_type(cmd, blob_type):
 def _adjust_block_blob_size(client, blob_type, length):
     if not blob_type or blob_type != 'block' or length is None:
         return
-
     # increase the block size to 100MB when the block list will contain more than 50,000 blocks(each block 4MB)
     if length > 50000 * 4 * 1024 * 1024:
         client._config.max_block_size = 100 * 1024 * 1024
@@ -623,7 +623,7 @@ def upload_blob(cmd, client, file_path=None, container_name=None, blob_name=None
     return response
 
 
-def download_blob(client, file_path, open_mode='wb', start_range=None, end_range=None,
+def download_blob(client, file_path=None, open_mode='wb', start_range=None, end_range=None,
                   progress_callback=None, **kwargs):
     offset = None
     length = None
@@ -632,11 +632,16 @@ def download_blob(client, file_path, open_mode='wb', start_range=None, end_range
         length = end_range - start_range + 1
     if progress_callback:
         kwargs['raw_response_hook'] = progress_callback
+    if not file_path:
+        kwargs['max_concurrency'] = 1
     download_stream = client.download_blob(offset=offset, length=length, **kwargs)
-    with open(file_path, open_mode) as stream:
+    if file_path:
+        with open(file_path, open_mode) as stream:
+            download_stream.readinto(stream)
+        return download_stream.properties
+    with os.fdopen(sys.stdout.fileno(), open_mode) as stream:
         download_stream.readinto(stream)
-
-    return download_stream.properties
+    return
 
 
 def get_block_ids(content_length, block_length):