[Storage] Add read to datalake StorageStreamDownloader (#25707)

sdk/storage/azure-storage-file-datalake/CHANGELOG.md

@@ -9,6 +9,7 @@ This version and all future versions will require Python 3.7+. Python 3.6 is no
 - Added support for `flush` to `append_data` API, allowing for append and flush in one operation.
 - Encryption Scope is now supported for both `create_file_system` APIs (`FileSystemClient`, `DataLakeServiceClient`).
 - Encryption Scope is now supported as a SAS permission.
+- Added standard `read` method to `StorageStreamDownloader`.
 
 ## 12.8.0 (2022-07-07)
 

sdk/storage/azure-storage-file-datalake/azure/storage/filedatalake/_download.py

@@ -3,7 +3,7 @@
 # Licensed under the MIT License. See License.txt in the project root for
 # license information.
 # --------------------------------------------------------------------------
-from typing import Iterator
+from typing import Iterator, Optional
 
 from ._deserialize import from_blob_properties
 
@@ -30,24 +30,36 @@ def __init__(self, downloader):
     def __len__(self):
         return self.size
 
-    def chunks(self):
-        # type: () -> Iterator[bytes]
+    def chunks(self) -> Iterator[bytes]:
         """Iterate over chunks in the download stream.
 
         :rtype: Iterator[bytes]
         """
         return self._downloader.chunks()
 
-    def readall(self):
-        # type: () -> bytes
+    def read(self, size: Optional[int] = -1) -> bytes:
+        """
+        Read up to size bytes from the stream and return them. If size
+        is unspecified or is -1, all bytes will be read.
+
+        :param size:
+            The number of bytes to download from the stream. Leave unsepcified
+            or set to -1 to download all bytes.
+        :returns:
+            The requsted data as bytes. If the return value is empty, there is no more data to read.
+        :rtype: bytes
+        """
+        return self._downloader.read(size)
+
+    def readall(self) -> bytes:
         """Download the contents of this file.
 
         This operation is blocking until all data is downloaded.
         :rtype: bytes
         """
         return self._downloader.readall()
 
-    def readinto(self, stream):
+    def readinto(self, stream) -> int:
         """Download the contents of this file to a stream.
 
         :param stream:

sdk/storage/azure-storage-file-datalake/azure/storage/filedatalake/aio/_download_async.py

@@ -3,7 +3,7 @@
 # Licensed under the MIT License. See License.txt in the project root for
 # license information.
 # --------------------------------------------------------------------------
-from typing import AsyncIterator
+from typing import AsyncIterator, Optional
 
 from .._deserialize import from_blob_properties
 
@@ -30,24 +30,36 @@ def __init__(self, downloader):
     def __len__(self):
         return self.size
 
-    def chunks(self):
-        # type: () -> AsyncIterator[bytes]
+    def chunks(self) -> AsyncIterator[bytes]:
         """Iterate over chunks in the download stream.
 
         :rtype: AsyncIterator[bytes]
         """
         return self._downloader.chunks()
 
-    async def readall(self):
-        # type: () -> bytes
+    async def read(self, size: Optional[int] = -1) -> bytes:
+        """
+        Read up to size bytes from the stream and return them. If size
+        is unspecified or is -1, all bytes will be read.
+
+        :param size:
+            The number of bytes to download from the stream. Leave unsepcified
+            or set to -1 to download all bytes.
+        :returns:
+            The requsted data as bytes. If the return value is empty, there is no more data to read.
+        :rtype: bytes
+        """
+        return await self._downloader.read(size)
+
+    async def readall(self) -> bytes:
         """Download the contents of this file.
 
         This operation is blocking until all data is downloaded.
         :rtype: bytes
         """
         return await self._downloader.readall()
 
-    async def readinto(self, stream):
+    async def readinto(self, stream) -> int:
         """Download the contents of this file to a stream.
 
         :param stream: