Added fixes for handling fetch_range extending beyond length of the file

adlfs/spec.py

@@ -1709,7 +1709,10 @@ def __init__(
                 self.details = self.fs.info(self.path)
             self.size = self.details["size"]
             self.cache = caches[cache_type](
-                self.blocksize, self._fetch_range, self.size, **cache_options
+                blocksize = self.blocksize, 
+                fetcher = self._fetch_range, 
+                size = self.size, 
+                **cache_options
             )
             self.metadata = sync(
                 self.loop, get_blob_metadata, self.container_client, self.blob
@@ -1769,20 +1772,23 @@ def connect_client(self):
                 f"Unable to fetch container_client with provided params for {e}!!"
             )
 
-    async def _async_fetch_range(self, start: int, end: int, **kwargs):
+    async def _async_fetch_range(self, start: int, length: int = None, **kwargs):
         """
-        Download a chunk of data specified by start and end
+        Download a chunk of data specified by start and length
 
         Parameters
         ----------
         start: int
             Start byte position to download blob from
-        end: int
-            End byte position to download blob from
+        length: int
+            Length to download
         """
+        if length is not None:
+            if start + length > self.size:
+                length = self.size - start
         async with self.container_client:
             stream = await self.container_client.download_blob(
-                blob=self.blob, offset=start, length=end
+                blob=self.blob, offset=start, length=length
             )
             blob = await stream.readall()
         return blob

adlfs/tests/test_fetch_range.py

@@ -0,0 +1,49 @@
+import pytest
+
+from adlfs import AzureBlobFileSystem, AzureBlobFile
+
+
+URL = "http://127.0.0.1:10000"
+ACCOUNT_NAME = "devstoreaccount1"
+KEY = "Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw=="  # NOQA
+CONN_STR = f"DefaultEndpointsProtocol=http;AccountName={ACCOUNT_NAME};AccountKey={KEY};BlobEndpoint={URL}/{ACCOUNT_NAME};"  # NOQA
+
+
+def test_fetch_entire_blob(storage):
+    fs = AzureBlobFileSystem(
+        account_name=storage.account_name, connection_string=CONN_STR,
+    )
+    blob = fs.open("data/top_file.txt")
+    assert len(blob._fetch_range(start=0, length=10)) == 10
+
+
+def test_fetch_first_half(storage):
+    fs = AzureBlobFileSystem(
+        account_name=storage.account_name, connection_string=CONN_STR,
+    )
+    blob = fs.open("data/top_file.txt")
+    assert len(blob._fetch_range(start=0, length=5)) == 5
+
+
+def test_fetch_second_half(storage):
+    # Verify if length extends beyond the end of file, truncate the read
+    fs = AzureBlobFileSystem(
+        account_name=storage.account_name, connection_string=CONN_STR,
+    )
+    blob = fs.open("data/top_file.txt")
+    assert len(blob._fetch_range(start=5, length=10)) == 5
+
+
+def test_fetch_middle(storage):
+    fs = AzureBlobFileSystem(
+        account_name=storage.account_name, connection_string=CONN_STR,
+    )
+    blob = fs.open("data/top_file.txt")
+    assert len(blob._fetch_range(start=2, length=7)) == 7
+
+def test_fetch_length_is_none(storage):
+    fs = AzureBlobFileSystem(
+        account_name=storage.account_name, connection_string=CONN_STR,
+    )
+    blob = fs.open("data/top_file.txt")
+    assert len(blob._fetch_range(start=2, length=None)) == 8