fix write race condition

lbrynet/blob/blob_file.py

@@ -66,7 +66,7 @@ class BlobFile:
         self.verified: asyncio.Event = asyncio.Event(loop=self.loop)
         self.finished_writing = asyncio.Event(loop=loop)
         self.blob_write_lock = asyncio.Lock(loop=loop)
-        if os.path.isfile(os.path.join(blob_dir, blob_hash)):
+        if self.file_exists:
             length = int(os.stat(os.path.join(blob_dir, blob_hash)).st_size)
             self.length = length
             self.verified.set()
@@ -74,6 +74,10 @@ class BlobFile:
         self.saved_verified_blob = False
         self.blob_completed_callback = blob_completed_callback
 
+    @property
+    def file_exists(self):
+        return os.path.isfile(self.file_path)
+
     def writer_finished(self, writer: HashBlobWriter):
         def callback(finished: asyncio.Future):
             try:
@@ -116,7 +120,7 @@ class BlobFile:
             self.verified.set()
 
     def open_for_writing(self) -> HashBlobWriter:
-        if os.path.exists(self.file_path):
+        if self.file_exists:
             raise OSError(f"File already exists '{self.file_path}'")
         fut = asyncio.Future(loop=self.loop)
         writer = HashBlobWriter(self.blob_hash, self.get_length, fut)

lbrynet/blob_exchange/client.py

@@ -137,7 +137,7 @@ class BlobExchangeClientProtocol(asyncio.Protocol):
         self.transport = None
 
     async def download_blob(self, blob: 'BlobFile') -> typing.Tuple[bool, typing.Optional[asyncio.Transport]]:
-        if blob.get_is_verified():
+        if blob.get_is_verified() or blob.file_exists:
             return False, self.transport
         try:
             self.blob, self.writer, self._blob_bytes_received = blob, blob.open_for_writing(), 0
@@ -175,7 +175,8 @@ async def request_blob(loop: asyncio.BaseEventLoop, blob: 'BlobFile', address: s
     Returns [<downloaded blob>, <keep connection>]
     """
 
-    if blob.get_is_verified():
+    if blob.get_is_verified() or blob.file_exists:
+        # file exists but not verified means someone is writing right now, give it time, come back later
         return False, connected_transport
     protocol = BlobExchangeClientProtocol(loop, blob_download_timeout)
     if connected_transport and not connected_transport.is_closing():